Simulation and Experiments On High Pressure Gas Feed Lines Of H2 Pellet Production In Cryocooler Of Pellet Injection System

Abstract

Refueling the plasma device like TOKAMAK is an important process. There are various methods for refueling the TOKAMAK device in which pellet injection method is most efficient and advantageous. The concept of forming the pellet using cryocooler provides easy maintenance, control of temperature, high efficiency and reasonable cost. High purity H2 gas is introduced at room temperature into a pipe held below the triple point temperature 13.8 K. Formed Pellet is injected by propellant, helium gas with a pressure up-to 150 bar. Theoretical analysis includes the projectile velocity of the pellet and behavior of applied pressure with respect to time. Calculation of the breech pressure is carried out for detaching the formed pellet. Simulation of transient thermal analysis of the sample holder is carried out for measuring the time for cooling. Thermal-Structural analysis is carried out for finding the thermal stress. Transient thermal analysis of Hydrogen pellet formation and structural analysis of pipe carrying the pellet during pellet injection. The project includes experiments on gas feed line, high pressure line and cooling stage. All stages are assembled separately and tested for gas leak with pressurized gas up to 7 bars. For forming the pellet, vacuum is necessary before starting the cryocooler. Vacuum of less than 10-4 Torr is carried out for all stages. The sample holder is used as a freezing cell for the hydrogen gas. The existing sample holder is made up of oxygen free high conductivity (OFHC) and coated with Gold. The other sample holder is fabricated with copper. The experiments of cool-down characteristic of cryocooler are carried out with existing and fabricated sample holder. Both the sample holders are cooled down from room temperature to about 4 K. Temperature with respect to time is recorded with the help of temperature monitor.