DOI: 10.1017/s0022377826102177 ISSN: 0022-3778
Facilitation of explosive bursts’ prevention in reversed magnetic shear tokamak plasmas through the current condensation effect for disruption avoidance
Kun Lin Yang, Tong Liu, Zheng-Xiong Wang, Lai Wei, Jialei Wang
The reversed magnetic shear (RMS) configuration, a promising candidate for steady-state tokamak operation, facilitates high bootstrap current fractions through internal transport barriers, but also hosts multiple rational surfaces vulnerable to tearing modes. Under high bootstrap current conditions, these modes can trigger explosive bursts via strong positive feedback during magnetic island interactions, posing serious disruption risks. This study numerically investigates the suppression of such explosive phenomena in RMS plasmas using a reduced MHD model that incorporates bootstrap current, electron cyclotron current drive (ECCD) and the radio-frequency current condensation effect (CCE). Numerical findings demonstrate that the CCE fundamentally enhances ECCD efficacy, particularly for large neoclassical tearing mode islands. For moderate bootstrap fractions (
f Subscript b Baseline equals 0.3
f
b
=
0.3
$f_b = 0.3$
), a counterintuitive control strategy is identified: intentionally delaying ECCD initiation until the island grows larger. This approach exploits the positive correlation between CCE effectiveness and island width, thereby achieving a shorter overall stabilisation time. In high bootstrap scenarios (
f Subscript b Baseline equals 0.6
f
b
=
0.6
$f_b = 0.6$
), prone to explosive bursts, the CCE introduces a nonlinear positive feedback mechanism that strongly localises current deposition at the O-point of the islands and creates a hysteresis-like response. This enables complete island stabilisation at identical ECCD power and delaying the required onset timing of ECCD by approximately 70
percent sign
%
$\%$
, substantially extending the control response window. The CCE also effectively mitigates rotation-induced control degradation through enhanced current localisation. This work establishes CCE-enhanced ECCD as a robust mechanism for explosive burst prevention in high-bootstrap-current plasmas. The results provide critical insights for developing advanced stabilisation strategies in future steady-state reactors like ITER, while highlighting the need for future research on integrated control approaches that balance suppression efficiency with disruption risks.