Tests of a Fail-Safe Vacuum Beam Line Using Acoustic Delay and a Fast-Closing Valve

An operational fail-safe line would consist of the following elements, listed in order of appearance as one proceeds from the beam exit foil window toward the accelerator: (1) pressure-rise detector; (2) acoustic-delay section; (3) fastclosing valve; and (4) straight-through liquid nitrogen trap, isolated by bakeable vacuum valves. Because of the thermal velocity distribution in the entering gas, it is practically impossible to stop all of it by the fast valve. The trap, however, will be effective in catching contaminants if the flow through the trap is well within the molecular flow regime at all times. The purpose of these tests is to ensure that this condition can be realized in a practical way.