Possibilities for a polarized (frozen spin) target for the WASA detector

Transcription

1 Possibilities for a polarized (frozen spin) target for the WASA detector Hartmut Dutz, A. Raccanelli Physikalisches Institut Universität Bonn FEMC04 Jülich 1

2 Possibilities for a polarized (frozen spin) target for the WASA detector General aspects Polarized Target Status Large Acceptance Frozen Spin Target (LAFST) Results Limitations New concepts Summary FEMC04 Jülich 2

3 counting rate: dσ N = L Ω dω luminosity : General aspects dσ : cross section dω Ω : angular acceptance Luminosity L L = I n t [ cm ] 2 sec 1 n t : areal target density L [ cm ] 2 sec 1 FEMC04 Jülich 3

4 Figure of Merit General aspects Figure of Merit Measurement of a polarization observable A Pure target material (no background nucleons) s r N N A = 1 P t : target polarization s r P N + N N s, N r : counting rate quality factor f = F target A = 1 P t t polarizable nucleons total number of nucleons 1 f s N s N 2 2 = L P t ft r N r + N 1 measuring time FEMC04 Jülich 4

5 The Polarized Target - Status optimize : P, f, n, Ω Vector polarization in thermal equilibrium : P12 / = tanh µ B kt strong magnetic field (B = 2,5 Tesla) low temperatures (T 1 Kelvin) P p 0,25% P e 100% ideal target material : H 2 non polarizable (paramodification) FEMC04 Jülich 5

6 The Polarized Target - Status Dynamic Nukleon Polarization (DNP) [Overhauser 1953] aim : P elektron P proton/deuteron dipol-dipol-i P Elektronen (>90%) P Protonen (<0.5%) coupling : microwaves DNP proton polarization P p 100% deuteron polarization P d 80% (new) target material + paramagnetic centers 6 LiD, NH 3, ND 3, alcohols target material reasearch : PT Bochum: W.Meyer, St. Goertz FEMC04 Jülich 6

7 The Polarized Target - Status the components of the target continuous mode target FEMC04 Jülich 7

8 The Polarized Target (LAFST) Large Acceptance Frozen Spin Target for GDH sum rule I GDH p dν = σ 3 ν 0 2 σ 1 2 Longitudinal polarized nucleons Circular polarized tagged photons (10 7 γ/s) large angular acceptance Ω 4π (p-direction, reaction) system integrability FEMC04 Jülich 8

9 The Polarized Target (LAFST) DAPHNE - detector FEMC04 Jülich 9

10 The Polarized Target (LAFST) Crystal Barrel detector FEMC04 Jülich 10

11 The Polarized Target (LAFST) WASA detector FEMC04 Jülich 11

12 The Polarized Target (LAFST) Large acceptance frozen spin target DAPHNE / CB-detector polarized γ- beam idea : horizontal cryosystem + nonexisting magnet system Longitudinal polarization vector FEMC04 Jülich 12

13 The Polarized Target (LAFST) GDH : longitudinal polarization, large acceptance T P 300 mk, Q = 48 mw, B P = 2.5 T, µ-waves = 70 GHz proton P p 90 %, deuteron P d 75 % horizontal 3 He/ 4 He-dilutionkryostat superconducting polarization magnet B max = 6.5 Tesla Target beam line polarization vector longitudinal in the scattering plane continuous mode target polarized target with a limited angular acceptance problem : magnet FEMC04 Jülich 13

14 The Polarized Target (LAFST) turn of DNP (mikrowave of) nucleon-relaxation time τ 1n 1 τ 1n 2 ω B e kt B e e low temperatures T 70 mk reduction of the magnetic field in the target region (holding field) Relaxationszeit [Tage] 10 1 Pentanol 45mK Butanol 55mK Ammoniak 70mK Butanol 64mK Butanol 73mK Butanol 86mK 'frozen spin mode' Ammoniak 250mK T 70 mk N γ 10 8 /s Haltefeld [Tesla] FEMC04 Jülich 14

15 The Polarized Target (LAFST) holding coil β NI 2 1+ β B h 0.2*Bp small and compact target region solving the problem : replacing the polarizing magnet superconducting solenoid integrated into the dilution cryostat FEMC04 Jülich 15

16 The Polarized Target (LAFST) current leads copper carrier superconducting coil Headexchanger tube NbTi-wire : 100µm 44 mm, l = 120 mm, N = 4000 d = 0.7mm internal holding coil developed at Bonn NIM A 356 (1995) reliable operation B h = A, T < 1.2 K FEMC04 Jülich 16

17 The Polarized Target (LAFST) frozen spin mode (data taking) internal holding coil target beam horizontal dilution cryostat T fsm 55 mk, B h = T, τ 1n 250 h DAPHNE - detector first Frozen Spin Target for 4π - particle detection acceptance : φ - symmetric, ϑ ± 165 max. beam intensity : 10 8 γ/s FEMC04 Jülich 17

18 A2 - experimental area (MAMI) Large acceptance target system requires dedicated railway system FEMC04 Jülich 18

19 The Polarized Target - Results Polarization behaviour of butanol (protons) polarization [%] τ = 43 min τ = 177 min τ = 143 min Mainz '98 Bonn '01 P MZ = 87.7 % ± 1.3% P BN = 83.4 % ± 1.1% time [hours] FEMC04 Jülich 19

20 The Polarized Target - Results Relaxation times of butanol (protons) Relaxation time [days] 14 Mainz '98 τ ~ 200 h Bonn 'Sep.01' 12 Bonn 'Jun.01' Bonn 'Jan.01' B H = T P P MZ BN = 65.2% = 57.3% Temperature [mk] FEMC04 Jülich 20

21 The Polarized Target - Results Polarization behaviour of d - butanol (neutrons) Mainz d-run 2003 D-butanol (trityl-complex) D-butanol (porphyrexide) d-polarization [%] Pmax 73 % τ 185 h Time [h] FEMC04 Jülich 21

22 LAFST - limitations limitations of the frozen spin principle Frozen Spin Target : good angular acceptance (~ 4π) moderate luminosity L ~ /cm²s (N 10 8 /s) moderate mean polarization moderate beam time efficiency Railway system to move magnet/detector continuous mode target : bad angular acceptance (#msrad) high luminosity L ~ /cm²s (N /s) high mean polarization good beam time efficiency fixed target/detector system Scope : combine both concepts 4π - continuous mode target : good angular acceptance (~ 4π) high luminosity L ~ /cm²s (N /s) high mean polarization good beam time efficiency fixed installation FEMC04 Jülich 22

23 New concepts 4π continuous mode target liquid helium from the still target internal superconducting 'holding coil internal polarizing magnet beam 60 mm 100 mm 44 mm, l ~ 160 mm, d 1.5 mm goal : B p ~ 2.5 Tesla, B/B ~ 10-4 FEMC04 Jülich 23

24 New concepts 4π continuous mode target wire- : 0.2 mm N = 2032 thickness of the coil : 1.33 mm B max = 1.5 I N = K in the GDH cryostat : I max ~ 40 A B max ~ 0.8 Tesla Problem :current leads (cryostat design!!!) FEMC04 Jülich 24

25 New concepts 4π continuous mode target 70 Polarization 1.8 T Polarization [%] GHz Pmax ~ 65% 70% Time [hours] FOM ~ frozen spin target FEMC04 Jülich 25

26 New concepts 4π continuous mode target new horizontal dilution cryostat with a variable internal magnet system design studies nearly completed combined 4 He evaporation, 3 He/ 4 He dilution refrigerator FEMC04 Jülich 26

27 conclusions frozen spin target with internal holding coil : ideal experimental tool for low intensity particle beams 4 π - angular acceptance railway system required new 4π continuous mode - target with an integrated polarizing magnet opens a new field of polarization experiments high luminosity large FOM (~ /cm²sec²) 4 π angular acceptance fixed target/detector combination electron scattering in a 4π - detector (CB - detector) Polarized solid state target reliable tool for (double) polarization experiments standard system for external beam scattering experiments total costs for a complete new facility : ca k invest. + personal FEMC04 Jülich 27