Results of shooting without a “hot bucket”

1. Results of shooting without a “hot bucket” Shemyakin MI departmental meeting March 31, 2009

2. Mining without the “hot bucket” • The proposal was to eliminate the special bucket for hot particles during TeV shots • Keeping them together with the cold portion should decrease chances for an instability • Was discussed on MI meeting on March 3, 2010 • Chandra prepared the necessary changes and tested on March 12 • In operation since March 22 • Possible drawbacks • higher losses during RR-> MI transfers • because of transferring a DC component • and during coalescing • Because of transferring more hot pbars captured into 2.5 MHz buckets Effective potential Effective potential S, µs S, µs Effective potential for “hot bucket” configuration (left) and without “hot bucket”(right)

3. Mining • March 22 – 30: 11 shots without “hot bucket” • Mining increased by 2% • Some of hot particles are cooled down into mined buckets • Is not considered as a plus • Pbars left in RR can be used for the next shot with roughly the same efficiency

4. Transfers RR -> MI • A possible decrease in the transfer efficiency is less than 0.5% • Therefore, no significant additional amount of DC pbars is likely to be send to MI 1% The ratio of Supertable columns #33/#32 (Np in MI at 8 GeV to amount unstacked from RR ). The red line indicates beginning of shots without “hot bucket”

5. Coalescing • Increase in RR 2.5 MHz LE is less than 0.1 eVs • Coalescing efficiency decreased by ~1.5% • Likely is the result of capturing the tails into mined buckets

6. Life time • Life time over a stashing cycle stays roughly the same with and without hot bucket. • It is worse than it used to be outside of the extraction • Reason is unclear Life time between transfers for stashing cycles with hot bucket (#7679 , 15-Mar-2010, left) and without (#7716, 29-Mar-2010, right).

7. Life time during extraction • Life time between extractions noticeably improved • Small contribution to the total loss: improvement from 0.7 – 0.12% of the total Np to 0.1- 0.3% • May be related to the RR momentum aperture • Maximum dp is lower without hot bucket Comparison of life time between extractions for stashing cycles with hot bucket (#7679 ) and without (#7716). Effect is reproducible. Effective potential Effective potential S, µs S, µs

8. Summary of results • The main effect of the past weeks is a degradation of the life time • Unrelated to the “hot bucket” • The additional net loss may be ~1% • Coalescing efficiency dropped by ~1.5% • There might be a ~0.5% gain because of a better life time during extraction

9. Possible modification of the scheme • Two last instabilities occurred with mined bunches, not with 2.5 MHz ones • May be a result of a higher synchrotron frequency • Possible modification • Decrease the amplitude of 2.5 MHz • To remove hot particles • Raise the anti-bucket • To separate the hot particle from the cold ones in 2.5 MHz • Increase 2.5 MHz amplitude to the full one • To match MI bucket • A dedicated study would be useful • Meanwhile, it may be rational to revert to mining with “hot bucket” • And be careful with avoiding an instability • Do not overcool • An additional transfer if there was a long delay before the TeV shot Effective potential S, µs