Excessive charge, beam loading, and impedance collapse thresholds for a velvet emitter

Coleman, J. E.; Howard, M. R.

doi:10.1063/5.0207544

Excessive charge, beam loading, and impedance collapse thresholds for a velvet emitter

Journal Article · Mon Jun 10 00:00:00 EDT 2024 · Journal of Applied Physics

DOI:https://doi.org/10.1063/5.0207544· OSTI ID:2426534

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Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Excess emission has been observed from velvet cathodes with total emission times >150 ns. In this diode experiment, we produce a sub-relativistic electron beam with the ability to consistently change γ from 1.2 to 1.5 and β = 0.5–0.75. Electron emission in this particular diode geometry requires electric fields >40 kV/cm. The current increases at steady rates >0.05 A/ns after the head of the pulse, indicating an expansion of the emission surface and reduction in the effective AK gap. Small transients of excess emission (or arcs) are consistently observed for current pulses exceeding 150 ns. The excess emission results in beam loaded levels ≥10 kV on the diode voltage. The effects described here are compounded as diode voltage is increased. The principal objective of these experiments is to quantify electric field emission thresholds, current ramps, excess emission delays, effective beam loading, and impedance collapse.

View Accepted Manuscript (DOE)

Research Organization:: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA)

Grant/Contract Number:: 89233218CNA000001

OSTI ID:: 2426534

Report Number(s):: LA-UR--24-20187

Journal Information:: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 22 Vol. 135; ISSN 0021-8979

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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Excessive charge, beam loading, and impedance collapse thresholds for a velvet emitter

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