For plasma with Radio Frequency(RF) heating, dose higher electron density have better RF heating effect?
The heating process depends on RF wave penetration depth into the plasma, which, if no magnetic field is applied, can be evaluated in planar incident wave approximation with Appleton equation, knowing the electron-neutrals&ions collision frequency and plasma frequency, which is related with electron density. The reflected power can be calculated numerically and sometimes evaluated analytically, also it can be measured. Then the efficiency can be derived from the absorbed power. Also the heated volume is related with penetration depth value. Here I don't mention the heat exchange in plasma via few mechanisms, which are significant for high energy density applications.
Electromagnetic wave (EMW) absorption in plasma strongly depends on wave polarization. For TM-polarized EMW the so called resonant absorption takes place when maximal electron plasma frequency of the plasma slab greater than wave frequency (see V.L.Ginzburg, Propagation of electromagnetic waves in plasma, Pergamon Press). This absorption does not depend on micro mechanizm of dissipation whether they are Joule losses or plasma wave generation. Absorption coefficient also strongy depends on the profile of plasma density in the vicinity of plasma resonance region (the region where resonant absorption occurs) and it can reach the value 100% that corresponds to total absorption of EMW (see Yu.Ya.Brodsky, V.L.Goltsman, and S.I.Nechuev, JETP Lett. 24, 504 (1976) (experiment), and A.A.Zharov, I.G.Kondrat'ev, and M.A.Miller, JETP Lett. 25, 330 (1977) (theory).
Dear Nan, electron- ion collision frequency deceases and and the electron neutral frequency increases with electron temperature. These frequencies will affect the plasma permittivity( or plasma permittivity tensor for magnetized plasma). Considering working pressure, plasma density and exciting frequency you can determine how the RF heating changes with Te (plasma may be transparent or it may reflect a fraction of the incident RF Power .Thus, the RF heating may deceases or increases with Te)
You can see the collision frequencies and permittivity tensor for a
collisional magnetized plasma in our following paper:
Article A Simulation Study of the Factors Affecting the Collisional ...
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