Beta-induced Alfvén eigenmodes destabilized by resonant magnetic perturbations in the J-TEXT tokamak

Abstract

Investigations of beta-induced Alfvén eigenmodes (BAEs) destabilized by resonant magnetic perturbations (RMPs) have been conducted on the J-TEXT tokamak. In the Ohmic discharges, with RMPs having finite perturbed amplitudes, two different types of Alfvén eigenmodes have been observed and identified. One is considered as m-BAE, due to the strong correlation with magnetic island in some noticeable aspects, for example, frequency characteristic, mode number and driving mechanism. Specifically, the standing wave nodes of m-BAE are located at the O point and X point of the magnetic island. Another one is discerned as the magnetic island-induced AE (labeled as the MIAE-like mode in this work), which is consistent with the prediction of theory (Biancalani et al 2010 Phys. Rev. Lett. 105 095002). The frequency of MIAE-like mode is found to be approximately proportional to the square of magnetic island width.

Alfvén waves in reversed-field pinch and tokamak ohmic plasmas: nonlinear 3D MHD modeling and comparison with RFX-mod

“…Such coupling has also been identified in the edge region of RFX-mod plasmas in the form of drift Alfvén vortex structures [75], so the role of TAE excitation played by the inverse cascade also for RFX-mod plasmas cannot be excluded. Similarly, BAE destabilization by resonant magnetic perturbations in ohmic discharges in the J-TEXT tokamak has also been observed [73]. Furthermore, it was shown [76,77] that the coupling of the pressure gradient and the averaged magnetic curvature is important and favorable to the existence of the RSAE, moreso in RFP configuration due to the low q value [39], and the possible identification of experimental peaks a, b and c as RSAEs has been speculated [41].…”

“…This may be due to approximations of the employed numerical model, which neglect the toroidal, finite beta and kinetic effects. A toroidal geometry and finite beta would allow for the TAE and the BAE gaps to be excited, with frequencies below the GAE one [63,73], by either energetic particle tails (observed in past studies in RFX-mod plasmas, for which a wave-particle interaction model was proposed [44]) or other mechanisms. Maraschek et al [74] proposed the role of the inverse energy cascades on the coupled drift Alfvén small-scalle turbulence to explain the observation of TAEs in ohmically heated tokamak plasmas.…”

Hybrid simulations of beta-induced Alfvén eigenmode with reversed safety factor profile

“…Investigations of BAEs are abundant, since they are ubiquitous in tokamak plasmas. Experimentally, the BAE was discovered on DIII-D [11] during neutral beam heating, and then it was also reported in FTU [14], HL-2A [15,16], EAST [17], and J-TEXT [18,19]. There are also many theoretical investigations [4,[20][21][22][23] and numerical simulations [24][25][26][27][28][29] of BAE.…”

Advances in physics and applications of 3D magnetic perturbations on the J-TEXT tokamak

“…Following the previous achievement of LM unlocking by rotating RMP [18], the electrode biasing (EB) has been applied successfully to unlock the LM from either a rotating or static RMP field [19]. In the presence of 2/1 LM, three kinds of SW structures [20][21][22] have been observed to share a similar connection to the island structure, i.e. the nodes of the SWs locate around the O-or X-points of the 2/1 island.…”