Subject:
Minutes of Pbar recycling seminar (fwd)
From:
Vladimir Shiltsev <shiltsev@fnal.gov>
Date:
Thu, 08 Dec 2005 17:41:39 -0600 (CST)
To:
vs <shiltsev@popgtw.fnal.gov>


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---------- Forwarded message ----------
Date: Thu, 08 Dec 2005 14:18:03 -0600
From: Mike Martens <martens@fnal.gov>
To: run2_up_all@fnal.gov, bd_runII_commissioning@FNAL.GOV
Subject: Minutes of Pbar recycling seminar

   On Thursday Dec 1, 2005 there was a meeting to revist the possibility
 of recycling pbars after a Collider Store. Please note that pbar
 recycling is not a part of the Run II upgrade and this meeting was meant
 only to explore the idea of pbar recycling since the last time it was
 examined in 2002.  These are notes from this meeting as I (Mike Martens)
 understood them.

 Valdimir Shiltsev presented his analyis of the resulting incease in
 integrated luminosity from pbar recycling and representatives from the
 Tevatron, Main Injector, and Recycler presented their initial thoughts
 on the idea. Vladimir's analysis showed that we could expect a 15% - 20%
 gain in integrated luminosity by recycling pbars based on todays
 operating beam parameters. The machine representatives gave rough
 estimates of the effort needed to implement pbar recycling and reported
 no major drawbacks and no need for significant hardware upgrades. The
 net gain in integrated luminosity for the remainder of Collider Run II
 from pbar recycling would be the increased luminosity minus the
 integrated luminosity lost during the comissioning of pbar recycling.
 One important unknown factor in this balance is the length of time
 remaining for Tevatron Collider operations.

 Vladimir's analysis of pbar recycling (see
 http://beamdocs.fnal.gov/cgi-bin/public/DocDB/ShowDocument?docid=1954)
 confirmed Valery Lebedev's analysis in 2002, but Vladimir updated his
 analysis to include the present collider operating conditions. These
 include an increase in Tevatron reliablity (from 70% to 80%), a weekly
 average stacking rate of 11 mA/hr, measured pbar and luminosity
 lifetimes, and the measured longitudinal emittance of the pbars at the
 end of the store. The recycled pbars would remain in the Recycler during
 the the next shot setup and the "hot pbars" would be cooled during the
 next store. Using this model the increase in itegrated luminosity would
 be about 20% if all of the pbars within a 4 eVs longitudinal emittance
 could be recycled and 15% if all of the pbars within a 2 eVs
 longitudinal emittance could be recycled.

 As far as the Tevatron is concerned proton removal, pbar decelaration,
 and pbar extraction are the main tasks for implementing pbar recycling.
 Proton removal has not been demonstrated at the rate needed for
 effective pbar recycling, but studies performed in 2003 led to a better
 understanding of the scraping process. The biggest discovery was the
 misalignment of the E0 collimator for scraping. With this understanding,
 and the shielding that has been added at A48,  there is confidence that
 proton removal can work. Deceleration has been demonstrated in the past
 with 100% efficiency using protons. There is nothing in the mechanics of
 pbar extraction from the Tevatron to the Main Injector that is expected
 to be difficult. Added up, the total amount of time to establish pbar
 recycling in the Tevatron is about 10 shifts. After this a number of
 pbar decelerations would be needed to fine tune the process.

 For the Main Injector, most of the work involves developing a ramp to
 decelerate pbars using a combination of 53 MHz RF and 2.5 MHz RF. Much
 of the work involves getting the orbits, tunes, coupling, and
 chromaticity correct on the deceleration of the MI ramp. This is due to
 signficant hystertic effects in the magnets which substantially change
 the magnetic fields on the down-ramp as compared to the up-ramp. In the
 past the MI has accomplished deceleration with 85% efficiency and no
 transverse emittance growth. However, the MI would need to be retuned to
 accomplish this again. Given the constraints on the MI for fixed target
 programs and the limited resources of the MI group, it was estimated
 that it would take about 1 calendar year to get pbar deceleration
 established in the MI.

 For the Recycler, there should not be a problem accepting "hot pbars"
 from the Tevatron for re-cooling. Operating in recycler mode would mean
 a reduction in the portion of RR circumfrence available for "cold pbars"
 which implies there would be a larger momentum spread in the cold pbar
 beam. Another concern is the behaviour of the stochastic cooling with
 "hot pbars" in the RR. The best guess at this time is that it would take
 2-3 hours to re-cool the pbars from the Tevatron before they are cool
 enough to return. No estimate was given on the amount of time it would
 take to commission the RR for pbar recycling.

 At the end of the meeting there was a discussion about the feasability
 of recycling pbars. There does not appear at this time to be any
 technical reasons that would limit the success of recycling pbars. The
 biggest uncertaintiy was the trade-off between integrating luminosity
 without pbar recycling and the loss of integrated luminosity due to
 commissioning. It was also noted that there is no new hardware required
 to implement pbar recycling.

 Mike Martens