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Page 26
Start Phase
To operate an ion pump with the Terranova® 752A, system pressure must be less than the
recommended values in
. Once high voltage operation is commenced, user should
observe the corresponding HIGH VOLTAGE and CURRENT display values. Decreasing current and
increasing high voltage values are an indication of a successfully started ion pump.
However, if high voltage output does not appear to increase, the ion pump or vacuum system is
still at too high of a pressure. User should terminate high voltage operation and further evacuate
the ion pump and vacuum system. Once a lower vacuum pressure is achieved, high voltage
operation should be restarted. As shown in
, current and thus, power, are highest during
the starting phase of an ion pump.
If high voltage output increases or remains constant as current decreases, user should isolate the
ion pump and chamber from the roughing system to help start the ion pump. If this isolation leads
to an increase in current, user should terminate high voltage operation and continue pumping
on the ion pump and vacuum system. Once a lower vacuum pressure is achieved, high voltage
operation should be restarted. Otherwise, the ion pump and chamber should remain isolated;
user should observe current and high voltage values for normal operation.
An increase in vacuum pressure may be observed during the starting phase of an ion pump. The
increase in pressure is due to outgassing of previously-absorbed atoms and molecules caused by
internal pump heating. Outgassing is beneficial as it helps lessen the overall gas load.
Normal Operation
Once an ion pump is successfully started, Terranova® 752A operation is almost automatic. As
shown in
, high voltage output will approach the open circuit value (i.e. MAXIMUM
VOLTAGE value) as current output approaches 0 μA. Units for the current value will auto range
during use as the ion pump current increases or decreases.
