Performance assessment of helicon wave heating andcurrent drive in EXL-50 spherical torus plasmas

Abstract

Analysis of helicon wave heating and current drive capability in EXL-50spherical torus plasmas has been conducted. It is found that the drivencurrent increases with the launched parallel refractive index n|| and peaksaround n|| = 4.0 when the frequency of the helicon wave is between 300 MHzand 380 MHz. The helicon wave current drive efficiency shows a relativelystable upward trend with increasing plasma temperature. Moreover, thedriven current decreases as the plasma density increases. We also analyzedthe current drive with helicon waves of 150 MHz and 170 MHz and foundthat the driven current at a lower frequency was lower than that at a higherfrequency. A positive proportional relationship exists between the drivencurrent and n||. Besides, as n|| increases, the profile of the driven currentbecomes wider. Finally, the effect of the scrape-off layer (SOL) region on thehelicon wave current drive was also investigated.