Design and development of the helicity injection system in Versatile Experiment Spherical Torus

- A high current electron gun with single pulse power for both arc and extraction is developed.
- The optimal gun operation is confirmed by impedance matching between the PFN and plasma.
- The gun injected currents of 0.95 kA with the voltage of ∼410 V for 5 ms with a 1.2 kV PFN.
- The helicity injection system using the gun has been developed and tested successfully in VEST.
- Toroidal currents of up to 3.8 kA confirm possible relaxation into tokamak-like plasma.