Theory and simulation of backbombardment in single-cell thermionic-cathode electron guns

Abstract

This paper presents a comparison between simulation results and a first principles analytical model of electron back-bombardment developed at Colorado State University for single-cell, thermionic-cathode rf guns. While most previous work on back-bombardment has been specific to particular accelerator systems, this work is generalized to a wide variety of guns within the applicable parameter space. The merits and limits of the analytic model will be discussed. This paper identifies the three fundamental parameters that drive the back-bombardment process, and demonstrates relative accuracy in calculating the predicted back-bombardment power of a single-cell thermionic gun.

Properties of quarter-wavelength coaxial cavity for triode-type thermionic RF gun

“…This is the so-called electron back-bombardment effect (BBE). 2) The ramped current is undesirable for linac-driven FEL facilities, since the beam energy decreases during a macropulse owing to the increase in beam loading. Especially troublesome is BBE for the oscillator-type FEL, since it requires long macropulses for lasing.…”

Current transmission and nonlinear effects in un-gated thermionic cathode RF guns

“…In order to estimate the transmission efficiency we calculate the boundary between particles that are back-bombarded and particles that are transmitted through the gun. This is accomplished using the effective transit time of particles in the gap defined by t transit = λ αv eff [14], where v eff is the effective velocity…”

“…As a result the beam often requires further compression, for instance by an alpha magnet, before being injected into further acceleration stages [13]. Additionally, some electrons emitted late relative to the RF will not gain enough energy to exit the cavity and will be accelerated back to the cathode [14]. These back-2 bombarded electrons can have adverse effects on the machine performance [15] and even damage the cathode [16].…”

Electromagnetic analogs of quantum mechanical tunneling

“…Atomistic effects become even more pronounced if the devices themselves are nanoscale [8][9][10] , which is becoming increasingly common as the push for smaller devices at higher frequencies intensifies. Even for mesoscale field emitters, nanoscale processes such as erosion 11 , adsorption of atoms and/or charged inclusions [12][13][14] , and a) Electronic mail: jeanne.riga@us.af.mil backbombardment/breakdown [15][16][17] impact the operation of these emitters. Therefore it becomes imperative to have accurate, well-characterized emission physics simulations at the atomistic level in order to accurately predict macroscale electron beam emission.…”