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1. First demonstration of Super-X divertor exhaust control for transient heat load management in compact fusion reactors

Author

Kool, B., Verhaegh, K., Derks, G. L., Wijkamp, T. A., Lonigro, N., Doyle, R., McArdle, G., Vincent, C., Lovell, J., Federici, F., Henderson, S. S., Osawa, R. T., Brida, D., Reimerdes, H., van Berkel, M., team, The EUROfusion tokamak exploitation, and team, the MAST-U

Subjects
Physics - Plasma Physics
Abstract

Nuclear fusion could offer clean, abundant energy. However, managing the immense power exhausted from the core fusion plasma towards the divertor remains a major challenge. This is compounded in emerging compact reactor designs which promise more cost-effective pathways towards commercial fusion energy. Alternative divertor configurations (ADCs) are a potential solution to this challenge. In this work, we demonstrate exhaust control in ADCs for the first time, on MAST-U. We employ a novel diagnostic strategy for the neutral gas buffer which shields the target. Our work shows that ADCs tackle key risks and uncertainties in realising fusion energy: 1) an enlarged operating window which 2) improves exhaust control through the absorption of transients which can remove the neutral shield and damage the divertor, 3) isolation of each divertor from other reactor regions, enabling combined control. This showcases real-world benefits of alternative divertors for effective heat load management and control in reactors.

Published
2024

2. First 2D electron density measurements using Coherence Imaging Spectroscopy in the MAST-U Super-X divertor

Author

Lonigro, N., Doyle, R., Allcock, J. S., Lipschultz, B., Verhaegh, K., Bowman, C., Brida, D., Harrison, J., Myatra, O., Silburn, S., Theiler, C., Wijkamp, T. A., Team, MAST-U, and Team, the EUROfusion Tokamak Exploitation

Subjects
Physics - Plasma Physics
Abstract

2D profiles of electron density and neutral temperature are inferred from multi-delay Coherence Imaging Spectroscopy data of divertor plasmas using a non-linear inversion technique. The inference is based on imaging the spectral line-broadening of Balmer lines and can differentiate between the Doppler and Stark broadening components by measuring the fringe contrast at multiple interferometric delays simultaneously. The model has been applied to images generated from simulated density profiles to evaluate its performance. Typical mean absolute errors of 30 percent are achieved, which are consistent with Monte Carlo uncertainty propagation accounting for noise, uncertainties in the calibrations, and in the model inputs. The analysis has been tested on experimental data from the MAST-U Super-X divertor, where it infers typical electron densities of 2-3 $10^{19}$ m$^{-3}$ and neutral temperatures of 0-2 eV during beam-heated L-mode discharges. The results are shown to be in reasonable agreement with the other available diagnostics.

Published
2024

3. Divertor shaping with neutral baffling as a solution to the tokamak power exhaust challenge

Author

Verhaegh, K., Harrison, J. R., Moulton, D., Lipschultz, B., Lonigro, N., Osborne, N., Ryan, P., Theiler, C., Wijkamp, T., Brida, D., Cowley, C., Derks, G., Doyle, R., Federici, F., Kool, B., Février, O., Hakola, A., Henderson, S., Reimerdes, H., Thornton, A. J., Vianello, N., Wischmeier, M., and Xiang, L.

Subjects
Physics - Plasma Physics
Abstract

Exhausting power from the hot fusion core to the plasma-facing components is one of the biggest challenges in fusion energy. The MAST Upgrade tokamak uniquely integrates strong containment of neutrals within the exhaust area (divertor) with extreme divertor shaping capability. By systematically altering the divertor shape, this study shows the strongest evidence to date that long-legged divertors with a high magnetic field gradient (total flux expansion) deliver key power exhaust benefits without adversely impacting the hot fusion core. These benefits are already achieved with relatively modest geometry adjustments that are more feasible to integrate in reactor designs. Benefits include reduced target heat loads and improved access to, and stability of, a neutral gas buffer that 'shields' the target and enhances power exhaust (detachment). Analysis and model comparisons shows these benefits are obtained by combining multiple shaping aspects: long-legged divertors have expanded plasma-neutral interaction volume that drive reductions in particle and power loads, while total flux expansion enhances detachment access and stability. Containing the neutrals in the exhaust area with physical structures further augments these shaping benefits. These results demonstrate strategic variation in the divertor geometry and magnetic topology is a potential solution to one of fusion's biggest challenges: power exhaust.

Published
2023

4. Investigations of atomic \& molecular processes of NBI-heated discharges in the MAST Upgrade Super-X divertor with implications for reactors

Author

Verhaegh, K., Harrison, J. R., Lipschultz, B., Lonigro, N., Kobussen, S., Moulton, D., Osborne, N., Ryan, P., Theiler, C., Wijkamp, T., Brida, D., Derks, G., Doyle, R., Federici, F., Hakola, A., Henderson, S., Kool, B., Newton, S., Osawa, R., Pope, X., Reimerdes, H., Vianello, N., and Wischmeier, M.

Subjects
Physics - Plasma Physics
Abstract

This experimental study presents an in-depth investigation of the performance of the MAST-U Super-X divertor during NBI-heated operation (up to 2.5 MW) focussing on volumetric ion sources and sinks as well as power losses during detachment. The particle balance and power loss analysis revealed the crucial role of Molecular Activated Recombination and Dissociation (MAR and MAD) ion sinks in divertor particle and power balance, which remain pronounced in the change from ohmic to higher power (NBI heated) L-mode conditions. The importance of MAR and MAD remains with double the absorbed NBI heating. MAD results in significant power dissipation (up to $\sim 20 \%$ of $P_{SOL}$), mostly in the cold ($T_e < 5$ eV) detached region. Theoretical and experimental evidence is found for the potential contribution of $D^-$ to MAR and MAD, which warrants further study. These results suggest that MAR and MAD can be relevant in higher power conditions than the ohmic conditions studied previously. Post-processing reactor-scale simulations shows that MAR and MAD can play a significant role in divertor physics and synthetic diagnostic signals of reactor-scale devices, which are currently underestimated in exhaust simulations. This raises implications for the accuracy of reactor-scale divertor simulations of particularly tightly baffled (alternative) divertor configurations.

Published
2023

7. I-mode pedestal relaxation events at ASDEX Upgrade

Author

Silvagni, D., Eich, T., Happel, T., Harrer, G. F., Griener, M., Dunne, M., Cavedon, M., Faitsch, M., Gil, L., Nille, D., Tal, B., Fischer, R., Stroth, U., Brida, D., David, P., Manz, P., Viezzer, E., team, the ASDEX Upgrade, and team, the EUROfusion MST1

Subjects
Physics - Plasma Physics
Abstract

The I-mode confinement regime can feature small edge temperature drops that can lead to an increase in the energy deposited onto the divertor targets. In this work, we show that these events are associated with a relaxation of both electron temperature and density edge profiles, with the largest drop found at the pedestal top position. Stability analysis of edge profiles reveals that the operational points are far from the ideal peeling-ballooning boundary. Also, we show that these events appear close to the H-mode transition in the typical I-mode operational space in ASDEX Upgrade, and that no further enhancement of energy confinement is found when they occur. Moreover, scrape-off layer transport during these events is found to be very similar to type-I ELMs, with regard to timescales ($\approx$ 800 $\mu$s), filament propagation, toroidally asymmetric energy effluxes at the midplane and asymmetry between inner and outer divertor deposited energy. In particular, the latter reveals that more energy reaches the outer divertor target. Lastly, first measurements of the divertor peak energy fluence are reported, and projections to ARC - a reactor designed to operate in I-mode - are drawn.

Published
2020
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8. Tracing of backward energy transfer from LH1 to LH2 in photosynthetic membranes grown under high and low irradiation.

Author

Lanzani G., Brida D., Hoseinkhani S., Polli D., Brotosudarmo T. H. P., Henry S., Moulisová V., Lüer L., Cerullo G., and Cogdell R. J.

Subjects
Physics, QC1-999
Abstract

By introducing derivative transient absorption spectroscopy, we obtain rate constants for backward and forward energy transfer between LH1 and LH2 complexes in purple bacterial membranes. We find that backward energy transfer is strongly reduced in membranes grown under low irradiation conditions, compared to high light grown ones. We conclude that backward energy transfer is managed actively by the bacteria to avoid LH1 exciton deactivation under high irradiation conditions. The analytical method is generally applicable to excitonically coupled systems.

Published
2013
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9. Ultrafast Non-Thermal Electron Dynamics in Single Layer Graphene

Author

Novoselov K.S., Geim A.K., Nair R.R., Polini M., Tomadin A., Cerullo G., Manzoni C., Brida D., Milana S., Lombardo A., and Ferrari A. C.

Subjects
Physics, QC1-999
Abstract

We study the ultrafast dynamics of non-thermal electron relaxation in graphene upon impulsive excitation. The 10-fs resolution two color pump-probe allows us to unveil the non-equilibrium electron gas decay at early times.

Published
2013
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10. Fully coherent spectral broadening of femtosecond pulses from an Er:fiber system

Author

Brida D., Krauss G., Kumkar S., and Leitenstorfer A.

Subjects
Physics, QC1-999
Abstract

Coherence properties of the ultrabroadband output from a highly nonlinear germanosilicate fiber pumped by a femtosecond Er:fiber source are investigated. Conditions necessary to achieve full spectral coherence are demonstrated experimentally and analyzed theoretically.

Published
2013
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11. Ultra-fast polariton dynamics in an organic microcavity

Author

Polli D., Brida D., Rajendran S.K., Michetti P., Clark C., Adawi A.M., Coles D., Virgili T., Cerullo G., and Lidzey D.G.

Subjects
Physics, QC1-999
Abstract

We study an organic semiconductor microcavity operating in the strong-coupling regime using femtosecond pump-probe spectroscopy. By probing the photo-induced absorption bands, we characterize the time-dependent population densities of states in the two polariton branches. We found evidence of a scattering process from the upper-branch cavity polaritons to the exciton reservoir having a rate of (150 fs)-1. A slower process similarly populates lower-branch polaritons with a rate of around (3ps)-1

Published
2013
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12. Ultrafast spectroscopy of linear carbon chains: the case of dinaphthylpolyynes

Author

Negro M., Cataldo F., Milani P., Ravagnan L., Cinquanta E., Brida D., Milani A., Scotognella F., Fazzi D., Stagira S., and Vozzi C.

Subjects
Physics, QC1-999
Abstract

The dynamics of excited streets in a special class of linear carbon chains, e.g. dinaphthyl polyynes, has been investigated by ultrafast transient absorption spectroscopy and DFT//TDDFT calculations. The ultrafast formation of a narrow photo-induced absorption band has been observed and assigned to an inter-system crossing event bringing to the formation of triplet excited streets.

Published
2013
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13. Ultrafast low-energy dynamics of graphite studied by nonlinear multi-THz spectroscopy

Author

Leitenstorfer A., Brida D., Huber R., Grupp A., Rebholz M., Junginger F., Mayer B., Schmidt C., and Pashkin A.

Subjects
Physics, QC1-999
Abstract

Ultraintense few-cycle THz pulses are employed to study the nonlinear response of graphite. A phase sensitive 2D spectroscopy setup is capable of detecting pump-induced transient changes as well as multi-wave mixing processes. The observed strong THz-pump THz-probe signals provide insight into ultrafast dynamics and the spectral response of the low-energy carriers. Here we report the observation of a pump-induced transmission in graphite. The relaxation dynamics shows three distinct time scales, which are assigned to carrier thermalization, phonon emission and a slow cooling down back to equilibrium.

Published
2013
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14. Quantum coherence controls the charge separation in a prototypical artificial light harvesting system

Author

Schramm H., Cerullo G., Maiuri M., Brida D., Molinari E., Rubio A., Spallanzani N., Rozzi C. A., Falke S.M., Christoffers J., and Lienau C.

Subjects
Physics, QC1-999
Abstract

Ultrafast spectroscopy and quantum-dynamics simulations of an artificial supramolecular light-harvesting system — a supramolecular triad - provide strong evidence that the quantum-correlated wavelike motion of electrons and nuclei on a timescale of few tens of femtoseconds governs the ultrafast electronic charge transfer.

Published
2013
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16. Comparison of reduced model predictions for divertor detachment onset and reattachment timescales in ASDEX Upgrade and JET experiments

Author

Henderson, S, Bernert, M, Brida, D, Cavedon, M, David, P, Dux, R, Fevrier, O, Jacquet, P, Jarvinen, A, Kallenbach, A, Karhunen, J, Kirov, K, Komm, M, Lennholm, M, Lomanowski, B, Lowry, C, Mcdermott, R, Meigs, A, Reimerdes, H, Sun, H, Thomas, B, Henderson S. S., Bernert M., Brida D., Cavedon M., David P., Dux R., Fevrier O., Jacquet P., Jarvinen A., Kallenbach A., Karhunen J., Kirov K., Komm M., Lennholm M., Lomanowski B., Lowry C., McDermott R., Meigs A., Reimerdes H., Sun H., Thomas B., Henderson, S, Bernert, M, Brida, D, Cavedon, M, David, P, Dux, R, Fevrier, O, Jacquet, P, Jarvinen, A, Kallenbach, A, Karhunen, J, Kirov, K, Komm, M, Lennholm, M, Lomanowski, B, Lowry, C, Mcdermott, R, Meigs, A, Reimerdes, H, Sun, H, Thomas, B, Henderson S. S., Bernert M., Brida D., Cavedon M., David P., Dux R., Fevrier O., Jacquet P., Jarvinen A., Kallenbach A., Karhunen J., Kirov K., Komm M., Lennholm M., Lomanowski B., Lowry C., McDermott R., Meigs A., Reimerdes H., Sun H., and Thomas B.

Abstract

Building on prior analysis of ASDEX Upgrade (AUG) experiments (Henderson et al 2023 Nucl. Fusion 63 086024), this study compares simple analytical formula predictions for divertor detachment onset and reattachment timescales in JET experiments. Detachment onset primarily scales with divertor neutral pressure, impurity concentration, power directed to the targets, machine size, and integral perpendicular power decay length. JET experiments, focusing on seeding mixtures of Ne and Ar, align with the detachment onset predictions. Radiation efficiencies among the impurities show good agreement with the model predictions, contrasting with AUG observations which suggested higher efficiency for Ar and lower efficiency for Ne. The time taken to re-ionise the neutral volume in front of the outer target in fully detached divertor conditions was measured following both abrupt increases in injected neutral beam power and, separately, cutting of the impurity gas flow. Re-ionisation of the neutrals occurs within approximately 1 s on JET, which aligns with the simple model prediction derived from AUG data. While the AUG results are not new, their comparison with the JET results enhances understanding, reinforcing confidence in using simple models to predict future reactor scenarios.

Published
2024

19. Three dimensional boundary displacement due to stable ideal kink modes excited by external n=2 magnetic perturbations

Author

Willensdorfer, M., Strumberger, E., Suttrop, W., Dunne, M., Fischer, R., Birkenmeier, G., Brida, D., Cavedon, M., Denk, S. S., Igochine, V., Giannone, L., Kirk, A., Kirschner, J., Medvedeva, A., Odstrcil, T., Ryan, D. A., Team, the ASDEX Upgrade, and Team, the EUROfusion MST1

Subjects
Physics - Plasma Physics
Abstract

In low-collisionality scenarios exhibiting mitigation of edge localized modes (ELMs), stable ideal kink modes at the edge are excited by externally applied magnetic perturbation (MP)-fields. In ASDEX Upgrade these modes can cause three-dimensional (3D) boundary displacements up to the centimeter range. These displacements have been measured using toroidally localized high resolution diagnostics and rigidly rotating n = 2 MP-fields with various applied poloidal mode spectra. These measurements are compared to non-linear 3D ideal magnetohydrodynamics (MHD) equilibria calculated by VMEC. Comprehensive comparisons have been conducted, which consider for instance plasma movements due to the position control system, attenuation due to internal conductors and changes in the edge pressure profiles. VMEC accurately reproduces the amplitude of the displacement and its dependencies on the applied poloidal mode spectra. Quantitative agreement is found around the low field side (LFS) midplane. The response at the plasma top is qualitatively compared. The measured and predicted displacements at the plasma top maximize when the applied spectra is optimized for ELM-mitigation. The predictions from the vacuum modeling generally fails to describe the displacement at the LFS midplane as well as at the plasma top. When the applied mode spectra is set to maximize the displacement, VMEC and the measurements clearly surpass the predictions from the vacuum modeling by a factor of four. Minor disagreements between VMEC and the measurements are discussed. This study underlines the importance of the stable ideal kink modes at the edge for the 3D boundary displacement in scenarios relevant for ELM-mitigation., Comment: 22 pages, 12 figure, for submission to nuclear fusion

Published
2017
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20. Plasma response measurements of external magnetic perturbations using electron cyclotron emission and comparisons to 3D ideal MHD equilibrium

Author

Willensdorfer, M., Denk, S. S., Strumberger, E., Suttrop, W., Vanovac, B., Brida, D., Cavedon, M., Classen, I., Dunne, M., Fietz, S., Fischer, R., Kirk, A., Laggner, F. M., Liu, Y. Q., Odstrcil, T., Ryan, D. A., Viezzer, E., Zohm, H., and Luhmann, I. C.

Subjects
Physics - Plasma Physics
Abstract

The plasma response from an external n = 2 magnetic perturbation field in ASDEX Upgrade has been measured using mainly electron cyclotron emission (ECE) diagnostics and a rigid rotating field. To interpret ECE and ECE-imaging (ECE-I) measurements accurately, forward modeling of the radiation transport has been combined with ray tracing. The measured data is compared to synthetic ECE data generated from a 3D ideal magnetohydrodynamics (MHD) equilibrium calculated by VMEC. The measured amplitudes of the helical displacement around the low field side midplane are in reasonable agreement with the one from the synthetic VMEC diagnostics. Both exceed the prediction from the vacuum field calculations and indicate the presence of a kink response at the edge, which amplifies the perturbation. VMEC and MARS-F have been used to calculate the properties of this kink mode. The poloidal mode structure of the magnetic perturbation of this kink mode at the edge peaks at poloidal mode numbers larger than the resonant components |m| > |nq|, whereas the poloidal mode structure of its displacement is almost resonant |m| ~ |nq|. This is expected from ideal MHD in the proximity of rational surfaces. The displacement measured by ECE-I confirms this resonant response., Comment: 34 pages, 19 figures. This is an author-created, un-copyedited version of an article submitted for publication in Plasma Physics and Controlled Fusion. IoP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it

Published
2016
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21. Characterization of highly radiating nitrogen-seeded H-mode plasmas in unfavorable B T at ASDEX Upgrade.

Author

Chen, L., Wolfrum, E., Pan, O., Kurzan, B., Bernert, M., Brida, D., Cavedon, M., Dux, R., Fischer, R., Griener, M., Grover, O., Plank, U., Stieglitz, D., and Zito, A.

Subjects
DEUTERIUM ions, ELECTRON density, ELECTRON temperature, PLASMA confinement, GRANULAR flow, THOMSON scattering, NITROGEN plasmas
Abstract

The highly radiating nitrogen-seeded H-mode plasmas in unfavorable BT has been characterized in the ASDEX Upgrade tokamak (AUG). Three levels of nitrogen puffing rates have been injected into a fully detached H-mode plasma, which is run in lower single null configuration with the ion B × ∇ B drift away from the X-point. A cold ( ∼ 1 − 2 eV) highly radiating ( ∼ 13.0 MW m − 3 ) region forms close to the X-point immediately after nitrogen seeding, as evidenced by measurements of the divertor Thomson scattering (DTS) and the two-dimensional bolometry reconstructions. In addition, the radiator moves further upwards above the X-point along the separatrix at the high-field side (HFS) with increasing nitrogen puffing rates, as evidenced by the Absolute eXtended UltraViolet (AXUV) measurements. The formation of the highly radiating regime is closely correlated to the modifications of the divertor plasma conditions. Along the line of sight of the DTS measurement, the electron temperature reduces down to a few eV, which initials near the X-point and further extends to the HFS scrape-off layer (SOL) simultaneously with the upward movement of the radiator, however, the electron temperature sustains ( ∼ 30 − 50 eV) at the low-field side (LFS) SOL with slightly decreased electron density. The highly radiating regime shows LFS/HFS divertor asymmetry, in contrast to that for H-mode plasmas in favorable BT, suggesting that the drifts play an important role for the formation of the highly radiating X-point regime at AUG. The neutral particle flux increases significantly (factor of ∼ 2 ) in the private flux region, while it increases slightly ( < 20 % ) in the main chamber, thus suggesting an enhanced sub-divertor neutral compression with the formation of the highly radiating regime. Furthermore, a degradation of the pedestal electron density was observed with an enhancement of the electron temperature further inside the pedestal, and complete divertor detachment was achieved by nitrogen seeding with sustained plasma confinement. Finally, particle sources and flow patterns of deuterium and nitrogen ions have been analyzed by SOLPS-ITER modelling, confirming that the E × B drift plays an important role for the formation of the highly radiating regime in unfavorable BT at AUG. [ABSTRACT FROM AUTHOR]

Published
2024
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22. Ultrafast pseudospin dynamics in graphene

Author

Trushin, M., Grupp, A., Soavi, G., Budweg, A., De Fazio, D., Sassi, U., Lombardo, A., Ferrari, A. C., Belzig, W., Leitenstorfer, A., and Brida, D.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Interband optical transitions in graphene are subject to pseudospin selection rules. Impulsive excitation with linearly polarized light generates an anisotropic photocarrier occupation in momentum space that evolves at timescales shorter than 100fs. Here, we investigate the evolution of non-equilibrium charges towards an isotropic distribution by means of fluence-dependent ultrafast spectroscopy and develop an analytical model able to quantify the isotropization process. In contrast to conventional semiconductors, the isotropization is governed by optical phonon emission, rather than electron-electron scattering, which nevertheless contributes in shaping the anisotropic photocarrier occupation within the first few fs., Comment: 9 pages

Published
2015
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23. Tunneling Breakdown of a Strongly Correlated Insulating State in VO$_2$ Induced by Intense Multi-Terahertz Excitation

Author

Mayer, B., Schmidt, C., Grupp, A., Bühler, J., Oelmann, J., Marvel, R. E., Haglund Jr., R. F., Oka, T., Brida, D., Leitenstorfer, A., and Pashkin, A.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We directly trace the near- and mid-infrared transmission change of a VO$_2$ thin film during an ultrafast insulator-to-metal transition triggered by high-field multi-terahertz transients. Non-thermal switching into a metastable metallic state is governed solely by the amplitude of the applied terahertz field. In contrast to resonant excitation below the threshold fluence, no signatures of excitonic self-trapping are observed. Our findings are consistent with the generation of spatially separated charge pairs and a cooperative transition into a delocalized metallic state by THz field-induced tunneling. The tunneling process is a condensed-matter analogue of the Schwinger effect in nonlinear quantum electrodynamics. We find good agreement with the pair production formula by replacing the Compton wavelength with an electronic correlation length of 2.1 $\AA$.

Published
2015
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24. Snapshots of the retarded interaction of charge carriers with ultrafast fluctuations in cuprates

Author

Conte, S. Dal, Vidmar, L., Golež, D., Mierzejewski, M., Soavi, G., Peli, S., Banfi, F., Ferrini, G., Comin, R., Ludbrook, B. M., Chauviere, L., Zhigadlo, N. D., Eisaki, H., Greven, M., Lupi, S., Damascelli, A., Brida, D., Capone, M., Bonča, J., Cerullo, G., and Giannetti, C.

Subjects
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons, Physics - Optics
Abstract

One of the pivotal questions in the physics of high-temperature superconductors is whether the low-energy dynamics of the charge carriers is mediated by bosons with a characteristic timescale. This issue has remained elusive since electronic correlations are expected to dramatically speed up the electron-boson scattering processes, confining them to the very femtosecond timescale that is hard to access even with state-of-the-art ultrafast techniques. Here we simultaneously push the time resolution and the frequency range of transient reflectivity measurements up to an unprecedented level that enables us to directly observe the 16 fs build-up of the effective electron-boson interaction in hole-doped copper oxides. This extremely fast timescale is in agreement with numerical calculations based on the t-J model and the repulsive Hubbard model, in which the relaxation of the photo-excited charges is achieved via inelastic scattering with short-range antiferromagnetic excitations., Comment: to appear in Nature Physics

Published
2015
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25. First SOLPS‐ITER simulations of ASDEX Upgrade partially detached H‐mode with boron impurity: The missing radiation at the outer strike‐point region.

Author

Makarov, S. O., Coster, D. P., Gleiter, T., Brida, D., Muraca, M., Dux, R., David, P., Kurzan, B., Bonnin, X., and O'Mullane, M.

Subjects
THOMSON scattering, LANGMUIR probes, BORON, SOWING, RADIATION
Abstract

Partially detached H‐modes are the baseline regime for the future ITER operation. The ASDEX Upgrade partially detached H‐mode is modeled using the SOLPS‐ITER code with drifts enabled and compared with experimental data. For the first time, boron (B) impurity is simulated in the Scrape‐off layer (SOL) and divertor. A comparison between divertor diagnostics and discrepancies between Langmuir probe and Divertor Thomson scattering/Stark broadening diagnostic are discussed. In the modeling, experimental target profiles are reproduced if the experimental level of radiation in the SOL and divertor is achieved using nitrogen (N) impurity seeding. Bolometry measurements detect substantial radiation from the partially detached outer strike point. With B radiation, this maximum in bolometry data is reproduced in the modeling, which is not possible with N alone. [ABSTRACT FROM AUTHOR]

Published
2024
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26. Existence of a detachment cliff at ASDEX Upgrade.

Author

Scotti, L, Cavedon, M, Bernert, M, Brida, D, Kurzan, B, and Dux, R

Subjects
POWER density, BOLOMETERS, DATABASES, MANOMETERS, TOKAMAKS, CLIFFS
Abstract

The detachment cliff is a bifurcative transition to partial detachment recently discovered at the DIII-D tokamak (McLean et al 2015 J. Nucl. Mater. 463 533–6). This work presents a database analysis of target parameters in L-mode and H-mode discharges to search for a detachment cliff at ASDEX Upgrade (AUG). Most of the transitions from attached to partially detached divertor conditions observed in H- and L-mode discharges in AUG show bifurcative-like characteristics that are consistent with the properties of the detachment cliff if the B × ∇ B drift is directed towards the active X-point. In the operational space of power and density, the bifurcative transitions identified during an L-mode discharge occur at injected power and density higher than a threshold value ( P tot > 0.7 MW and n e > 1.6 × 10 19 m−3, respectively). Furthermore, the temperatures at which the transitions start are found to be insensitive to the injected impurity, the injected power and the value of the upstream density. Finally, the study of the evolution of the target parameters, of the intensity of the D α line and of specific manometers and bolometer lines of sights shows that the physical process underlying the detachment cliff and the self-sustained divertor oscillations (Heinrich 2020 Nucl. Fusion 60 076013) might be the same. [ABSTRACT FROM AUTHOR]

Published
2024
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28. Divertor detachment and reattachment with mixed impurity seeding on ASDEX Upgrade

Author

Henderson, S, Bernert, M, Brida, D, Cavedon, M, David, P, Dux, R, Fevrier, O, Jarvinen, A, Kallenbach, A, Komm, M, Mcdermott, R, O'Mullane, M, Henderson S. S., Bernert M., Brida D., Cavedon M., David P., Dux R., Fevrier O., Jarvinen A., Kallenbach A., Komm M., McDermott R., O'Mullane M., Henderson, S, Bernert, M, Brida, D, Cavedon, M, David, P, Dux, R, Fevrier, O, Jarvinen, A, Kallenbach, A, Komm, M, Mcdermott, R, O'Mullane, M, Henderson S. S., Bernert M., Brida D., Cavedon M., David P., Dux R., Fevrier O., Jarvinen A., Kallenbach A., Komm M., McDermott R., and O'Mullane M.

Abstract

Using newly developed spectroscopic models to measure the divertor concentration of Ne and Ar, it is shown that the experimental detachment threshold on ASDEX Upgrade with Ar-only and mixtures of Ar+N or Ne+N scales as expected in comparison with an analytical equation derived by Kallenbach et al (2016 Plasma Phys. Control. Fusion 58 045013). However, it is found that Ar radiates more efficiently and Ne less efficiently in the scrape-off layer than the model predicts. By separately increasing the neutral beam injection power and cutting the impurity gas flow, it is shown that the partially detached and strongly detached X-point radiator scenarios reattach in ≈100 ms and ≈250 ms, respectively. The former timescale is set by the core energy confinement time, whereas the latter has an additional delay caused by the time required for the ionisation front to move from the X-point to the target. A simple equation with scalable geometric terms to predict the ionisation front movement time in future machines is proposed.

Published
2023

29. Experimental study of the edge radial electric field in different drift configurations and its role in the access to H-mode at ASDEX Upgrade

Author

Plank, U, Brida, D, Conway, G, Happel, T, Hubbard, A, Putterich, T, Angioni, C, Cavedon, M, Dux, R, Eich, T, Fischer, R, Hennequin, P, Plank U., Brida D., Conway G. D., Happel T., Hubbard A. E., Putterich T., Angioni C., Cavedon M., Dux R., Eich T., Fischer R., Hennequin P., Plank, U, Brida, D, Conway, G, Happel, T, Hubbard, A, Putterich, T, Angioni, C, Cavedon, M, Dux, R, Eich, T, Fischer, R, Hennequin, P, Plank U., Brida D., Conway G. D., Happel T., Hubbard A. E., Putterich T., Angioni C., Cavedon M., Dux R., Eich T., Fischer R., and Hennequin P.

Abstract

The formation of the equilibrium radial electric field (Er) has been studied experimentally at ASDEX Upgrade (AUG) in L-modes of "favorable"(ion ∇ B-drift toward primary X-point) and "unfavorable"(ion ∇ B-drift away from primary X-point) drift configurations, in view of its impact on H-mode access, which changes with drift configurations. Edge electron and ion kinetic profiles and impurity velocity and mean-field Er profiles across the separatrix are investigated, employing new and improved measurement techniques. The experimental results are compared to local neoclassical theory as well as to a simple 1D scrape-off layer (SOL) model. It is found that in L-modes of matched heating power and plasma density, the upstream SOL Er and the main ion pressure gradient in the plasma edge are the same for either drift configurations, whereas the Er well in the confined plasma is shallower in unfavorable compared to the favorable drift configuration. The contributions of toroidal and poloidal main ion flows to Er, which are inferred from local neoclassical theory and the experiment, cannot account for these observed differences. Furthermore, it is found that in the L-mode, the intrinsic toroidal edge rotation decreases with increasing collisionality and it is co-current in the banana-plateau regime for all different drift configurations at AUG. This gives rise to a possible interaction of parallel Pfirsch-Schlüter flows in the SOL with the confined plasma. Thus, the different H-mode power threshold for the two drift configurations cannot be explained in the same way at AUG as suggested by LaBombard et al. [Phys. Plasmas 12, 056111 (2005)] for Alcator C-Mod. Finally, comparisons of Er profiles in favorable and unfavorable drift configurations at the respective confinement transitions show that also the Er gradients are all different, which indirectly indicates a different type or strength of the characteristic edge turbulence in the two drift configurations.

Published
2023

30. Turbulence characterization during the suppression of edge-localized modes by magnetic perturbations on ASDEX Upgrade

Author

Leuthold, N, Suttrop, W, Willensdorfer, M, Birkenmeier, G, Brida, D, Cavedon, M, Dunne, M, Conway, G, Fischer, R, Gil, L, Happel, T, Hennequin, P, Kappatou, A, Kirk, A, Manz, P, Mcdermott, R, Vicente, J, Zohm, H, Leuthold N., Suttrop W., Willensdorfer M., Birkenmeier G., Brida D., Cavedon M., Dunne M., Conway G., Fischer R., Gil L., Happel T., Hennequin P., Kappatou A., Kirk A., Manz P., McDermott R., Vicente J., Zohm H., Leuthold, N, Suttrop, W, Willensdorfer, M, Birkenmeier, G, Brida, D, Cavedon, M, Dunne, M, Conway, G, Fischer, R, Gil, L, Happel, T, Hennequin, P, Kappatou, A, Kirk, A, Manz, P, Mcdermott, R, Vicente, J, Zohm, H, Leuthold N., Suttrop W., Willensdorfer M., Birkenmeier G., Brida D., Cavedon M., Dunne M., Conway G., Fischer R., Gil L., Happel T., Hennequin P., Kappatou A., Kirk A., Manz P., McDermott R., Vicente J., and Zohm H.

Abstract

We study localized edge turbulence in the ASDEX Upgrade tokamak that appears if resonant magnetic perturbations (RMP) are applied to suppress edge localized modes (ELMs) in the high confinement mode. The concomitant density fluctuations are detected by microwave reflectometry at the outboard midplane. Two modes can be distinguished, (a) a broadband fluctuation below a threshold of the RMP field amplitude, and (b) a narrow-band quasi-coherent mode (QCM) above the threshold. The broadband fluctuation is toroidally spread out but disappears at the toroidal position of maximum E × B shear in the gradient region. Temporal and spatial correlation along field lines of the midplane density fluctuation and the divertor particle flux suggests that this mode is producing significant particle transport across the gradient region and into the divertor, hence contributing to the plasma density reduction that is often observed when applying RMP fields (the so-called ‘pump-out’ effect). The QCM is also toroidally localized, its radial extent grows with increasing RMP field amplitude, and leads to further increased divertor particle flux compared to the broadband mode. Our observations suggest that both modes not only play an important role in keeping the plasma density stationary in the absence of ELMs but also to reduce the plasma pressure such that the plasma edge becomes stable against ELMs.

Published
2023

31. The X-Point radiating regime at ASDEX Upgrade and TCV

Author

Bernert, M, Wiesen, S, Fevrier, O, Kallenbach, A, Koenders, J, Sieglin, B, Stroth, U, Bosman, T, Brida, D, Cavedon, M, David, P, Dunne, M, Henderson, S, Kool, B, Lunt, T, Mcdermott, R, Pan, O, Perek, A, Reimerdes, H, Sheikh, U, Theiler, C, van Berkel, M, Wijkamp, T, Wischmeier, M, Bernert M., Wiesen S., Fevrier O., Kallenbach A., Koenders J. T. W., Sieglin B., Stroth U., Bosman T. O. S. J., Brida D., Cavedon M., David P., Dunne M. G., Henderson S., Kool B., Lunt T., McDermott R. M., Pan O., Perek A., Reimerdes H., Sheikh U., Theiler C., van Berkel M., Wijkamp T., Wischmeier M., Bernert, M, Wiesen, S, Fevrier, O, Kallenbach, A, Koenders, J, Sieglin, B, Stroth, U, Bosman, T, Brida, D, Cavedon, M, David, P, Dunne, M, Henderson, S, Kool, B, Lunt, T, Mcdermott, R, Pan, O, Perek, A, Reimerdes, H, Sheikh, U, Theiler, C, van Berkel, M, Wijkamp, T, Wischmeier, M, Bernert M., Wiesen S., Fevrier O., Kallenbach A., Koenders J. T. W., Sieglin B., Stroth U., Bosman T. O. S. J., Brida D., Cavedon M., David P., Dunne M. G., Henderson S., Kool B., Lunt T., McDermott R. M., Pan O., Perek A., Reimerdes H., Sheikh U., Theiler C., van Berkel M., Wijkamp T., and Wischmeier M.

Abstract

Future fusion reactors require a safe, steady-state divertor operation. With deep divertor detachment, which is typically induced by impurity seeding, the radiation concentrates in a small region at the X-point or on closed flux surfaces above the X-point. This so-called X-point radiator (XPR) moves further inside the confined region with increasing seeding and the location can be actively controlled. At AUG, the parameter space for operation with an XPR was significantly extended, using active feedback on the XPR location. The XPR is observed in nearly the whole operational space of AUG in the high-densities or high collisionality regime. ELM suppression is consistently observed in all cases where the XPR was moved to a significant height above the X-point. Direct measurements of density and temperature from the region around the XPR using the new divertor Thomson scattering system at AUG indicate that the temperature at the location of the XPR remains high (>30eV) and only the region towards the X-point cools down further. In this cold XPR core, the temperature reduces to about 1eV. An XPR is also observed in TCV by the injection of nitrogen as extrinsic impurity. This highlights that the wall material (W for AUG, C for TCV) or machine size does not play a significant role for the existence of the regime. However, the scenario appears to be less stable in TCV. First experiments show the necessity of an active control for the XPR: Depending on the wall conditions and the nitrogen wall storage, the required nitrogen seeding level to achieve an XPR changes. Both, the low temperatures measured radially outside of the radiation zone at AUG, and the lower stability of the XPR regime at TCV with the presence of carbon are consistent with the predictions of a one-dimensional model of the XPR. However, the model would predict the development of the cold XPR core, and significant radiation at the X-point might already exist before reaching this cold temperature solution.

Published
2023

32. Ultrafast collinear scattering and carrier multiplication in graphene

Author

Brida, D., Tomadin, A., Manzoni, C., Kim, Y. J., Lombardo, A., Milana, S., Nair, R. R., Novoselov, K. S., Ferrari, A. C., Cerullo, G., and Polini, M.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Graphene is emerging as a viable alternative to conventional optoelectronic, plasmonic, and nanophotonic materials. The interaction of light with carriers creates an out-of-equilibrium distribution, which relaxes on an ultrafast timescale to a hot Fermi-Dirac distribution, that subsequently cools via phonon emission. Here we combine pump-probe spectroscopy, featuring extreme temporal resolution and broad spectral coverage, with a microscopic theory based on the quantum Boltzmann equation, to investigate electron-electron collisions in graphene during the very early stages of relaxation. We identify the fundamental physical mechanisms controlling the ultrafast dynamics in graphene, in particular the significant role of ultrafast collinear scattering, enabling Auger processes, including charge multiplication, key to improving photovoltage generation and photodetectors., Comment: 11 pages, 5 figures

Published
2012
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33. Dynamics of four-photon photoluminescence in gold nanoantennas

Author

Biagioni, P., Brida, D., Huang, J. -S., Kern, J., Duò, L., Hecht, B., Finazzi, M., and Cerullo, G.

Subjects
Physics - Optics
Abstract

Two-pulse correlation is employed to investigate the temporal dynamics of both two-photon photoluminescence (2PPL) and four-photon photoluminescence (4PPL) in resonant and nonresonant nanoantennas excited at a wavelength of 800 nm. Our data are consistent with the same two-step model being the cause of both 4PPL and 2PPL, implying that the first excitation step in 4PPL is a three-photon sp->sp direct interband transition. Considering energy and parity conservation, we also explain why 4PPL behavior is favored over three-and five-photon photoluminescence in the power range below the damage threshold of our antennas. Since sizeable 4PPL requires larger peak intensities of the local field, we are able to select either 2PPL or 4PPL in the same gold nanoantennas by choosing a suitable laser pulse duration. We thus provide a first consistent model for the understanding of multiphoton photoluminescence generation in gold nanoantennas, opening new perspectives for applications ranging from the characterization of plasmonic resonances to biomedical imaging.

Published
2011
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34. Quantum interference between charge excitation paths in a solid state Mott insulator

Author

Wall, S., Brida, D., Clark, S. R., Ehrke, H. P., Jaksch, D., Ardavan, A., Bonora, S., Uemura, H., Takahashi, Y., Hasegawa, T., Okamoto, H., Cerullo, G., and Cavalleri, A.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

The competition between electron localization and de-localization in Mott insulators underpins the physics of strongly-correlated electron systems. Photo-excitation, which re-distributes charge between sites, can control this many-body process on the ultrafast timescale. To date, time-resolved studies have been performed in solids in which other degrees of freedom, such as lattice, spin, or orbital excitations come into play. However, the underlying quantum dynamics of bare electronic excitations has remained out of reach. Quantum many-body dynamics have only been detected in the controlled environment of optical lattices where the dynamics are slower and lattice excitations are absent. By using nearly-single-cycle near-IR pulses, we have measured coherent electronic excitations in the organic salt ET-F2TCNQ, a prototypical one-dimensional Mott Insulator. After photo-excitation, a new resonance appears on the low-energy side of the Mott gap, which oscillates at 25 THz. Time-dependent simulations of the Mott-Hubbard Hamiltonian reproduce the oscillations, showing that electronic delocalization occurs through quantum interference between bound and ionized holon-doublon pairs., Comment: 4 figures and supplementary information

Published
2009
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35. Electron-Phonon Coupling in High-Temperature Cuprate Superconductors Determined from Electron Relaxation Rates

Author

Gadermaier, C., Alexandrov, A. S., Kabanov, V. V., Kusar, P., Mertelj, T., Yao, X., Manzoni, C., Brida, D., Cerullo, G., and Mihailovic, D.

Subjects
Condensed Matter - Superconductivity
Abstract

We determined electronic relaxation times via pump-probe optical spectroscopy using sub-15 fs pulses for the normal state of two different cuprate superconductors.We show that the primary relaxation process is the electron-phonon interaction and extract a measure of its strength, the second moment of the Eliashberg function\lambda<\omega^{2}>=800\pm200 meV^{2} for La_{1.85}Sr_{0.15}CuO_{4} and \lambda<\omega^{2}>=400\pm100 meV^{2} for YBa_{2}Cu_{3}O_{6.5}. These values suggest a possible fundamental role of the electron-phonon interaction in the superconducting pairing mechanism., Comment: As published in PRL

Published
2009
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37. The X-Point radiating regime at ASDEX Upgrade and TCV

Author

Bernert, M., Wiesen, S., Février, O., Kallenbach, A., Koenders, J.T.W., Sieglin, B., Bosman, T.O.S.J., Kool, B., van Berkel, M., Wijkamp, T.A., Stroth, U., Brida, D., Cavedon, M., David, P., Dunne, M.G., Henderson, S., Lunt, T., McDermott, R.M., Pan, O., Perek, A., Reimerdes, H., Sheikh, U., Theiler, C., Wischmeier, M., Team, EUROfusionMST1, team, TCV, Team, ASDEXUpgrade, Bernert, M, Wiesen, S, Fevrier, O, Kallenbach, A, Koenders, J, Sieglin, B, Stroth, U, Bosman, T, Brida, D, Cavedon, M, David, P, Dunne, M, Henderson, S, Kool, B, Lunt, T, Mcdermott, R, Pan, O, Perek, A, Reimerdes, H, Sheikh, U, Theiler, C, van Berkel, M, Wijkamp, T, Wischmeier, M, Group Heemels, Control Systems Technology, Science and Technology of Nuclear Fusion, Fluids and Flows, EUROfusion MST1 Team, TCV Team, and ASDEX Upgrade Team, Max Planck Institute for Plasma Physics, Max Planck Society

Subjects
Radiative scenario, operation, Nuclear and High Energy Physics, Nuclear Energy and Engineering, X-point radiation, Materials Science (miscellaneous), Divertor detachment, Power exhaust, Radiative scenarios, marfe
Abstract

Future fusion reactors require a safe, steady-state divertor operation. With deep divertor detachment, which is typically induced by impurity seeding, the radiation concentrates in a small region at the X-point or on closed flux surfaces above the X-point. This so-called X-point radiator (XPR) moves further inside the confined region with increasing seeding and the location can be actively controlled. At AUG, the parameter space for operation with an XPR was significantly extended, using active feedback on the XPR location. The XPR is observed in nearly the whole operational space of AUG in the high-densities or high collisionality regime. ELM suppression is consistently observed in all cases where the XPR was moved to a significant height above the X-point. Direct measurements of density and temperature from the region around the XPR using the new divertor Thomson scattering system at AUG indicate that the temperature at the location of the XPR remains high (>30eV) and only the region towards the X-point cools down further. In this cold XPR core, the temperature reduces to about 1eV. An XPR is also observed in TCV by the injection of nitrogen as extrinsic impurity. This highlights that the wall material (W for AUG, C for TCV) or machine size does not play a significant role for the existence of the regime. However, the scenario appears to be less stable in TCV. First experiments show the necessity of an active control for the XPR: Depending on the wall conditions and the nitrogen wall storage, the required nitrogen seeding level to achieve an XPR changes. Both, the low temperatures measured radially outside of the radiation zone at AUG, and the lower stability of the XPR regime at TCV with the presence of carbon are consistent with the predictions of a one-dimensional model of the XPR. However, the model would predict the development of the cold XPR core, and significant radiation at the X-point might already exist before reaching this cold temperature solution.

Published
2023

40. Physics Exploitation of the new Divertor Thomson Scattering at ASDEX Upgrade

Author

Cavedon, M, Dux, R, Kurzan, B, Bernert, M, Brida, D, Henderson, S, Nishizawa, T, Lunt, T, Pan, O, Reimold, F, Stroth, U, Wischmeier, M, Wu, H, Cavedon M., Dux R., Kurzan B., Bernert M., Brida D., Henderson S., Nishizawa T., Lunt T., Pan O., Reimold F., Stroth U., Wischmeier M., Wu H., Cavedon, M, Dux, R, Kurzan, B, Bernert, M, Brida, D, Henderson, S, Nishizawa, T, Lunt, T, Pan, O, Reimold, F, Stroth, U, Wischmeier, M, Wu, H, Cavedon M., Dux R., Kurzan B., Bernert M., Brida D., Henderson S., Nishizawa T., Lunt T., Pan O., Reimold F., Stroth U., Wischmeier M., and Wu H.

Published
2022

41. Model for access and stability of the X-point radiator and the threshold for marfes in tokamak plasmas

Author

Stroth, U, Bernert, M, Brida, D, Cavedon, M, Dux, R, Huett, E, Lunt, T, Pan, O, Wischmeier, M, Stroth U., Bernert M., Brida D., Cavedon M., Dux R., Huett E., Lunt T., Pan O., Wischmeier M., Stroth, U, Bernert, M, Brida, D, Cavedon, M, Dux, R, Huett, E, Lunt, T, Pan, O, Wischmeier, M, Stroth U., Bernert M., Brida D., Cavedon M., Dux R., Huett E., Lunt T., Pan O., and Wischmeier M.

Abstract

Based on particle and energy balances, a reduced model is derived for the physical mechanisms leading to the occurrence of stable and unstable X-point radiators (XPRs), the latter also known as marfes. The leading roles of the neutral deuterium density in the divertor region for initiating XPRs is highlighted. An access condition is formulated whose parameter dependencies are consistent with experimental observations and which could also apply to the process of divertor detachment. With an exponential increase of the recombination rate at low temperature, the XPR becomes magnetohydrodynamically unstable, leading to a marfe and, possibly, to a disruption. A critical density for marfe occurrence is formulated with the upstream density and safety factor as leading parameters, as in the experiment. Marfes are predicted to be more likely in carbon devices than in impurity-seeded plasmas in tungsten devices. The edge plasma parameter domain where marfes occur resembles that used for active marfe avoidance schemes. Both the XPR and marfe occurrence parameter can be used to guide active discharge control.

Published
2022

42. Experimental investigation of L- and H-mode detachment via the divertor Thomson scattering at ASDEX Upgrade

Author

Cavedon, M, Kurzan, B, Bernert, M, Brida, D, Dux, R, Griener, M, Henderson, S, Huett, E, Nishizawa, T, Lunt, T, Pan, O, Stroth, U, Wischmeier, M, Wolfrum, E, Cavedon M., Kurzan B., Bernert M., Brida D., Dux R., Griener M., Henderson S., Huett E., Nishizawa T., Lunt T., Pan O., Stroth U., Wischmeier M., Wolfrum E., Cavedon, M, Kurzan, B, Bernert, M, Brida, D, Dux, R, Griener, M, Henderson, S, Huett, E, Nishizawa, T, Lunt, T, Pan, O, Stroth, U, Wischmeier, M, Wolfrum, E, Cavedon M., Kurzan B., Bernert M., Brida D., Dux R., Griener M., Henderson S., Huett E., Nishizawa T., Lunt T., Pan O., Stroth U., Wischmeier M., and Wolfrum E.

Abstract

The capabilities of the newly installed divertor Thomson Scattering (DTS) diagnostic (Kurzan et al 2021 J. Inst. 16 C09012) at ASDEX Upgrade (AUG) have been demonstrated by measuring 2D electron densities n e and temperatures T e from attached to fully detached divertor conditions in L- and H-mode. The collected dataset is a breakthrough for divertor studies at AUG in which such measurements have been so far missing. Besides highlighting the strengths and limits of the DTS system, this work provides confirmations and new insights into detachment physics. The transition between partial and pronounced detachment correlates with a 2D redistribution of the electron density from the inner to the outer divertor in both L- and H-mode. In pronounced detachment, a strong parallel pressure gradient could be confirmed throughout the complete SOL. Finally, measurements of n e and T e of a stable X-point radiator revealed local temperatures as low as 1 eV within the confined plasma, whereas the pressure is shown to be constant on closed field lines.

Published
2022

43. Overview of the TCV tokamak experimental programme

Author

Reimerdes, H, Agostini, M, Alessi, E, Alberti, S, Andrebe, Y, Arnichand, H, Balbin, J, Bagnato, F, Baquero-Ruiz, M, Bernert, M, Bin, W, Blanchard, P, Blanken, T, Boedo, J, Brida, D, Brunner, S, Bogar, C, Bogar, O, Bolzonella, T, Bombarda, F, Bouquey, F, Bowman, C, Brunetti, D, Buermans, J, Bufferand, H, Calacci, L, Camenen, Y, Carli, S, Carnevale, D, Carpanese, F, Causa, F, Cavalier, J, Cavedon, M, Cazabonne, J, Cerovsky, J, Chandra, R, Chandrarajan Jayalekshmi, A, Chellai, O, Chmielewski, P, Choi, D, Ciraolo, G, Classen, I, Coda, S, Colandrea, C, Dal Molin, A, David, P, De Baar, M, Decker, J, Dekeyser, W, De Oliveira, H, Douai, D, Dreval, M, Dunne, M, Duval, B, Elmore, S, Embreus, O, Eriksson, F, Faitsch, M, Falchetto, G, Farnik, M, Fasoli, A, Fedorczak, N, Felici, F, Fevrier, O, Ficker, O, Fil, A, Fontana, M, Fransson, E, Frassinetti, L, Furno, I, Gahle, D, Galassi, D, Galazka, K, Galperti, C, Garavaglia, S, Garcia-Munoz, M, Geiger, B, Giacomin, M, Giruzzi, G, Gobbin, M, Golfinopoulos, T, Goodman, T, Gorno, S, Granucci, G, Graves, J, Griener, M, Gruca, M, Gyergyek, T, Haelterman, R, Hakola, A, Han, W, Happel, T, Harrer, G, Harrison, J, Henderson, S, Hogeweij, G, Hogge, J, Hoppe, M, Horacek, J, Huang, Z, Iantchenko, A, Innocente, P, Insulander Bjork, K, Ionita-Schrittweiser, C, Isliker, H, Jardin, A, Jaspers, R, Karimov, R, Karpushov, A, Kazakov, Y, Komm, M, Kong, M, Kovacic, J, Krutkin, O, Kudlacek, O, Kumar, U, Kwiatkowski, R, Labit, B, Laguardia, L, Lammers, J, Laribi, E, Laszynska, E, Lazaros, A, Linder, O, Linehan, B, Lipschultz, B, Llobet, X, Loizu, J, Lunt, T, Macusova, E, Marandet, Y, Maraschek, M, Marceca, G, Marchetto, C, Marchioni, S, Marmar, E, Martin, Y, Martinelli, L, Matos, F, Maurizio, R, Mayoral, M, Mazon, D, Menkovski, V, Merle, A, Merlo, G, Meyer, H, Mikszuta-Michalik, K, Molina Cabrera, P, Morales, J, Moret, J, Moro, A, Moulton, D, Muhammed, H, Myatra, O, Mykytchuk, D, Napoli, F, Nem, R, Nielsen, A, Nocente, M, Nowak, S, Offeddu, N, Olsen, J, Orsitto, F, Pan, O, Papp, G, Pau, A, Perek, A, Pesamosca, F, Peysson, Y, Pigatto, L, Piron, C, Poradzinski, M, Porte, L, Putterich, T, Rabinski, M, Raj, H, Rasmussen, J, Ratta, G, Ravensbergen, T, Ricci, D, Ricci, P, Rispoli, N, Riva, F, Rivero-Rodriguez, J, Salewski, M, Sauter, O, Schmidt, B, Schrittweiser, R, Sharapov, S, Sheikh, U, Sieglin, B, Silva, M, Smolders, A, Snicker, A, Sozzi, C, Spolaore, M, Stagni, A, Stipani, L, Sun, G, Tala, T, Tamain, P, Tanaka, K, Tema Biwole, A, Terranova, D, Terry, J, Testa, D, Theiler, C, Thornton, A, Thrysoe, A, Torreblanca, H, Tsui, C, Vaccaro, D, Vallar, M, Van Berkel, M, Van Eester, D, Van Kampen, R, Van Mulders, S, Verhaegh, K, Verhaeghe, T, Vianello, N, Villone, F, Viezzer, E, Vincent, B, Voitsekhovitch, I, Vu, N, Walkden, N, Wauters, T, Weisen, H, Wendler, N, Wensing, M, Widmer, F, Wiesen, S, Wischmeier, M, Wijkamp, T, Wunderlich, D, Wuthrich, C, Yanovskiy, V, Zebrowski, J, Reimerdes H., Agostini M., Alessi E., Alberti S., Andrebe Y., Arnichand H., Balbin J., Bagnato F., Baquero-Ruiz M., Bernert M., Bin W., Blanchard P., Blanken T. C., Boedo J. A., Brida D., Brunner S., Bogar C., Bogar O., Bolzonella T., Bombarda F., Bouquey F., Bowman C., Brunetti D., Buermans J., Bufferand H., Calacci L., Camenen Y., Carli S., Carnevale D., Carpanese F., Causa F., Cavalier J., Cavedon M., Cazabonne J. A., Cerovsky J., Chandra R., Chandrarajan Jayalekshmi A., Chellai O., Chmielewski P., Choi D., Ciraolo G., Classen I. G. J., Coda S., Colandrea C., Dal Molin A., David P., De Baar M. R., Decker J., Dekeyser W., De Oliveira H., Douai D., Dreval M., Dunne M. G., Duval B. P., Elmore S., Embreus O., Eriksson F., Faitsch M., Falchetto G., Farnik M., Fasoli A., Fedorczak N., Felici F., Fevrier O., Ficker O., Fil A., Fontana M., Fransson E., Frassinetti L., Furno I., Gahle D. S., Galassi D., Galazka K., Galperti C., Garavaglia S., Garcia-Munoz M., Geiger B., Giacomin M., Giruzzi G., Gobbin M., Golfinopoulos T., Goodman T., Gorno S., Granucci G., Graves J. P., Griener M., Gruca M., Gyergyek T., Haelterman R., Hakola A., Han W., Happel T., Harrer G., Harrison J. R., Henderson S., Hogeweij G. M. D., Hogge J. -P., Hoppe M., Horacek J., Huang Z., Iantchenko A., Innocente P., Insulander Bjork K., Ionita-Schrittweiser C., Isliker H., Jardin A., Jaspers R. J. E., Karimov R., Karpushov A. N., Kazakov Y., Komm M., Kong M., Kovacic J., Krutkin O., Kudlacek O., Kumar U., Kwiatkowski R., Labit B., Laguardia L., Lammers J. T., Laribi E., Laszynska E., Lazaros A., Linder O., Linehan B., Lipschultz B., Llobet X., Loizu J., Lunt T., Macusova E., Marandet Y., Maraschek M., Marceca G., Marchetto C., Marchioni S., Marmar E. S., Martin Y., Martinelli L., Matos F., Maurizio R., Mayoral M. -L., Mazon D., Menkovski V., Merle A., Merlo G., Meyer H., Mikszuta-Michalik K., Molina Cabrera P. A., Morales J., Moret J. -M., Moro A., Moulton D., Muhammed H., Myatra O., Mykytchuk D., Napoli F., Nem R. D., Nielsen A. H., Nocente M., Nowak S., Offeddu N., Olsen J., Orsitto F. P., Pan O., Papp G., Pau A., Perek A., Pesamosca F., Peysson Y., Pigatto L., Piron C., Poradzinski M., Porte L., Putterich T., Rabinski M., Raj H., Rasmussen J. J., Ratta G. A., Ravensbergen T., Ricci D., Ricci P., Rispoli N., Riva F., Rivero-Rodriguez J. F., Salewski M., Sauter O., Schmidt B. S., Schrittweiser R., Sharapov S., Sheikh U. A., Sieglin B., Silva M., Smolders A., Snicker A., Sozzi C., Spolaore M., Stagni A., Stipani L., Sun G., Tala T., Tamain P., Tanaka K., Tema Biwole A., Terranova D., Terry J. L., Testa D., Theiler C., Thornton A., Thrysoe A., Torreblanca H., Tsui C. K., Vaccaro D., Vallar M., Van Berkel M., Van Eester D., Van Kampen R. J. R., Van Mulders S., Verhaegh K., Verhaeghe T., Vianello N., Villone F., Viezzer E., Vincent B., Voitsekhovitch I., Vu N. M. T., Walkden N., Wauters T., Weisen H., Wendler N., Wensing M., Widmer F., Wiesen S., Wischmeier M., Wijkamp T. A., Wunderlich D., Wuthrich C., Yanovskiy V., Zebrowski J., Reimerdes, H, Agostini, M, Alessi, E, Alberti, S, Andrebe, Y, Arnichand, H, Balbin, J, Bagnato, F, Baquero-Ruiz, M, Bernert, M, Bin, W, Blanchard, P, Blanken, T, Boedo, J, Brida, D, Brunner, S, Bogar, C, Bogar, O, Bolzonella, T, Bombarda, F, Bouquey, F, Bowman, C, Brunetti, D, Buermans, J, Bufferand, H, Calacci, L, Camenen, Y, Carli, S, Carnevale, D, Carpanese, F, Causa, F, Cavalier, J, Cavedon, M, Cazabonne, J, Cerovsky, J, Chandra, R, Chandrarajan Jayalekshmi, A, Chellai, O, Chmielewski, P, Choi, D, Ciraolo, G, Classen, I, Coda, S, Colandrea, C, Dal Molin, A, David, P, De Baar, M, Decker, J, Dekeyser, W, De Oliveira, H, Douai, D, Dreval, M, Dunne, M, Duval, B, Elmore, S, Embreus, O, Eriksson, F, Faitsch, M, Falchetto, G, Farnik, M, Fasoli, A, Fedorczak, N, Felici, F, Fevrier, O, Ficker, O, Fil, A, Fontana, M, Fransson, E, Frassinetti, L, Furno, I, Gahle, D, Galassi, D, Galazka, K, Galperti, C, Garavaglia, S, Garcia-Munoz, M, Geiger, B, Giacomin, M, Giruzzi, G, Gobbin, M, Golfinopoulos, T, Goodman, T, Gorno, S, Granucci, G, Graves, J, Griener, M, Gruca, M, Gyergyek, T, Haelterman, R, Hakola, A, Han, W, Happel, T, Harrer, G, Harrison, J, Henderson, S, Hogeweij, G, Hogge, J, Hoppe, M, Horacek, J, Huang, Z, Iantchenko, A, Innocente, P, Insulander Bjork, K, Ionita-Schrittweiser, C, Isliker, H, Jardin, A, Jaspers, R, Karimov, R, Karpushov, A, Kazakov, Y, Komm, M, Kong, M, Kovacic, J, Krutkin, O, Kudlacek, O, Kumar, U, Kwiatkowski, R, Labit, B, Laguardia, L, Lammers, J, Laribi, E, Laszynska, E, Lazaros, A, Linder, O, Linehan, B, Lipschultz, B, Llobet, X, Loizu, J, Lunt, T, Macusova, E, Marandet, Y, Maraschek, M, Marceca, G, Marchetto, C, Marchioni, S, Marmar, E, Martin, Y, Martinelli, L, Matos, F, Maurizio, R, Mayoral, M, Mazon, D, Menkovski, V, Merle, A, Merlo, G, Meyer, H, Mikszuta-Michalik, K, Molina Cabrera, P, Morales, J, Moret, J, Moro, A, Moulton, D, Muhammed, H, Myatra, O, Mykytchuk, D, Napoli, F, Nem, R, Nielsen, A, Nocente, M, Nowak, S, Offeddu, N, Olsen, J, Orsitto, F, Pan, O, Papp, G, Pau, A, Perek, A, Pesamosca, F, Peysson, Y, Pigatto, L, Piron, C, Poradzinski, M, Porte, L, Putterich, T, Rabinski, M, Raj, H, Rasmussen, J, Ratta, G, Ravensbergen, T, Ricci, D, Ricci, P, Rispoli, N, Riva, F, Rivero-Rodriguez, J, Salewski, M, Sauter, O, Schmidt, B, Schrittweiser, R, Sharapov, S, Sheikh, U, Sieglin, B, Silva, M, Smolders, A, Snicker, A, Sozzi, C, Spolaore, M, Stagni, A, Stipani, L, Sun, G, Tala, T, Tamain, P, Tanaka, K, Tema Biwole, A, Terranova, D, Terry, J, Testa, D, Theiler, C, Thornton, A, Thrysoe, A, Torreblanca, H, Tsui, C, Vaccaro, D, Vallar, M, Van Berkel, M, Van Eester, D, Van Kampen, R, Van Mulders, S, Verhaegh, K, Verhaeghe, T, Vianello, N, Villone, F, Viezzer, E, Vincent, B, Voitsekhovitch, I, Vu, N, Walkden, N, Wauters, T, Weisen, H, Wendler, N, Wensing, M, Widmer, F, Wiesen, S, Wischmeier, M, Wijkamp, T, Wunderlich, D, Wuthrich, C, Yanovskiy, V, Zebrowski, J, Reimerdes H., Agostini M., Alessi E., Alberti S., Andrebe Y., Arnichand H., Balbin J., Bagnato F., Baquero-Ruiz M., Bernert M., Bin W., Blanchard P., Blanken T. C., Boedo J. A., Brida D., Brunner S., Bogar C., Bogar O., Bolzonella T., Bombarda F., Bouquey F., Bowman C., Brunetti D., Buermans J., Bufferand H., Calacci L., Camenen Y., Carli S., Carnevale D., Carpanese F., Causa F., Cavalier J., Cavedon M., Cazabonne J. A., Cerovsky J., Chandra R., Chandrarajan Jayalekshmi A., Chellai O., Chmielewski P., Choi D., Ciraolo G., Classen I. G. J., Coda S., Colandrea C., Dal Molin A., David P., De Baar M. R., Decker J., Dekeyser W., De Oliveira H., Douai D., Dreval M., Dunne M. G., Duval B. P., Elmore S., Embreus O., Eriksson F., Faitsch M., Falchetto G., Farnik M., Fasoli A., Fedorczak N., Felici F., Fevrier O., Ficker O., Fil A., Fontana M., Fransson E., Frassinetti L., Furno I., Gahle D. S., Galassi D., Galazka K., Galperti C., Garavaglia S., Garcia-Munoz M., Geiger B., Giacomin M., Giruzzi G., Gobbin M., Golfinopoulos T., Goodman T., Gorno S., Granucci G., Graves J. P., Griener M., Gruca M., Gyergyek T., Haelterman R., Hakola A., Han W., Happel T., Harrer G., Harrison J. R., Henderson S., Hogeweij G. M. D., Hogge J. -P., Hoppe M., Horacek J., Huang Z., Iantchenko A., Innocente P., Insulander Bjork K., Ionita-Schrittweiser C., Isliker H., Jardin A., Jaspers R. J. E., Karimov R., Karpushov A. N., Kazakov Y., Komm M., Kong M., Kovacic J., Krutkin O., Kudlacek O., Kumar U., Kwiatkowski R., Labit B., Laguardia L., Lammers J. T., Laribi E., Laszynska E., Lazaros A., Linder O., Linehan B., Lipschultz B., Llobet X., Loizu J., Lunt T., Macusova E., Marandet Y., Maraschek M., Marceca G., Marchetto C., Marchioni S., Marmar E. S., Martin Y., Martinelli L., Matos F., Maurizio R., Mayoral M. -L., Mazon D., Menkovski V., Merle A., Merlo G., Meyer H., Mikszuta-Michalik K., Molina Cabrera P. A., Morales J., Moret J. -M., Moro A., Moulton D., Muhammed H., Myatra O., Mykytchuk D., Napoli F., Nem R. D., Nielsen A. H., Nocente M., Nowak S., Offeddu N., Olsen J., Orsitto F. P., Pan O., Papp G., Pau A., Perek A., Pesamosca F., Peysson Y., Pigatto L., Piron C., Poradzinski M., Porte L., Putterich T., Rabinski M., Raj H., Rasmussen J. J., Ratta G. A., Ravensbergen T., Ricci D., Ricci P., Rispoli N., Riva F., Rivero-Rodriguez J. F., Salewski M., Sauter O., Schmidt B. S., Schrittweiser R., Sharapov S., Sheikh U. A., Sieglin B., Silva M., Smolders A., Snicker A., Sozzi C., Spolaore M., Stagni A., Stipani L., Sun G., Tala T., Tamain P., Tanaka K., Tema Biwole A., Terranova D., Terry J. L., Testa D., Theiler C., Thornton A., Thrysoe A., Torreblanca H., Tsui C. K., Vaccaro D., Vallar M., Van Berkel M., Van Eester D., Van Kampen R. J. R., Van Mulders S., Verhaegh K., Verhaeghe T., Vianello N., Villone F., Viezzer E., Vincent B., Voitsekhovitch I., Vu N. M. T., Walkden N., Wauters T., Weisen H., Wendler N., Wensing M., Widmer F., Wiesen S., Wischmeier M., Wijkamp T. A., Wunderlich D., Wuthrich C., Yanovskiy V., and Zebrowski J.

Abstract

The tokamak à configuration variable (TCV) continues to leverage its unique shaping capabilities, flexible heating systems and modern control system to address critical issues in preparation for ITER and a fusion power plant. For the 2019-20 campaign its configurational flexibility has been enhanced with the installation of removable divertor gas baffles, its diagnostic capabilities with an extensive set of upgrades and its heating systems with new dual frequency gyrotrons. The gas baffles reduce coupling between the divertor and the main chamber and allow for detailed investigations on the role of fuelling in general and, together with upgraded boundary diagnostics, test divertor and edge models in particular. The increased heating capabilities broaden the operational regime to include Te/Ti ∼1 and have stimulated refocussing studies from L-mode to H-mode across a range of research topics. ITER baseline parameters were reached in type-I ELMy H-modes and alternative regimes with 'small' (or no) ELMs explored. Most prominently, negative triangularity was investigated in detail and confirmed as an attractive scenario with H-mode level core confinement but an L-mode edge. Emphasis was also placed on control, where an increased number of observers, actuators and control solutions became available and are now integrated into a generic control framework as will be needed in future devices. The quantity and quality of results of the 2019-20 TCV campaign are a testament to its successful integration within the European research effort alongside a vibrant domestic programme and international collaborations.

Published
2022

48. The X-Point radiating regime at ASDEX Upgrade and TCV

Author

EUROfusion MST1 Team, the TCV team, the ASDEX-Upgrade team, Bernert, M., Wiesen, S., Février, O., Kallenbach, A., Koenders, J.T.W., Sieglin, B., Stroth, U., Bosman, T.O.S.J., Brida, D., Cavedon, M., David, P., Dunne, M.G., Henderson, S., Kool, B., Lunt, T., McDermott, R.M., Pan, O., Perek, A., Reimerdes, H., Sheikh, U., Theiler, C., van Berkel, M., Wijkamp, T., Wischmeier, M., EUROfusion MST1 Team, the TCV team, the ASDEX-Upgrade team, Bernert, M., Wiesen, S., Février, O., Kallenbach, A., Koenders, J.T.W., Sieglin, B., Stroth, U., Bosman, T.O.S.J., Brida, D., Cavedon, M., David, P., Dunne, M.G., Henderson, S., Kool, B., Lunt, T., McDermott, R.M., Pan, O., Perek, A., Reimerdes, H., Sheikh, U., Theiler, C., van Berkel, M., Wijkamp, T., and Wischmeier, M.

Abstract

Future fusion reactors require a safe, steady-state divertor operation. With deep divertor detachment, which is typically induced by impurity seeding, the radiation concentrates in a small region at the X-point or on closed flux surfaces above the X-point. This so-called X-point radiator (XPR) moves further inside the confined region with increasing seeding and the location can be actively controlled. At AUG, the parameter space for operation with an XPR was significantly extended, using active feedback on the XPR location. The XPR is observed in nearly the whole operational space of AUG in the high-densities or high collisionality regime. ELM suppression is consistently observed in all cases where the XPR was moved to a significant height above the X-point. Direct measurements of density and temperature from the region around the XPR using the new divertor Thomson scattering system at AUG indicate that the temperature at the location of the XPR remains high (>30eV) and only the region towards the X-point cools down further. In this cold XPR core, the temperature reduces to about 1eV. An XPR is also observed in TCV by the injection of nitrogen as extrinsic impurity. This highlights that the wall material (W for AUG, C for TCV) or machine size does not play a significant role for the existence of the regime. However, the scenario appears to be less stable in TCV. First experiments show the necessity of an active control for the XPR: Depending on the wall conditions and the nitrogen wall storage, the required nitrogen seeding level to achieve an XPR changes. Both, the low temperatures measured radially outside of the radiation zone at AUG, and the lower stability of the XPR regime at TCV with the presence of carbon are consistent with the predictions of a one-dimensional model of the XPR. However, the model would predict the development of the cold XPR core, and significant radiation at the X-point might already exist before reaching this cold temperature soluti

Published
2023

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