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Thermo Fisher Scientific

Low FEG emission current, unable to find beam

 

Issue

Low emission current, unable to find beam

Environment

Titan Krios, Titan G2 60-300

Resolution

These are possible resolutions for the issue:

  • Adjusted R29 on HBF (WI 105845)

Cause

These are possible causes for the issue:

  • Filament supply voltage too low (<26.5V)

Details

After replacing the HT Tank everything started as expected but the beam could not be found. FEG Emission was present, the test lines "looked" ok. After a deeper analysis it was noticed that the Filament current was dropping during the Extractor ramp up or Gun Lens change.

Case 1 -Titan Krios:
FEG SERVICE DIALOG AND UI XFEG 

  • The emission current dropped from 297 uA to 65 uA.
  • The filament current is normally 1885 mA
  • When the GL is increased (GL8 1800V) the emission drops to about 22uA
  • The Filament current drops to about 1600 mA.
  • When the GL is decreased (GL1 350V) the emission goes up to about 120 uA
  • The filament current goes up to 1775 mA

Case 2 - TitanG2 60-300 (see picture):

Troubleshooting actions and their results:
Test 26.5V Fil Supply (WI 105843)
Adjust R29 on HBF (WI 105845)

 In both cases, the 26.5V Filament supply was low (<18V) and needed correction.

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