Microwave plasma generation by end-on and side-on irradiation in the pressure range 0.1 10 mTorr of hydrogen
This paper describes investigations of hydrogen plasmas produced by mean of linearly polarized microwaves ( f=2.45 GHz, P 0=2.2 5.0 kW). A superimposed uniform and stationary magnetic fielděc B_z is tuned in most of the experiments to the electron cyclotron resonance. The RF is coupled to the plasma by different antennae. A conical horn is used for end-on irradiation (wave vectorěc kallel ěc B_z ). With regard to toroidal discharge geometries the side-on irradiationěc k bot ěc B_z is of particular interest. For this purpose two new T-shaped antennae were developed. In the pressure range investigated the plasma produced by the microwaves fills up the whole discharge vessel ( l=200 cm, V≈104cm3). The electron densities are in the range between 2.5 · 1010 and 1.5 · 1011 cm-3 and the electron temperatures between 1.2 and 5.0 eV. The plasma produced by side-on RF irradiation(ěc k bot ěc B_z ,ěc Eallel ěc B_z ) is used as a pre-ionization plasma for a Z-pinch discharge. The degree of ionization obtained in this way is ≳5%. The optimum conditions for this type of preionization are evaluated from density measurements at higher cyclotron harmonics.