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This paper presents a correlation between time evolution of ions and electrons with soft and hard x-rays emitted from argon plasma. The plasma setup comprises of two copper electrodes connected with a dc power supply. Faraday cups were used to monitor time evolution of ions, to extract their energy, temperature, and flux. Double Langmuir probe was employed to determine electron temperature, energy, and density. To explore time-resolved emission of soft x-rays, PIN photodiodes filtered with 24 μm aluminum, 90 μm Mylar, 80 μm copper, and 10 μm silver have been used. To evaluate temporal evolution of hard x-rays, a scintillator–photomultiplier system was utilized. The plasma was generated using argon gas at atmospheric pressure 760 Torr and constant flow rate 5 L/min at 7, 9, and 11 kV. The flux, energy, and temperature of Ar ions increase with the increase in the operating potential. Soft x-ray signals last much longer (3000 ns) than those of electrons' and ions' signals (300 ns). The plasma operated at 11 kV permits highest emission of ions, electrons, and x-rays. The ions, electrons, and hard and soft x-ray irradiation on silicon wafer exhibited the presence of damaged trails. Ion irradiation showed the presence of latent damaged trails. Electron irradiation caused more damage to the Si surface compared to ion irradiation due to higher flux and density. Soft x-rays had a lesser effect as compared to Si exposed to hard x-rays due to higher energy of the hard x-rays. In the case of hard x-rays irradiated Si, erupted volcano-like structure is formed. [ABSTRACT FROM AUTHOR]

This paper presents numerical characterization of a recently developed compact soft x-ray source based on a nanosecond electric discharge in a gas-filled capillary. When operated in CO2 and Ar:He mixture, the source is capable of producing line radiation in wavelength ranges corresponding to the carbon (4.5–5.0 nm) and water (2.3–4.4 nm) transparency windows. Experimentally obtained trends in emission properties are analyzed using a two-temperature magnetohydrodynamic model, which utilizes mean ion approximation for calculation of basic properties of multicomponent plasma. Spatiotemporal distributions of plasma parameters were obtained for a range of gas pressures corresponding to the studied experimental conditions of the soft x-ray source. Peak values of electron density and electron temperature were analyzed and used to interpret the experimentally obtained trends in dependence of the source operation on inlet gas pressure. [ABSTRACT FROM AUTHOR]

Z-pinches have been explored as efficient soft x-ray sources for many years. To optimize x-ray emission, various z-pinch configurations were tested. This paper presents data obtained with a hybrid gas-puff z-pinch imploding onto on-axis wires on a microsecond, multi-megaampere GIT-12 generator. In our previous experiments, the hybrid gas puff, i.e., an inner deuterium gas puff surrounded by an outer hollow cylindrical plasma shell, was used to produce energetic protons, deuterons, and neutrons up to 60 MeV [Klir et al., New J. Phys. 22, 103036 (2020)]. The behavior of the hybrid gas-puff z-pinch on GIT-12 was interpreted as a high-density plasma opening switch with a microsecond conduction time, 3 MA conduction current, nanosecond opening, and up to 60 MV stand-off voltage. These properties can be employed to transfer the current into an on-axis load with a high rise rate. In the recent experiments on GIT-12, we therefore placed single or multiple aluminum wires on the axis of the hybrid gas-puff z-pinch. Before a current sheath arrived at the axis, a coronal plasma was seen around the wire. A rapid increase in x-ray radiation was observed when the coronal plasma imploded onto the axis. The coronal plasma implosion resulted in a long (2 cm), narrow (∼mm) column radiating in the Al K-shell lines. With the single Al wire of 80 μm diameter, the K-shell x-ray output reached 5.5 ± 0.8 kJ in a 0.6 ± 0.1 TW peak power and 7 ± 1 ns pulse. The higher K-shell yield of 12 ± 2 kJ and peak K-shell power of 0.7 ± 0.1 TW were achieved with four 38 μm diameter Al wires. (Their cross section formed the corners of a square with 1 mm side.) The presence of the wires on the axis significantly suppressed ion acceleration and neutron production. Deuterium-deuterium (DD) neutron yields of about 1.2 × 1011 were 20 times smaller than the yields produced in shots without any wire. The DD neutron yield was increased up to 4.5 × 1011 when the Al wire was replaced by a fiber from deuterated polyethylene. A characteristic feature of the experiments with the (CD2)n fiber was a rapid expansion with the velocity approaching 900 km/s. [ABSTRACT FROM AUTHOR]

The paper describes the behaviour of plasma within a MA plasma-focus with a novel electrode configuration, in which the anode and anti-anode were both equipped with conical tips. This configuration was applied to test the possibility of reducing the pinch axial dimensions during the radial compression of a current sheath. It made it possible to strengthen a dense plasma jet near the anode end, which ejected plasma into a bigger plasmoidal structure formed in the central pinch region. It did not allow forming an opposite anti-anode jet and stopped the axial motion of this structure. In plasma focus discharges with the deuterium filling, the decay of the anode jet and the corresponding plasmoid evolution were accompanied by the fusion-neutron production. Some results obtained with this configuration have also supported the hypothesis of the acceleration of fast electrons and ions at a release of the magnetic energy during magnetic reconnections in the organized dense plasma structures. [ABSTRACT FROM AUTHOR]

Laser produced plasma (LPP) soft x-ray and extreme ultraviolet sources utilize various types of targets. Some of them are based on gaseous targets. The most important disadvantage of such targets is the very limited number of elements that can be used in the gaseous form under normal conditions, including chemical compounds in the gaseous state. In this paper, the authors propose a new type of target, constituting an extension of the gaseous target, namely aerosol target, based on solutions of solid chemical compounds in liquids. Unlike previous attempts to produce aerosol targets from overheated liquids, in our system, the target is created by injection of a mist, preformed in a dedicated cell, into the vacuum chamber. Such targets have many advantages: the emission spectra can be adjusted by choosing proper chemical compounds, the aerosol target is elongated, hence, the laser focus can be positioned at a relatively long distance from the nozzle outlet, its average density can be higher compared to gaseous targets. In this work, such a target and its usefulness for the LPP soft x-ray source was demonstrated. The target was investigated by the soft x-ray backlighting method. Its density distribution at the position of the laser focus was determined. The emission spectra from the soft x-ray range, corresponding to multiple charged ions, originating from the solvent and the diluted salt were measured. Based on numerical simulations of the spectra, an ionic composition of the resulting plasmas was determined. [ABSTRACT FROM AUTHOR]

Mid-Z dopant in ablator is very important in point design targets. In this paper, we develop a method to evaluate the soft x-ray transport of doped material with one dimensional planar target. The targets are designed as sandwich, so that the mid-layer is heated by M band, shock and thermal wave. The transmission fluxes from heated targets are measured with band-pass x-ray diodes. The Si and Ge dopants are evaluated with this method. The experimental results show that 1-1.6 keV x-ray transmission flux through Si-sandwich is higher than that through Ge-sandwich all the time. Also, the comparison of opacities shows that the opacity of Si is lower than that of Ge in the range of 1-1.6 keV, which is consistent with the experimental results. [ABSTRACT FROM AUTHOR]

We detail results of an experiment performed at the Ligne d'Intégration Laser facility aimed at studying supersonic and diffusive radiation front propagation in low-density SiO2 aerogel (20 and 40 mg/cm3) enclosed in a gold tube, driven by thermal emission from a laser-heated spherical gold cavity. The evolution of the front is studied continuously by measuring its self-emission with a 1D (one-dimensional) time-resolved soft x-ray imager. Measurement is performed along (through a 200-μm-wide observation slit) and at the exit of the tube giving access to the dynamics and the curvature of the front. Experimental results are then compared successfully to results from the 3D (three-dimensional) radiation hydrodynamics code TROLL, which shows that if continuous tracking of the front position is accessible with this experimental scheme, measurement of its maximum radiation temperature is on the contrary affected by radiation closure of the observation slit. 3D simulations also indicate that this effect can even be worsened if one includes pointing errors of the x-ray imager. Radiation temperature along the tube was then inferred by combining results from the imager to a wall shock breakout time measurement using a velocity interferometer system for any reflector and results from a broadband x-ray spectrometer used to determine the temperature at the exit of the tube. A decrease in the radiation temperature along the tube is observed, the decrease being more important for the higher SiO2 aerogel density. [ABSTRACT FROM AUTHOR]

A significant reduction in neutron yield in the plasma core has been observed in EAST neutral beam injection into plasmas with a low-edge safe factor of q 95 = 3.5 and a n = 2 resonant magnetic perturbation (RMP) during a sawtooth crash. Harmonics of the m/n = 1/1 mode (m and n being the poloidal and toroidal mode numbers) develop simultaneously. A sawtooth crash is triggered when the current of the RMP exceeds a critical value; saturated fishbone phase occurs with small RMP currents. Soft x-ray (SXR) tomographic patterns obtained during sawtooth crashes have annular hot-ring shapes outside the q = 1 surface that are similar to those of double tearing modes triggered by off-axis sawtooth crashes in TFTR reversed magnetic shear plasma. M3D nonlinear simulations confirmed the initial penetration of the n = 2 RMP in the plasma core and further demonstrated a complete sawtooth crash with the appearance of a right annular hot ring near the q = 1 surface. Reconstruction of the trajectory of SXR signals before the crash shows chaotic behavior. Moreover, a high-frequency mode was seen to appear just before the sawtooth crash, accompanied by an edge geodesic acoustic mode. This edge mode is free in the saturated fishbone phase. The role of high-frequency mode in the sawtooth crash remains unclear. [ABSTRACT FROM AUTHOR]

In this work, the time development of plasmas produced by interaction of laser pulses, with a nitrogen gas, was investigated. The interaction took place inside a small portion of dense nitrogen gas injected temporarily into a chamber filled with the gas under low pressure. High-temperature plasmas produced directly by the laser pulse were a source of soft x rays and charged particles, ionizing and exciting the surrounding gas. In this way, low-temperature plasmas were produced. The formation of high-temperature plasmas was studied using soft x-ray spectroscopy and x-ray streak imaging. Low-temperature plasmas formed at various distances from the laser focus were investigated using an optical streak camera. Interpretation of the experimental data was supported by numerical modeling of the laser-produced plasma hydrodynamics. It was concluded that depending on the distance from the focal spot, the formation of the low-temperature plasmas was dominated by ion streams or by soft x-ray radiation. [ABSTRACT FROM AUTHOR]

Detailed radiation hydrodynamic simulations are carried out to investigate the x-ray emission process in four high-Z planar targets, namely, tungsten (W), gold (Au), lead (Pb), and uranium (U) irradiated by 1 ns, 351 nm flat top laser pulses. A thorough zoning analysis is performed for all laser-driven high-Z foils over a wide intensity range of 10 12 – 10 15 W/cm2 with appropriately chosen photon energy range and recombination parameter. The resulting variation of conversion efficiency over the full intensity range exhibits an optimum for all materials, which is explained by considering the characteristic emission contributions from two different regions of laser irradiated plasma, namely, conversion layer and re-emission zone. A new generalized single scaling relation based upon smooth broken power law is proposed for conversion efficiency variation along with the separate determination (ηS, ηM) in soft and hard/M-band x-ray regions. It has been observed that ηS for Pb and W always lies in between that for Au and U for intensities smaller than ∼ 3 × 10 13 W/cm2. On further increase in intensity, ηS is observed to be maximum for Au and U, whereas it is minimum for W. Significant contribution to M-band conversion efficiencies is observed in all elements for intensities higher than ∼ 2 × 10 13 W/cm2 with maximum and minimum values attained by W and U, respectively. The results are explained by considering the contributions from the emission coefficients of all materials in both conversion layer and re-emission zone up to corresponding photon cutoff energies at different laser intensities. [ABSTRACT FROM AUTHOR]

Predicting and modeling the behavior of experiments with radiation waves propagating through low-density foams require a detailed quantification of the numerous uncertainties present. In regimes where a prominent radiative shock is produced, key dynamical features include the shock position, temperature, and curvature and the spatial distribution and temperature of the corresponding supersonic radiation wave. The COAX experimental platform is designed to constrain numerical models of such a radiative shock propagating through a low-density foam by employing radiography for spatial and shock information, Dante for characterizing the x-ray flux from the indirectly driven target, and a novel spectral diagnostic designed to probe the temperature profile of the wave. In this work, we model COAX with parameterized 2D simulations and a Hohlraum-laser modeling package to study uncertainties in diagnosing the experiment. The inferred temperature profile of the COAX radiation transport experiments has been shown to differ from simulations more than expected from drive uncertainties that have been constrained by simultaneous soft x-ray flux and radiography measurements. [ABSTRACT FROM AUTHOR]

Detailed investigations are carried out on shock, preheat, and ablation characteristics in x-ray driven beryllium based targets, a candidate ablator material for many inertial confinement fusion studies due to its high mass ablation rate. The study involves extensive radiation hydrodynamic simulations performed on pure and 1% copper doped beryllium foils irradiated by a temperature drive source consisting of both Planckian and Gaussian distributions with peaks lying in soft and hard x-ray regions, respectively. The results of steady state x-ray driven ablation and radiant heat exchange in a sub-critical shock are extended to a non-Planckian source. Based on that, new scaling relations are proposed for shock velocity, shock breakout temperature, maximum preheat temperature, and mass ablation rate with the temperature (120 − 200 eV) and the fraction of total energy density due to Gaussian distribution (0 − 0.25) of the incident drive. All parameters increase with drive temperature strength, but the presence of hard x rays does not affect them uniformly. Among all, preheat and shock breakout temperature exhibit a strong dependence on fraction of hard x rays present in the drive spectrum. The effect of doping translates into a pronounced decrease in preheat and shock breakout temperature, while mass ablation rate reduces marginally. The resulting variations in different parameters are explained on the basis of distribution of total extinction coefficient over the spectral form of an incident drive source. [ABSTRACT FROM AUTHOR]

In an x-ray driven cavity experiment, an intense flux of soft x rays on the emitting surface produces significant emission of photoelectrons having several kiloelectronvolts of kinetic energy. At the same time, rapid heating of the emitting surface occurs, resulting in the release of adsorbed surface impurities and subsequent formation of an impurity plasma. This numerical study explores a simple model for the photoelectric currents and the impurity plasma. Attention is given to the effect of varying the composition of the impurity plasma. The presence of protons or hydrogen molecular ions leads to a substantially enhanced cavity current, while heavier plasma ions are seen to have a limited effect on the cavity current due to their lower mobility. Additionally, it is demonstrated that an additional peak in the current waveform can appear due to the impurity plasma. A correlation between the impurity plasma composition and the timing of this peak is elucidated. [ABSTRACT FROM AUTHOR]

The current research has continued on the PF-1000 plasma focus device at the current of 2 MA by comparison of the shots with and without injected deuterium. The increase of the total neutron yield at the level of 1010-1011 per shot was achieved after the compression of about 10 μg/cm of the deuterium from the gas-valve by about 46 μg/cm of the neon or deuterium plasma sheath. It increases five times at the decrease of the puffing deuterium mass to one-half. In shots with neon in the chamber and with puffing deuterium, a considerable decrease was confirmed of the soft X-ray emission in comparison with shots without deuterium injection. This decrease can be explained by the absence of the neon in the region of the compressed and hot plasma. The deuterium plasma from the gas-puff should then be confined in the internal structures both in the phase of implosion as well as during their formation and transformation. In shots with puffing deuterium, the evolution of instabilities in the plasma column was suppressed. The deuterium plasma has a higher conductance and better ability to form expressive and dense plasmoids and to transport the internal current in comparison with neon plasma. Neutrons were produced both at the initial phase of stagnation, as well as at a later time at the evolution of the constrictions and dense plasmoids. [ABSTRACT FROM AUTHOR]

A new scheme is proposed to enhance the conversion efficiency (CE) of soft x-rays (0.1–1.5 keV) generated by irradiating a double-gold-foil target using double laser pulses to collide gold plasmas. A detailed analysis of the hydrodynamic evolution of the colliding plasmas is performed by using one-dimensional radiation hydrodynamic simulations. The results show that the total soft x-ray CE can be enhanced up to 71.5% by setting the foil thickness as d1 = 0.3 μm, and this is 14.5% higher than that for a single laser irradiating a single-gold-foil target. Most of the enhanced soft x-ray CEs are generated from a stagnation layer formed by plasma collisions. Such a scheme is simple and practical, which is beneficial for their applications in astrophysical opacity calculations, inertial confinement fusion, and hydrodynamic instability analyses. [ABSTRACT FROM AUTHOR]

A hybrid early time x-ray drive followed by conventional laser direct drive obtained by utilizing a thin high-Z overcoat on plastic ablator targets has proven to be very effective at reducing laser imprint in experiments driven by the Nike krypton-fluoride laser. An inherent low level laser prepulse from that laser system heated and expanded the coating prior to the main pulse. Here, we report on results using a frequency tripled Nd:glass laser system (Omega EP) where the inherent prepulse was several orders of magnitude smaller. By applying a separate prepulse, these experiments allowed us to test if the prepulse is important for mitigating imprint with the high-Z layer. The results show that the high-Z coating is much more effective at reducing laser imprint when it is pre-expanded, in this case, by an externally generated low level soft x-ray prepulse of ∼ 10 J/cm2. With the x-ray prepulse, laser imprint at spatial wavelengths below 100 μm was reduced by an order of magnitude, similar to that observed with the laser prepulse on Nike. Furthermore, the experiments here establish that high-Z coating is effective in reducing imprint even in the case of a fixed speckle pattern. Rayleigh–Taylor-amplified laser imprint and high-Z layer dynamics were measured using through-foil and side-on x-ray radiography. Pre-expansion times from 30 down to 6 ns were effective, potentially compatible with laser prepulse generation using existing NIF and OMEGA front ends; however, temporal beam smoothing appears to be necessary for the laser prepulse that directly illuminates the high-Z coating. The highest imprint reduction is observed for Pd and Au coatings of at least 400 Å thickness; thicknesses down to 200 Å show a reduction in imprint with an adjusted prepulse. [ABSTRACT FROM AUTHOR]

M-band transitions (n = 4 → 3) in gold are responsible for a population of x-rays with energy >1.8 keV in indirect drive inertial fusion. These x-rays can preheat the fuel, cause the ablator–fuel interface to become unstable to Rayleigh–Taylor instabilities, and introduce radiation nonuniformity to the x-ray drive. This work investigates the performance of mid-Z lined Hohlraums for producing an efficient drive spectrum absent of M-band x-rays using the two-dimensional Lagrangian radiation hydrodynamics code h2d. The removal of the M-band transitions is observed in the Cu-lined Hohlraum reducing the total x-ray energy above 1.8 keV to 58% that of the un-lined Hohlraum. Total radiation energy in the Cu-lined Hohlraum is 93% that of the energy in the pure Au Hohlraum for a 1 ns pulse. However, the soft x-ray drive energy (below 1.8 keV) for the lined Hohlraum is 98% that of the pure Au Hohlraum. [ABSTRACT FROM AUTHOR]

Laser heating of a gas in a cylindrical liner held in by a thin foil window is a critical process in the MagLIF (magnetized liner inertial fusion) concept [S. A. Slutz and R. A. Vesey, Phys. Rev. Lett. 108, 025003 (2012)]. Window burnthrough and gas heating for OMEGA scale MagLIF cylinders as a function of time have been determined using spectrally integrated soft x-ray diagnostics. Window laser absorption is classified in terms of the emitted x-rays from the window plasma as a function of laser energy and shows that the laser energy absorbed is weakly dependent on incident intensity. Radiation–hydrodynamic simulations overestimate the amount of laser energy absorbed by the window as evidenced by the increase in x-ray radiation across several photon energy bands compared to experiments. Gas temperatures inferred from soft x-ray emission from the front 1mm of the liner are shown to evolve in time in a similar manner to simulation predictions. Soft x-ray emission from the gas within the region of the liner that is normally imploded is shown to meet the 100 eV requirements set by the initial point design for laser-driven MagLIF. [ABSTRACT FROM AUTHOR]

Laser blow-off injections of aluminum and tungsten have been performed on the DIII-D tokamak to investigate the variation of impurity transport in a set of dedicated ion and electron heating scans with a fixed value of the external torque. The particle transport is quantified via the Bayesian inference method, which, constrained by a combination of a charge exchange recombination spectroscopy, soft x-ray measurements, and vacuum ultraviolet spectroscopy provides a detailed uncertainty quantification of transport coefficients. Contrasting discharge phases with a dominant electron and ion heating reveal a threefold drop in the impurity confinement time and order of magnitude increase in midradius impurity diffusion, when additional electron heating is applied. Furthermore, the calculated stationary aluminum density profiles reverse from peaked in electron heated to hollow in the ion heated case, following a similar trend to electron and carbon density. Comparable values of a core diffusion have been observed for W and Al ions, while differences in the propagation dynamics of these impurities are attributed to pedestal and edge transport. Modeling of the core transport with non-linear gyrokinetics code CGYRO [J. Candy and E. Belly, J. Comput. Phys. 324, 73 (2016)], significantly underpredicts the magnitude of the variation in Al transport. Diffusion increases three-times steeper with additional electron heat flux, and 10-times lower diffusion is observed in ion heated case than predicted by the modeling. The CGYRO model quantitatively matches the increase in the Al diffusion when approaching the linear threshold for the transition from the ion temperature gradient to trapped electron mode. [ABSTRACT FROM AUTHOR]

The derivation of the ignition energy for fast ignition inertial confinement fusion is reviewed and one-dimensional simulations are used to produce a revised formula for the ignition energy of an isochoric central hot-spot, which accounts for variation in the radius of the hot-spot rh as well as the density ρ. The required energy may be as low as 1 kJ when ρ r h ≈ 0.36 g c m − 2 , T ≈ 20 keV , and ρ ≥ 700 g c m − 2 . Although there are many physical challenges to creating these conditions, a possible route to producing such a hot-spot is via a bright source of non-thermal soft x-rays. Further one-dimensional simulations are used to study the non-thermal soft x-ray heating of dense DT and it is found to offer the potential to significantly reduce hydrodynamic losses as compared to particle driven fast ignition due to the hotspot being heated supersonically in a layer-by-layer fashion. A sufficiently powerful soft x-ray source would be difficult to produce, but line emission from laser-produced-plasma is the most promising option. [ABSTRACT FROM AUTHOR]

The mechanism of decay of the superheated metastable metal produced by a thin foil explosion was investigated experimentally. The decay of the metastable metal was indicated by the occurrence of bubbles detected using soft x-ray backlighting. The experiments were carried out on a research facility comprising three current generators. One of them was used to initiate the explosion of a test foil, and the other two, X-pinch backlighting sources, were used for diagnostics. In the experiments, an upper limit has been determined for the decay time of the metastable state of a superheated metal. For aluminum, at a foil thickness of 6 μm and a deposited energy of 1.49 ± 0.08 eV/atom, the metastable state decay time was about 90 ns; for copper, at the same foil thickness and a deposited energy of 1.46 ± 0.07 eV/atom, it was about 250 ns. Analysis of the experimental results based on the classical nucleation theory has made it possible to estimate the work required for the formation of a critical bubble, the radius of the critical bubble, and the Tolman length, which characterizes the effect of the surface curvature on the surface tension. The work required for the formation of a critical bubble has been estimated to be 16.6 ± 1.5 eV for aluminum and 18.3 ± 1.2 eV for copper. The critical bubble radius and the Tolman length turned out to be several nanometers for both test metals. [ABSTRACT FROM AUTHOR]

The design principles of a xenon gas shield device that is intended to protect optical components from x-ray induced opacity ("x-ray blanking") have been experimentally demonstrated at the OMEGA-60 Laser Facility at the Laboratory for Laser Energetics, University of Rochester. A volume of xenon gas placed in front of an optical component absorbs the incoming soft x-ray radiation but transmits optical and ultra-violet radiation. The time-resolved optical (532 nm) transmission of samples was recorded as they were exposed to soft x-rays produced by a gold sphere source (1.5 kJ sr-1, 250-300 eV). Blanking of fused silica (SiO2) was measured to occur over a range of time-integrated soft x-ray (<3 keV) fluence from ~0.2-2.5 J cm-2. A shield test device consisting of a 30 nm silicon nitride (Si3N4) and a 10 cm long volume of 0.04 bar xenon gas succeeded in delaying loss of transmission through a magnesium fluoride sample; optical transmission was observed over a longer period than for the unprotected sample. It is hoped that the design of this x-ray shield can be scaled in order to produce a shield device for the National Ignition Facility optical Thomson scattering collection telescope, in order to allow measurements of hohlraum plasma conditions produced in inertial confinement fusion experiments. If successful, it will also have applications in many other high energy density experiments where optical and ultra-violet measurements are desirable. [ABSTRACT FROM AUTHOR]

A comparative study of photoionized plasmas created by two soft X-ray and extreme ultraviolet (SXR/EUV) laser plasma sources with different parameters is presented. The two sources are based on double-stream Xe/He gas-puff targets irradiated with high (500 J/0.3 ns) and low energy (10 J/ 1 ns) laser pulses. In both cases, the SXR/EUV beam irradiated the gas stream, injected into a vacuum chamber synchronously with the radiation pulse. Irradiation of gases resulted in formation of photoionized plasmas emitting radiation in the SXR/EUV range. The measured Ne plasma radiation spectra are dominated by emission lines corresponding to radiative transitions in singly charged ions. A significant difference concerns origin of the lines: K-shell or L-shell emissions occur in case of the high and low energy irradiating system, respectively. In high energy system, the electron density measurements were also performed by laser interferometry, employing a femtosecond laser system. A maximum electron density for Ne plasma reached the value of 2·1018cm-3. For the low energy system, a detection limit was too high for the interferometric measurements, thus only an upper estimation for electron density could be made. [ABSTRACT FROM AUTHOR]

Recent observations on DIII-D have advanced the understanding of plasma response to applied resonant magnetic perturbations (RMPs) in both H-mode and L-mode plasmas. Three distinct 3D features localized in minor radius are imaged via filtered soft x-ray emission: (i) the formation of lobes extending from the unperturbed separatrix in the X-point region at the plasma boundary, (ii) helical kink-like perturbations in the steep-gradient region inside the separatrix, and (iii) amplified islands in the core of a low-rotation L-mode plasma. These measurements are used to test and to validate plasma response models, which are crucial for providing predictive capability of edge-localized mode control. In particular, vacuum and two-fluid resistive magnetohydrodynamic (MHD) responses are tested in the regions of these measurements. At the plasma boundary in H-mode discharges with n=3 RMPs applied, measurements compare well to vacuum-field calculations that predict lobe structures. Yet in the steep-gradient region, measurements agree better with calculations from the linear resistive two-fluid MHD code, M3D-C1. Relative to the vacuum fields, the resistive two-fluid MHD calculations show a reduction in the pitch-resonant components of the normal magnetic field (screening), and amplification of non-resonant components associated with ideal kink modes. However, the calculations still over-predict the amplitude of the measured perturbation by a factor of 4. In a slowly rotating L-mode plasma with n=1 RMPs, core islands are observed amplified from vacuum predictions. These results indicate that while the vacuum approach describes measurements in the edge region well, it is important to include effects of extended MHD in the pedestal and deeper in the plasma core. [ABSTRACT FROM AUTHOR]

Wire-array two-component Z-pinch plasmas containing Al and other elements were studied experimentally and the observations interpreted with the help of theoretical modeling. Special attention was given to achieving reproducible implosions. Cascading implosions in star wire arrays mix components during the implosion phase and implosion dynamics were not affected by changes in concentration. A reduction in Al K-shell radiation and an increase in soft x-ray radiation emission were observed in Al-W plasma with 84% concentration of Al ions compared to only-Al plasma. Plasma with 84% of Al ions has radiative properties like those of W Z-pinches. The analysis of Al K-shell x-ray spectra with a collisional-radiative atomic kinetics model shows a drop of the electron temperature from 400 eV in pure Al plasma to below 300 eV in the Al-W mix. Al-Au Z-pinches present radiation features similar to Al-W plasma. This is indicative of a similar plasma cooling effect due to the presence of a high-Z element. [ABSTRACT FROM AUTHOR]