Overview of recent experimental results from the ADITYA-U tokamak

Since the 2018 IAEA-FEC conference, in addition to expanding the parameter horizons of the ADITYA-U machine, emphasis has been given to dedicated experiments on inductively driven particle injection (IPI) for disruption studies, runaway electron (RE) dynamics and mitigation, plasma rotation reversal, radiative-improved modes using Ne and Ar injection, modulation of magneto-hydrodynamic modes, edge turbulence using periodic gas puffs and electrode biasing (E-B). Plasma parameters close to the design parameters of circular plasmas with H-2 and D-2 as fuel have been realized, and the shaped plasma operation has also been initiated. Consistent plasma discharges having I (P) similar to 100-210 kA, t similar to 300-400 ms, n (e) similar to 3-6 x 10(19) m(-3), core T (e) similar to 300-500 eV were achieved with a maximum B (T) of similar to 1.5 T. The enhanced plasma parameters are the outcome of repeated cycles of baking (135 degrees C), followed by extensive wall conditioning, which includes pulsed glow discharge cleaning in H, He and Ar-H mixture, and lithiumization. A higher confinement time has been observed in D-2 compared to H-2 plasmas. Furthermore, shaped plasmas are attempted for the first time in ADITYA-U. A first of its kind inductively driven particle injection for disruption mitigation studies has been developed and operated. The injection of solid particles into the plasma core leads to a fast current quench. Two pulses of electron cyclotron resonance wave at 42 GHz are launched in a single discharge: one pulse is used for pre-ionization and the second for heating. In a novel approach, a positively biased electrode is used to confine REs after discharge termination. E-B is also used for controlling the rotation of drift-tearing modes by changing the plasma rotation. Cold pulse propagation and signatures of detachment are observed during the injection of short gas puffs. A correlation between the plasma toroidal rotation and the total radiated power has been observed with neon gas injection-induced improved confinement modes.