The impact of plasma dynamics on the self-magnetic-pinch diode impedance

Abstract

The self-magnetic-pinch diode is being developed as an intense electron beam source for pulsedpower-driven x-ray radiography. The basic operation of this diode has long been understood in the context of pinched diodes, including the dynamic effect that the diode impedance decreases during the pulse due to electrode plasma formation and expansion. Experiments being conducted at Sandia National Laboratories' RITS-6 accelerator are helping to characterize these plasmas using timeresolved and time-integrated camera systems in the x-ray and visible. These diagnostics are analyzed in conjunction with particle-in-cell simulations of anode plasma formation and evolution. The results confirm the long-standing theory of critical-current operation with the addition of a time-dependent anode-cathode gap length. The results may suggest that anomalous impedance collapse is driven by increased plasma radial drift, leading to larger-than-average ion v r  B h acceleration into the gap. V C 2015 AIP Publishing LLC. [http://dx.

Plasma dynamics in the rod-pinch diode at 2MV

“…Carbon atoms are the assumed surface contaminant species for Al, W, and C materials because of high levels of adsorbed hydrocarbon. A 1-eV binding energy is chosen from the high-end of the expected range [10,11]. Using a modest contaminant inventory of 3-5 ML provides a good match to the measured diode current.…”

Zeeman spectroscopy as a method for determining the magnetic field distribution in self-magnetic-pinch diodes (invited)

“…The beam is produced through explosive field emission, as the cathode surface breaks down and plasma formation occurs. 2 The planar anode consists of a high-Z target material, such as tantalum, which converts the beam energy into bremsstrahlung x-rays. The electron beam impacts the anode and heats the anode surface to temperatures greater than 400 • C within a few nanoseconds, desorbing contaminants 3 and forming a dense surface plasma, which is shown in Fig.…”

Design and experimental research on a self-magnetic pinch diode under MV

“…Paraxial diodes are disadvantageous because of their complicated structure and large focal spots (diameter=4-6 mm), and their impedance is than that of rod pinch or self pinch diodes [9]. Self-magnetic pinch diodes (SMPD), which can achieve high radiation dosage (hundreds of rad) and small focal spots (approximately 2 mm) at high voltages (>10 MV), have been examined in current theoretical and application studies to satisfy the requirements of flash radiography for thick materials with high atomic numbers [10][11][12][13][14][15].…”

“…In 2003, the diode structure was optimized, SMPD was driven by Mogul D, and 54 rad at 1 m and 2.1 mm focal spots were obtained at 4.2 MV. Sandia National Laboratories in the United States tested SMPD on RITS-6 at high voltages (6.5 MV), achieved 350 rad at 1 m and 2.9 mm focal spots, and focused on the impedance stability of SMPD [12][13][14].…”