A novel approach for mitigating disruptions using biased electrode in Aditya tokamak

Abstract

Disruptions, induced in Aditya tokamak by hydrogen gas puffing, are successfully mitigated through stabilization of magnetohydrodynamic (MHD) modes by applying a bias voltage to an electrode placed inside the last-closed flux surface prior to the gas injection. Above a threshold voltage sheared E r × B φ rotation of the plasma generated by the edge biasing leads to substantial reduction in the growth of MHD modes (m/n = 3/1, 2/1), which causes avoidance of disruptions through prevention of mode overlapping and subsequent ergodization of magnetic field lines.

Effect of periodic gas-puffs on drift-tearing modes in ADITYA/ADITYA-U tokamak discharges

“…and γ ≲ 1 [13]), the values of * /γ remains on the side of the transition point where the γ/γ is an increasing function of * /γ . However a linear theory of the drift-tearing mode is not adequate to explain our observations since the mode is likely to be in the nonlinear regime.…”

Effect of electrode biasing on m/n = 2/1 tearing modes in J-TEXT experiments

“…Suppression of MHD activity with electrode [28] or limiter biasing [26] has been observed in experiments. The sheared poloidal rotation generated by biased electrode is shown to decrease the linear stability index Δ′ [27].…”

“…On T-10, the frequency and amplitude of MHD modes are found to be able controlled by a non-disruptive halo-current [22]. In some medium or small size tokamaks, the biased electrode is an efficient method to change the plasma parameters and flows [23][24][25][26][27][28]. Suppression of MHD activity with electrode [28] or limiter biasing [26] has been observed in experiments.…”

First observation of unlocking the locked mode by electrode biasing on J-TEXT tokamak

“…It increases the rotation derivation ∆Ω 𝜃 , which strengthens the viscous torque and pulls the locked magnetic island to the unlocking direction. The momentum transport can also increase the flow shear at the rational surface [34,39] , which is a candidate to weaken the intensity of Ψ, and induces the unlocking. The other way is that the improved confinement under biasing could increase the electron temperature to heighten the natural frequency according to the equation( 2).…”