Several experiments, related to controlled thermonuclear fusion research and highly relevant for large size tokamaks, including ITER, have been carried out in ADITYA, an ohmically heated circular limiter tokamak. Repeatable plasma discharges of a maximum plasma current of ~160 kA and discharge duration beyond ~250 ms with a plasma current flattop duration of ~140 ms have been obtained for the first time in ADITYA. The reproducibility of the discharge reproducibility has been improved considerably with lithium wall conditioning, and improved plasma discharges are obtained by precisely controlling the position of the plasma. In these discharges, chord-averaged electron density ~3.0–4.0 × 1019 m−3 using multiple hydrogen gas puffs, with a temperature of the order of ~500–700 eV, have been achieved. Novel experiments related to disruption control are carried out and disruptions, induced by hydrogen gas puffing, are successfully mitigated using the biased electrode and ion cyclotron resonance pulse techniques. Runaway electrons are successfully mitigated by applying a short local vertical field (LVF) pulse. A thorough disruption database has been generated by identifying the different categories of disruption. Detailed analysis of several hundred disrupted discharges showed that the current quench time is inversely proportional to the q edge. Apart from this, for volt–sec recovery during the plasma formation phase, low loop voltage start-up and current ramp-up experiments have been carried out using electron cyclotron resonance heating (ECRH). Successful recovery of volt–sec leads to the achievement of longer plasma discharge durations. In addition, the neon gas puff assisted radiative improved confinement mode has also been achieved in ADITYA. All of the above mentioned experiments will be discussed in this paper.
Extraction of large-scale coherent structure from plasma turbulence using rake probe and wavelet analysis in a tokamak Rev. Sci. Instrum. 77, 063505 (2006); Vortex-like coherent structures are observed in the edge plasma of ohmically heated ADITYA tokamak ͓ Phys. Rev. Lett. 69, 1375 ͑1992͔͒. The structures are observed on statistical basis when the floating potential fluctuations are analyzed using conditional averaging technique. The structures, which have dipole nature, experience stretching until their radial isolation across the limiter is destroyed. The potential fluctuation also shows non-Gaussian statistics indicating intermittency in broadband turbulence of the edge plasma.
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.
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