2000 MS Hardware Maintenance
16
Functional Description
Diffusion Pump Vacuum Manifold
The vacuum manifold is a stainless steel tube that maintains the ion trap
assembly in a vacuum. Carrier gas is fed into the ion trap via the transfer line,
and calibration gas and Chemical Ionization gases are fed into the ion trap via
the pneumatics assembly. The vacuum manifold is evacuated and maintained at
vacuum of approximately 1 x 10
-5
Torr (1.3 x 10
-3
Pa) by a diffusion pump. A
Peltier baffle is incorporated in the manifold to minimize background
contamination caused by the back streaming of pump vapors.
The vacuum manifold, analyzer assembly, pneumatics assembly, Peltier baffle,
and diffusion pump, are shown.
A
Manifold
B
Peltier Baffle
C
Diffusion Pump
D
Inlet Seal
E
Inlet Clamp
F
Analyzer Assembly
G
Pneumatics Manifold
H
RF Coil
Cross Section of the Diffusion Pump Vacuum System
Peltier Baffle
The Peltier baffle is a cooled line of sight baffle that reduces back streaming of
vacuum pump vapors into the vacuum manifold. The design consists of a one-
piece baffle that is cooled by a thermoelectric cooling element (TEC). The TEC
is essentially an electronic heat pump based on the Peltier effect. A voltage is
applied to the TEC, causing heat to be pumped from the cold side of the TEC to
the hot side. The cold side of the TEC draws heat from the baffle, thereby
cooling it, and the hot side of the TEC pushes heat into the heat sink. The heat
sink is cooled by forced air convection.
The TEC is activated when the system is started, and remains on until it is
switched off during the shutdown procedure.
