Microwave Heating of Low-Temperature Plasma and Its Application

Jetp Letters, 1999

It is shown theoretically and experimentally that stochastic heating of plasma electrons is highly efficient. Calculations have shown that over the course of 100 periods of an external microwave field the kinetic energy of the particles reaches values of around 1.0 MeV and the average energy reaches values of the order of 0.3 MeV in the field of two oppositely propagating characteristic ͑eigen͒ waves of a cylindrical waveguide, with amplitudes 24 kV/cm in a 1 kG stationary magnetic field. Stochastic instability develops as a result of overlapping of nonlinear cyclotron resonances. The experimental results agree with the theory: When these waves are excited by a 0.9 MW external source, above a threshold of 0.45 MW one obtains x rays with a photon energy corresponding to a maximum electron energy of the order of 1 MeV over about 800 periods of the external microwave field.

2014

The results of the investigation of the dynamics of particles and waves at the interaction of intense electromagnetic pulses with plasmas are presented. It is shown that under conditions when regimes with dynamic chaos for wave-particle and wave-wave interactions are realized, there are still some correlation processes. They occur in the appearance of electromagnetic bursts that occur after sufficiently long time after the pulse, which acts on the plasma. In addition, the shape of instantaneous spectra of oscillations in plasma has a line structure. PACS: 52.40.Mj, 52.50.-b

Applied Physics Letters, 1996

The mechanisms of electron heating in low-pressure bounded rf plasmas are analyzed. These processes are determined by the combined effect of electron interaction with the rf electric field, reflections from the walls and collisions. It is shown that when the discharge gap is small with respect to the electron mean-free path the finite size of the plasmas is crucial for the stochastic heating. A classification of heating regimes is performed and expressions for the power deposition are derived. In many cases, even though in a semi-infinite plasma heating exists, in a bounded plasma the electron motion is regular and there is no collisionless heating.

Physics of Plasmas, 1998

A theory of plasma-filled traveling-wave tubes ͑TWTs͒ is developed in which the effect of magnetosonic waves excited in plasma by the operating wave is taken into account. These waves are excited by the ponderomotive force caused by the radial inhomogeneity of the axial component of the electric field of the operating wave. In the simplest case considered in the paper, this effect leads to an additional reactive nonlinearity in the wave envelope equation. This leads to a shrinkage of the region of stable oscillations in TWTs with the feedback causing the self-excitation; at the same time, the region of stochastic oscillations becomes larger. The radiation spectrum of stochastic oscillations in plasma-filled TWTs in which magnetosonic waves are excited is much wider and more continuous than the spectrum of stochastic oscillations in vacuum TWTs with the same feedback.

Voprosy atomnoj nauki i techniki = Pytannja atomnoï nauky i techniky = Problems of atomic science and technology

Stochastic heating of electrons by plasma oscillations excited in the capacitive discharge plasma is investigated theoretically. We have obtained criteria, when the stochastic heating take place, and demonstrated numerically that this heating mechanism can be sufficiently effective.

Chaos: An Interdisciplinary Journal of Nonlinear Science, 1996

We study the dynamics of charged particles in the presence of two electrostatic waves propagating obliquely to an ambient magnetic field. The presence of a second wave makes the problem a two-dimensional and time-dependent one with a complicated phase space behavior. We derive a set of difference equations ͑maps͒ for the nonrelativistic particle motion limit and numerically study them to elucidate the various aspects of the phase space dynamics. For the general case of oblique propagation, we observe synergistic effects leading to the lowering of the stochasticity threshold and the concomitant reduction in electric field amplitudes for particle heating applications. These results can be understood in terms of the resonance structures associated with the two waves and we obtain approximate analytic expressions for the thresholds. For the degenerate case of 1 ϭn⍀, 2 ϭm⍀ ͑where 1 , 2 are the frequencies of the two waves, ⍀ is the cyclotron frequency and n,m are integers͒ and strictly perpendicular propagation, the problem simplifies to a one-and-one-half-dimensional one. We observe the presence of stochastic webs in this situation.

AIP Conference Proceedings, 2009

It is pointed out that the unmagnetized inhomogeneous plasmas can support a low frequency electromagnetic ion wave as a normal mode like Alfven wave of magnetized plasmas. But this is a coupled mode produced by the mixing of longitudinal and transverse components of perturbed electric field due to density inhomogeneity. The ion acoustic wave does not remain electrostatic in non-uniform plasmas. On the other hand, a low frequency electrostatic wave can also exist in the pure electron plasmas. But the magnetic field fluctuations in both electron as well as in electron-ion plasmas are coupled with the electrostatic perturbations in unmagnetized case. The main instability condition for these low frequency electrostatic and electromagnetic modes is the same 2 3 κ n < κ T (where κ n and κ T are inverse of the scale lengths of density and electron temperature, respectively).

Radiophysics and Quantum Electronics, 1970

The European Physical Journal D, 2011

Ion sources have a significant number of applications in accelerator facilities and in industrial applications. In particular, the electron cyclotron resonance ion sources (ECRIS) are nowadays the most effective devices that can feed particle accelerators in a continuous and reliable way, providing high current beams of low and medium charge state ions and lower, but still remarkable, beam current for highly charged ions. In recent years several experiments have shown that the current, the charge states and even the beam shape change by slightly varying the microwave frequency (the so-called frequency tuning effect -FTE). The theoretical explanation of these results is based on the difference in the electromagnetic field pattern over the resonance surface, i.e. that region where the electrons resonantly interact with the incoming wave. In order to be consistent with the experiments, this model requires that standing waves are formed also in presence of a dense plasma. The proof was sought by means of a series of measurements performed with a network analyzer and with a plasma reactor operating at 2.45 GHz, according to the principles of the microwave discharge ion sources (MDIS). The measurements have been carried out with the aim to achieve the electromagnetic characterization of the plasma chamber in terms of possible excited resonant modes with and without plasma, and they reported that resonant modes are excited inside the cavity even in presence of a dense plasma. It was observed that the plasma dynamics strongly depends on the structure of the standing waves that are generated. The measurement of the eigen-frequencies' shifts were carried out for several values of pressure and RF power, thus linking the shift with the plasma density measured by a Langmuir probe. The changes in plasma shape, density and electron temperature have been also monitored for different operating conditions. A strong variation of plasma properties has been observed as a consequence of the introduction of the Langmuir probe inside the resonant cavity, thus demonstrating that the standing wave can be strongly perturbed even by means of relatively small metallic electrodes. The measurements reported hereinafter are relevant also for ECRIS, because they confirm the validity of the theoretical model that describes the frequency tuning.

A theory of spontaneous plasma oscillations is developed from basic equations. Longitudinal modes in a one-dimensional system are presented in detail, while possible extensions to three dimensions and the effects of external magnetic fields are indicated. The basic equations lead to a Van der Pol equation. Similarities are noted between plasmas and two-level lasers.