The combined drive current of the lower hybrid wave (LHW) and the high harmonic fast wave (HHFW) is studied for the first time, based on the use of low and higher β_e operational parameters in EAST. Broad and significant synergistic effects are found in the simulation, the local synergy factor reaching a factor of 4.3 in the off-axis region. The current drive (CD) efficiency is greatly improved, and the current profile is modified as a result of the synergy between the two types of waves . the LHW interacted with the resonant electrons in low parallel velocity region and pushes them into the adjacent resonance region of the high phase velocity wave (HHFW), the number of fast electrons resonant with the HHFW is increased dramatically, and the driven current is enhanced. Therefore the synergy effect strongly depends on the positional relational between the velocity resonance regions of the two waves. Moreover, the effects of the parallel refractive index and the wave power on the synergy effect are examined. Some problems well known in the single LHW CD or the HHFW CD may be overcome by the combined CD.
Heating with the wave in the ion cyclotron range of frequencies (ICRF) has been used in the development of high-performance H-mode operations in EAST. A different ion cyclotron resonance heating scenario in three-ion component plasma with real experimental parameters on EAST was investigated using a numerical tool. Excellent radio frequency wave absorption was found with an extremely low 3He concentration (0.1%–0.4%) in D-H-(3He) plasma, by adjusting the plasma composition appropriately in our simulation. In this case, the 3He fundamental resonance layer is located between the two ion–ion hybrid resonance-cutoff pairs in close proximity, and therefore E+ of the wave was considerably enhanced near the 3He fundamental resonance layer. The minority 3He tail was estimated to be superenergetic (∼1 MeV) because of the high power carried by each resonant 3He ion. The potential of the three-ion ICRF heating means on EAST was shown, and the scenarios investigated are particularly promising for fast particle generation schemes.
For a fusion device, plasma pre-heating is required before the self-sustaining burning-state reactions of deuterium (D) and tritium (T) commence. Plasma heating with waves in the ion-cyclotron range of frequencies (ICRF) is effective in tokamaks. A new three-ion ICRF heating scheme for plasmas in the Chinese Fusion Engineering Test Reactor (CFETR) that require an increase in the bulk ion temperature via heating the lithium impurities in the D–T plasmas, was studied numerically. Our simulations show that the radio-frequency wave power is strongly absorbed by very few 7Li ions with concentrations of 0.01%–0.2% in a suitable mixture of D–T plasmas, the enhanced minority ion heating is related to that the 7Li fundamental resonance layer is very close to the two mode conversion layers. In adjusting the mixtures over a wide range of composition, an oscillatory behaviour in the 7Li absorption efficiency arises because of interference. Moreover, from estimates of the 7Li ion tail energy, most of the tail energy of the minority ions is found to be transferred to background ions via collisions. Compared with the routine (3He)-D–T scheme, the ICRF power is absorbed more effectively by the 7Li ions in the (7Li)-D–T heating scenario, and after the Fokker–Planck equations were solved, a large fraction of bulk ion heating was evident in the (7Li)-D–T heating scenario. The new three-ion scenario may therefore be an attractive proposition for bulk ion heating during the activated phase of the reactor.
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.
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