TECHNICAL INFORMATION
be reduced later to optimize pumping and
achieve the lowest vacuum pressure.
5. If started at 10
-4
Torr (mbar) the voltage will
start at approximately 800 volts and increase
to full voltage as the pump starts operating.
The current will start at several milliamps and
slowly decrease to microamps or nanoamps
as low vacuum pressure is achieved.
6. When first starting the pump, if the voltage de-
creases instead of increasing, reduce the vac-
uum pressure then start the ion pump again.
7. When the pump reaches its full operating volt-
age, you may close the roughing valve.
8. If the pump does not start after 30 minutes of
pumping, see the section PUMP
TROUBLESHOOTING.
9. Once the pump reaches its base pressure with
stable voltage and current, the ion pump may
be baked at high temperature if required per
the section titled BAKEOUT OPERATION.
10. To stop the ion pump, simply switch off the
high voltage. The pump surfaces will continue
to pump for a few minutes de
pending on the
system pressure.
11. When venting the pump use clean,
dr
y nitro-
gen. This will avoid water absorption on the
pump surfaces and make subsequent pump
do
wns
easier
.
MAINTENANCE
,
WARNING!
The high voltage present in the high voltage cable
which connects the control unit to the ion pump,
can cause severe injury or death. Before mounting
the high voltage connector of the cable on the
pump high voltage feedthrough, or before remov-
ing it, be sure the main power is removed from the
control unit.
Before removing the high voltage connector of the
cable from the control unit, be sure the main power
is removed from the control unit. Wait at least 10
seconds after removing the main power from the
control unit, to allow capacitors to discharge com-
pletely.
VacIon
Plus
pumps are maintenance free. In case
of life time expiry or premature failure of the pump,
please contact your nearest Varian sales/service
office for repair.
The VacIon
Plus
20 pumps are designed with ex-
changeable high-voltage feedthrough and pump
elements.
Exchange of the high voltage feedthrough.
CAUTION
The high voltage feedthrough contains a ceramic
insulator that can be damaged if excessive force is
applied in torque, in bending, or in tension. When
installing or removing the feedthrough, the applied
torque should not exceed 2 Nm. Rotate the
feedthrough gently when making the threaded
connection to avoid excessive force.
1. Remove the 6 bolts of the Mini-ConFlat flange
connection (see Fig. 19).
2. Remove the cable connection disc.
3. Gently relieve the feedthrough from the metal
gasket connection and turn the feedthrough
counterclockwise until it is completely detached
from the internal high voltage threaded connec-
tion.
4. Replace the feedthrough and the copper gas-
ket, making sure that the feedthrough is con-
nected to the pumps internal connector. Check
that the feedthrough is not shorted.
5. Bake out the pump while it is operating, and
leave it to cool down; then verify that the base
pressure is below 10
-9
Torr (mbar).
Fig. 19 - High voltage feedthrough connection
18
87-900-106-01(B)
