| Özet: | The voltage reflexion coefficient from a vacuum-plasma boundary in a co-axial transmission line with an axial magnetic field B<sub>0</sub> applied has been measured. The results agree well with a previously published theory for conditions where the microwave-, plasma-, electron collision-, and electron cyclotron-frequencies are of the same order. A 9 GHz co-axial microwave probe is mounted along the axis of a 44 mm diameter, hydrogen driven, dry air filled, shock tube in an axial d.c. magnetic field. Shock ionized air (M<sub>s</sub>=9-14, T 4000°K, electron density n<sub>c</sub>=10<sup>17</sup> to 3x10<sup>19</sup>m<sup>-3</sup>, initial pressure p<sub>0</sub> = 1-10 Torr, electron collision frequency v = 10<sup>10</sup> to 10<sup>11</sup>/s) fills the coaxial line and partially reflects a microwave signal. Initially this probe, and a similar rectangular waveguide probe, were used with B<sub>0</sub> = 0 to calibrate the plasma (n<sub>c</sub>,v) in terms of the shock tube parameters (p<sub>0</sub>, M<sub>s</sub>). Measurement of the saturated-ion current to electrostatic probes inset into a flat plate in the shock tube flow showed that the sheath-edge ion density is close to the predicted free-stream equilibrium ion density. The apparent ionization potential derived from electrostatic probe results decreased as p<sub>0</sub> was reduced from 10 to 1 Torr.
|
|---|