An Electron Plasma Wave Driven By Beating Counter Propagating Microwaves

An electron plasma wave driven by optical mixing of two oppositely propagating microwaves was experimentally studied. Two microwaves (w
₀
2π = f
₀
=9445 MHz, w
₁
2π = f
₁
= 8500 ∿ 9600 MHz, maximum output power P
₀
= P
₁
= 45 kW and pulse duration 1.5 μsec) were injected into a target plasma through each standard horn at both ends of a vacuum chamber (38 cm in diameter and 1 m long). The target plasma was produced by an RF afterglow discharge. The plasma density and electron temperature measured by a Langmuir probe were n
₀
= 2 x 10
⁹
cm
^-3
and T
_e
= 1 ev, respectively. The density has the spatial uniformity of 2 in the 40 cm-axial direction. The excited wave signals, detected by a capacitive probe or the Langmuir probe, were mixed with a local oscillator, allowing us to display beat signals on an oscilloscope. The absolute amplitude of excited waves was determined using the capacitive probe which has high frequency response of up to 500 MHz.