Imaging X-ray crystal spectrometer for laser-produced plasmas

X-ray Thomson scattering (XRTS) is a powerful technique for measuring state variables in dense plasmas. In this paper, we report on the development of a one-dimensional imaging spectrometer for use in characterizing spatially nonuniform, dense plasmas using XRTS. Diffraction of scattered x-rays from a toroidally curved crystal images along a one-dimensional spatial profile while simultaneously spectrally resolving along the other. An imaging spectrometer was fielded at the Trident laser at Los Alamos National Laboratory, yielding a FWHM spatial resolution of 3 mm. A geometrical analysis is performed yielding a simple analytical expression for the throughput of the imaging spectrometer scheme. The SHADOW code is used to perform a ray tracing analysis on the spectrometer fielded at the Trident Laser Facility understand the alignment tolerances on the spatial and spectral resolutions. The analytical expression for the throughput was found to agree well with the results from the ray tracing.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90829/1/1748-0221_6_04_P04004.pd

Final Technical Report, DOE Grant DE-FG02-98ER54496, Physics of High-Energy-Density X Pinch Plasmas

Abstract for the Final Technical Report, DOE Grant DE-FG02-98ER54496 An X-pinch plasma is produced by driving a high current (100-500 kiloamperes) through two or more fine wires that cross and touch at a point, forming an X in the case of two wires. The wires explode because of the high current, and then the resulting plasma is imploded radially inward by the magnetic field from the current. When the imploding material briefly stagnates at very small radius and high density, an intense burst of x-rays is produced and the plasma disassembles as rapidly as it imploded. When this project began, we could confidently state that at its minimum radius, X pinch plasmas made from such materials as titanium and molybdenum might be as hot as 10,000,000 K and had densities almost as high as the solid wire density, but their X-ray pulse durations were below one billionth of a second. We could also say that the X pinch was useful for point-projection imaging of rapidly changing objects, such as exploding wires, with high resolution, indicative of a very small X-ray source spot size. We can now confidently say that X-pinch plasma temperatures at the moment of the X-ray burst are 10-25 million K in titanium, molybdenum and several other wire X-pinches based upon the spectrum of emitted X-rays in the radiation burst. By the same means, as well as from the penetration of X-rays through the dense plasma, we know that ion densities are close to or higher than one-tenth of the density of the original (solid) wire material in molybdenum and a few other X-pinch plasmas. Furthermore, using the diffraction of X-rays radiated by the X-pinch when it reaches minimum radius, we have determined that the x-ray source size is about 1 thousandth of a millimeter for such wire materials as molybdenum and niobium, while it is 2-10 times larger for tungsten, titanium and aluminum wires. Finally, using a very high speed X-ray imaging “streak camera,” we have determined that X pinch X-ray pulses can be as short as 30 trillionths of a second. Additional experiments have demonstrated that a spherical shell of plasma expands away from the cross point region after the x-ray burst. It reaches millimeter scale in a few billionths of a second, leaving a small (less than 0.1 millimeter) gap in the middle that enables energetic electrons to be accelerated to 10 or a few 10’s of kilovolts of energy. In addition to gaining an understanding of the physics of the X pinch plasmas, we have had to develop several new X-ray diagnostic devices in order to obtain and verify the above results. On the non-technical side, 4 students have completed Ph.D.s working under the auspices of this project, including one woman, and another woman has begun her Ph.D. research under this project. In addition, several undergraduate students have worked with us on the X-pinch experiments, including one who is now a graduate student in plasma physics at Princeton University

Plasma Imaging and Spectroscopy Diagnostics Developed on 100–500-kA Pulsed Power Devices

We discuss the development of high-resolution plasma imaging and spectroscopy diagnostics for the soft X-ray and ultraviolet energy ranges developed and used on 100–500 kA pulsed power facilities. Requiring just a few people to run and modest infrastructure investment, these facilities are cost-effective test beds for new ideas and technologies as well as for training students. Most of the diagnostics discussed here are presently or will soon be in use on larger scale facilities worldwide. Keywords—Plasma pinch, ultraviolet (UV) spectroscopy, X-ray imaging, X-ray spectroscopy. I

Spatially-resolved x-ray Scattering Experiments.

In many laboratory astrophysics experiments, intense laser irradiation creates novel material conditions with large, one-dimensional gradients in the temperature, density, and ionization state. X-ray Thomson scattering (XRTS) is a powerful technique for measuring these parameters in dense plasmas. However, the scattered signal has previously been measured with little or no spatial resolution. This limits XRTS to characterizing homogenous plasmas like steady shocks or isochorically heated matter. This dissertation reports on the development of the imaging x-ray Thomson spectrometer diagnostic for the Omega laser facility, which extends XRTS to the general case of plasmas with one-dimensional structure. The diffraction of x-rays from a toroidally-curved crystal creates high-resolution images that are simultaneously spectrally and spatially resolved along a one-dimensional profile. The technique of imaging x-ray Thomson scattering is applied to produce the first measurements of the spatial profiles of the temperature, ionization state, relative material density, and shock speed of a blast wave in a high-energy density system. A decaying shock is probed with 90 degree scattering of 7.8 keV helium-like nickel x-rays. The spatially-resolved scattering is used to infer the material conditions along the shock axis. These measurements enable direct comparison of the temperature as observed with that inferred from other quantities, with good agreement.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102287/1/eliseo_1.pd