Temporal response of a surface flashover on a velvet cathode in a relativistic diode

Abstract

Surface flashover of a carbon fiber velvet cathode generates a discharge from which electrons are relativistically accelerated to c ranging from 4.9 to 8.8 through a 17.8 cm diode. This discharge is assumed to be a hydrocarbon mixture. The principal objective of these experiments is to quantify the dynamics over the $100 ns pulse of the plasma discharge generated on the surface of the velvet cathode and across the anode-cathode (A-K) gap. A qualitative comparison of calculated and measured results is presented, which includes time resolved measurements with a photomultiplier tube and charge-coupled device images. In addition, initial visible spectroscopy measurements will also be presented confirming the ion species are dominated by hydrogen. V C 2015 AIP Publishing LLC.

High power electron diode for linear induction accelerator at a flash radiographic facility

“…Based on these fits, the motion of the plasma emissive surface over 45 ns is estimated at 0.24 mm, corresponding to an average velocity of 0.53 cm=μs. This value is consistent with the one obtained by Coleman and co-coworkers who found an estimated plasma velocity of 0.59 cm=μs at 3.8 MV for a 1800 A electron diode [16]. Krasik and co-workers [27] inferred the plasma expansion velocity at 1.0 AE 0.2 cm=μs by monitoring the appearance of the Hα spectral line at different distances from the cathode.…”

“…In spite of these theoretical advances, multidimensional codes remain necessary tools for gaining insight into the physics of multidimensional space charge limited flow that takes place within the injector diode. More recently, Coleman and co-workers [16] carried out a quantitative study of the plasma dynamics within the DARHT-1 high power diode to gain a better understanding of the electron beam generation. Diode transport simulations were performed, in the injector of the FXR induction accelerator [17], in order to lower the beam emittance which is a contributing factor that affects radiographic spot size [18].…”

Diagnosing the DARHT Electron Beam-Target Interaction and Hydrodynamic Expansion [Dissertation]

“…3.1. The thermal energy spread of an electron beam produced from a cold cathode can be characterized by measuring the temperature of the plasma on the cathode surface through which the electrons are extracted [18]. It is described by the following expression:…”

Diagnosing the DARHT electron beam-target interaction and hydrodynamic expansion [Slides]

“…The cathode employed for electron production via field emission is a circular piece of velvet with a diameter of 50 mm [18]. The cathode size, and thus extracted current, can be varied from 19 mm to 70 mm to provide a range of space charge limited beam currents (200 A to 2.9 kA).…”