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The description of the apparatus can be broken down into three areas: Ion source, laser and detection systems. The laser and detection apparatus are those outlined in Chapter 2. The jet source consists of two differentially pumped chambers, one chamber housing the nozzle and skimmer and the second containing ion optics and a flight region. The source and flight chambers are pumped by Edwards EO6K and Balzers BG540 diffusion pumps respectively, which are backed by an Edwards EM18 rotary pump. The source chamber is separated from the diffusion pump by an Edwards butterfly valve, allowing the source to be removed without the need for the diffusion pump to be cold. The flight chamber has an solenoid controlled pneumatic baffle valve (to isolate the diffusion pump), controlled by in-house electronics, a nitrogen cylinder providing the constant gas supply to the valve.
A gas line connected to the flight chamber is used to `rough' both chambers through the rotary pump. This line is sealed when not in use using a VG isolation gate valve. Each diffusion pump can be individually sealed from the backing line using Speedivac valves.
Pressure in the backing lines and in the jet region are measured by a VG Pirani gauge (VGPV1) and a ZWW16 ion gauge respectively. Both gauges are controlled and displayed using a VG IGPA3 ion gauge control unit. A second ion gauge (Kratos Analytical) is mounted in the flight region, the pressure reading displayed on a Kratos Vacuum Controller.
The diffusion pumps, ion gauge controllers, rotary pump and electric/gas baffle are all powered through an in-house device, which cuts power to the diffusion pumps in the event of a power cut or loss of vacuum in either chamber.
Figure 5.1:
Construction of the premixture apparatus.
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Tim Gibbon
1999-09-06