Diocotron modulation in an electron plasma through continuous radio-frequency excitation

Abstract

The application of a radio-frequency (RF) excitation to any electrode of a Penning-Malmberg trap may result in significant electron heating and ionization of the residual gas with the formation of a plasma column when the RF frequency is of the order or larger than the typical axial bounce frequencies of few-eV electrons. The use of a quadrupolar excitation can induce additional phenomena, like formation of dense, narrow-cross section columns which exhibit an mθ=1 diocotron mode, i.e., a rotation of their center around the trap axis. A series of experiments is presented and discussed showing that the continuous application of such excitation causes a dramatic perturbation of the plasma equilibrium also involving continuous production and loss of particles in the trapping region. In particular, the growth of the first diocotron mode is suppressed even in the presence of ion resonance and resistive instability and the mode exhibits steady-state or underdamped amplitude and frequency modulations, typically in the Hertz range.

The development and interaction of instabilities in intense relativistic electron beams

“…The diocotron instability is the shear instability that is driven by shear in the drift velocity of charged particles perpendicular to the magnetic field, and it leads to the filamentation of a beam and often to the vortex formation. 36,[55][56][57][58] This instability is observed in many plasma systems including planetary atmospheres, pulsar magnetospheres, aurora borealis, beams of charged particles, etc. 57,59 The Bursian instability 19,60-62 appears in the beam of the charged particles travelling through a drift space due to an uncompensated space charge leading to the sagging of potential in the system.…”

“…In this case, the intense high-energy beams of charged particles are used on relatively long distances or for long times (like in the beam traps). 8,[33][34][35][36] Different methods for mitigation or control of such instabilities are actively studied at present. 34,37,38 At the same time, the diocotron and slipping instabilities could be useful for the development of novel methods for HPM generation (see, for example, the work 23 where the effect of the microwave generation from the filamentation and vortex formation within magnetically confined electron beams was discovered and investigated).…”

Coherent structures and turbulence evolution in magnetized non-neutral plasmas

“…These studies also present an experimental interest. Namely, radio-frequency (RF) drives are routinely used for the manipulation of non-neutral plasmas and the study of related particle transport phenomena [4,55,56,57,58,59,60,61,62].…”

Low-power radio-frequency excitation as a plasma source in a Penning–Malmberg trap: a systematic study

“…Despite the difficulties in the interpretation of experimental observations, previous experiments have demonstrated several interesting features of the RF-generated plasma and secondary phenomena concerning its stability properties (Paroli et al. 2010 b , 2014). The goal of the experimental campaign we discuss in the following is to gain a better understanding of the plasma generation as a function of the control parameters, so as to possibly identify optimal conditions and to suggest key features leading to a thorough modelling of this system.…”