PLASMA PARAMETERS & RF POWER COUPLING MECHANISM TO THE LOW
PRESSURE RF INDUCTIVE DISCHARGE
A.F.Alexandrov, E.A.Kralkina, P.A.Nekhludova, V.B.Pavlov, A.K.Petrov A.A.Rukhadze,
K.V.Vavilin
Physical faculty of Moscow State University, Moscow, Russia, ekralkina@mail.ru
The paper represents the results of many years work in the field of both theoretical and
experimental study of the efficiency of RF power absorption by the low pressure inductive
discharge plasma. The systematic study of the dependencies of plasma absorption ability on the
plasma density, the elastic collisional frequency, the dimensions of the plasma source and the
external magnetic field value was carried out.
CONCEPT OF THE EQUIVALENT PLASMA RESISTANCE
The expression [1]:


2
L
2
2
r  Er   E  ig  E Er*  Er E*  || Ez dr

4 0
R
Ppl 


(1)
determines the relationship between power absorbed by plasma and RF electric field
components. All RF electric fields generated in plasma of inductive discharge are proportional to
antenna current I. Thus the power Ppl absorbed in plasma is defined by a square of the current
through antenna I, and multiplier Rpl, having dimensionality of resistance:
Ppl =1/2 Rpl I2,
(2)
Multiplier Rpl is worth to name as equivalent plasma resistance. It can be treated as a value
characterizing the ability of plasma to absorb RF power.
GENERAL FEATURES OF PLASMA EQUIVALENT RESISTANCE
Theoretical consideration as well as experimental results [2,3] showed that as a whole the
dependence of Rpl on plasma density is non-monotonous due to the competition of two factors,
i.e. growth of the number of electrons participating in power absorption with plasma density
increase ne and decrease of this number due to the decrease of skin width. In the realm of low
electron densities (ne<<1011cm-3) Rpl can be approached by the data calculated [3] for the case of
weak spatial dispersion while in the realm of high electron densities ne>>1011cm-3 where the
conditions of the anomalous skin effect take place Rpl can be approached by the data [3]
calculated for the case of strong spatial dispersion
Calculations showed that at the Ar pressure of 0.1mTorr the RF power is coupled to
plasma due to collisionless Cherenkov power absorption mechanism. The increase of the Ar
pressure leads to the rise of contribution of the collisional mechanism to the RF power
absorbtion, so at pressures higher than 1mTorr it becomes predominant. Here the Rpl values are
controlled by the frequency of elastic collisions.
In case when RF inductive discharge is located in the external magnetic field the
dependence of Rpl values on the external magnetic field B induction shows the presence of a
number of local maxima appearing due to the resonance conditions of the coupled helicon and
TG waves excitation [2,3]. The analysis shows that at low Ar pressures the collisionless Landau
damping mechanism is responsible for RF coupling to plasma. Calculations bring that it is the
absorption of TG wave that contributes to the Rpl values.
REFERENCES.
1. Ginzburg V.L., Rukhadze A.A., “Waves in magnetized plasma”. Science, (1970).
2. Kralkina E.A. Physics-Uspekhi (Advances in Physical Sciences), 178 519–540 (2008).
3. Vavilin K.V., Rukhadze A.A., Lee M.X.,.Plaksin V.Yu.,Technical Physics , 74, N5, 44-49
(2004); 74, N6, 25-28 (2004); 74, N6, 29-34 (2004).