Gas puffing by molecular beam injection in Aditya tokamak

Plasma density control is a prime requirement of tokamak plasma. Various methods are used for fuelling the gas for tokamak plasma. Gas fuelling in tokamak with molecular beam injection is developed for efficient gas injection during the plasma discharge. The penetration depth of the injected molecular beam is more than normal gas puffing. Due to more penetration and very less divergence of beam (1) wall loading due to fuel gas reduces causing reduction in recycling, and (2) there is an increase in the fuelling efficiency. A supersonic molecular beam injection (MBI) system for Aditya tokamak is developed in house by modifying a piezoelectric gas inlet valve and using 400 μm diameter nozzle at 2-5 kg/cm2 gas pressure. This valve is mounted directly on the Aditya vacuum vessel. Experiments are performed with this MBI system by puffing hydrogen gas of different pulse duration, different number of pulses at various time of tokamak discharge. The change in cord average electron density for different MBI gas pulse sequence is studied. In the present experiment, the plasma density could be raised by 1.5 times by MBI