Self-bunching electron guns

Abstract

This paper presents several new approaches for producing bunched electron beams. The need for higher power injectors and microwave sources for various applications has in turn created the need for higher emission current density electron guns with a means for bunching at the gun. Four different cathode/gun approaches are presented. The first three utilize external methods of bunching. They are based on: field emission, photoemission and ferroelectric emission. The fourth is based on secondary emission and utilizes self-bunching. The latter is emphasized in this presentation. This self-bunching electron gun produces naturally bunched electron beams with the use of microwave fields to generate secondary emission and multipacting of electrons. This type of electron gun is called the Micro-Pulse Gun + (MPG). One wall of an RF cavity is made opaque to an input RF electric field but is partially transparent to electrons in order to extract the beam. FMT has studied using simulation codes the resonant bunching process which gives rise to high current densities (0.01−5 kA/cm 2 ), high charge bunches (up to 500 nC/bunch), and short pulses (1−100 ps) for frequencies from 1 to 12 GHz. The beam pulse width is nominally ~5% of the RF period. Experimental verification of self-bunching, cold electron emission, long life, and tolerance to contamination has been achieved. Measurements of current density, bunch length and lifetime are presented for the MPG.

Recent advances in electron and positron sources

“…While the pulse spacing is fixed by the rf frequency, the pulses are automatically synchronous with the rf. Proof of principle testing has been carried out at low charge, but simulations show that the charge per bunch can be up to 500 nC [20]. There appears to be some possibility of modulating the charge using a separate grid.…”

Theoretical analysis and simulation of the influence of self-bunching effects and longitudinal space charge effects on the propagation of keV electron bunch produced by a novel S-band Micro-Pulse electron Gun

“…Some applications of the multipacting effect require to suppress the secondary-electron emission while the others such as crossed-field devices, need to enhance the emission. 8 Micro-Pulse electron Gun (MPG) which was proposed and developed by Mako [9][10][11][12] needs to select the materials judiciously. Actually, the Multipactor Electron Gun (MEG) which is essentially the same to MPG has been deeply studied.…”

“…[13][14][15] And the MPG has also been researched for many years both in theory and experiment. [16][17][18] However, although the electron bunching has been observed in some experiments, 12 the mechanism of the self-bunching effects has never been studied systematically. Due to its self-bunching property, 19 MPG is capable of providing high Pulse Repetition Frequency (PRF) electron bunch which means high average current and short pulse electron beam.…”

High-current micro-pulse electron guns and accelerator applications

“…Several groups [1][2][3][4][5][6][7] have been working on microwave generation, especially in view of the requirements of future TeV linear colliders. A major research and development activity is being conducted at FMT, and robust micropulse electron guns (MPG) have been developed [8,9] to produce selfbunched, high-current-density beams. The natural bunch formation in this cavity is a phase locking resonant process which is not prone to phase instability.…”

“…This article describes the development of an X-band gun for a micropulse klystron (MPK). Work on S-and L-bands were described earlier [8,9]; updates on current activities on L-band gun are discussed here briefly. This MPK gun will provide a high-power, high frequency source for many applications including high energy accelerators for linear colliders, free electron lasers, medical and industrial rf linacs.…”