Progress in potential formation and findings in the associated radially sheared electric-field effects on suppressing intermittent turbulent vortex-like fluctuations and reducing transverse losses

Abstract

Following the 19th IAEA Fusion Energy Conference (Lyon, 2002), (1) three-time progress in the formation of ion-confining potential heights ϕc including a record of 2.1 kV in comparison to those attained 1992–2002 is achieved for tandem-mirror plasmas in the hot-ion mode with ion temperatures of several kiloelectronvolts. (2) The advance in the potential formation gives the bases for finding the remarkable effects of radially produced shear of electric fields Er, or non-uniform sheared plasma rotation on the suppression of intermittent vortex-like turbulent fluctuations. (i) Such a shear effect is visually highlighted by x-ray tomography diagnostics; that is, spatially and temporally intermittent vortex-like fluctuated structures are clearly observed as two-dimensionally reconstructed visual structures for the first time in kiloelectronvolt order ion-cyclotron heated plasmas having a weak shear in GAMMA 10. (ii) However, during the application of plug electron-cyclotron heatings (ECH), the associated potential rise produces a stronger shear (dEr/dr = several 10 kV m−2) resulting in the disappearance of such intermittent turbulent vortices with plasma confinement improvement. X-ray observations also show elongation of a vortex structure from a circular into an ellipsoidal shape, as depicted in H-mode theories, with an outward shift. (3) For the physics interpretations and control of such potential and the associated shear formation, the validity of our proposed theory of the potential formation is extensionally tested under the conditions with auxiliary heating. The data described above fit well to the extended surfaces calculated from our proposed consolidated theory of the strong ECH theory (plateau formation) with Pastukhov's theory on energy confinement.

Rotational Instabilities

“…For straight, or nearly straight, cylindrical geometry, as in the LAPD in Chapter 3, the Tandem Mirror central cells, as in Hooper, et al (1982) and Cho, et al (2005), and in the Field Reversed Configuration the rotational modes are often unstable in themselves and thus add to the wave-induced transport processes. An analysis of these linear geometries is given since the theoretical formulations are much clearer and simpler.…”

Electron Density Measurement by Using a Multi-Channel Interferometer System in the Tandem Mirror GAMMA 10

“…The tandem mirror GAMMA 10 utilizes an electron cyclotron resonance heating (ECRH) for forming a confinement potential [1][2][3][4][5][6][7]. A new record of the formation of highest ion-confining potential 3.0 kV is achieved in the hot-ion mode; that is four times progress as compared with that potential attained 1992-2002 [1][2][3][4]. Fluctuation in the plasma is important to be measured for studying the improvement of the plasma confinement by the formation of the plasma confinement potential.…”

“…On the basis of the physics understanding of E r shear importance, preliminary central ECRH (c-ECRH) is applied in a standard tandem-mirror operation with plug ECRH, which plays an essential role in both E z plugging for an axial confinement improvement and automatically associated strong E r shear flow for a radial confinement improvement simultaneously. The fluctuation is excited in the hot-ion mode plasma [1][2][3][4]. When the ECRH is applied, electron density in the central cell increases gradually due to the improvement of the plasma potential confinement.…”

Electron density fluctuation measurements using a multichannel microwave interferometer in GAMMA 10

“…[1][2][3][4][5][6][7] The measurement of the fluctuation in the plasma is important for studying the improvement in plasma confinement by the formation of a plasma confinement potential. 1,2,8 Density fluctuation is observed using microwaves, such as interferometer, [8][9][10][11] reflectometry 8 and Fraunhofer diffraction ͑FD͒ methods, 9,10 and electrostatic probes. 11 Ultrashort-pulse reflectometry has an advantage of detecting fluctuation locally.…”

“…The fluctuation is excited in the hot-ion mode plasma. [1][2][3][4] When the ECRH is applied, the electron density in the central cell increases gradually due to an improvement in the plasma confinement potential. The intensity of the density fluctuation is suppressed when good plasma confinement is achieved in a good plasma condition.…”