Between 2018 and 2019, ENN successfully designed and constructed China's first medium-scale spherical torus experimental device, the EXL-50U (ENN Xuanlong-50). EXL-50 commenced its full-field experimental research in April 2020 and maintained four years of stable operation, during which approximately 24,000 physics experiments were conducted.
The EXL-50 features a major radius of 50 cm with a toroidal field of ~0.5 T. Its primary research focus involves CS-free (central solenoid-free) operation and non-inductive current drive via electron cyclotron resonance heating (ECRH). The device routinely achieved plasma currents ranging from 50 kA to 180 kA, with current flattops sustained for durations ≥2 s.
Notable performance metrics include:
A current drive efficiency of up to 1 A/W in low-density discharges using only 28 GHz ECRH at heating powers <200 kW
Plasma currents exceeding 80 kA in high-density discharges (5×10¹⁸ m⁻²) with 150 kW 28 GHz ECRH
Enhanced performance (Ip ≈ 120 kA, core density ≈ 1×10¹⁹ m⁻³) achieved using 150 kW 50 GHz ECRH