AGS vacuum chamber beam damage report Time meeting
AGS vacuum chamber beam damage – report Time meeting 11 dec 07 leif ahrens • Not a resolved situation • Vacuum leaks (massive) at L 5 ss (15 Nov 07) and J 17 ss (7 Dec 07) – Hori beta max points, dispersion max points (two of many) • Replace 5’ straight section tubes – At the moment no spares left (not true)
L 5 5 foot straight section pipe (upstream end)
J 17 5 foot straight section (upstream end) (glyptol attempt to seal leak, then removed and replaced with new tube; ~400 m. Rem, two quads to move, big job).
Why/how did this happen (now)? • What is obviously different (this year vs last year) is the deuteron acceleration but • Vacuum failures occurred while accelerating gold, but • Gold setup unchanged from last year. • we note that Gold (z=77+) generates high d. E/dx (goes as z squared) energy density at dumping spot.
The beam dumping: • Internal dump – block of Cu and Fe at J 10 straight section. – Beam is moved (slowly) into block using an orbit bump + the Main Magnet field increase just at the end of the flat top (rf off). • Loss pictures when this happens – Deuterons: textbook, easy – Au not (this year, last year) • Without bump – misses J 10 dump, into L 5 – Dump bump was (inadvertantly) left off for gold setup which then “explained” the first failure – a week of tuning with all beam into L 5 ss. – Dump bump was probably off (for 4 minutes) before the second failure – which explains nothing – from the loss monitors this should remove whatever beam is hitting J 17.
Deuteron dump - loss pattern (in ags)
Gold dump – loss pattern (in ags)
Loss monitor plot (last year) – gold dump (23 Mar 07) Later (12 April) this was improved – closer to ideal.
Loss pattern at beam dump with the dump bump off
Plan • Rule for Operations have changed! – Dump beam at ags injection energy (100 Me. V vs 10 Ge. V /nucleon) when possible – This covers the hard tuning (Tt. B, Booster, Bt. A) – Use the extraction into At. R to W line dump when accelerating if possible – When using internal dump, bump must be operating. This mode is still necessary.
Plan (cont) • Searching for differences relative to last year continues – Beam quality – better? – Behavior of beam after rf turnoff – before dump – different? – Something else in the setup – tunes, bump, Main. Magnet function?
End of cycle in ags. 20 ms/box Blue: Wall monitor (envelope of the beam in AGS) Green: gap volts Gold: Main Magnet voltage
- Slides: 13