Current Hole in JT-60U
In the experimental research in JT-60U on the reversed shear plasmas, a plasma with a 'current hole', a zero-current region at the core part of the toroidal plasma, was discovered in the fall of 2000 and a brief report was given at the International Toki Conference (ITC-11) in December 2000 (ref. 1)). The zero current in the core region was also reported from JET (ref. 2)).
Confirmation of the discovery including verification of consistency with the current profiles over the plasma cross section and the pressure profiles have been intensively carried out since then. The result confirms the existence of the current hole and the current hole extended up to 40 % of the plasma radius. The current hole existed stably for 5 s. The ion temperature and the electron density inside the current hall were ~10 keV and ~4x1019 m-3, respectively (ref. 3)).
The current hole is an unexpected discovery and gives many possibility in the future. The coexistence of the unconfined plasma at the center and the confined plasma at the periphery seems to give a new experimental object. As for fusion core plasma, it may be one of the desirable current profile in several points : no current driven instability inside the current hole, no need to drive current at the core which saves high energy beam, and best point seems that the current profile is just fit to a current drive by bootstrap current which is the key to a steady state tokamak.
1) S. Ide, et al., in Proc 11th Int. Toki Conf. on Potential and Structures in Plasmas (Dec. 5, 2000), JSPF Series, Vol. 4.
2) Hawkes, N.C., et al., Phys. Rev. Lett., Vol. 87, 115001 (2001).
3) Fujita, T. et al., Phys. Rev. Lett., Vol. 87, 245001 (2001).
Fig. Profiles of the plasma current and the ion temperature with the current hole.