Driving Sudden Current and Voltage in Expanding and Compressing Plasma

Abstract

A magnetized plasma preseeded with an initially undamped Langmuir wave is shown to transition suddenly to a collisionless damping regime upon expansion of the plasma perpendicular to the background magnetic field. The resulting anisotropic fast particle distribution then leads to an electrical current and dc voltage induction. The current drive efficiency of this effect in nonstationary plasmas is shown to depend on the rate of expansion of the plasma, the time-varying collisionality, and the plasma L/R time. Subsequent re-compression of the plasma enhances this current drive effect by reducing further the collision rate of the current-carrying electrons. Here, a new scheme to drive sudden bursts of current and voltage is predicted in nonstationary plasma, whereby an initially undamped monochromatic wave, embedded in a magnetized plasma and propagating in one direction parallel to the magnetic field, is induced into wave-particle resonance with plasma particles due to magnetic expansion perpendicular to the wavevector. The sudden, collisionless damping causes the wave to transfer its energy anisotropically onto the co-moving high-energy tail of the resonant particle distribution, while subsequent velocity-dependent collisional relaxation of the modified distribution results in a rise and fall of the total fast-particle current.As a paradigmatic example, embedded Langmuir waves are considered, though other waves may prove more suitable for specific applications. The peak attainable fast-particle current densities occur for expansion rates, η, comparable to the electron collision rate, ν c . However, expansion rates significantly faster than the collision rate lead to more prolonged current as a result of enhanced electron trapping by the wave, which carries more electrons to superthermal velocities and, hence, reduces their collisionality. Interestingly, the current can be prolonged by magnetically compressing the plasma to higher densities following the collisionless damping, which increases perpendicular velocities sufficiently to lower the collisionality of the current-carrying electrons.Before presenting the results of the numerical simulations, the basic current drive mechanism will be explained briefly. For slow variation of external forces, the Langmuir wave dispersion relation obeys the eikonal equation [3]: ω 2 = ω

Chirped resonance dynamics in phase space

“…The final distribution, after passage of ω through the distribution, in this case is shown for constant P 1 = 0.1 in figure 2(b) and increasing P 1 = βτ , β = 0.0067 in figure 2(c). One can see in the figure that in both cases, after passage through the resonances, the distributions remained uniform except in the boundary regions and that the whole distribution is shifted on average to lower energies (the phenomenon discussed in Friedland, Khain & Shagalov (2006) and Schmit & Fisch (2012)). In addition, for the increasing P 1 case, some phase space area S of the initial distribution is captured into resonance forming a ring of the same uniform initial density.…”

Creating localized plasma waves by ionization of doped semiconductors

“…According to Refs. [3,4], the mechanical energy of compression is partially transferred into the plasma wave leading to increasing the wave energy E∝V −1/2 . The compression also increases the plasma wave vector k∝V −1 until Landau damping suddenly dominates and damps the wave energy into hot electrons.…”

“…Localized plasma wave, because they linger in plasma, can potentially manipulate intense lasers in a variety of applications. Examples include replacing a seed laser pulse [1] for initiating backward Raman amplification [2] to avoid the technological challenges of frequency-shifting and synchronizing laser pulses, and heating hot electrons in compressing plasma [3,4] for the purpose of inertial confinement fusion. Localized plasma waves can also be formed to create a plasma holograph [5].…”

Negative-mass Instability in Nonlinear Plasma Waves

“…A selfconsistent phase-mixed electron plasma wave is seeded, with ions modeled as a homogeneous background. We then emulate [25] plasma compression perpendicularly to the wavevector. During this compression,n t /n ≡ τ ,k, and v T remain fixed, butω ∼ ω p (t) grows proportionally to n(t)/n 0 ≡ N .…”