Session GP1 - Poster Session IV.
POSTER session, Tuesday afternoon, October 30
Exhibit Hall B,
Injection of lower hybrid heating and current drive into the current ramp-up phase of JET discharges can produce extremely reversed q-profiles characterized by a core region (r/a less than 0.2) of zero current density (within Motional Stark Effect diagnostic measurement errors) and q greater than 1 everywhere [1]. Electron temperature measurements show sawtooth-like collapses and the presence of an internal transport barrier. The core current density does not appear to go negative, although TSC/LSC code modeling indicates that the drive for this is present. A 2-D, two fluid simulation predicts that discharges with negative core current would be unstable to n=0, m=1 modes. The possibility that these modes redistribute the core current to prevent it from becoming negative is examined.
[1] N. C. Hawkes, et al., Phys. Rev. Lett. (accepted July 2001).