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

David Hammer

关键词: ALUMINIUM;    DIFFRACTION;    ELECTRON TEMPERATURE;    EXPLODING WIRES;    ION TEMPERATURE;    MAGNETIC FIELDS;    MOLYBDENUM;    NIOBIUM;    PHYSICS;    PLASMA;    RADIATIONS;    RESOLUTION;    TAIL ELECTRONS;    TITANIUM;    TUNGSTEN;    VELOCITY;    X-RAY SOURCES High-energy-density plasma;    z-pinch plasma;    X-pinch plasma;    X-ray source;    X-ray spectra;    point-projection radiography;   

DOI  :  10.2172/943298
RP-ID  :  DOE/ER/54496-FNL
PID  :  OSTI ID: 943298
Others  :  TRN: US1002785

美国|英语

来源: SciTech Connect

【 摘 要 】

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.