Plasma Radiation Source Research Articles

MK-200 Plasma Gun Facility

Plasma flows with high velocity, density, and energy are widely used in research on the interaction of plasma with materials, modeling of astrophysical processes, development of plasma thrusters and plasma radiation sources, and plasma injection into fusion devices. Electrodynamic plasma guns can be used to generate such flows. This paper describes the design features of a powerful pulsed plasma gun and diagnostic tools for measuring the parameters of the plasma flow generated by it.

Plasma diagnostics using fast cameras at the GOLEM tokamak

Tomographic inversion of radiation determines spatial distribution of tokamak plasma radiation sources using line integrated plasma projections data. For measurements of the projections, fast visible radiation matrix cameras became broadly applied on tokamaks in recent past. These novel cameras opened new possibilities in high temperature plasma studies.The GOLEM tokamak of the Czech Technical University in Prague strives to implement up-to-date diagnostics with enhanced temporal and spatial resolution. Therefore, a novel diagnostic system of two crossed monochrome cameras Photron FASTCAM MINI UX50 was integrated into the GOLEM diagnostics. The proposed contribution will detail their novel port mounts (vertical and horizontal) at the GOLEM tokamak which have been designed so that additional optical measurements of the plasma core (e.g. plasma spectroscopy) is possible.As the main purpose of this study, we shall focus in particular on the frame rate potential which is high enough to make detection and observation of highly transient phenomena in the GOLEM plasmas possible. Progress in solving specific challenges of the ill-conditioned tomographic inversion via the algorithm optimization and testing for the GOLEM tokamak will be presented together with the first tomographic results.

Development of radiation sources for nuclear analysis beyond ITER bio-shield: SRC-UNED code

ITER reference MCNP models are the portentous result of years of geometric modelling, and they share the bio-shield as the natural boundary for practical reasons. Models representing the Tokamak, or fractions of it, end in the bio-shield. Those representing the Tokamak Complex start in the bio-shield. Nuclear analysis beyond the bio-shield is of high relevance to forecast radiation conditions for electrical and electronic equipment, as well as for human intervention, affecting both economics and safety. Nevertheless, it presents a challenge when dealing with the plasma radiation source: the radiation source is not contained in the MCNP model under study. Coupling both simulations inside and outside the bio-shield is one solution. But standard options offered by MCNP, including SSW/SSR and SDEF cards, show relevant limitations. We present a methodology overcoming the MCNP limitations to transfer the plasma radiation information at the bio-shield. It is based on grouping the pointwise information stored in WSSA files to build piecewise probability distributions (PPDs). One or more PPDs are later processed by an MCNP source subroutine coded ad hoc to sample them as the radiation source. Successful and noticeable applications to ITER are shown.

Parametric study of high-energy ring-shaped electron beams from a laser wakefield accelerator

Laser wakefield accelerators commonly produce on-axis, low-divergence, high-energy electron beams. However, a high charge, annular shaped beam can be trapped outside the bubble and accelerated to high energies. Here we present a parametric study on the production of low-energy-spread, ultra-relativistic electron ring beams in a two-stage gas cell. Ring-shaped beams with energies higher than 750 MeV are observed simultaneously with on axis, continuously injected electrons. Often multiple ring shaped beams with different energies are produced and parametric studies to control the generation and properties of these structures were conducted. Particle tracking and particle-in-cell simulations are used to determine properties of these beams and investigate how they are formed and trapped outside the bubble by the wake produced by on-axis injected electrons. These unusual femtosecond duration, high-charge, high-energy, ring electron beams may find use in beam driven plasma wakefield accelerators and radiation sources.

Theoretical study of soft X-ray emission and dynamics of laser-induced plasma of double stream gas puff

The double stream gas puff-based laser-produced plasma is studied as a source of soft X-ray radiation in nm wavelength spectral range. Dynamics of plasma induced by Nd:YAG laser beam and its emission is simulated with radiation-magnetohydrodynamic code Zstar. The modeling results for krypton gas stream in an annular helium jet as a circumferential gas for various picosecond and nanosecond laser pulses corresponding to the experiments are presented. The spatial–spectral features and temporal behavior of the soft X-ray and EUV emission are investigated. Under ps pulse, the gas is rapidly ionized in the laser beam channel, but it does not have enough time to shift sensibly during the pulse, and the plasma electron density grows against the background of almost constant ion density during the ionization in the laser radiation field. There is ionization instability only capable to be developed in ps range. At ns pulse, the gas ionization and heating leads to gas pushing out of the channel, and the formation of a divergent compression wave transforming into the shock wave. Behind the compression wave front, conditions arise for the development of Rayleigh–Taylor-type instability. The instability leads to the redistribution of plasma temperature and density, and to the formation of increased soft X-ray emission spots. Time evolution of spatial distributions and spectral characteristics of emitted SXR radiation is analyzed for different laser pulses. Transient effects in multicharged ion plasma are discussed, fundamental understanding of those is required for optimization of plasma radiation source. A conversion efficiency of laser energy into soft X-ray wavebands from krypton plasma is scanned by laser parameters and analyzed.

Potential use of plasma focus radiation sources in superficial cancer therapy

The new multidisciplinary field of plasma medicine combines plasma physics, electrical engineering, life sciences and clinical medicine. Bekeschus et al. [Plasma Processes Polym. 16, 1800033 (2019)]. Here we explore potential uses in medicine, most particularly cancer therapy, the plasma source being brought out of the field of industrial applications into the life sciences, the focus being on superficial cancer radiotherapy strategies. Existing radiotherapy practices for such cancers rely on the use of rather large facilities, most popularly the electron linear accelerator and X-ray tube-based devices. Conversely, a compact plasma radiation source can be housed in a relatively small space, there being considerable promise for such devices to produce the fluence requirements of radiotherapy for treatment of skin cancers. The present study of feasibility investigates the plasma focus device, with the emission produced by a single discharge shown to generate an X-ray dose of few tens of mGy. The X-ray dose is the integration of emission in the discharge durations of less than a μs, it is therefore possible using these devices to build up fractional irradiation dose through repetitive operation of the discharge system.

Generation of K-Shell Radiation of Noble Gases in the Microsecond Implosion Regime

Studies of K-shell plasma radiation sources were performed on the GIT-12 generator (4.7 MA, 1.7 μs). In the experiments, a new type of load configuration was used to form the Z-pinch plasma – a gas puff with an outer plasma shell. Noble gases neon and argon were used as working gases. The gas puff consisted of two cascades: a hollow cylindrical shell outside and a solid jet inside. The outer plasma shell was created with the help of plasma guns located on a diameter of 350 mm. A distinctive feature of these studies is that the experiments with the plasma radiation source were carried out in the microsecond implosion regime usually leading to a significant decrease in the efficiency of generation of K-shell x-rays. The use of the Z-pinch load of a new type significantly improved the efficiency of the microsecond plasma radiation source. As a result of optimization of the initial gas-puff parameters, a neon K-shell radiation yield of 14.7 kJ/cm at a peak implosion current of 3.5 MA was achieved. In experiments with argon gas puffs, the radiation yield reached 1.9 kJ/cm at a peak implosion current of 3.1 MA.

Opacity effects on laser-produced plasma radiation sources

The escape of spectral line radiation from laser-produced plasma radiation sources with moderate opacity is examined using a simple model of emission with a planar geometry, constant source function, and an empirically determined optical depth. The model is applied to determine the radiation produced by laser irradiation of tin targets used as the source of radiation in extreme ultraviolet (EUV) lithography. Variations in emission relative to optically thin plasmas in agreement with previous experimental measurements of both the angular variation of the emission of EUV light at 13.5 nm and the effect of plasma opacity in reducing EUV emission at laser intensities above 1011 W cm−2 are found. The model is extended to predict optimum conditions for future lithography radiation sources at ≈6.7 nm.

Effect of the gas distribution on implosion dynamics and the K-shell yield of the neon gas-puffs with the outer plasma shell

The experiments have been carried out on the GIT-12 generator to characterize the effect of the anode and cathode meshes installed on the path of the gas flow on the initial gas density distribution, the gas-puff implosion dynamics, and the resulting radiative characteristics of the Ne K-shell plasma radiation source (PRS) operated in the microsecond implosion regime. The experiments showed that the obstacles located directly on the way of the main gas flow have the greatest influence on the gas distribution in the interelectrode gap of the generator. At all other factors being the same, the presence or absence of the anode and cathode meshes changed significantly the implosion dynamics and radiative characteristics of the Ne K-shell PRS. In our experiments, we observed two-fold decrease in the K-shell radiation yield and more than four-fold decrease in the K-shell radiation power. These observations should be taking into account in development of the gas-puff loads for Z-pinch experiments.

X-ray and VUV reflectometry and metrology of plasma radiation sources

Comparison of various methods for quantitative (absolute) measurements of intensities in soft X-ray and VUV spectral ranges is considered. These methods include calibration of separate spectrometer elements, the use of absolutely calibrated spectrometers and formation of quasi-monochromatic with a large angle of divergence X-ray beams. Their use together with spectroscopy methods allows a providing complete plasma diagnostics: determination of plasma parameters and measuring of plasma radiation characteristics.

Luminescent Characteristics of a Pulsed Discharge Plasma in Xe–KBr Mixture

A mixture of xenon with a nontoxic halogen carrier Xe–KBr is used to create a plasma radiation source at the 282-nm transition of the XeBr* molecule excited by a high-voltage pulsed-periodic discharge. The luminescence spectra of the plasma of a longitudinal pulsed-periodic discharge in the Xe–KBr mixture at low pressures are studied experimentally. The most intense UV bands of exciplex XeBr* molecules are recorded in the spectral range of 250–350 nm. The spectral, temporal, and energetic characteristics of the radiation source are presented, as well as the dependence of the XeBr* exciplex molecule formation efficiency on the discharge excitation conditions. The optimal conditions for the excitation of UV radiation in the pulsed-periodic discharge plasma are determined.

Plasma Radiation Source on the Basis of the Gas Puff with Outer Plasma Shell in the Circuit of a Mega-Ampere Load Current Doubler

Characteristics of Z-pinch plasma radiation in the form of a double shell neon gas puff with outer plasma shell are investigated in the microsecond implosion mode. Experiments are performed using a GIT-12 mega-joule generator with load current doubler having a ferromagnetic core at implosion currents up to 5 MA. Conditions for matching of the nonlinear load with the mega-ampere current multiplier circuit are determined. The load parameters (plasma shell characteristics and mass and geometry of gas puff shells) are optimized on the energy supplied to the gas puff and n energy characteristics of radiation. It is established that the best modes of K-shell radiation in neon are realized for such radial distribution of the gas-puff material at which the compression velocity of the shell is close to a constant and amounts to 27–30 cm/μs. In these modes, up to 40% of energy supplied to the gas puff is converted into K-shell radiation. The reasons limiting the efficiency of the radiation source with increasing implosion current are analyzed. A modernized version of the energy supply from the current doubler to the Z-pinch is proposed.

Versatile and compact wide-range VUV spectrometer for quantitative measurements

Main parameters of a new scheme of a compact VUV grazing incidence spectrometer based on a plane amplitude diffraction grating are considered. The spectrometer will allow simultaneous detection of spectra at the +1st order diffraction edge with a sufficiently high (λ/δ λ ∼ 150) spectral resolution and in the –1st order with a moderate resolution (λ/δ λ ∼ 15 – 30), but in a very wide (5 – 200 nm) spectral range. The use of such a spectrometer is promising for measuring the absolute radiation yield in these spectral regions, which is necessary for the diagnostics and control of plasma radiation sources, including those intended for projection EUV nanolithography.

The differential absorption hard x-ray spectrometer at the Z facility

The differential absorption hard X-ray (DAHX) spectrometer is a diagnostic developed to measure time-resolved radiation between 60 keV and 2 MeV at the Z Facility. It consists of an array of seven Si PIN diodes in a tungsten housing that provides collimation and coarse spectral resolution through differential filters. DAHX is a revitalization of the hard X-ray spectrometer that was fielded on Z prior to refurbishment in 2006. DAHX has been tailored to the present radiation environment in Z to provide information on the power, spectral shape, and time profile of the hard emission by plasma radiation sources driven by the Z machine.

An oil-free compact X-pinch plasma radiation source: Design and radiation performance.

This paper describes a new, high-current, X-pinch radiation source recently developed and tested at Idaho State University. Our design is based on two linear transformer driver (LTD) bricks arranged in side-by-side geometry and directly coupled with an X-pinch load. The salient features of our 2-LTD-bricks are its simplicity, compactness, and portability: there is no oil, no water, and no SF6. It can be easily relocated to any place where a compact X-pinch radiation source is wanted. The driver can store up to 2.8 kJ of initial energy and can deliver more than 200-kA peak-current with less than 200-ns, 10%-90%, rise time into a short-circuit load. When the driver is coupled with an X-pinch load, it generates a very fast and bright radiation pulse. Source size measurements indicate that this radiation originates from a very small dense plasma, known as a "hot spot."

A method for determination of spatial distribution of gas concentration in supersonic jets outflowing into vacuum

An experimental method for determination of the spatial distribution of gas concentration in millimeter-sized supersonic jets outflowing into vacuum is proposed. This method is based on jet visualization by its illumination with a laser–plasma radiation source and processing of the obtained intensity distribution of the jet glow. The spatial distribution of the jet glow intensity for the visualized jet is measured. The gas concentration distribution in the jet is determined, and the results of experiment are compared with the calculated data obtained by numerical hydrodynamic simulation.

Extreme ultraviolet (EUV) source and ultra-high vacuum chamber for studying EUV-induced processes

An experimental setup that directly reproduces extreme ultraviolet (EUV) lithography relevant conditions for detailed component exposure tests is described. The EUV setup includes a pulsed plasma radiation source, operating at 13.5 nm; a debris mitigation system; collection and filtering optics; and an ultra-high vacuum experimental chamber, equipped with optical and plasma diagnostics. The first results, identifying the physical parameters and evolution of EUV-induced plasmas, are presented. Finally, the applicability and accuracy of the in situ diagnostics is briefly discussed.

Simulation and mitigation of the magneto-Rayleigh-Taylor instabilities in Z-pinch gas discharge extreme ultraviolet plasma radiation sources

The development and use of a single-fluid two-temperature approximated 2-D Magneto-Hydrodynamics code is reported. Z-pinch dynamics and the evolution of Magneto-Rayleigh-Taylor (MRT) instabilities in a gas jet type Extreme Ultraviolet (EUV) source are investigated with this code. The implosion and stagnation processes of the Z-pinch dynamics and the influence of initial perturbations (single mode, multi- mode, and random seeds) on MRT instability are discussed in detail. In the case of single mode seeds, the simulation shows that the growth rates for mm-scale wavelengths up to 4 mm are between 0.05 and 0.065 ns−1. For multi-mode seeds, the mode coupling effect leads to a series of other harmonics, and complicates MRT instability evolution. For perturbation by random seeds, the modes evolve to longer wavelengths and finally converge to a mm-scale wavelength approximately 1 mm. MRT instabilities can also alter the pinch stagnation state and lead to temperature and density fluctuations along the Z axis, which eventually affects the homogeneity of the EUV radiation output. Finally, the simulation results are related to experimental results to discuss the mitigations of MRT instability.

Basis set expansion for inverse problems in plasma diagnostic analysis

A basis set expansion method [V. Dribinski, A. Ossadtchi, V. A. Mandelshtam, and H. Reisler, Rev. Sci. Instrum. 73, 2634 (2002)] is applied to recover physical information about plasma radiation sources from instrument data, which has been forward transformed due to the nature of the measurement technique. This method provides a general approach for inverse problems, and we discuss two specific examples relevant to diagnosing fast z pinches on the 20-25 MA Z machine [M. E. Savage, L. F. Bennett, D. E. Bliss, W. T. Clark, R. S. Coats, J. M. Elizondo, K. R. LeChien, H. C. Harjes, J. M. Lehr, J. E. Maenchen, D. H. McDaniel, M. F. Pasik, T. D. Pointon, A. C. Owen, D. B. Seidel, D. L. Smith, B. S. Stoltzfus, K. W. Struve, W. A. Stygar, L. K. Warne, J. R. Woodworth, C. W. Mendel, K. R. Prestwich, R. W. Shoup, D. L. Johnson, J. P. Corley, K. C. Hodge, T. C. Wagoner, and P. E. Wakeland, in Proceedings of the Pulsed Power Plasma Sciences Conference (IEEE, 2007), p. 979]. First, Abel inversion of time-gated, self-emission x-ray images from a wire array implosion is studied. Second, we present an approach for unfolding neutron time-of-flight measurements from a deuterium gas puff z pinch to recover information about emission time history and energy distribution. Through these examples, we discuss how noise in the measured data limits the practical resolution of the inversion, and how the method handles discontinuities in the source function and artifacts in the projected image. We add to the method a propagation of errors calculation for estimating uncertainties in the inverted solution.

Normal-incidence multilayer mirrors for the wavelength range

Periodic and aperiodic multilayer structures have been theoretically calculated and synthesised for the first time for the application in soft X-ray optics in the range. The reflection spectra of the periodic multilayer mirrors are measured using synchrotron radiation and laser plasma-generated radiation. The experimental spectra are theoretically interpreted with the inclusion of transition layers and substrate roughness. The density of antimony layers is supposedly , and the thickness of transition layers (if any) in the multilayer structures does not exceed . A peak reflectivity of is attained at a wavelength of . An aperiodic mirror optimised for maximum uniform reflectivity in the range is tested employing the laser plasma radiation source.