Transport analysis of the EHL-2 spherical torus in a high-ion-temperature scenario

EHL-2 is an ENN second-generation device aimed at studying proton-boron (p-B-11) fusion reactions in a spherical torus. The design parameters are T-i0 similar to 30 keV, T-i/T-e > 2, n(e0) similar to 1 x 10(20) m(-3), I-p similar to 3 MA, B-t similar to 3 T, and tau(E) similar to 0.5 s. High ion temperature is one of the standard operation scenarios of EHL-2, aiming to reduce bremsstrahlung radiation while enhancing plasma parameters by elevating the ion to electron temperature ratio. In order to achieve high ion temperature, neutral beam injection is considered the primary heating method during the flat-top phase. The neutral beam system for EHL-2 comprises 3-5 beams with energy/power ranging from 60 keV/4 MW, 80-100 keV/10 MW, to 200 keV/3 MW. This work conducts predictive analysis on core transport during the flat-top phase of EHL-2's high-ion-temperature scenario utilizing ASTRA. The study delineates the potential operating range of core temperature and other parameters given the designed heating capacity. Specifically, the study presents predictive simulations based on CDBM, GLF23, Bohm-gyro-Bohm, and IFSPPPL transport models, evaluating the steady-state power balance, energy confinement time, and impact of various parameters such as plasma density and NBI power on core ion temperature. The simulations demonstrate that the design parameters of the EHL-2 high-T-i scenario, although sensitive to varying transport models, are hopefully attainable as long as adequate ion heating and controlled ion transport levels are ensured.