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 Ip. Therefore, the poloidal beta due to tail electrons, ßptai1, becomes much larger than that in the usual case of unidirectional current drive, where ßptai1 exceeds unity only when Ip is smaller than the Alfvèn critical current IA. In the WT-3 tokamak, lower hybrid current drive plasmas produced by bidirectional and unidirectional injection have been compared in terms of ßp. The experimental results show that a high ßp plasma is generated with Ip larger than IA in the bidirectional case.
All Science Journal Classification (ASJC) codes