A. Zelenskia, G. Atoiana*, A. Bogdanovb, D.Rapariaa, M.Runtsob, D. Steskia, V. Zajica

 

aBrookhaven National Laboratory, Upton, NY, 11973, USAbMoscow Engineering Physical Institute (MEPHI), Moscow 115409, Russia

Precision, Absolute Proton Beam Polarimeter at 200MeV

PSTP-2013

Polarization facilities at RHIC.

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STARPHENIX

AGS, 24GeV

LINAC

BOOSTER 2.5 GeVOPPIS

200MeV polarimeter

RHIC pC “CNI” polarimeters

RHIC

Absolute H-jet polarimeter

AGS pC “CNI” polarimeter

Polarized injector, 200MeV LINAC and injection lines

OPPIS

200MeV polarimeter

200MeV LINACRFQ

Booster

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The 200 The 200 MeV LINAC Polarimeter LINAC Polarimeter

Target

proton 200MeV

Scattered proton

Recoil Atom

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A new polarimeter for absolute proton beam polarization measurements at 200 MeV to accuracy better than ±0.5% has been developed as a part of the RHIC polarized source upgrade.

The polarimeter is based on the elastic pC scattering at 16.2° angle, where the analyzing power is large 99.35% and was measured with high accuracy. The elastically and in-elastically scattered protons are clearly identified by the difference in the propagation through variable copper absorber and energy deposition of the stopped protons in the detectors. The 16.2° elastic scattering polarimeter was used for calibration of a high rate inclusive 12° polarimer, which was used for the on-line polarization tuning and monitoring.

Measurements of the cross section and analyzing power for proton scattering from 12C at 200 MeV. The blue curves correspond to protons exiting from the ground state of carbon. The green curve corresponds two protons exiting from the first excited state (-4.44MeV). The black curve represents the sum of the two data sets.

Edward J. Stephenson, 10/22/2009

~16.2o

~50mb/sr

~5mb/sr

~82%

Cross section and analyzing power for pC scattering at 200 MeV

~12

~99.35%

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elastic

GEANT calculation of pC polarimeter for 200MeV proton beam

Collimator Absorber

Sc1 Sc2 Sc3

inelastic

Ep=198.7MeV

Ep=194.3MeV

41mm of Cu

We have shown the possibility of suppression of an inelastic scattering proton from a carbon by an absorber.

C- targetP-beamSc1 Sc2 Sc3

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GEANT calculation of pC polarimeter for 200MeV proton beam

Energy deposited in the scintillator

E, MeV

inelastic

elastic

Ratio N(Inelastic)/N(elastic) by the Cu absorber thickness ~41mm with energy threshold ~15MeV is less than 0.5%

3.7 3.8 3.9 4.0 4.1 4.2 4.4 4.3

elastic

inelastic

L, cm

N, particles stopped in the slice of absorber

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A sharp edges promises a good separation of the inelastic scattered proton from an elastic

Beam setup of the polarimeter

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Polarimeter setup for 200MeV proton beam

Cu ~5 mm

Horizontal 120 and vertical 16.20 polarimetersHorizontal 16.20 polarimeter

Absorber: Cu from 0 to 1 mm(step by 0.1mm)

Absorber: Cu from 0 to 9 mm (step by 1mm)

Absorber: Cu from 0 to 38.1 mm (step by 12.7mm)

Cu collimator: D=8mm

Counters:Sc3 Sc2 Sc1

Motion system

Fast photomultiplier with fast scintillator BC-404 (decay time ~1.8nsec) gave the output pulse less than 15nsec (rise time ~2.4nsec).Coincidence signal is formed in the vicinity of the detector in the beam line by fast discriminators. Time resolution without amplitude correction is less then 0.5nsec.

Mostly the elastic protons passed through the absorber (41mm) and absorbed into the second scintillator, depositing ~5-40.0MeV of energy.

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Spectrum of counters and efficiency vs. threshold of discriminator

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Systematic error an analyzing power

C target

proton 200MeV

Scattered proton

Recoil Carbon

The systematic error of the Ay by:• detector alignment 5mm• energy of the beam 2001.0 MeV• size of the scintillators ~10x10mm• multiple scattering in target, vacuum wall and airIs about 0.2 %.

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Horizontal scan of the beam by vertical polarimeterTarget#1 Target#2 Target#3 Target#4 Target#5

Width x thickness, mm 2 x 0.1 2 x 0.1 2 x 0.06 D 0.3 4 x 0.1

Rate of horizontal 120 polar.evnt./pulse (Labs=6mm of Cu)

~400 ~400 ~220 ~200 ~800

Rate of horizontal 16.20 polar.evnt./pulse (Labs=40.1mm of Cu)

~30 ~30 ~18 ~15 ~60

Rate of vertical 16.20 polar.events /pulse (Labs=5mm of Cu)

~1600 ~1600 ~1100 ~900 ~2500

By the different targets we can change the rate of the detector almost 4 times.

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Systematic error an accidental coincidence by:• beam halo (depends on the adjustment of the LINAC) and•the rate of the detector. (By Linac elements and using different targets we can change the rate of the detector almost 4 times).Average counts in the target ‘out’ are less than 1 and target ‘in’ ~250, gave the systematic error ~0.3%

Systematic error in polarization measurement by beam halo

Target position ‘OUT’

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I(T9)=295MKA (4.9*10^11)

83.9+/-0.7%

84.2+/-0.5%

15 min

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~83%

Polarization fluctuation of 200Mev beam (March 1-4, 2013

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Measured Analyzing Power vs thickness of absorber

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Suppression of the inelastic scattering proton to first excited state by absorber

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Inelastic scattering protons well suppression

First excited state drops the analyzing power ~ 2%

Prototype of the first excited state (Energy was decreases by the LINAC)

Ratio of the rate Sc1*Sc2:R(200)/R(200-4.4) > 10for the 41mm thick of Cu absorber

Calibration curve of energy monitoring using 16.20 polarimeterDifference of the rate in the subsequent detectors of the telescope in both arms was used for the beam energy monitoring and tuning to improve polarization measurement accuracy.The energy calibration 16.20 polarimeter with accuracy better than 0.5 MeV were done by using the magnetic spectrometer and cross-checked at injection to the Booster.

Beam energy vs. ratio S3*S1/S2*S1x100 (thickness of absorber 40.1mm)

Sc3 Sc2 Sc1

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Time chart of energy monitoring using calibration curve

Ratio N(Sc1*Sc2) / N(Sc1*Sc3) is simple and stabile monitor of beam energy with accuracy better than 0.5 MeV per tens of pulses.

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Horizontal scan and polarization profile of the beamWe have a program that makes automatic measurements of a horizontal scan and polarization profile of the beam.

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Polarization vs current of the spin rotator

Polarization at the horizontal 16.20 polarimeter ~ 80.5%

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THE ANALYZING POWER OF THE ELASTIC SCATTERING PROTON FROM 12C IS WELL KNOWN WITH GOOD ACCURACY AND FOR 16.2 DEGREE SCATTERING ANGLE IT IS CLOSE TO 100%. (PHYS. REV. C, VOL. 45 NUMBER 2, 504 -1992)WE SHOWN POSSIBILITY OF SUPPRESSION OF THE INELASTIC SCATTERING PROTON FROM AN ELASTIC FOR 41MM CUPPER ABSORBER IS ABOUT 1% ( ~10 TIMES BY CROSS SECTION AND MORE THAN ~10 TIMES BY ABSORBER ). THE IDENTIFIED ELASTIC PROTONS WERE USED FOR POLARIZATION MEASUREMENT.

16.20 polarimeter used for the determine of analyzing power 120 polarimeter and reference polarization measurement;

Rate effect for polarization measurement less 0.2% to 400 event/pulse (~1.3MHz) and the estimated systematic error ~0.3 %;

Polarization dependence of gain of PMT and threshold of discriminators are insignificant. Deposited energy on the scintillators more then 10MeV (5-40MeV);

Ratio N(Sc1*Sc2)/N(Sc1*Sc3) is simple and stabile monitor of beam energy with accuracy better than 0.5MeV per tens of pulses;

We are capable accuracy measurement of horizontal beam and polarization profile.

Summery

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BACKUP

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Beam setup of 200MeV proton polarimeter (before)

pD-polarimeter:• The analyzing power for pD known with good accuracy: A = 0.507 +/- 0.002 (IUCF);• pD polarimeter was used for calibration of the 12 deg. pC polarimeter •The rate - less then 1 event per pulse => In 8 hrs a statistical accuracy about 2%;

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