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Alarge superconducting machine, JT-60SA has been constructed to provide major contributions to the ITER program and DEMO design. For the success of the ITER project and fusion reactor, understanding and development of plasma controllability in ITER and DEMO relevant higher beta regimes are essential. JT-60SA has focused the program on the plasma controllability for scenario development and risk mitigation in ITER as well as on investigating DEMO relevant regimes. This paper summarizes the high research priorities and strategy for the JT-60SA project. Recent works on simulation studies to prepare the plasma physics and control experiments are presented, such as plasma breakdown and equilibrium controls, hybrid and steady-state scenario development, and risk mitigation techniques. Contributions of JT-60SA to ITER and DEMOhave been clarified through those studies. Peer Reviewed Article escrit per 127 autors/autores: M Yoshida, G Giruzzi, N Aiba, J F Artaud, J Ayllon-Guerola, L Balbinot, OBeeke, E Belonohy, P Bettini, W Bin, A Bierwage, T Bolzonella, M Bonotto, CBoulbe, J Buermans, M Chernyshova, S Coda, R Coelho, S Davis, C Day, GDeTommasi, M Dibon, A Ejiri, G Falchetto, A Fassina, B Faugeras, L Figini, M Fukumoto, S Futatani, K Galazka, J Garcia, M Garcia-Muñoz, L Garzotti, L Giacomelli, L Giudicotti, S Hall, N Hayashi, C Hoa, M Honda, K Hoshino, M Iafrati, A Iantchenko, S Ide, S Iio, R Imazawa, S Inoue, A Isayama, E Joffrin, K Kamiya, Y Ko, M Kobayashi, T Kobayashi, G Kocsis, A Kovacsik, T Kurki-Suonio, B Lacroix, P Lang, Ph Lauber, A Louzguiti, E de la Luna, G Marchiori, M Mattei, A Matsuyama, S Mazzi, A Mele, F Michel, Y Miyata, J Morales, P Moreau, A Moro, T Nakano, M Nakata, E Narita, R Neu, S Nicollet, M Nocente, S Nowak, F P Orsitto, V Ostuni, Y Ohtani, N Oyama, R Pasqualotto, B Pégourié, E Perelli, L Pigatto, C Piccinni, A Pironti, P Platania, B Ploeckl, D Ricci, P Roussel, G Rubino, R Sano, K Särkimäki, K Shinohara, S Soare, C Sozzi, S Sumida, T Suzuki, Y Suzuki, T Szabolics, T Szepesi, Y Takase, M Takech, N Tamura, K Tanaka, H Tanaka, M Tardocchi, A Terakado, H Tojo, T Tokuzawa, A Torre, N Tsujii, H Tsutsui, Y Ueda, H Urano, M Valisa, M Vallar, J Vega, F Villone, T Wakatsuki, T Wauters, M Wischmeier, S Yamoto, L Zani

This paper suggests the use of two optical elements for laser transfer in Thomson scattering diagnostics, which are widely used for other laser applications. YAG lasers amplified by flash lamps (repetition frequency of 50–100 Hz having a few Joules output) can sometimes have adverse effects such as peaked beam profiles and wavefront distortion. We used a beam homogenizer, which is a refractive optical element, to change the beam profile from peaked to non-peaked at a designated position. Using a super-Gaussian output profile when amplifying lasers facilitated longer—by a factor of 1.5 (=300 mm/200 mm) compared with top-hat beam profile—sustained distances, i.e. the distance along the laser path having a non-peaked profile. In terms of beam quality, wavefront distortion broke the beam profile in the far field. We used a deformable mirror to correct and flatten the wavefront of the beam. A YAG laser having a wavefront distortion of 0.46λ peak-to-valley was used to test the application of the deformable mirror, the results of which improved wavefront distortion to a wavelength of 0.1λ peak-to-valley.

Tulips have a variety of floral scents. Although the charm of tulip is a variety of colours and shapes, there are a few fragrant cultivars. When you smell the tulip scent well, you can feel various scents such as citrus-like, honey-like, green-like. We selected 86 cultivars of tulip that have characteristics floral odor. About 183 scent compounds ranging from terpenoids and benzenoids to fatty acid-derivatives were detected by GC-MS analysis. The major scent compounds were five monoterpenoids (eucalyptol, linalool, d-limonene, trans-b-ocimene, and a-pinene), four sesquiterpenoids (caryophyllene, a-farnesene, geranyl acetone, and b-ionone), six benzenoids (acetophenone, benzaldehyde, benzyl alcohol, 3,5-dimethoxytoluene, methyl salicylate, and 2-phenylethanol), and five fatty acid derivatives (decanal, 2-hexenal, cis-3-hexenol, cis-3-hexenyl acetate, and octanal). Tulip cultivars were classified into nine groups according to the composition of major scent components and sensory assessment of a living flower: group 1, anise (7 cultivars, e.g. ‘Candy Prince’); group 2, citrus (21 cultivars, e.g. ‘Advance’); group 3, fruity (14 cultivars, e.g. ‘Sane’); group 4, green (16 cultivars, e.g. ‘Cum Laude’); group 5, herbal (16 cultivars, e.g. ‘Davenport’); group 6, herbal-honey (1 cultivar, ‘Nagoriyuki’); group 7, rosy (2 cultivars, e.g. ‘Monte Rosa’); group 8, spicy (7 cultivars, e.g. ‘Ben van Zanten’); and group 9, woody (2 cultivars, e.g. ‘Queen of night’). It is thought that the diversity of floral scent of tulips is cause.

Measuring the time variation of the wavenumber spectrum of turbulence is important for understanding the characteristics of high-temperature plasmas, and the application of a Doppler reflectometer with simultaneous multi-frequency sources is expected. To implement this diagnostic in future fusion devices, the use of a phased array antenna (PAA) that can scan microwave beams without moving antennas is recommended. Since the frequency-scanning waveguide leaky-wave antenna-type PAA has a complex structure, we have investigated its characteristics by modeling it with 3D metal powder additive manufacturing (AM). First, a single waveguide is fabricated to understand the characteristics of 3D AM techniques, and it is clear that there are differences in performance depending on the direction of manufacture and surface treatment. Then, a PAA is made, and it is confirmed that the beam can be emitted in any direction by frequency scanning. The plasma flow velocity can be measured by applying the 3D manufacturing PAA to plasma measurement.

Two types of back scattering systems are utilized for high temperature fusion plasma turbulence study. W-band backscattering system is used for measuring the electron Larmor radius scale turbulence and around Q-band frequency comb Doppler backscattering system have been designed for measuring the ion Larmor radius scale turbulence.

A fast charge exchange recombination spectroscopy (CXRS) system has been developed for the real-time measurement and feedback control of ion temperature ( T i ) profile and toroidal rotation velocity ( V t ) in JT-60U. In order to control T i and V t in real-time, the charge exchange recombination spectroscopy with high time resolution, the real-time processor system, and the real-time control system have been developed. Utilizing this system, real-time control of the T i gradient between r / a ∼ 0.25–0.5 has been demonstrated with neutral beams at high beta plasmas (normalized beta β N ∼ 1.6–2.8). The strength of the internal transport barrier is controlled. Moreover, the real-time control of V t has been demonstrated from counter (anti-parallel to the plasma current, I p ) to co (parallel to the I p ) direction. Then the behavior of edge localized mode (ELM) is changed by controlling the V t .

We performed the elastic neutron scattering experiments on the mixed compounds CeRh 1 - x Co x In 5 , and found that doping Co into CeRhIn 5 dramatically changes the antiferromagnetic (AF) structure. The incommensurate AF state with the propagation vector of q h = ( 1 2 , 1 2 , ∼ 0.3 ) observed in pure CeRhIn 5 is suppressed with increasing x , and new AF states with an incommensurate q 1 = ( 1 2 , 1 2 , ∼ 0.4 ) and a commensurate q c = ( 1 2 , 1 2 , 1 2 ) modulations simultaneously develop near the AF quantum critical point: x c ∼ 0.8 . These results suggest that the AF correlations with the q c and q 1 modulations enhanced in the intermediate Co concentrations may play a crucial role in the evolution of the superconductivity observed above x ∼ 0.4 .

Purpose: The quantification of coronary flow reserve（CFR）calculated as the ratio of the myocardial blood flow（MBF）during adenosine triphosphate（ATP）stress to MBF at rest is a useful method for evaluating the functional severity of coronary artery disease（CAD）using 15O-H2O positron emission tomography（PET）. The shorter acquisition time may reduce dyspnea and other side effects of ATP stress and may also reduce the effect of body movements during data acquisition. However, the impact of the shorter data acquisition time on the accuracy of MBF quantification has not been studied. In this retrospective study, we evaluated the accuracy of the MBF and CFR values obtained with shorter scan times using 15O-H2O PET. Methods: Thirty patients suspected of having CAD（22 males, 8 females; age 56.5±8.8 yrs）and 17 healthy controls（17 males; age 27.7±6.2 yrs）underwent PET during rest and PET with ATP stress dynamic 15O-H2O. The MBF was estimated with a one-tissue compartment model analysis. MBF and CFR values were calculated using the first 2-min and 3-min PET data of 15O-H2O as shorter data acquisitions. These data were compared to the standard 6-min PET acquisition data. Results: With the use of the 3-min data, the regions of interest（ROIs）in the left ventricular（LV）chamber and myocardium could be set for all of the subjects. The intraclass correlation coefficients （ICCs）between the 3-min data and 6-min data of the rest MBF, stress MBF and CFR were 0.869, 0.870, and 0.819 in the patients, and 0.912, 0.910, and 0.930 in the controls. The 3-min CFR data showed a significant difference between the patients and controls（2.22±1.02 vs. 4.02±1.50, p＜0.01）, as did the 6-min data（2.19±0.92 vs. 4.16±1.39, p＜0.01）. However, the CFR based on 2-min data did not show a significant difference（1.96±1.66 vs. 2.73±1.03, p=0.088）. Using a receiver operating characteristic（ROC）analysis, we observed that both the 3-min and 6-min CFR data could be used to separate the CAD patients and controls. Conclusions: A 3-min, but not 2-min, scan with 15O-H2O PET can be used for the quantitative evaluation of MBF and CFR. Keywords: 15O-H2O, Myocardial blood flow, Pharmacological stress, Positron emission tomography, Shorter acquisition time Ann Nucl Cardiol 2016；2（1）：0-0

The concept for a compact DEMO reactor named 'SlimCS' is presented. Distinctive features of the concept are low aspect ratio (A = 2.6) and use of a reduced-size centre solenoid (CS) which has the function of plasma shaping rather than poloidal flux supply. The reduced-size CS enables us to introduce a thin toroidal field coil system which contributes to reducing the weight and perhaps lessening the construction cost. Low-A has merits of vertical stability for high elongation (κ) and high normalized beta (βN), which leads to a high power density with reasonable physics requirements. This is because high κ facilitates high nGW (because of an increase in Ip), which allows efficient use of the capacity of high βN. From an engineering aspect, low-A may ensure ease in designing blanket modules robust to electromagnetic forces acting on disruptions. Thus, a superconducting low-A tokamak reactor such as SlimCS can be a promising DEMO concept with physics and engineering advantages.

The characteristics of momentum transport and plasma rotation in the toroidal direction are studied, using near-perpendicular neutral beam injection (PERP-NBI), co tangential and counter (CTR) tangential NBI in JT-60U. Diffusive and non-diffusive terms of momentum transport are evaluated from the transient analysis by using the momentum source modulation. Fast ion losses due to the toroidal field ripple, which locally induces the edge CTR rotation, are used as a novel momentum source. Parameter dependence of these transport coefficients i.e. the toroidal momentum diffusivity (?) and the convection velocity (Vconv), and the relation between momentum and heat diffusivities (?i) are investigated in L-mode plasmas systematically. The toroidal momentum diffusivity increases with increasing heating power and decreases with increasing plasma current. The relation of ? and ?i to some non-dimensional parameters is investigated. A clear dependence of ?/?i on normalized plasma pressure (?N) is observed. It is also found that toroidal rotation velocity profiles in the case with and without external torque input can be almost reproduced by ? and Vconv estimated from the transient momentum transport analysis at low ? (?N < 0.4).

Results of active control of neoclassical tearing modes (NTMs) by electron cyclotron current drive (ECCD) in JT-60U are described. Growth of an NTM with poloidal mode number m = 3 and toroidal mode number n = 2 has been suppressed by ECCD inside the sawtooth inversion radius in the co-direction, showing the possibility of the coexistence of sawtooth oscillations and a small-amplitude m/n = 3/2 NTM without large confinement degradation. Stabilization of an m/n = 2/1 NTM by ECCD at the mode rational surface has been demonstrated with a small ratio of the current density driven by the electron cyclotron (EC) wave to the local bootstrap current density (∼0.5). In addition, dependence of the stabilization effect on ECCD location has been investigated in detail. It has been found that an m/n = 2/1 NTM can be completely stabilized with the misalignment of the ECCD location less than about half of the full island width, and that the m/n = 2/1 NTM is destabilized with the misalignment comparable to the full island width. Time-dependent, self-consistent simulation of magnetic island evolution using the TOPICS code has shown that the stabilization and destabilization of an m/n = 2/1 NTM are well reproduced with the same set of coefficients of the modified Rutherford equation. The TOPICS simulation has also clarified that EC wave power required for complete stabilization can be significantly reduced by narrowing the ECCD deposition width.

The effects of toroidal rotation and toroidal field (TF) ripple on the edge pedestal structure and edge-localized-modes (ELMs) were examined in JT-60U. The amplitude of the TF ripple was changed by the installation of ferritic steel tiles (FSTs). The profile of toroidal rotation VT became less counter with FSTs, particularly in the case where co-NBI was used in a large volume configuration. In this case, the plasma pressure was raised across the whole profile of the plasma. At the plasma edge, higher pedestal temperature was obtained with the growth of pedestal width. However, the effect of FSTs became less significant in a small volume configuration. As the VT became less counter at the pedestal, ELM frequency fELM was reduced and ELM energy loss ΔWELM was increased at fixed power crossing the separatrix Psep. The observed larger ELM energy drop at VT in a relatively co-direction involves the ELM perturbations of the electron temperature profile across an ELM that extends radially more inward. In addition, the inter-ELM transport loss is reduced and the pedestal pressure pped is weakly raised. The effect of FSTs appeared clearly in the large volume configuration where pped is raised even at a given VT at the pedestal while pped is not changed by FSTs at the small volume configuration. This suggests that the reduction of the TF ripple, the magnitude of which can affect the VT profile, plays a role in the increasing of pped. For increased pped due to the use of co-NBI and the reduction of TF ripple, the spatial width of the pedestal ion temperature became greater.

After installation of ferritic steel tiles, fast ion losses due to toroidal field ripple have been reduced by 1/2–1/3. The increase in absorbed power at same injection power can reduce the required number of neutral beam injector (NBI) units to sustain a given normalized beta, βN, resulting in a better flexibility of torque input by increasing the available combination of tangential NBI units. By making use of these advantages to sustain an internal transport barrier (ITB), the performance of long-pulse ELMy H-mode plasmas was improved in terms of sustained duration time for both high βN and high thermal confinement enhancement factor (HH98(y,2)). High βN > 2.3 together with HH98(y,2) ~ 1 was sustained for 23.1 s (~12τR, where τR is the current diffusion time) at q95 ~ 3.3, which also provide high βNHH98(y,2) ≥ 2.2 and a bootstrap current fraction of ≥40%. βNHH98(y,2) of 2.0 was sustained for 28.6 s, which is limited by the maximum injection period of 30s for NBI system. These long-pulse plasmas are possible candidates for ITER hybrid operation scenario. Improved confinement is characterized by the larger thermal components at a given density maintained by lower heating power than in previous experiments. The strength of the ITB depends on the pedestal temperature, which varies with edge density while keeping constant the edge pressure (limited by type I ELMs). The fact that co-toroidal rotation as a result of reduced fast ion losses provides better quality of Te-ITB also contributes the improvement of thermal plasma confinement. These long-pulse plasmas indicate that further investigation to establish high performance plasmas longer than the time scale of wall saturation (τW) with active particle control is essential to establish the operational scenarios for next step devices, where the wall pumping does not work.

Pedestal and global plasma parameters are compared in conventional ELMy H-modes and improved confinement discharges from ASDEX Upgrade (AUG), DIII-D, JET and JT-60U with varying net input power. Both electron and ion pedestal pressures are studied. The pedestal top pressure pPED increases moderately with power in all tokamaks, in broad agreement with the power dependence of the IPB98(y, 2) scaling. Higher pedestal pressures are observed in AUG improved H-modes and in JT-60U high βpol discharges at q95 ~ 6.5 and high triangularity. For all machines and all scenarios a robust correlation between the total and the pedestal thermal stored energy is observed, with the ratio of the two varying between ~0.3 and 0.5. However the relative importance of pedestal and core confinement varies from regime to regime. In AUG the confinement improvement with respect to the IPB98(y, 2) scaling is due to improved pedestal confinement in improved H-modes with early heating and to both improved pedestal and core confinement in improved H-modes with late heating. In DIII-D hybrid discharges the increase in confinement factor compared with conventional H-modes is due to improved confinement in the plasma core. JT-60U reversed shear H-modes have strong internal transport barriers and thus improved core performance. In all four tokamaks improved edge stability is correlated with increasing total βpol and H98(y,2) increases with pedestal βpol. The analysed multimachine data set supports a scaling expression for the pedestal stored energy derived under the assumption that the dominant loss term for the pedestal is by thermal conduction in the edge transport barrier region.

Edge localized mode (ELM) measurements in many tokamaks, including ASDEX-Upgrade, DIII-D, JET, JT-60U and MAST, are reviewed, which includes progress in experimental observations at the plasma edge region by means of fast-time resolved diagnostics with high precision, such as scanning probe, radial interferometer chord, BES and tangentially viewing fast-gated camera at the midplane. ELM dynamics data show that the majority of the ELM particle and energy transport should be dominated by ion convection physics and associated timescales. Furthermore, recent diagnostic upgrades on many tokamaks reveal the ELM filament structure and their complex motion towards radial, poloidal and toroidal directions. Approaches to control the Type-I ELMs, in addition to the alternative scenarios to Type-I ELMy H-mode operation (so-called, small/no ELM regimes) are also a key area of research for current tokamaks, which demonstrated a high confinement (being comparable to that of Type-I ELMy H-mode plasmas at similar parameters) in the absence of large, ELM induced, transient heat/particle fluxes to the divertor targets. Although tolerable ELM regimes are obtained in existing devices, their application to ITER is uncertain. Issues of these regimes towards further experiments and power deposition on divertor targets and main chamber wall are discussed.

A systematic study of the effect of the level of toroidal plasma rotation at the top of the ion temperature pedestal ( ) on the edge localised mode (ELM) characteristics in JT-60U has been performed. The level of toroidal plasma rotation was varied by using different combinations of tangential and perpendicular neutral beam injection (NBI). In the grassy ELM regime at high triangularity (δ) and high safety factor (q), the ELM frequency clearly increased up to ~1400 Hz, when counter (ctr) plasma rotation was increased. The response of the ELM frequency was independent of poloidal beta (βp) in the range 0.84 0.53. Even in non-rotating plasma with balanced-NBIs, a high ELM frequency of ~400 Hz was observed without a large energy loss. When the frequency of the plasma rotation in the co-direction of the plasma current became higher than ~1 kHz, type I ELMs with a frequency of ~20 Hz was observed. The achieved pedestal pressure and plasma confinement were similar both in plasmas with type I ELMs and in plasmas with grassy ELMs. The energy loss due to grassy ELMs was evaluated from the reduction in the electron temperature, and the ratio of the energy loss to the pedestal stored energy was less than 1%.

沖縄産ヒメサザンカ野生種13系統，芳香性ツバキの花粉親の一つであるヒメサザンカの系統1118（海外経由系統），芳香性ツバキ4品種の香気成分の比較を行った．ヒメサザンカの香気成分について，新たにリモネンおよび6種の芳香族化合物，安息香酸ベンジル，オイゲノール，サリチル酸メチル，o-アニス酸メチル，フェニルアセトアルデヒド，ベンズアルデヒドを同定した．沖縄産野生種13系統の香気成分量は，ほとんどのものが海外経由系統より多く，特に系統3と36が多かった．この二つを比較すると，花様の香調の2-フェニルエタノールやフェニルアセトアルデヒドの割合が多い系統36の香りの方が強く感じられた．ヒメサザンカを花粉親とする芳香性ツバキ‘姫の香’，‘港の曙’，‘春風’，‘フレグラントピンク’の香気成分の組成もヒメサザンカとほぼ同じであったが，組成比は品種ごとに大きく異なり，花様の香調を持つ成分の割合の多い‘姫の香’，‘港の曙’で香りが強く感じられた．

The driving mechanism of toroidal rotation and the momentum transport are studied on JT-60U in relation to the toroidal rotation in the direction antiparallel to the plasma current, i.e. counter (CTR) direction, with near-perpendicular neutral beam (PERP-NB) injection. Fast ion losses due to the toroidal field ripple induce CTR rotation in the peripheral region, and the magnitude of CTR rotation with PERP-NBs reduces by installing the ferritic steel tiles as a consequence of the reduction in the ripple losses. It is also found that toroidal rotation velocity profiles in the core region can be explained by momentum transport considering diffusivity and convective velocity estimated from transient momentum transport analysis in L-mode plasmas.

This report summarizes Type I edge localized mode (ELM) dynamics measurements from a number of tokamaks, including ASDEX-Upgrade, DIII-D, JET, JT-60U and MAST, with the goal of providing guidance and insight for the development of ELM simulation and modelling. Several transport mechanisms are conjectured to be responsible for ELM transport, including convective transport due to filamentary structures ejected from the pedestal, parallel transport due to edge ergodization or magnetic reconnection and turbulent transport driven by the high edge gradients when the radial electric field shear is suppressed. The experimental observations are assessed for their validation, or conflict, with these ELM transport conjectures.

Several small/no ELM regimes such as EDA, grassy ELM, HRS, QH-mode, type II and V ELMs with good confinement properties have been obtained in Alcator C-Mod, ASDEX-Upgrade, DIII-D, JET, JFT-2M, JT-60U and NSTX. All these regimes show considerable reduction of instantaneous ELM heat load onto divertor target plates in contrast to conventional type I ELM, and ELM energy losses are evaluated as less than 5% of the pedestal stored energy. These small/no ELM regimes are summarized and widely categorized by their pedestal conditions in terms of the operational space in non-dimensional pedestal parameters and requirement of plasma shape/configuration. The characteristics of edge fluctuations and activities of ideal MHD stability leading to small/no ELMs are also summarized.

By conducting power scan experiments in three cases of toroidal field ripple configurations (δ r ≃ 0.4, 1.0 and 2.0%) with variation of the toroidal momentum source (co, balanced, counter) relative to the direction of the plasma current, the roles of the loss of fast ions and toroidal rotation on the H-mode pedestal structure were investigated. It was found that the pedestal pressure was increased with a decrease in fast ion loss power. On the other hand, the variation in toroidal rotation did not affect strongly the pedestal pressure, although the loss of fast ions due to existing large toroidal field ripple forced the toroidal rotation basically to the counter direction in JT-60U. Due to the enhanced counter toroidal rotation induced by the loss of fast ions, similar V tor profiles were obtained for discharges with different toroidal momentum source and loss of fast ions. When the loss of fast ions became smaller, pedestal density was raised remarkably while there was no significant difference in the temperature profiles.

Effects of plasma rotation and losses of fast ions on Type-I ELM characteristics have been systematically studied in the JT-60U tokamak, scanning combinations of NBI (tangential co-, balanced- and counter-NBI plus perpendicular NBI) in the three types of plasma configurations (corresponding toroidal field ripple at the plasma edge, δ r ∼0.4, 1.0 and 2.0%). New findings on the Type-I ELM characteristics are as follows: smaller ELM energy loss normalized by pedestal stored energy, ΔW ELM /W ped , and faster ELM frequency, f ELM , are confirmed in the counter-NBI in comparison with the co-NBI discharges. Nevertheless, the power loss due to ELM, P ELM (= ΔW ELM × f ELM ), normalized by heating power crossing the separatrix, P SEP , is constant regardless of the direction of the momentum injection at each plasma configuration. In contrast, the P ELM /P SEP decreases with increasing δ r . The relationship between ELMs, rotation and the losses of fast ions are discussed.

Comparisons of H-mode regimes were carried out on the Alcator C-Mod and JFT-2M tokamaks. Shapes were matched apart from aspect ratio, which is lower on C-Mod. The high recycling steady H-mode on JFT-2M and enhanced D-alpha (EDA) regime on C-Mod, both of which feature very small or no ELMs, are found to have similar access conditions in q 95 - v* space, occurring for pedestal collisionality v* ? 1. Differences in edge fluctuations were found, with lower frequencies but higher mode numbers on C-Mod. In both tokamaks an attractive regime with small ELMs on top of an enhanced D α baseline was obtained at moderate v* and higher pressure. The JFT-2M shape favoured the appearance of ELMs on C-Mod and also resulted in the appearance of a lower frequency component of the quasicoherent mode during EDA.

Three options of fusion DEMO plant are proposed characterized by functions of the center solenoid (CS). The prime option uses a downsized CS, which does not provide sufficient V-s for plasma current ramp-up but supplies enough coil current for plasma shaping. This option produces a fusion output of 3 GW with a major radius of 5.5 m, aspect ratio of 2.6, normalized beta of 4.3 and maximum field of 16.4 T. The estimated reactor weight is lighter than that of other conventional tokamak reactors, suggesting an economic advantage. The plant uses rather conservative technologies such as Nb3Al superconductor, water-cooled solid breeder blanket, low activation ferritic steel as the structural material and tungsten monoblock divertor plate. The design philosophy and key issues related to the constituent technologies of the plant are described in the present paper.

A key feature of the 'high recycling steady' (HRS) H-mode regimes is the reduction of the transient heat load to the divertor target due to large ELMs. The heat flux to the divertor targets measured by means of a Langmuir probe in the scrape-off layer on the target plate is about ~0.3 MW m−2 in the typical HRS plasmas, which is very small in comparison with the transient heat load in the ELMy H-mode discharge. In addition, the effects of the plasma shaping on the access to and improved plasma performance of HRS H-mode regimes have been investigated. Furthermore, simultaneous measurements of both density fluctuations and potential profiles at the plasma edge region using a heavy ion beam probe are also presented.

Stabilization of an m = 3/n = 2 neoclassical tearing mode (NTM) by a local electron cyclotron current drive (ECCD) has been studied in high βp ELMy H-mode plasmas in the JT-60U tokamak. In the stabilization experiment, the electron cyclotron (EC) injection timing is scanned from the 'before mode onset' phase (preemptive ECCD) to the mode saturation phase (late ECCD). It has been demonstrated that the ECCD is more effective when it is applied before the mode onset and the critical timing for effective ECCD is related to the mode excitation phase. The EC power to prevent the 3/2 NTM excitation by preemptive ECCD is lower by about 20% compared with complete stabilization by late ECCD. Even when the 3/2 NTM is excited, the stabilization effect is stronger than for late ECCD. For a high performance plasma of the normalized beta, βN = 3.0, the H-factor H89PL improves from 1.9 to 2.1 when the 3/2 NTM is suppressed. A numerical study has been made based on the modified Rutherford equation coupled with a 1.5D transport code and an EC code. The simulation reproduces well the time evolution of the magnetic island both at the growing and stabilizing phases. The simulation results show that it is important to adjust not only the EC current position but also its width to stabilize the NTM effectively. The reduction of EC power for NTM prevention in experiments for preemptive ECCD can be explained by the increase of the minimum seed island size for NTM excitation.

Compatibility of advanced tokamak plasmas with high density and high radiation loss has been investigated in both reversed shear (RS) plasmas and high βp H-mode plasmas with a weak positive shear on JT-60U. In the RS plasmas, the operating regime is extended to high density above the Greenwald density (nGW) with high confinement (HHy2 > 1) and high radiation loss fraction (frad > 0.9) by tailoring the internal transport barriers (ITBs). With a small plasma-wall gap, the radiation loss in the main plasma (inside the magnetic separatrix) reaches 80% of the heating power due to metal impurity accumulation. However, high confinement of HHy2 = 1.2 is sustained even with such a large radiation loss in the main plasma. By neon seeding, the divertor radiation loss is enhanced from 20% to 40% of the total radiation loss. In the high βp H-mode plasmas, high confinement (HHy2 = 0.96) is maintained at high density ( ) with high radiation loss fraction (frad ~ 1) by utilizing high-field-side pellets and argon (Ar) injection. The high is attributed to the formation of strong density ITB. Strong core-edge parameter linkage for confinement improvement is observed, where the pedestal pressure and the core plasma confinement increase together. The measured radiation profile including contributions from all impurities in the main plasma is peaked, and the central radiation is ascribed to the contribution from Ar accumulated inside the ITB. Impurity transport analyses indicate that the Ar density profile, twice as peaked as the electron density profile, which is the same level as that observed in the high βp H-mode plasma, can yield an acceptable radiation profile even with a peaked density profile in a fusion reactor.

Since it is uncertain if ITER operation is compatible with type-l edge localized modes (ELMS), the study of alternative ELM regimes is an urgent issue. This paper reports on experiments on JET aiming to find scenarios with small ELMS and good confinement, such as the type-II ELMS in ASDEX Upgrade, the enhanced D-alpha H-mode in Alcator C-mod or the grassy ELMS in JT-60U. The study includes shape variations, especially the closeness to a double-null configuration, variations of q(95), density and beta poloidal. H-mode pedestals without type-I ELMs have been observed only at the lowest currents (

The energy loss for grassy edge localized modes (ELMs) has been studied to investigate the applicability of the grassy ELM regime to ITER. The grassy ELM regime is characterized by high frequency periodic collapses of 800–1500 Hz, which is ~15 times faster than that for type I ELMs. The divertor peak heat flux due to grassy ELMs is less than 10% of that for type I ELMs. This smaller heat flux is caused by a narrower radial extent of the collapse of the temperature pedestal. The different radial extent between type I ELMs and grassy ELMs agrees qualitatively with the different radial distribution of the eigenfunctions as determined from ideal MHD stability analysis. The dominant ELM energy loss for grassy ELMs appears to be caused by temperature reduction, and its ratio to the pedestal stored energy was 0.4–1%. This ratio is lower by a factor of about 10 than that for type I ELMs, which typically have between 2–10% fractional loss of the pedestal energy. A systematic study of the effects of counter (CTR) plasma rotation on the ELM characteristics has been performed using a combination of tangential and perpendicular neutral beam injections (NBIs) in JT-60U. In the high plasma triangularity (δ) regime, ELM characteristics (e.g. amplitude, frequency and type) can be changed from type I ELMs to high frequency grassy ELMs as the CTR plasma rotation is increased. On the other hand, in the low δ regime, complete ELM suppression (QH-mode) can be sustained for long periods up to 3.4 s (~18τE or energy confinement times), when the plasma position in terms of the clearance between the first wall and the plasma separatrix is optimized during the application of CTR-NBIs. In JT-60U, a transient QH phase was also observed during the CO-NBI phase with almost no net toroidal rotation at the plasma edge.

This paper reports the results of the progress in stationary discharges with a large bootstrap current fraction in JT-60U towards steady-state tokamak operation. In the weak shear plasma regime, high-βp ELMy H-mode discharges have been optimized under nearly full non-inductive current drive conditions by the large bootstrap current fraction (fBS ~ 45%) and the beam driven current fraction (fBD ~ 50%), which was sustained for 5.8 s in the stationary condition. This duration corresponds to ~26τE and ~2.8τR, which was limited by the pulse length of negative-ion-based neutral beams. The high confinement enhancement factor H89 ~ 2.2 (HH98y2 ~ 1.0) was obtained and the profiles of current and pressure reached the stationary condition. In the reversed shear plasma regime, a large bootstrap current fraction (fBS ~ 75%) has been sustained for 7.4 s under nearly full non-inductive current drive conditions. This duration corresponds to ~16τE and ~2.7τR. The high confinement enhancement factor H89 ~ 3.0 (HH98y2 ~ 1.7) was also sustained, and the profiles of current and pressure reached the stationary condition. The large bootstrap current and the off-axis beam driven current sustained this reversed q profile. This duration was limited only by the duration of the neutral beam injection.

Recent experiments in the JFT-2M tokamak have concentrated on studies of the access conditions for H-mode operation without any large ELMs, namely the 'high recycling steady' (HRS) H-mode regime, in terms of the pedestal parameters. The HRS regime is more likely to occur at higher edge density and lower edge temperature, while the ELMy H-mode having large ELMs appears at lower edge density and higher edge temperature. It is found that the ELMy/HRS operational boundary occurs at the normalized electron collisionality of in the plasma edge region, depending slightly on the safety factor at 95% flux surface q95. A key feature of the HRS H-mode is the presence of coherent magnetic fluctuations in the frequency range of the order of 10?100?kHz. It is suggested that the edge MHD activities may keep the edge pressure below a certain level needed to induce a large ELM.

The dependence of the thermal diffusivity on the heat flux has been investigated in JT-60U plasmas by varying the neutral beam power. In positive magnetic shear (PS) plasmas, the ion thermal diffusivity (χi) in the core region generally increases with the heating power, as with the L mode at low heating powers. However, as a result of the intensive central heating, a weak internal transport barrier (ITB) is formed, and the χi value in the core region starts to decrease. Corresponding to a further increase in the heating power, a strong ITB is formed and the χi value is reduced substantially. In the case of reversed magnetic shear (RS) plasmas, on the other hand, no power degradation of the χi value is observed in any of the heating regimes. The electron thermal diffusivity (χe) is correlated with the χi value in PS and RS plasmas. Furthermore, the dependence of the ion thermal diffusivity on the radial electric field (Er) shear has also been investigated. By considering the non-locality in the relation between the Er shear and the χi value, a threshold in the effective Er shear to change the state from a weak to a strong ITB is identified.

A new operating regime, 'high recycling steady' (HRS) H-mode regime, has been discovered in the JFT-2M tokamak. It is easily reproduced with neutral beam heating of any co-, balanced-, or counter-injection under wall fuelling from the boronized first wall. The HRS is characterized by good energy confinement (H89P ~ 1.6) at a high density (ne/nGW ~ 0.7; nGW is the Greenwald density), low radiation loss power fraction ( , typically), and the complete disappearance of large ELMs. Accompanying the HRS H-mode transition, the coherent magnetic fluctuations in the frequency range of the order of 10–100 kHz with significant variation are seen on magnetic probes at the vessel wall. In addition, the HRS H-mode edge condition is compatible with an improved core confinement. We have demonstrated that an internal transport barrier can be produced under a HRS H-mode edge condition, achieving βNH89P ~ 6 at ne/nGW ~ 0.7–1.0, transiently.

Results of coherent edge fluctuation measurements using three diagnostics (a reciprocating Langmuir probe, a two channel O-mode reflectometer, and fast magnetic probes) in H-mode discharges on JFT-2M are presented. In discharges in which a high recycling steady (HRS) H-mode phase is obtained through a transient phase with slightly enhanced Dα intensity, two types of coherent fluctuations are observed. The higher frequency mode (around 300 kHz) is the high frequency mode (HFM) observed in the HRS H-mode (Kamiya K et al 2003 9th IAEA Tech. Meeting H-mode Workshop Topic B-14). The lower frequency mode has a frequency of around 80 kHz. The HFM is detected by a Langmuir probe over a wide region in the SOL, as well as by the reflectometer and magnetic probes. However, the HFM is not detected by the higher frequency (38 GHz) channel of the reflectometer after the HRS transition, suggesting that the HFM is not located deeply inside the plasma. The 80 kHz mode is detected by both channels of the reflectometer and by a Langmuir probe, but not by magnetic probes, suggesting that it is an electrostatic mode. In contrast to the HFM, the 80 kHz mode is detected by the Langmuir probe only near the separatrix during the transient phase, which leads to either the HRS phase or the ELMy phase, and is similar to the fluctuations reported in Shinohara K et al (1998 J. Plasma Fusion Res. 74 607).

Simultaneous fast ELM measurements using a reflectometer, interferometers, Dα intensity and a magnetic probe reveal the detailed characteristics of type I ELMs. From the phase signal of the reflectometer indicating the radial movement of the cut-off layer, four different phases in the ELM event, i.e. a precursor phase, collapse phase, recovery phase and a relaxation phase, were observed. In the collapse phase, the radial extent of the collapse of the density pedestal reached up to twice the pedestal width. A fast drop of the horizontal interferometer signal was observed, while the vertical interferometer on the high-field side edge plasma only exhibited a small and delayed reduction. These features of the plasma response due to ELMs might indicate a non-uniform collapse of the density pedestal in the poloidal direction, localized near the low-field side (LFS) midplane. Expelled particles from the LFS midplane were measured by using scrape-off layer Mach probes, and the heat flux to the divertor target was measured using a fast infrared TV camera. The time constant of the peak heat load was comparable to that of the enhancement of the plasma flow towards the divertor target. The normalized ELM energy loss by pedestal stored energy in JT-60U was found to be less than 10% of the pedestal stored energy. It shows weak dependence on the pedestal parameters such as electron collisionality, parallel ion loss time and the ratio of the pedestal density to the Greenwald density limit.

The influence of dominant electron heating on internal transport barriers (ITBs) was investigated in JT-60U. The electron cyclotron waves were mainly utilized in order to extend the experimental space into a dominant electron heating regime. The experiments were carried out on both reversed magnetic shear (RS) and positive magnetic shear (PS) plasmas. It was found that in RS plasmas clear ITBs in Te, Ti and ne profiles remained even under dominant electron heating. Energy confinement in excess of twice the H-mode scaling has been obtained in the regime. On the other hand, it was found that in PS plasmas the Ti ITB was degraded by dominant electron heating.

The relationship between particle and heat transport in an internal transport barrier (ITB) has been systematically investigated in reversed shear (RS) and high βp mode plasmas of JT-60U. The electron effective diffusivity is well correlated with the ion thermal diffusivity in the ITB region. The ratio of particle flux to electron heat flux, calculated on the basis of the linear stability analysis, shows a similar tendency to an experiment in the RS plasma with a strong ITB. However, the calculated ratio of ion anomalous heat flux to electron heat flux is smaller than the experiment in the ITB region. Helium and carbon are not accumulated inside the ITB even with ion heat transport close to a neoclassical level, but argon is accumulated. The helium diffusivity (DHe) and the ion thermal diffusivity (χi) are 5–15 times higher than the neoclassical level in the high βp mode plasma. In the RS plasma, DHe is reduced from 6–7 times to a 1.4–2 times higher level than the neoclassical level when χi is reduced from 7–18 times to a 1.2–2.6 times higher level than the neoclassical level. The carbon and argon diffusivities estimated assuming the neoclassical inward convection velocity are 4–5 times larger than the neoclassical value, even when χi is close to the neoclassical level. Argon exhaust from the inside of the ITB is demonstrated by applying electron cyclotron heating (ECH) in the high βp mode plasma, where both electron and argon density profiles become flatter. The flattening of the argon density profile is consistent with the reduction of the neoclassical inward convection velocity due to the reduction of the bulk plasma density gradient. In the RS plasma, the density gradient is not decreased by ECH and argon is not exhausted. These results suggest the importance of density gradient control in suppressing impurity accumulation.

Bursting modes in the frequency range of the toroidicity induced Alfv?n eigenmode are observed in the plasma to which the negative-ion-based neutral beam (N-NB) is injected. A bursting mode changes its frequency by 10-20?kHz in 1-5?ms and is called fast frequency sweeping (fast FS) mode. Another bursting mode evolves explosively in ?400??s and is called an abrupt large-amplitude event. The dependence of their saturation level was compared?with the experimentally observed growth rate and damping rate. The mode amplitude increases with the observed growth rate for fast FS modes. The modes with large amplitude and a large enhanced transport were observed when a large neutron emission rate was observed. The burst period increases as the drop ratio of the neutron emission increases.

We phenomenologically investigate the growth behavior in lattice-mismatched heteroepitaxy. We focus on the critical thickness of misfit dislocations (MDs) in Volmer–Weber (VW) and Stranski–Krastanov (SK) modes. Calculated results show that critical thickness in VW mode is much smaller than that in SK mode. This is because energy loss in MD formation in VW islands is smaller than that in SK islands due to the absence of wetting layers during VW growth.