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Recent Antiproton Lifetimes in the Recycler Ring

Recent Antiproton Lifetimes in the Recycler Ring. All Experimenters Meeting November 16 th , 2009 L. Prost for the Main Injector Dpt. Coming out of the Summer shutdown….

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Recent Antiproton Lifetimes in the Recycler Ring

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  1. Recent Antiproton Lifetimes in the Recycler Ring All Experimenters Meeting November 16th, 2009 L. Prost for the Main Injector Dpt.

  2. Coming out of the Summer shutdown… • Expected some lifetime degradation (w.r.t. pre-shutdown) because of poorer vacuum in the two regions (401-409 & 103-109) that were vented up • Good recovery overall but larger N2 partial pressure RGA scans at 401-409(IPs ON, TSPs sublimated) After Before 10-10 Torr full scale H2(out of scale) H2(out of scale) N2 Note: There was ~one month of pumping time before seeing protons (for this region only)

  3. Evolution of symptoms • First check out of the Recycler showed good lifetime • Although was never back to pre-shutdown typical values • Recycler performance appeared to have continuously degraded since early October • Lifetime startedto get poor atall intensities(next slide) • High averageemittanceswhile stashing • Poor extractionefficiency Average Schottky emittance, 95% n Electron beam position, mm Pbar intensity, E10

  4. Lifetime (as measured) vs Time • Lifetime is worse by a factor of ~2 for comparable conditions • We were losing an extra ~5% of pbars in the Recycler 10-min average lifetime, hrs # of pbars, E10 ~1 month

  5. Possible reasons and checks • Large emittances from Accumulator ? • Unlikely because the lifetime does not improve toward a steady state, when the ‘memory’ about the transfers should disappear • Worse electron cooling ? • Measurements indicate that it cools better than ever • Actually, worse cooling efficiency would likely improve lifetime • Heating by stochastic cooling system ? • Checked and adjusted parameters • Turning some systems off does not improve the lifetime • Cannot explain a higher diffusion rate • Diffusion rate obtained while measuring the electron cooling rate • Dampers ? • Phasing was checked • On or Off does not make any difference

  6. Possible reasons and checks (cont.) • Vacuum ? • No clear indications from ion gauges (or ion pumps) • Should be a constant offset in rates at all intensities • Storing of ions ? • Would be the most consistent explanation • All clearing PS are shown to be working and were checked; connections were visually checked during the final tour of the tunnel • Changes in the lattice ? • Was measured • Changes are at the ~10% level at max. • Too small a change for our large acceptance (which was also checked)

  7. Emittance growth rate measurement Vertical emittance (fast monitor) Horizontal emittance (fast monitor) Vertical emittance (slow monitor) Expected rate(~0.8 p mm mrad) Horizontal emittance (slow monitor) • Almost all systems are turned off (electron beam, dampers, RF, stochastic cooling) and the beam is let diffuse • Path length compensation (MI ramping) was kept on • Best way to indicate a problem with vacuum • Transverse emittance growth rate is 4-6 times higher than normal • Need totake acloserlook atvacuum

  8. Vacuum history at 313 (since early April) • Even though the magnitude of the vacuum degradation cannot explain the emittance growth measurement, we decided to sublimate the TSPs in this region (308-319) • Leak checking is noteasy in the Recycler • Also applied vacseal to an ionpump connector(ceramic part) Shutdown Ion pump (Torr) Ion gauge (Torr) TSPs sublimated on Nov 4

  9. Current Status (I) • Although the vacuum did not return to the pre-shutdown level, the lifetime greatly improved • Likely to itspre-shutdowntypical values • There is still thepossibility of asmall leak in thearea(313 pressurecontinues to rise very slowly) Before vacuum work After vacuum work 10-min average lifetime, hrs Pelletron repair # of pbars, E10

  10. Emittance growth rate check Dotted line: rates before vacuum work Vertical emittance (fast monitor)p mm mrad Horizontal emittance (fast monitor)p mm mrad Vertical emittance (slow monitor) p mm mrad Horizontal emittance (slow monitor) p mm mrad Reduced by a factor ~2

  11. Summary • Average antiproton lifetime decreased continuously since coming out of the Summer Shutdown • Only vacuum degradation seemed to be a possible explanation (around sector 313 in particular) • Lifetime in the Recycler greatly improved after sublimating TSPs in the 308-319 region • Will request sublimating more TSPs around the ring over the next few weeks • Many TSPs have not been sublimated in more than 4 years and may be saturated (i.e. slow to no pumping)

  12. EXTRAS

  13. Life time comparison under “steady-state” The life time was found to correlate only with the linear density of the pbar beam. Sep-Oct points were collected slightly differently. Sep-09 points are lower than Dec08, and Oct-09 point is much lower. Part of this can be attributed to a worse vacuum. 13 No transfers (for more than 1.5 hours) No changes of e-beam position No changes in the pbar beam length or structure Emittances close to an equilibrium at the end of the period, where all parameters are recorded

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