Recent advances in multipactor physics and mitigation

Abstract

Recent progress made in the prediction, characterisation, and mitigation of multipactor discharge is reviewed for single‐ and two‐surface geometries. First, an overview of basic concepts including secondary electron emission, electron kinetics under the force law, multipactor susceptibility, and saturation mechanisms is provided, followed by a discussion on multipactor mitigation strategies. These strategies are categorised into two broad areas – mitigation by engineered devices and engineered radio frequency (rf) fields. Each approach is useful in different applications. Recent advances in multipactor physics and engineering during the past decade, such as novel multipactor prediction methods, understanding space charge effects, schemes for controlling multipacting particle trajectories, frequency domain analysis, high frequency effects, and impact on rf signal quality are presented. In addition to vacuum electron multipaction, multipactor‐induced ionization breakdown is also reviewed, and the recent advances are summarised.

Suppression of multipacting growth in a superconducting spoke resonator by the use of higher order modes

“…In this work, a different approach is proposed to blunt the avalanche of secondary electrons in the operation of a superconducting spoke cavity, employing higher-order modes. Although, multipacting suppression using a second carrier frequency has been asserted [10][11][12][13][14][15][16][17] quite often, but those were done in case of simple geometries (parallel plate and co-axial) only. Semenov et al [10] has made the first attempt [to the best of our knowledge] to investigate the multipactor phenomenon in a simple geometry of a one-dimensional metallic gap exposed to a homogeneous RF-field containing two carrier frequencies.…”

Pulsed photoemission induced plasma breakdown

“…Plasma discharges have been a topic of continuous great interest because of their numerous applications in surface treatment and spectroscopy, space propulsion, environmental and agricultural fields, and plasma medicine [1][2][3][4][5][6][7][8][9][10][11][12][13]. They are * Authors to whom any correspondence should be addressed.…”

Oblique streaming waves observed in multipactor-induced plasma discharge above a dielectric surface

“…The avalanche charges positively the dielectric surface, thereby producing a positive transverse electric field E x within a thin multipactor layer (the thickness of ∼10 µm) near the dielectric surface [38,39], as shown in figure 1(b). Out of this layer, E x is effectively shielded as the amount of positive surface charges on the dielectric surface should be equal to the negative space charges in the multipactor, which is known as the multipactor shielding effect [1,40]. The avalanche is saturated until the average secondary electron yield in a RF period reaches unity [5,33,39].…”

“…Since the Guttons [40,41] and Farnsworth [42] first found the multipactor effects, numerous studies focused on the aforementioned two stages and provided a comprehensive understanding, including the susceptibility curve [1,[43][44][45][46], saturation [43,47,48], secondary electron emission avalanche [34][35][36][37] and mitigation strategies [49][50][51][52] in the first stage, discharge formation time [30] and plasma sheaths [33,[53][54][55] in the second stage. Recently, Wen et al [6,7,40] studied further the transient physics in the gas discharge stage by means of one-dimensional particle-in-cell (PIC) simulations along the transverse direction. They found that the interaction between secondary electrons and the produced plasma gives rise to the excitation of streaming waves.…”