Investigation of the synergistic effects of ICRF + NBI heating in EAST plasma discharges

Abstract

Following an upgrade of the neutral beam injection (NBI) system, obvious synergy between combined NBI and ion cyclotron resonance frequency (ICRF) heating was observed in recent experiments conducted at EAST. To investigate the effects of beam-ions accelerated by radiofrequency (RF) wave, analyses are performed by using TRANSP code based on the experimental results. The calculated results argue that only a small fraction of the ICRF power is absorbed by the beam ions in the ICRF+NBI synergistic heating of the (H)D plasma. To enhance the beam-RF interactions in synergistic heating and achieve high plasma performance of EAST, different experimental conditions, including multiple injection powers and diverse beam injection options, were explored. Beam injected fast ions are passing particles, trapped particles observed when synergy heating between ICRF and NBI. In particular, by varying the injection direction of the beam ions it was observed that more tangential beam yields better synergy in comparison with more perpendicular beam. The neutron emission rate of D–D fusion in tokamaks is improved and less fast ion loss is produced with tangential NBI + ICRF heating. Also, the effect of the ratio PICRF/PNBI on ICRF+NBI combined heating is demonstrated, the higher power boosts the fusion enhancement. The study of the performed synergistic heating provides an important reference for the subsequent combined NBI + ICRF heating experiments on EAST.

Numerical simulations on loss of ICRF-heated NBI ions in EAST

“…For similar plasma shapes and toroidal field, the increase in plasma current leads to a decrease in the safety factor (see figure 15), which will make the loss boundary closer to the plasma periphery. Moreover, ICRF + NBI synergistic heating experiment revealed that the density of ICRF-heated NBI ions is high at the core as the cyclotron resonance layer of D ions is located at the plasma center [14]. Nevertheless, if the stochastic ripple diffusion-free domain around the plasma core is more extensive, fewer energetic ions will be scattered into the loss region.…”

“…However, little research has been conducted on the loss of ICRF-heated beam ions on EAST. In previous work [14], we investigated the effects of ICRF + NBI synergistic heating of EAST hydrogendeuterium plasma, finding that D-beam ions can be transformed into even more energetic ions via second harmonic resonance heating. However, high-energy ions striking the wall of the vacuum vessel may cause sputtering of impurity ions and result in the disruption of long-pulse duration discharge.…”

Study on stray electrons ejecting from a long-pulse negative ion source for fusion

“…Neutral beam injection with hydrogen isotope (H/D/T) has been demonstrated as an effective plasma heating and current drive (H&CD) method in many magnetic confined fusion devices in service [1][2][3][4][5][6][7], and is still favorable for future fusion development [8][9][10][11]. As the fusion device scaling up, the required injecting particle energy is higher and higher to attain a better H&CD effect on the core plasma.…”