thermionics laboratory, inc
3kW Rod fed e-gun manual Page 5
FINAL CHECK PRIOR TO PUMPDOWN
1. Turn on the water and check visually for leaks.
2. Make sure the crucible is loaded with material.
3. Visually check the high voltage and sweep leads making sure you have ½ inch
clearance around all high voltage leads. Make sure the sweep leads do no pass
directly behind the source (if they must make sure to install a grounded shield around
them).
At this point you are ready to pump down the system.
WARNING: e-GUN SYSTEMS REQUIRE AN INDEPENDENT EARTH GROUND IN
ADDITION TO POWER SUPPLY RETURN AND SAFETY GROUND. SEE APPENDIX B
FOR DETAILS.
e-GUN OPERATION
1. Make sure the vacuum chamber is operating at a pressure less than 5x10^-4 Torr.
2. Make certain all interlocks are operating properly. All grounds must be secure.
3. Turn on the e-GUN cooling water (this should be interlocked to the high voltage
power supply).
4. Assure desired crucible is selected and properly located.
5. Set the power supply emission current potentiometer to zero.
6. Turn on the power supply and check to see that all interlocks are satisfied.
7. Turn on the high voltage. Thermionics 150-0040 3kW power supplies use a fixed
voltage. If using a variable voltage power supply, slowly bring up voltage to negative
4,200 volts DC.
8. Turn on the emission current and slowly increase the potentiometer until you see a
slight glow on the tip of the rod. This will normally appear as a blue glow at an
emission current of about 20 to 30 milliamperes. Slowly increase the power to 50
milliamperes, or until you can clearly see the beam spot.
9. Advance the rod as the material melts down to the crucible. Typical advancement
is 2-3mm.
Note:
The e-gun is factory set to locate the beam just off the center of the crucible. If
the crucible is not close to center you must make adjustments. If you have a variable
voltage power supply, adjust the voltage to center the beam. If you do not have
variable voltage, you will need to make magnetic adjustments to the e-gun. Contact
the factory for adjustment procedures.
DEPOSITING MATERIALS THAT MELT
After following the above procedure (steps 1 through 8), continue to slowly increase
power in 20 to 30 milliamp increments. If the material appears unstable (flickering light or
waves in the melt) stop and let it set until it re-stabilizes (you may have to reduce power if
stability cannot be restored). Arcing will occur and is normal in e-Gun evaporation. Stop
increasing power when arcing is observed and let the source soak until arcing stops (on
melting materials arcing is normally caused by outgassing). Continue to increase power
until reaching the desired rate.
