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Title: Analysis of Vernier Scans during the PP2PP run in 2009 (pp at 100 GeV/beam)

Abstract

At the end of RHIC's 2009 operation a dedicated run for the PP2PP experiment (part of the STAR experiment) took place from Jun 29 to Jul 06 2009. Polarized protons were accelerated to 100 GeV using ramp-file pp100-90pp2pp with a {beta}* = 22 m in IR6. Since only transverse polarization was required no rotator ramp was in use. The PP2PP experiment consists mainly of two Roman Pot detectors (one horizontal and one vertical) on either side of IR6 in the outgoing-beam arms between the Q3 and Q4 magnets. The yellow pots are in sector 5, the blue ones in sector 6. Roman Pot type detectors are installed inside the beampipe causing an accelerator safety concern. To address this concern there is a limit to the allowable total beam current in the machine while Roman Pots are enabled to move closer to the beam. This limit was set to a motion limit of 5 mm from the center of the beampipe and 50 {center_dot} 10{sup 11} beam current per ring. In order to reduce the background in the detectors, beams were scraped using the RHIC collimator system prior to moving the pots closer. This was typically repeated several times throughout amore » store since beam halo reforms over the course of hours.« less

Authors:
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) Relativistic Heavy Ion Collider
Sponsoring Org.:
USDOE SC OFFICE OF SCIENCE (SC)
OSTI Identifier:
1039649
Report Number(s):
BNL-96818-2011-IR
R&D Project: KBCH139; 18031; KB0202011; TRN: US1202267
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ACCELERATORS; BEAM CURRENTS; COLLIMATORS; MAGNETS; POLARIZATION; PROTONS; SAFETY; relativistic heavy ion collider

Citation Formats

Drees, A. Analysis of Vernier Scans during the PP2PP run in 2009 (pp at 100 GeV/beam). United States: N. p., 2011. Web. doi:10.2172/1039649.
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Drees, A. Analysis of Vernier Scans during the PP2PP run in 2009 (pp at 100 GeV/beam). United States. doi:10.2172/1039649.
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Drees, A. Tue . "Analysis of Vernier Scans during the PP2PP run in 2009 (pp at 100 GeV/beam)". United States. doi:10.2172/1039649. https://www.osti.gov/servlets/purl/1039649.
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@article{osti_1039649,
title = {Analysis of Vernier Scans during the PP2PP run in 2009 (pp at 100 GeV/beam)},
author = {Drees, A.},
abstractNote = {At the end of RHIC's 2009 operation a dedicated run for the PP2PP experiment (part of the STAR experiment) took place from Jun 29 to Jul 06 2009. Polarized protons were accelerated to 100 GeV using ramp-file pp100-90pp2pp with a {beta}* = 22 m in IR6. Since only transverse polarization was required no rotator ramp was in use. The PP2PP experiment consists mainly of two Roman Pot detectors (one horizontal and one vertical) on either side of IR6 in the outgoing-beam arms between the Q3 and Q4 magnets. The yellow pots are in sector 5, the blue ones in sector 6. Roman Pot type detectors are installed inside the beampipe causing an accelerator safety concern. To address this concern there is a limit to the allowable total beam current in the machine while Roman Pots are enabled to move closer to the beam. This limit was set to a motion limit of 5 mm from the center of the beampipe and 50 {center_dot} 10{sup 11} beam current per ring. In order to reduce the background in the detectors, beams were scraped using the RHIC collimator system prior to moving the pots closer. This was typically repeated several times throughout a store since beam halo reforms over the course of hours.},
doi = {10.2172/1039649},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Dec 13 00:00:00 EST 2011},
month = {Tue Dec 13 00:00:00 EST 2011}
}
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DOI:  10.2172/1039649
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  • Emittance measurements using the vernier scan technique give reliable results for 250 GeV protons even though the transverse beam profiles have non-Gaussian tails. Those non-Gaussian tails were observed for the first time this run at the 250 GeV beam energy. The vernier scan measurements are in excellent agreement with the emittances derived from collision rates and show practically no fill to fill scatter if compared to the latter. The results are consistent with a {beta}* of 0.7 m and round beams. The IPM measurements show a discrepancy of up to 80% compared with the vernier scan data and a fillmore » to fill scatter of up to 30%. If an uncertainty in the beta-function at the location of the IPM is the root cause, this uncertainty seems to be quite large. In any case, such an uncertainty could not explain the fill to fill variations of up to 30% which indicate yet another underlying reason that could explain fill to fill variations (candidates could be beam intensity issues with the IPM, beam position at the IPM, varying background etc.).« less

  • ;
    Using the vernier scan or Van der Meer scan technique, where one beam is swept stepwise across the other while measuring the collision rate as a function of beam displacement, the transverse beam profiles, the luminosity and the effective cross section of the detector in question can be measured. This report briefly recalls the vernier scan method and presents results from the 100 GeV 2008 RHIC polarized proton (pp) run.

  • Several luminosity issues are reviewed. Questions remain, which are stated for further investigation. Some suggestions are made for possible luminosity improvement. There are several factors affecting the luminosity in 2009 100 GeV polarized proton run: (1) The highest bunch intensity at RHIC early store (1.5 hour after accramp in this note) in 2009 is 1.25 x 10{sup 11} protons. In 2008 run, it was 1.42 x 10{sup 11} protons, which gives rise to 30% higher luminosity if other conditions are the same. Yellow ramp efficiency is identified as one of the main problem. Meanwhile, the beam-beam induced loss in aboutmore » 1 hour into collision accounts actually no less than the ramp. (2) The typical transverse emittance at early store is 13 {pi}{micro}m for bunch intensity of 10{sup 11} protons, but it is 17 {pi}{micro} for 1.25 x 10{sup 11} protons. The increase of the emittance implies a 30% difference in luminosity if other conditions are the same. The emittance growth with electron cloud below instability threshold may be partially responsible. Meanwhile, the Booster scraping may also be relevant. (3) The luminosity lifetime in 2009 run is significantly lower than that in 2005, 2006, and 2008 runs. At the beam-beam parameter of 0.01, the typical average luminosity lifetime in early store is 10 hours in 2009, and it is 15 hours in previous runs. Given 8 hours of store time, this implies more than 20% of the difference in integrated luminosity. The 0.7 m betastar adopted in 2009 might be relevant, but the evidence is not fully convincing. On the other hand, the continuing RF voltage ramp in store may be of concern. (4) In the last month of the run, the polarization at RHIC early store is declined from 60% to 55%, a 30% reduction in p{sup 4} factor. It is noted that the Booster scraping is reduced in order to increase bunch intensity at RHIC, and the source polarization is also declined at the same time. Questions regarding these issues are discussed, and some suggestions are made.« less