Experiments And Analysis Of Wave Absorption And Backscattering In Plasmas

We present measurements and analysis of the absorption, reflection and scattering of electromagnetic waves due to electron cyclotron absorption zones and the presence of scatterers in a plasma. The 12 cm diameter by 2 m laboratory plasma is produced by a 2.45 GHz microwave source. The plasma density that can be reached is in the range of 5 x 10
⁹
cm
^-3
- 5 x 10
¹¹
cm
^-3
with electron temperatures in the 3 - 6 eV range and 0.5 - 1.5 kG magnetic fields. Wideband wave absorption of 30 - 50 dB due to the electron cyclotron resonance zone in the 1.5 - 3.0 GHz range is measured. A modulated homodyne detection system has been developed that is sensitive to the backscatter from a movable probe in the plasma, and suppresses the scattering from the walls, other probes and background. This system is used to measure the reduction in backscatter signal produced by an intervening cyclotron resonance zone between the transmitter and modulated scatterer. For collisional, low magnetic field plasma conditions comparable to those that can be obtained in our experiments, the electromagnetic wave reflectivity is calculated using various Epstein profiles. We have also constructed a UV flashtube facility and pulsing system for creating collisional plasmas by photoionization. Initial results of this experiment will be presented.