Developmental Aspects of Microwave–Plasma Interaction Experiments: Phase-1

Abstract

An experimental system, SYstem for Microwave PLasma Experiments (SYMPLE), is being developed in order to investigate the physics of linear and nonlinear interaction of a high-power microwave (HPM) with an overdense plasma (plasma frequency $f_{p} \,\, >$ microwave frequency $f_{\mu })$ . The physics of interaction has implications in inertial fusion. The developmental task is taken up in two phases: Phase-1 using moderate microwave power ( $\sim 3$ MW), satisfying the condition ${\scriptstyle{\raise2pt\hbox{$\scriptscriptstyle1$}\mkern-4mu/\mkern-2mu{\scriptscriptstyle 2}}}\varepsilon _{\textrm {o}}\textrm {E}_{\mu }^{2}/\textrm {n}_{\textrm {e}}\, \textrm {kT}_{\textrm {e}} \sim 1$ and Phase-2 involving HPM sources of much higher power. Here, $E_{\mu }$ is the microwave electric field, $n_{e}$ the plasma electron density, $T_{e}$ the electron temperature, $m$ the electron mass, $\varepsilon _{o}$ is the free space permittivity, and $k$ is the Boltzmann constant. The Phase-1 system consists of a pulsed ( $5~\mu \text{s}$ ), $S$ -band magnetron (3 MW, 3 GHz) coupled to a pulsed ( $100~\mu \text{s}$ ) washer-gun plasma ( $n_{e} \sim 1\times 10^{18}/\text{m}^{3})$ . The tasks associated with interfacing of the magnetron and plasma have involved the indigenous design and development of different subsystems, each satisfying the specific technical requisites of the Phase-1 system. These subsystems include a washer-gun plasma ( $n_{e} \sim 1\times 10^{18}/\text{m}^{3})$ driven by a pulse forming network, a line-type modulator (52-KV 120-A, 5- $\mu \text{s}$ pulsewidth, $\sim 450$ -ns rise time) that drives the $S$ -band magnetron, an HPM–plasma coupling system, and an HPM TE10 – TM01 mode converter. The developmental aspects of the subsystems form the subject of this paper.