Non-inductive current drive via helicity injection by Alfvén waves in low-aspect-ratio tokamaks

S. Cuperman, C. Bruma, K. Komoshvili

Research output: Contribution to journalArticlepeer-review

Abstract

A theoretical investigation of radio-frequency (RF) current drive via helicity injection in low aspect ratio tokamaks is carried out. A current-carrying cylindrical plasma surrounded by a helical sheet-current antenna and situated inside a perfectly conducting shell is considered. Toroidal features of low-aspect-ratio tokamaks are simulated by incorporating the following effects: (i) arbitrarily small aspect ratio, R0/a = 1/ε; (ii) strongly sheared equilibrium magnetic field; and (iii) relatively large poloidal component of the equilibrium magnetic field. This study concentrates on the Alfvén continuum, i.e. the case in which the wave frequency satisfies the condition {ωAlf(r)}min ≤ ω ≤ {ωAlf(r)}max, where ωAlf(r) ≡ ωAlf[n(r), B0(r)] is an eigenfrequency of the shear Alfvén wave (SAW). Thus, using low-β magnetohydrodynamics, the wave equation with correct boundary (matching) conditions is solved, the RF field components are found, and subsequently current drive, power deposition and efficiency are computed. The results of our investigation clearly demonstrate the possibility of generation of RF-driven currents via helicity injection by Alfvén waves in low-aspect-ratio tokamaks, in the SAW mode. A special algorithm is developed that enables one to select the antenna parameters providing optimal current drive efficiency.

Original languageEnglish
Pages (from-to)149-174
Number of pages26
JournalJournal of Plasma Physics
Volume56
Issue number1
DOIs
StatePublished - Aug 1996

Fingerprint

Dive into the research topics of 'Non-inductive current drive via helicity injection by Alfvén waves in low-aspect-ratio tokamaks'. Together they form a unique fingerprint.

Cite this