ICRF current drive experiment on JIPP T-IIU

Abstract

In the JIPP T-IIU tokamak an experiment to demonstrate the feasibility of fast wave current drive using five loop antennas has been successfully carried out with a relatively high density plasma (ωpe2/ωce2∼5). The RF frequency is 40 MHz and the toroidal field is 2 kG, which corresponds to ω = 13ωcH. The experiment is conducted in the density range n̄e ∼ 2 × 1018 m−3 where only the fast wave can propagate, eliminating the possibility of slow wave current drive. This density is two orders of magnitude higher than the density limit predicted for slow wave current drive. The dependence of the drive efficiency on the relative phase difference Δφ is clearly observed with a maximum of about Δφ = π/4. The plasma current was limited by MHD instability which begins to occur around qa = 10.

Perpendicular Ferromagnetic-Resonance Equations Derived by Effective Demagnetizing Factors

“…Only a steady state toroidal field and a steady state vertical field were applied. The present experiment was performed mostly at a toroidal field of 0.46 T in a deuterium majority plasma, which corresponds to a) ss 11G D for 40 MHz and to u = 37Q D for 130 MHz, with a vertical field of 10 G. As reported previously [11], it was possible to drive a plasma current with the 40 MHz system, but only at low filling pressures ( p $ 3 x 10" 4 torr). While it was possible to create a currentless low density (h^ £ 2 x 10 l8 nr 3 ) plasma with 130 MHz power alone, the range of filling pressures for successful plasma creation was restricted to higher values (p £ 3 x 10" 4 torr) and the amount of RF current driven by the 130 MHz system was much less than 1 kA.…”

“…However, no current drive was observed above the slow wave density limit. In a subsequent experiment on JIPP T-IIU it was possible to initiate the plasma current with a fast wave at a frequency of 40 MHz and at a reduced toroidal field, B T = 0.2 T, so that the wave frequency corresponded to w = 13fl H [11]. The plasma current was driven at a density 50 times higher than the LH density where co = w LH .…”

Synergy of Electron-Cyclotron and Lower-Hybrid Current Drive in Steady-State Plasmas

“…This property, hereafter called the synergy effect, has been subsequently confirmed by a different Fokker-Planck code [10], by a self-consistent kinetic-transport code [11], and by analytical calculations [12]. The above-mentioned experiments [3][4][5][6][7][8] have shown that EC waves could couple to the fast electron tail sustained by LH waves and thus provide efficient current ramp-up, despite the fact that in most cases the EC waves absorption took place after multiple reflections on the tokamak walls. However, it is well known [1] that the physics of current ramp-up is dominated by the inductive response of the plasma, i.e., the transient reverse electric field, and not simply by the kinetic balance of quasilinear wave diffusion and Coulomb collisions.…”

“…LH waves can efficiently drive electrons from low to substantially higher parallel velocities, making them poorly collisional and insensitive to trapping, thus carrying a larger current than the slower electrons interacting with the EC waves. For these reasons, the idea of combining the two CD systems has been proposed and investigated since the early 1980s [2] and has stimulated dedicated experiments on the WT-2 [3,4], JFT-2M [5,6], and WT-3 [7,8] tokamaks. Moreover, kinetic calculations [9] performed with a 3D Fokker-Planck code have numerically demonstrated an interesting property: the current driven by the simultaneous use of the two waves, I LHEC , can be significantly larger than the sum of the currents separately driven by the two waves, I LH I EC , in the same plasma conditions.…”

Parametric decay instabilities of the fast wave in the lower hybrid frequency regime

“…It was concluded that the occurrence of parametric decay correlates with the ion tail formation and results in the deposition of a part of the RF power at the peripheral region. In an other JIPPT-IIU experiment [9], density limit for the fast wave is also observed, but this density is two orders of magnitude higher than the density limit predicted for the slow wave current drive. Some mechanisms [11], [12] have been suggested for the generation of slow waves during fast wave current drive experiments.…”