Production of high poloidal beta plasma by bidirectional lower hybrid current drive in the WT-3 tokamak

Lower hybrid waves propagating both parallel and anti-parallel to the toroidal field (bidirectional waves) produce suprathermal electron tails in both directions. The contribution of these tails is additive for the pressure but subtractive for the plasma current I p . Therefore, the poloidal beta due to tail electrons, β p tai1 , becomes much larger than that in the usual case of unidirectional current drive, where β p tai1 exceeds unity only when I p is smaller than the Alfvén critical current I A . In the WT-3 tokamak, lower hybrid current drive plasmas produced by bidirectional and unidirectional injection have been compared in terms of β p . The experimental results show that a high β p plasma is generated with I p larger than I A in the bidirectional case.