Experimental investigation of scattering of microwaves in cool plasma

Powerful EM waves can perturb plasma resulting in complex non-linear effects. These can manifest in practical applications including in microwave interactions in both hot, magnetically confined fusion plasma, and in a range of cool plasma scenarios. They may also arise in laser-plasma interactions and where radio waves couple in the ionosphere. These interactions may present useful mechanisms to locally modify the plasma, injecting energy, manipulating the particle kinetic properties, but may also result in undesriable consequences. Understanding these dynamics is therefore important. Here we exploit a stable cool plasma, excited inductively, with a plasma frequency in the range of 10¹⁵/m³ with its critical frequencies in the UHF range to benefit from the relative ease with which such plasma can be diagnosed. Experiments and simulations have been undertaken to study dynamics of microwave beams counter propagating in such plasma. A fixed tone is generated by a magnetron oscillator whilst a frequency flexible TWT amplifier provides the counter propagating signal. This allows the signals to be tuned to excite Langmuir oscillations in a beat-wave Raman interaction. The strength of the effect is being studied as a function of the plasma density by observing second order non-linear sidebands. Simulations have also been undertaken of aspects of this system using the particle-in-cell method.