Recycling control for LHD using Carbon Sheet Pump

Carbon Sheet Pump (CHS) has been proposed to be installed on the vacuum vessel wall of the Large Helical Device (LHD) in order to reduce the hydrogen recycling and improve the energy confinement. The CSP of C/C composite with temperature below 200 degree C can pump high energy hydrogen particles such as charge exchange fast neutrals by trapping them. The saturated hydrogen particles can be removed simply by heating the carbon sheet above 800 degree C. One of the requirement on the CSP design for LHD is that the temperature of the vacuum vessel must be maintained to be below 70 degree C to avoid excessive heat flux to the LHD superconducting magnet system. The first design of CSP for LHD is presented, and a successful demonstration of heating the CSP is carried out. 5 refs., 5 figs