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

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_μ). The physics of interaction has implications in inertial fusion. The developmental task is taken up in two phases: Phase-1 using moderate microwave power (~3 MW), satisfying the condition 1/_2εoE²_μ/ne kT_e~ 1 and Phase-2 involving HPM sources of much higher power. Here, Eμ is the microwave electric field, ne the plasma electron density, Te the electron temperature, m the electron mass, ε_o is the free space permittivity, and k is the Boltzmann constant. The Phase-1 system consists of a pulsed (5 μs), S-band magnetron (3 MW, 3 GHz) coupled to a pulsed (100 μs) washer-gun plasma (ne~ 1 × 10¹⁸/m³). 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~ 1 × 10¹⁸/m³) driven by a pulse forming network, a line-type modulator (52-KV 120-A, 5-μs pulsewidth, ~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.