Plasma Measurements in High Intensity Electron Beam Diodes

Program Document · Thu Oct 01 04:00:00 EDT 2015

OSTI ID:1427289

Kiefer, Mark L.; Patel, Sonal; Bennett, Nichelle; Welch, Dale Robert; Bernshtam, V.; Doron, R.; Maron, Yitzhak

Experiments are being performed on the Self-Magnetic Pinch (SMP) electron beam diode on the RITS-6 accelerator at Sandia National Laboratories. This diode produces a tightly focused electron beam (< 3mm diameter) which is incident on a high atomic number bremsstrahlung x-ray converter. Typical diode parameters are 120 kA, 7 MeV, and 70ns current pulse, giving a ~45ns x-ray pulse. Plasmas from contaminants on the electrode surfaces propagate into the A-K vacuum gap, affecting the impedance, x-ray spectrum, and pulse width. These plasmas are measured using diagnostics, which include: spectroscopy, optical imaging, and photon detection; to obtain velocity, density, and temperature information. These parameters are measured both spatially, using multi-fiber arrays, and temporally, using streak cameras and avalanche photodiodes. Plasma densities and temperatures are determined from detailed, time-dependent, collisional-radiative (CT) and radiation transport (RT) models, which include Stark broadening of the hydrogen-alpha transition line and carbon ion line ratios. These results are combined with hybrid PIC/fluid simulations to model the plasma’s overall behavior. Densities of up to 10^19 cm-3 have been measured on the electrode surfaces, decreasing by several orders of magnitude both radially and axially across the vacuum gap. Electrode plasma expansion velocities of up to 10 cm/microsecond correlate well with the decreasing impedance profile (~0.5 Ohms/ns) observed during the pulse.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 1427289
• Report Number(s): SAND--2015-8898J; 609820
• Country of Publication: United States
• Language: English

Related Subjects

electron beam diodes
flash x-ray radiography
plasma spectroscopy
pulsed-power