EC   LH current drive efficiency in the presence of an internal transport barrier

Abstract

In this paper we study the effects of the presence of an internal transport barrier (ITB) on the current drive efficiency and power deposition profiles in the case of electron cyclotron waves interacting with an extended tail generated by lower hybrid (LH) waves. We study the subject by numerically solving the Fokker-Planck equation, with temperature and density profiles corrected along the time evolution at each collision time, based on the actual time-evolving electron distribution function. The results obtained show that the LH and electron cyclotron (EC) power absorption profiles and the current driven by the combined action of both types of waves are weakly dependent on the depth of the ITB, slightly more dependent on the level of magnetic turbulence and much more dependent on the level of EC wave power.

Effect of radial transport on the LH current drive efficiency in tokamaks featuring an internal transport barrier

“…1b of Ref. [10]). This profile intends to simulate the reversed q profiles typically found in situations where there is ITB formation.…”

“…In all calculations which follow, we assume barriers centered at x p = a/2, with half-width β = 3 cm. Specifically, we assume a parabolic reduction of the magnetic turbulence level at the barrier position (for x p − β < x < x p + β), such that b = b 0 a 1 + a 2 x + a 3 x 2 and e = e 0 a 1 + a 2 x + a 3 x 2 , where the a i are constants [10].…”

“…1a of Ref. [10] shows the profile of magnetic and electrostatic turbulence, for several values of α, and β = 3 cm. The barrier width and position are in accordance with experimental results [11].…”

Alpha channeling with high-field launch of lower hybrid waves

“…26 . Note that the use here of a second wave is essentially different from other uses of a second wave to optimize the current drive efficiency, [27][28][29][30][31][32][33][34][35] since, rather than promoting absorption by higher velocity electrons, the second wave facilitates the absorption of energy to the LH wave from the α particles. Both methods should lead to an effective increase in the efficiency.…”

Optimized calculation of the synergy conditions between electron cyclotron current drive and lower hybrid current drive on EAST

“…The relationship between the synergistic effect and the powers of ECW and LHW has been studied numerically and experimentally in many fusion devices. Research shows that the fraction of the trapped electrons, the changes of the local temperature, [7] the profile of the wave power deposition and its absorption position [19] are affected strongly by the levels of the powers of the two waves, which make the synergy current change, even lower than zero, i.e., a negative synergy effect (I EC+LH < I EC + I LH ) can be obtained when the ratio between the powers of the two waves satisfies a certain condition. [20,21] Therefore, it is necessary to study the dependences of the synergistic effect on ECW power and LHW power in the EAST to avoid the negative synergy effect, which is meaningful for guiding the relevant physical experiments in the future.…”