The schematic of the experiment with the main components indicated, including the turbo molecular pump (TMP), residual gas analyzer (RGA), and fast ionization gauges (FIGs). Not to scale. The paired Ti evaporator in the NB dump (not shown) is placed symmetrically with respect to the vertical midplane.
The schematic of the Ti evaporator.
The schematic of the arc ignition unit.
The schematic of the power supply.
The scanning electron microscope image of the Ti coating on the beam dump plate.
The measured pumping speed and the amount of gettered hydrogen as functions of time for the NB dump exposed to the background hydrogen pressure of ∼10−4 Torr.
The gas pressure in the test vessel (a) and beam dump chamber (b) due to the neutral beam. The beam is turned on at t = 1 ms and turned off at t = 4 ms. Case A: the beam fired into the closed gate valve isolating the NB dump chamber. Case B: the beam fired into an old Ti film in the dump chamber. Case C: the beam fired into a fresh Ti film in the dump chamber. The small pressure decay following the sharp rise in (a) has to do with the pressure equilibration across the test vessel. The apparently slower time response in (b) is due to the ion gauge shielding in the NB dump, as schematically shown in Fig. 3.
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