Progress in potential formation and radial-transport-barrier production for turbulence suppression and improved confinement in GAMMA 10

(1) A transverse energy-transport barrier is externally controlled for the first time by off-axis electron-cyclotron heating (ECH). This internal energy-transport barrier is produced by ECH controlled cylindrical-layer formation (4<rc<7 cm) with energetic electrons. The electrons flow through the whole device and are partially lost into the end region. As a result, a radially localized ambipolar-potential bump, with strongly sheared electric fields Er (or peaked vorticity) is formed along with the direction reversal of ErxB shear flow near the ΦC peak. This leads to suppress L-mode-like intermittent turbulent vortex-like structures near the layer in the central cell, and results in Te and Ti rises surrounded by this strong shear flow layer just like the characteristics of an internal transport barrier (ITB) in tokamaks and stellarators. (2) Such results are based on four-time progress in ion-confining potentials (φc=3 kV) in comparison to φc attained 1992-2002 in association with the formation of a strong Er shear. The data on φc well fit to a favorably increasing scaling with plug ECH powers. The advance in the potential formation leads to a finding of remarkable effects of dEr/dr on turbulence suppression and a transverse-loss reduction. (3) Under such physics understanding, the first preliminary central ECH (250 kW) raises Te0=750 eV (a new five-time larger Te record) together with Tiperpendicular0=6.5 keV, and Tiparallel0=2.5 keV. On-axis energy drag (confinement) time from central-mirror trapped 'Tiperpendicular' ions to electrons is significantly improved to be 0.14 s. On-axis energy confinement time for φc (=2.5 kV) confined 'Tiparallel' ions reaches 0.16 s with 380-kW plug ECH applied for both axial Ez plugging and strong ErxB sheared flow formation simultaneously. (4) The stored energy of φc potential confined ions between both plug regions exceeds that (diamagnetism) of the central-cell magnetically trapped ions for the first time. (5) A weak decrease in φc with increasing nc ranging to ∼1019 m-3 along with the recovery of φc with increasing plug ECH powers is preferably obtained. (author)