Simulation of a Secondary Electron Emission Cathode in a Crossed-Field Amplifier
Year: 2026
Type: conference-paper
Abstract: The L-4953 Cross-Field Amplifier (CFA) is a high-power$(\approx 5 \text{MW})$, moderate-gain$(\approx 11.2 ~\text{dB})$, pulsed, L-band (1.28-1.35 GHz), reentrant, backward-wave amplifier that uses a thermionic cathode [1]. Typical operating parameters include 88-96 kV on the cathode with a peak current of 98 A. In this study, we develop a secondary-electron-emission (SEE) driven CFA model with the VSim particle-in-cell framework, adjusting operating conditions to enable stable operation with a secondary emission cathode [2]. This CFA is not a Cold Cathode emitting sole CFA, and the device is not optimized for performance. The SEE process is modeled using a Vaughan emission model with$\delta_{\max }=80$and$\mathrm{W}_{\max }=2200 \text{eV}$to achieve a reasonable gain (3-4 dB) with an injected beam that induces secondary emission, using an RF input power of 300 kW compared to 450 kW in the thermionic case. The primary injected electrons are emitted over a 10° arc of the 19.83 mm diameter cathode, while the remaining surface of the cathode is secondary emitting. The operating voltage with this model is 81.25 kV, with a peak circuit current of 6 A during steady state. To reach this operating condition, the primary continuous injected current is 3 A. The goal of this work is to develop a quantitative understanding of secondary emission physics by examining the contrasting behaviors of secondary electrons generated in-phase and out-of-phase with the RF field, and how these phase relationships influence electron multiplication, current transport, and overall device gain. To analyze these effects, the primary emission is temporally modulated using a square-wave profile synchronized with the input RF signal. During steady-state operation, the total circuit current ranges from 3.5 to 6 A, depending on the phase of the primary emission. Two primary emission duty cycles, 35% and 50%, are considered, and, for each, the peak injected current is adjusted to maintain an average injected current of 3 A. The phase of the primary emission is systematically varied in 45° steps over a full RF cycle for each duty cycle. For the 35% duty cycle, phase offsets of 90° and 270° are identified as representative of in-phase and out-of-phase emission conditions, respectively. Under these conditions, 15.47% and 30.38% of the injected current, respectively, reach the circuit directly, with the remainder attributed to secondary emission processes. These findings highlight the strong dependence of current transport and secondary electron contribution on the relative phase between the emitted electrons and the RF field.
Institutions: Boise State University, Purdue University West Lafayette
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W7204525041