Beam Instability

Issue

Beam instability

Environment

Titan G2 60-300

Resolution

These are possible resolutions for the issue:

• cleaning the arching traces & re-bake out, filled with clean & fresh SF6.

Cause

These are possible causes for the issue:

• arching inside the outer jacket of accelerator due to contaminated SF6

Details

• Instability shown after replaced FEG and bake out completed.
• Localized the instability above C1 Lens by inverting the polarity of C1 Lens.
• HT stability measured without load (dummy plug) and it is in-spec and stable.
• @ 80 kV the beam stable and @300kV unstable. Proven by measuring ZLP.
• HT cable replaced and didn't solve the issue.
• Checked inside the outer jacket of the accelerator (ACC), found arching traces (see attached file). Examined the cause of the arching and found out the supply of SF6 was not clean enough. Inspected spark gaps, looks good.
• Cleaning the arching traces inside the outer jacket and re-bake out . Filled with clean and fresh SF6. Issue solved.

Arching inside the outer jacket of ACC