Input impedance of a powerful single-core ferromagnetic inductively coupled plasma source

Abstract

An experimental study of the recently developed version of the ferromagnetic inductively coupled plasma source has shown that under certain circumstances its input impedance becomes almost independent of the delivered rf driving power and (therefore) of the produced plasma density. This plasma source consists of a large ferromagnetic core, which is fully immersed in plasma. This core is surrounded by a primary winding and plasma appears due to gas discharge driven by an rf voltage applied to this primary winding. We have found values of parameters which determine the input impedance in such an “independent” regime and derived a quantitative theory which is in good agreement with the measured impedance values.

Physical limitations in ferromagnetic inductively coupled plasma sources

“…Comparing the voltage required to get the saturation and the evaluated values of T eff (tens of volt vs volts), one might expect that intensive electron beams exist in the "cold" bulk plasma. The evaluated T eff was about 2-3 times smaller than the one obtained formerly in these plasma sources [4][5][6][7][8][9] . To verify this point we compared the decay time of the afterglow plasma t dec at high and low plasma current I pl .…”

“…So, derivation of the plasma parameters from probe characteristics became problematic, in particular taking into account that in the present experiments the induced voltages and currents are definitely higher than even those in Ref. 8 . Oppositely, when the probe bias is sufficiently high, the ion saturation current I p is proportional to the plasma density n and almost insensitive to the above mentioned factors 9,11 .…”

“…This indicated a minimal pressure p for each sort of gas, namely 0.1 mTorr for Xe, 0.3 mTorr for Ar, and 5 mTorr for He. In all these cases the measurements were started from plasma current I pl = 200−300A, which was actually the maximal current for all former experiments [4][5][6][7][8][9] .…”

“…1, but it was described in detail in our recent work 10 . For plasma diagnostics we used combination of two methods: the plasma probing and microwave cut-off methods 4,[6][7][8][9][10] . To measure the parameters of the dense plasma produced by FICP during a high-current pulse we used a small semi-spherical single probe with collecting area of about 5 mm 2 .…”

“…by discharging a preliminary charged capacitor via the FICP primary winding 4 . However, almost all studies of this device were performed with various rf drivers [5][6][7][8][9] because of a clear reason: in this case the FICP devices produce stationary plasmas where the plasma exists during the whole operation time of the rf oscillator, including CW regime. On the other hand these powerful (10-15 kW) oscillators could be rather sophisticated and expensive units.…”