WAVE ACCESSIBILITY EFFECTS ON LOWER-HYBRID CURRENT DRIVE IN JT-60U

The effects of the wave accessibility condition on lower hybrid curren t drive (LHCD) are investigated in JT-60U. The density dependence of t he detectable maximum photon energy of hard X rays in LHCD plasmas is consistent with that of the maximum electron energy which is limited b y the accessibility condition. The current drive efficiency and the dr iven current profile are affected by the accessibility condition. Inac cessible wave power enhances impurity content, particle recycling and main plasma radiation loss, and in extreme cases triggers a MARFE. The wave intensity on the plasma periphery, which is detected by a Langmu ir probe located on the divertor plate, is also consistent with an ina ccessible power fraction going into the plasma interior. A ray trace a nalysis taking account of toroidal effect indicates that the inaccessi ble wave power is localized on the plasma periphery and finally propag ates into the divertor plasma region.