Using evaporators

Differentially pumped ports

On the experimental chamber two CF38 gate valves with roughing ports are installed. On the preparation chamber - bottom one such valve can be installed. These gate valves, accompanied by a z-retractor and pumping valve connection, permit to exchange the inserted evaporator without venting the whole chamber. The pumping is done through preparation chamber - bottom, preparation chamber - top or using an auxiliary pumping stage.

The inserted evaporator can be up to 35 cm long, which allows the minimum sample-to-evaporaror working distance about 12 cm.

Evaporator exchange:

  1. Disconnect the electrical and water (if any) connection from the old evaporator. Blow out the residual water from inside using compressed air.
  2. Carefully retract the old evaporator using the corresponding z-retractor. It is good if the device is shaking a bit which allows to pass safer through the copper gaskets. Stop and shake more if you feel sudden change of resistance during the retraction.
  3. Fully close the gate valve.
  4. Check that the pumping valve is closed.
  5. Slowly loosen the nuts on the evaporator flange. The area will be vented through this flange. Observe the pressure in the chamber all the time. If it starts increasing considerably tighten the gate valve more in order to minimize the leak.
  6. Remove the old evaporator and prepare the new one. Use a new copper gasket.
  7. Install the new evaporator into the retractor. Be careful with its rotaton. Some parts too out of axis might interfere later with the retractor mechanism during the insertion. Moreover, gravity might influence the alignment of the internal part of the evaporator; the parts too out of axis (at the chosen rotation) might not pass well through the gate valve.
  8. Tighten the nuts on the evaporator flange.
  9. Perform the electric check of the evaporator feedthroughs (e.g. filament or thermocouple resistance, no short contacts).
  10. If the evaporator is to be pumped through preparation chamber - top or preparation chamber - bottom slow down the corresponding turbopumps (Standby regime) and switch off the cold-cathode gauge in order not to overload them. Full-range gauges can remain on, as the pressure in the next step will rise to mbars.
  11. Very slowly and in a step-wise manner open the roughing valve, after each step observe the pressure and the load on the turbopump. Continue until the valve is fully open.
  12. The pressure should decrease fast in the 10-5 mbar range or below. Then you can switch on the cold-cathode gauge and switch off the Standby regime of the turbopumps; they should reach full speed easily.
  13. Repeat the electric check of the evaporator.
  14. Perform a bakeout of the evaporator area. A 165 W/1.1 m-long heating tape and several layers of aluminum foil are enough to reach 130 °C. Reasonable bake-out time is several hours or overnight.
  15. When the evaporator cools down a bit remove the aluminum foil and the heating tape.
  16. Once again repeat the electrical check of the evaporator.
  17. Slowly open the gate valve. Observe the pressure in the chamber. It should not get worse than 10-8 mbar.
  18. Carefully insert the evaporator in the chamber using the x-retractor. Again, it is good if the device is shaking a bit which allows to pass safer through the copper gaskets. Stop, go back and shake more if you feel sudden change of resistance during the insertion.
  19. When the evaporator is fully inserted close the roughing valve.
  20. Connect electric cables and water cooling pipes (if any) to the evaporator.
  21. Perform a degas procedure of the evaporator.
If you use the auxiliary turbopumping stage for roughing modify steps 10-12 accordingly.
Last Updated on Thursday, 23 November 2017 10:04