For interaction studies, impurity pellets of stainless steel and plastic carbon with a diameter of 0.5 mm and a velocity of 400 ± 100 m·s−1 have been injected into plasmas driven by fast wave current, with a sustained plasma current of 35-50 kA and an electron density of (2-5) × 1012 cm−3. The density rise is (6-8) × 1012 cm−3 for stainless steel pellets and 4 × 1012 cm−3 for plastic carbon pellets. At pellet injection, the current driven plasmas show no disruption, whereas all of the Ohmic discharges are disruptive. These phenomena are interpreted by a difference in the collision time with ablated pellets between thermal and non-thermal electrons. From measurements of the temporal evolution of the soft X-ray emission, the decay time of the injected impurity is estimated to be 25 ms. The effective charge states of the material of the injected pellets are calculated from the density rise and it is found that they are in the range of 0.8-1.5.

Electrical and optical measurements of atmospheric pressure radio frequency (RF) (13.56 MHz) He/CF 4 /O 2 discharges are carried out by changing the mixture ratio of CF 4 and O 2 at the volume fraction of He higher than 99%. These discharges are produced between two planar electrodes of 40 mm ∅ at a gap length of 1.0 mm or 1.44 mm in the dissipated power range from 30 to 150 W. The relationship between the applied voltage and the current in the He/CF 4 /O 2 discharges does not strongly depend on the mixture ratio of CF 4 and O 2 . The atomic fluorine density estimated by actinometry markedly increases with the increase in the O 2 addition and then reaches a maximum when the ratio of the O 2 fraction to the sum of CF 4 and O 2 fractions is around 0.2. The density of fluorine atoms produced in those discharges is on the order of 10 14 cm −3 . In addition, the density of fluorine atoms in the afterglow downstream of the reactor is also estimated using the ozone titration and is compared with the density in the plasma, which is estimated by actinometry.

Electrical and optical measurements of atmospheric-pressure radio frequency (13.56 MHz) He/SF 6 /O 2 and He/CF 4 /O 2 discharges are carried out by changing the mixture ratio of a fluoride compound gas to oxygen, where the fraction of He is fixed at 99.5%. Such discharges are produced between two planar electrodes of 40 mm at a gap length of 1.0 or 1.44 mm in the dissipated power range from 30 to 170 W. The phase difference between applied voltage and current in the He/SF 6 /O 2 discharges is approximately 20 -30 , whereas that in the He/CF 4 /O 2 discharges is approximately 50 -60 . The density of fluorine atoms in such discharges, which should be estimated by actinometry, depends on the mixture ratio of the fluorine compound gas to oxygen. The maximum density is observed when the ratios of the oxygen fraction to the sum of the oxygen and fluoride compound gas fractions are approximately 0.3 -0.5 for the He/SF 6 /O 2 discharges and 0.2 for the He/CF 4 /O 2 discharges. The density of fluorine atoms in such discharges is on the order of 10 14 cm À3 . In addition, the results obtained by ozone titration are compared with the density of fluorine atoms in the plasma, which is estimated by actinometry. #