Neutral particle balance in GDT with fast titanium coating of the first wall

Summary form only given, as follows. The GDT is an axisymmetric open trap with a high mirror ratio for confinement of a collisional plasma. The experimental program of the GDT was focused on the generation of plasma physics database necessary for a GDT-based neutron source. A distinct feature of both GDT and the GDT-based neutron source is that the Larmor radius of the fast sloshing ions is comparable to the plasma radius. In this case, the sloshing ions cannot be well shielded by the plasma halo from penetration of the neutral gas from periphery that results in high charge exchange losses. The plasma parameters are then very sensitive to gas pressure near the plasma boundary. To reduce the gas pressure to the desired value during the beam heating, we have used arc-type evaporators developed at the Budker INP for fast titanium coating of the GDT first wall. If needed, the coating can be done a few seconds before each shot. We investigated the neutral particle balance in presence of NB-heating. The inverted magnetron gauges were used to study the temporal dependance of gas pressure inside the central cell. Piezoelectric bolometers were employed to measure the flux of charge exchange neutrals. Neutral particle balance has also been studied numerically by using a gas-transport code. The results of our investigations are the following. 1. Sloshing ion lifetime was increased about 10 times compared to that without the coating of the first wall. 2. The wall recycling coefficient of the Ti-coated wall does not exceed 1 for 8 keV mean energy of the neutral hydrogen atoms striking the wall.