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Functional Description
Diffusion Pump
The ion trap assembly requires a vacuum of approximately 1 x 10
-5
Torr (1.3 x
10
-3
Pa) for the generation and detection of ions. The Varian AX65 air-cooled
diffusion pump with a pumping speed of 30 l/s for air and 65 l/s for helium
provides this.
The pump features two safety devices. The first is an over temperature switch
that prevents catastrophic pump failure and subsequent ion trap contamination
from over heating problems, such as a cooling fan failure or a blocked air inlet.
The second feature is a sight glass that allows inspection of the diffusion pump
fluid level and condition without breaking vacuum. This reduces periodic
maintenance time, and helps prevent the pump being run without fluid.
Diffusion Pump Controller
The diffusion pump controller controls and provides power to the following
vacuum components:
•
TEC in the Peltier Baffle
•
Peltier baffle fan
•
Diffusion pump
•
Diffusion pump fan
•
Thermocouple gauge
The diffusion pump controller is activated when the system’s main power switch
is in the ON position. It will remain activated until the system is switched OFF.
Upon activation, the controller will provide power to the TEC, Peltier baffle fan,
and diffusion pump fan. It will also check the foreline pressure reading from the
thermocouple gauge. If the foreline pressure has reached the diffusion pump’s
required operational pressure after fifteen minutes, the controller will provide
power to the diffusion pump. After another fifteen minutes (thirty minutes total)
the diffusion pump will reach operational temperature, and the controller will
issue a “DIFFUSION PUMP NORMAL” signal to the SAP/Wave board, which in
turn provides power to the ion trap.
During normal running conditions the diffusion pump controller will continue to
monitor the TEC, Peltier baffle fan, diffusion pump, and thermocouple gauge.
The controller will initiate a system shutdown and send a fault signal to the
SAP/Wave board if a power failure is detected on any of these components, or a
pump over temperature is detected. The SAP/Wave board will shut off power to
the ion trap. The controller will also discontinue power to the diffusion pump, and
send a fault signal to the SAP/Wave board if a foreline overpressure is detected.
Power to the diffusion pump will be restored, and the fault signal canceled when
the overpressure problem no longer exists.
The diffusion pump controller also ensures a safe shutdown when the instrument
must be switched off for maintenance, repair, or relocation. The controller
receives a shut down command from the SAP/Wave board, and immediately
discontinues power to the diffusion pump. The controller will wait fifteen minutes
before discontinuing power to the TEC. After another fifteen minutes (thirty
minutes total) the controller issues a DIFFUSION PUMP OFF signal to the
SAP/Wave board, and the shut down procedure may be completed.
