Effects of magnetic field and microwave power on electron cyclotron resonance-type plasma characteristics

Abstract

Microwave plasmas were excited in cylindrical cavities of 2.5–5.0 cm diam in the presence of magnetic field of 800–1000 G. Microwave cw power of 100–1000 W at a frequency of 2.45 GHz was delivered in the plasma via a matched introduction (quartz) window. It was found that microwaves could propagate in cavities with diameters smaller than cutoff through the overdense plasma (Ne>Ncr,Ncut-off) if the magnetic field in the plasma is higher than electron cyclotron resonance (ECR) field. When the magnetic field is lower than 875 G no detectable microwave propagation through the overdense plasma was observed. The microwave power absorption was located mainly in two sites: (i) near the vacuum window (2–3 cm) where the microwave electric field seems to have a maximum amplitude and plasma density has a steep gradient with a magnitude of Ne≊Ncr (Landau damping), and (ii) at sites along the plasma chamber where the magnetic field has a value of 875 G (ECR heating). Two electron temperatures on the Langmuir probe I–V characteristics −Te1=3–6 eV, and Te2=7–12 eV, and effects of magnetic field and plasma density on the microwave propagation are discussed.