Experimental results of complex studies of x-ray/EUV radiation from hot dense x-pinch Ti, Fe, Mo, and W plasmas generated by a pulse-powered z-pinch machine with Imax~0.9 ÷ 1.0 MA and a current rise time of 100 ns are overviewed. Structures and spatial dimensions of 0.9-1.0 MA x-pinch sources in a wide energy range of 0.15 - 0.6 keV, 1-10 keV and 10-100 keV are analyzed. Generation of different types of hot spots in high-current multiburst x-pinches are described and a possible explanation of observed effects based on generation of shockwaves in plasmas are discussed. Hard x-ray x-pinch spectra are analyzed. The analysis of time and energy scaling of 0.9 - 1.0 MA x-pinch x-ray/EUV pulses indicate the possible existence of competing mechanisms of the dissipation of the initial discharge x-pinch energy. The future applications of the high current x-pinch as the sub-keV-10 keV radiation driver and the 50 - 100 keV backlighter are discussed.
The results of theoretical and experimental studies of anisotropic plasma sources are reported. They are based on x-ray line spectropolarimetry, a powerful new tool for investigating anisotropy of high-temperature plasmas. It is based on theoretical modeling of polarization-sensitive x-ray line spectra recorded simultaneously by two spectrometers with different sensitivities to polarization. The difference in these polarization-sensitive spectra is used to diagnose the parameters of anisotropic electron beams in plasmas. Theoretical predictions of polarization which cover a broad spectral range from K- to M-shell line radiation are presented. The results of Ti and Mo x-pinch polarization-sensitive experiments at UNR are overviewed. This diagnostic can be applied not only to x-pinches as demonstrated here but to laser-generated and other laboratory x-ray sources.
Victor Kantsyrev, Bruno Bauer, Alla Shlyaptseva, Dmitri Fedin, Stephanie Hansen, Radu Presura, Stephan Fuelling, Steve Batie, Andrew Oxner, Harold Faretto, Nick Ouart, Sean Keely, Hank LeBeau, David Chamberlain
The x-ray emission of Ti, Fe, Mo, W and Pt x-pinches are currently bieng studied at the Nevada Terawatt Facility z- pinch machine (0.9-1.0 MA, 100 ns). New x-ray diagnostics for time-resolved spectroscopy and imaging has been developed and used in x-pinch experiments. The total x- ray/EUV yield was more than 10 kJ. The minimum x-ray pulse duration was 1.1 ns (Mo, W, Pt). For Ti, Mo and W pinches x-ray pulses occurred in two or three groups in the narrow time intervals after the start of the current. The most compact emitting region has been observed for a planar-loop Mo x-pinch (the number of hot spots ranging from 1-5 with a minimum size smaller than 30 micrometers at (lambda) <1.5-2 Angstoms). Strong jets were observed (Ti, Fe, Mo) directed toward the discharge axis, perpendicular to the wires. A structure of an x-pinch includes energetic electron beams directed toward the anode and along wires. The total beam energy increases from Ti to W. A pulse of hard x-ray radiation was observed moving upwards along the axial axis with an energy of several hundred keV(Mo). The size of this source was smaller than 1 mm. The measurements of temperature and density of x-pinch plasmas were based on theoretical modeling of K-shell Ti and L-shell Mo spectra (Te=1.5 keV for Ti, 0.8 keV for Mo, Ne up to 2- 3x1022 cm-3 with 1-10% of hot electrons).
A wide variety of x-ray and extreme ultraviolet (EUV) diagnostics are being developed to study z-pinch plasmas at the Nevada Terawatt Facility (NTF) at the University of Nevada, Reno. Time-resolved x-ray/EUV imaging and spectroscopy, polarization spectroscopy, and backlighting will be employed to measure profiles of plasma temperature, density, flow, and charge state and to investigate electron distribution functions and magnetic fields. These diagnostics are used to study the NTF pinch as an x-ray/EUV source for plasma spectroscopy research and to examine the early-time evolution of a current-driven wire, the formation of a plasma sheet from the explosion and merging of wires, etc. The instruments are state-of-the-art applications of glass capillary converters (GCC), multilayer mirrors (MLM), and crystals. Devices include: a novel glass-capillary-based two- dimensional imaging spectrometer, a time-resolved x-ray spectrometer, a 5-channel crystal/MLM spectrometer ('Polychromator') with a transmission grating spectrometer, and two-channel x-ray/EUV polarimeters-spectrometers (to study simultaneously polarization of K- and L-shell radiation). An x-pinch backlighter, yielding point-projection microscopy with ns resolution is under development. X-ray convex-crystal survey spectrometers, and fast filtered x-ray diodes have observed single Ti-, Fe and W-wire z-pinches, and Ti and Fe x- pinches. The NTF x-ray yield and x-ray pulse duration depend sensitively on the wire load. There is evidence of a strong energetic electron beam with a complex spatial structure in x- pinch plasmas. This work is supported by DOE, DOD, SNL, and UNR.
Victor Kantsyrev, Bruno Bauer, Alla Shlyaptseva, Dmitry Fedin, Stephanie Hansen, Radu Presura, Steve Batie, Wade Cline, Harold Faretto, Bruno Le Galloudec, Andrew Oxner, Diana McCrorey, Nick Ouart, Hank LeBeau
Powerful pulsed soft x-ray point sources are being developed, driven by the Zebra z-pinch at the Nevada Terawatt Facility. A wide variety of x-ray and EUV pulses can be generated, depending on the z-pinch load. X-ray and EUV pulses have been produced with duration from 1.5 ns to 40 ns, energy from 30 J to 9 kJ, and effective source size smaller than 100 micrometers . These pulses will be used for the development of plasma diagnostics, for the study of surface physics, and for microscopy.
A new multichannel x-ray/extreme ultra violet (EUV) spectrometer is developed for monitoring the time history of x-ray/EUV spectral line intensities from a hot plasma to estimate an electron density and temperature of plasmas. Each independently controlled channel includes a crystal (or multilayer mirror) and a fast x-ray diode. At the same time, an imaging transmission grating is applied to study a spatial distribution of spectral line intensities in a wide spectral region with time gated resolution. The multichannel spectrometer can be applied for measurements of polarization- dependent spectra which will be used for diagnostics of electron beams and measuring a magnetic field in z-pinch plasmas.
The results of the study and application of the prototype of the novel imaging spectrometer with a glass-capillary multiplexer of a 2D x-ray image of Z-pinch plasma are presented. Output channels are used to obtain an array of time-resolved spectra, which covers the full plasma evolution. A spatial resolution of the spectrometer is about 100-250 micrometers for plasma size up to 5 by 20 mm. A spectral resolution is 700-1000. A time-gated resolution is 1-2 ns.
Short-pulse laser-produced plasmas look very promising for the generation of sub-picosecond X-rays. By combining several experimental techniques, we have significantly progressed towards a better understanding of ultrafast laser-matter interaction. The X-ray yield is a sensitive function of the electron density gradient scale length of the target plasma. In this work, the scale length has been changed by varying the temporal separation between the main laser pulse and a lower intensity prepulse. X-ray spectroscopic diagnostics of the plasma parameters have been used from the analysis of resonance and dielectronic satellite lines. The angular and energy distribution of suprathermal electrons emitted during the ultrafast laser- plasma interaction have been measured as a function of laser polarization and prepulse delay. Frequency-domain interferometry and optical measurements of the reflected probe pulse have been used to study the velocity and the gradient scale length of the expanding plasma. The Kα emission yield peaks for a scale length where resonant absorption is optimized. Hydrodynamic simulations have been performed to investigate the plasma dynamics and the basic processes which control the X-ray emission duration and intensity. Applications of ultrashort Kα X-rays to the diagnostic of solid plasma conditions and as a source for time-resolved diffraction and spectroscopy of transient chemical, biological or physical phenomena are underway.
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