Gas fueling system in LHD

Gas fueling is the basic method of plasma density control for thermonuclear fusion devices. It outperforms other fueling methods with respect to ease of steady state operation by density feedback control, ease of handling, low costs for both construction and maintenance, and flexibility in working gas selection. The gas fueling system of the Large Helical Device (LHD) is composed of gas cylinders, gas purifiers, gas reserve tanks, vacuum pumps, and pressure gauges. Hydrogen, helium, neon (or methane), argon, and xenon (or krypton, or helium-3) are regularly filled in the gas reserve tanks. These gases are injected to the vacuum vessel through “mass flow controllers (MFCs)” and/or “piezo-electric valves (PVs)”. The MFC feedback controls the flow rate to the preordered value. The PV is driven by preprogrammed mode or density feedback mode. The flow rates of PVs are calibrated in situ. All components in the system are directly controlled by a programmable logic controller, which is connected to a private local area network. Users can control the system from personal computers through the network. The graphical user interface for system control and that for setting waveforms to drive PVs are working on MS Windows.