Ion pump hipotting

Brief instructions on hipotting a non-working ion pump

Written by SDS

Last updated 1-10-2017

• I think this is good, but multiple steps could use more explanation. Pics would help in some case.

• E.g.: Where is the hipotter? Do the ground lugs snap on or need to be bolted on?

• For the Variac, is the a specific cable ready with AC plug and crimp terminals? A picture of the plug jumper-ing would is highly suggested.

1. First step is to determine if hipotting is the appropriate step. An ion pump should be hipotted if it is suspected that debris is causing a short or arcing condition within the pump, preventing its normal operation. Due to the high voltages involved within the ion pump, a short can occur by arcing across two conductors that are closely spaced, yet not physically touching. This type of short circuit will not be measurable by a multimeter or continuity checker.

   1. Test the electrical continuity between the high-voltage input and ground. If there is electrical continuity across this path, the ion pump has a dead short inside, i.e. there is a physical conduction path to ground from the high-voltage input. If there is no continuity, there may be a small enough gap that, with a high enough potential, can act as a short if dielectric breakdown occurs and there is arcing across the gap.

   2. If a dead short, proceed by using a variac.

   3. If not a dead short, hipotting can be performed.

2. Hipotting is the process of using a high potential ('Hi'gh 'Pot'ential) between the pump electrical input and ground to test for shorts that may not show up using multimeter continuity checks.

   1. The hipotter has a DC output and an AC output. Use the AC side.

   2. Connect the ground lugs on the front of the hipotter to chassis grounds on the pump/system being hipotted.

   3. Connect the high voltage cable to the high voltage input on the ion pump.

   4. Make sure the current limit sensitivity is set to minimum.

   5. Turn on power to the hipotter. Wait ~1 minute for the supply to warm up.

   6. Turn on the high voltage output. Wait ~1 minute for the supply to warm up.

      1. If the current meter shows current with no applied voltage, hipotting is likely not the way to go. Use a variac.

   7. Slowly, slowly turn up the potential using the knob. Monitor the chamber pressure that the pump is connected to and the current meter on the high potter. If either begins to spike, pause the ramp up of the potential until things settle down.

   8. Keep increasing the applied potential until you reach the operating voltage of the pump. If the current limit has not tripped, then the pump has been successfully hipotted and should be good for operation.

3. If hipotting does not work (current limit keeps being exceeded) or continuity checks indicate a dead short, proceed by using a variac to Joule heat the short and blow it away.

   1. Set up a variac with an AC plug with crimp terminals on the AC output.

   2. Jumper the output of the AC plug to the high voltage input to the ion pump and a chassis ground.

   3. Slowly, slowly, slowly ramp up the variac. Monitor the chamber pressure of the chamber attached to the ion pump. If/when it rises, immediately stop increasing the variac output until the pressure drops back down to about previous levels.

   4. Keep ramping up the variac very very slowly until it seems as if further increases are not having an effect on the system.

   5. Ramp the variac back to zero (the ramp rate here is not important), turn it off, and disconnect the AC plug from the variac.

   6. Test continuity between the high voltage input and ground of the ion pump. If there is a short, restart the variac steps over again. If it is open, proceed with the hipotter steps above.

4. Once multimeter continuity shows an open circuit and the hipotter test passes, the ion pump should be ready for restart.

5. Restart the ion pump.