Møller Polarimetry in Hall A and Beyond

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1 Outline E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 1 Møller Polarimetry in Hall A and Beyond E.Chudakov 1 1 Hall A, JLab EIC Polarimetry Workshop, Ann Arbor, Aug 23-24, 2007

2 Outline E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 2 Outline 1 Introduction Compton and Møller Polarimetry 2 Møller polarimeter in Hall A General Description Target Polarization High field upgrade 3 Møller Polarimetry at EIC? EIC Atomic hydrogen trap Jet targets 4 Appendix

3 Outline E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 2 Outline 1 Introduction Compton and Møller Polarimetry 2 Møller polarimeter in Hall A General Description Target Polarization High field upgrade 3 Møller Polarimetry at EIC? EIC Atomic hydrogen trap Jet targets 4 Appendix

4 Outline E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 2 Outline 1 Introduction Compton and Møller Polarimetry 2 Møller polarimeter in Hall A General Description Target Polarization High field upgrade 3 Møller Polarimetry at EIC? EIC Atomic hydrogen trap Jet targets 4 Appendix

5 Outline E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 2 Outline 1 Introduction Compton and Møller Polarimetry 2 Møller polarimeter in Hall A General Description Target Polarization High field upgrade 3 Møller Polarimetry at EIC? EIC Atomic hydrogen trap Jet targets 4 Appendix

6 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 3 Compton versus Møller Polarimetry Compton Polarimetry Møller Polarimetry A = 7 9 lab 180 mb ster Kinematics/asymmetry Rad. corr. to Born < 0.1% Detect γ at 0, e < E beam Strong da dk - need σe γ/e γ 1 A ke at E < 20 GeV T 1/(σ A 2 ) 1/k 2 1/E 2 Rad. corr. to Born < 0.3% Detect the e at θ CM 90 da dθ CM good systematics Beam energy independent Coincidence - no background

7 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 3 Compton versus Møller Polarimetry Compton Polarimetry Møller Polarimetry A = 7 9 lab 180 mb ster P laser 100% Non-invasive measurement Polarized target Ferromagnetic target P T 8% > 1 µm: invasive Beam I B < 2 4 µa (heating) Levchuk effect Low P T dead time Syst. error σ(p T ) 2% for B < 2 T 0.3% for B > 3 T

8 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 3 Compton versus Møller Polarimetry Compton Polarimetry Møller Polarimetry A = 7 9 lab 180 mb ster Syst. error 3 50 GeV: % Hard at < 1 GeV: (JLab project) 0.8% Accuracy Syst. error 3% typically, 0.5%(1%?) at high magn. fields

9 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 4 Hall A Møller Polarimeter Y cm X cm Target commissioned target upgrade Collimator Coils Quad 1 Quad 2 Quad 3 Dipole non-scattered beam Z cm target upgrade planned (high field) Detector (a) (b) Z cm B GeV Minimal Levchuk σ stat = 1% in 2 3 min B Z 25 mt field Foil at 20 to field Foils 5 3-µm thick Beam <2-µA

10 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 5 Foil Polarization The polarization is calculated from the magnetization B > 3 T full saturation data on Fe magnetization used B 2 T magnetization has to be measured P foil = B foil g 1 2πg 1 N eµ B = g 1 2πg 1 µ B Φ foil length A weight Av Z New method to measure Φ foil (z) Pickup coil fixed in the Helmholtz coils The foil is pulled through the pickup coil, dφ foil dt sampled Is the foil thickness(z ) = const? Is B foil (Z ) = const? = ε(t)

11 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 6 Foil Polarization Measurements Find the source of variation: scan the beam across the foils

12 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 7 Foil Mounting

13 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 8 Results of measurements with the beam About 60% of variations due to thickness Variations between different foils (Fe, Supermendur alloy, 7 30µm thick) are 2% In order to increase the accuracy (needed for PREX) high magnetic field: Hall C clone

14 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 9 Systematic Errors The goal for the systematic error Variable Error OLD Present PREX goal Target polarization 3.5% 2.0% 0.5% Target angle 0.5% 0.5% 0.0% Analyzing power 0.3% 0.3% 0.3% Levchuk effect 0.2% 0.2% 0.2% Dead time 0.3% 0.3% 0.3% Others % Total 3.6% 2.1% 1.0%

15 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 10 How to measure the real beam? PREX will run at 50 µa Target heating < 50 K to avoid errors on depolarization Run the injector as close to the regular running as possible Average current I beam < 2 µa T <30 K Laser cycle: 1 ms pulse at 30 Hz T pulse 12 K Beat frequency laser chopper: 500 MHz 500/4 MHz Lower average rate 1% statistically in min

16 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 11 EIC electron beam Taken from ELIC specs Current 2.4 A, bunches of e at 1.5 GHz Bunch size: σ Z = 5 mm or σ t = 17 ps, σ X 0.1 mm Helicity flipping scheme??...no way to use an iron foil...

17 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 12 Fantasies: Beam with self e e 3 3 GeV GeV a new collision point at the center L cm 2 dσ dω CM Moller 1000 pb/ster Stat. 1% in 5 min for P Z, 50 for P T A high luminosity collision point - some other interest?

18 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 13 Polarized atomic hydrogen in a cold magnetic trap beam H 0.3K Ultra-cold traps 30K 40 cm Solenoid 8T Storage Cell E. Chudakov and V. Luppov, IEEE Trans. Nucl. Sci. 51, 1533 (2004). 4 cm Atom H 1 : µ µ e, E = µ B Population exp( E/kT ) At 300 mk P e Density cm 3 Lifetime > 1 h Stat. 1% in 10 min at 100 µa Contamination and Depolarization at 100µA CEBAF Hydrogen molecules < Upper states c and d < 10 5 Excited states < 10 5 Helium, residual gas <0.1% - measurable Depolarization by beam RF < Ion, electron contamination < 10 5 Ionization heating < Expected depolarization < 10 4 Limitations Problems Ib 2 /F continuous beam Complexity of the target Advantages Expected accuracy < 0.5% Non-invasive, continuous, the same beam

19 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 14 Can one put the trap in the EIC beam? Very unlikely! Advantages versus CEBAF RF-driven depolarization negligible (long bunch) Problems Gas heating by radiation I b n: drop density to cm 3 Beam creates a field 2 kv/cm - a trap for positive ions; no way to clean it with a low electrical field B E Beam RF power : cell heating?

20 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 15 Jet target A.Grigoriev, EPAC 2004, VEPP-3, Novosibirsk. Proceedings of EPAC 200. VEPP ma, transverse Jet: polarized Deuterium e /cm 2 Polarization 100% Rate 6 Hz Møller BG 60 Hz from trapped ions Stat: 20% in 8 minutes e BEAM What is the electron polarization in a jet? HOLDING FIELD MAGNET ANODE WIRE WIRE CHAMBER 116 cm PLASTIC SCINTILLATOR POLARIZED JET PADS 10 cm CONVERTOR (TUNGSTEN) Y + X = Z. Figure 1: Lay-out of Møller Polarimeter with Internal Target.

Poelker et al) G0: laser running at 499/16MHz - too long to install For

21 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 16 Bunch suppression Options (from the draft of a paper by M.Poelker et al) G0: laser running at 499/16MHz - too long to install For regular bunch charges: laser at F laser < F RF bunch suppresssion on the chopper. Beat frequency condition (F RF = 499MHz): F laser (n + 1) = F RF n, n = 3, 4, 7, 15, 31,... - magic numbers regular F laser = F RF n = 15 continuous

E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 17 Beat frequency mode - leak through Pulses overlap τ pulse 200 ps @50 µa τ pulse grows with I beam (electro-repulsion)

22 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 17 Beat frequency mode - leak through Pulses overlap τ pulse 200 µa τ pulse grows with I beam (electro-repulsion) Fully open slit 110 ps No leak: τ > 160 ps Optimization n=15 same slit τ = 133 ps, contamination 5% - bad n=7 same slit τ = 285 ps, no contamination; other slit τ = 95 ps leak 30% - invasive for other halls n=4 other slit τ = 166 ps non-invasive?

23 E.Chudakov EIC, Ann Arbor, Aug 2007 Møller Polarimetry: Hall A and beyond 18 Macro-pulsing - tune beam Pulses t > 4 µs at repetition rate k 30 Hz Limitation: at I inst = 50 µa accelerator stabilization time 100 µs No micro-suppresssion: t = 1 ms at k 30 Hz Micro-suppresssion n=4: t = 1 ms at k 120 Hz

Polarimetry in Hall A

Outline E.Chudakov Moller-12 Workshop, Aug 2008 Polarimetry in Hall A 1 Polarimetry in Hall A E.Chudakov 1 1 Hall A, JLab Moller-12 Workshop, Aug 2008 Outline E.Chudakov Moller-12 Workshop, Aug 2008 Polarimetry