ICRF plasma production and heating in the URAGAN-3M torsatron

The results of experimental and theoretical studies of Alfven wave production and heating of plasma in the frequency range below the ion cyclotron frequency (ω0 < ωci) are presented. Several types of antenna have been studied for plasma RF production and heating in the URAGAN-3M torsatron (R = 100 cm, apl ≤ 12.5 cm, B ≤ 1.3 T): A frame type antenna (FTA) conventionally used for plasma RF production and heating with the best operational properties at low and moderate plasma densities (n-bare ≤ 5 x 1012 cm-3); compact three-half-turn antenna (THTA) proposed for plasma heating and density ramp up (up to 3 x 1013 cm-3) after the low density target plasma (n-bare ≥ 4 x 1011 cm-3) had been produced by FTA; recently proposed antenna of combined type (''crankshaft''), which has the best properties of both above mentioned antennae in the whole range of densities. The excitation of the electromagnetic fields in URAGAN-3M plasmas by FTA, THTA and crankshaft antenna has been studied numerically using 1-D wave code. To study the dynamics of RF plasma production in the URAGAN-3M torsatron the 0-dimensional code have been used. The results of calculations showed better performance of crankshaft antenna compared with FTA and THTA in the whole range of plasma densities. When using the THTA at the scenario with FTA as a target plasma source, the experiments performed showed the possibility of dense plasma production (n-bare > 2 x 1013 cm-3) and heating, which had not been obtained earlier in the URAGAN-3M torsatron. The shifted towards the plasma core power deposition profile of THTA resulted in modification of plasma density profile and improvement in plasma confinement. The preliminary experiments with crankshaft antenna on plasma production showed that this antenna can produce the dense (up to 1013 cm-3) plasma in the URAGAN-3M without any additional source of target plasma and it can be used for subsequent Alfven heating. (author)