PENeLOPE. a UCN storage experiment with superconducting magnets for measuring the neutron lifetime

Transcription

1 PENeLOPE a UCN storage experiment with superconducting magnets for measuring the neutron lifetime by Stefan Materne, I. Altarev, B. Franke, E. Gutsmiedl, F.J. Hartmann A. Mann, A.R. Müller, J. Nitschke, S. Paul, R. Picker, R. Stoepler, C. Tietze TU München, Physik Department E18 supported by MLL, DFG and the Cluster of Excellence EXC 153

2 Outline PENeLOPE λ = g A g v Concept Design Experimental procedure proton detection losses in the storage phase u d p u e - ν e 3 He Error budget 4 He Summary and outlook W - 1 H D n 3 H n + ν e p + e - p + n D + y u d d n

3 PENeLOPE - concept Precision Experiment on Neutron Lifetime Operating with Proton Extraction Δ τ n ~ 0.1 s

4 PENeLOPE - concept Precision Experiment on Neutron Lifetime Operating with Proton Extraction Magnetic storage Δ τ n ~ 0.1 s F = -. ( μ. Β ) μ n = 60 nev/t store low-field seekers avoid wall collisions no absorption or upscattering no extrapolation needed

5 PENeLOPE - concept Precision Experiment on Neutron Lifetime Operating with Proton Extraction Magnetic storage F = -. ( μ. Β ) μ n = 60 nev/t Δ τ n ~ 0.1 s neu utrons x Proton detection second measuring principle besides neutron counting real-time measurement of decay curve counting of surviving UCN store low-field seekers avoid wall collisions no absorption or upscattering no extrapolation needed time (sec)

6 PENeLOPE - concept Precision Experiment on Neutron Lifetime Operating with Proton Extraction Magnetic storage F = -. ( μ. Β ) μ n = 60 nev/t Δ τ n ~ 0.1 s Proton detection second measuring principle besides neutron counting real-time measurement of decay curve store low-field seekers avoid wall collisions no absorption or upscattering no extrapolation needed counting of decay particles on-line

7 PENeLOPE - concept Precision Experiment on Neutron Lifetime Operating with Proton Extraction Magnetic storage F = -. ( μ. Β ) μ n = 60 nev/t Δ τ n ~ 0.1 s Proton detection second measuring principle besides neutron counting real-time measurement of decay curve store low-field seekers avoid wall collisions no absorption or upscattering no extrapolation needed Systematic studies large storage volume (~ 700 dm 3 ) next generation UCN sources expect densities of cm -3 good statistics extensive study of systematic effects Stefan Materne 7 th`workshop on UCN & CN, `09 St.Petersburg

8 PENeLOPE design 1.1 m 42 superconducting storage coils max. storage field: ~ 1.8 T storage volume

9 PENeLOPE design proton detector 1.1 m 42 superconducting storage coils max. storage field: ~ 1.8 T storage volume

10 PENeLOPE design proton detector 1.1 m 42 superconducting storage coils max. storage field: ~ 1.8 T UCN buffer volume UCN filling slit storage volume Stefan Materne 7 th`workshop on UCN & CN, `09 St.Petersburg

11 PENeLOPE design proton detector 1.1 m racetrack coils for zero-field suppression: min. storage field: > 2.8 mt adiabatic condition. Β / Β << ω Larmor 42 superconducting storage coils max. storage field: ~ 1.8 T UCN buffer volume UCN filling slit storage volume Stefan Materne 7 th`workshop on UCN & CN, `09 St.Petersburg

12 PENeLOPE design proton detector neutron absorber to remove marginally trapped neutrons 1.1 m racetrack coils for zero-field suppression: min. storage field: > 2.8 mt adiabatic condition. Β / Β << ω Larmor 42 superconducting storage coils max. storage field: ~ 1.8 T UCN buffer volume UCN filling slit storage volume Stefan Materne 7 th`workshop on UCN & CN, `09 St.Petersburg

13 PENeLOPE design cryostat, radiation shield and vacuum tank proton detector neutron absorber to remove marginally trapped neutrons 1.1 m racetrack coils for zero-field suppression: min. storage field: > 2.8 mt adiabatic condition. Β / Β << ω Larmor 42 superconducting storage coils max. storage field: ~ 1.8 T UCN buffer volume UCN filling slit storage volume Stefan Materne 7 th`workshop on UCN & CN, `09 St.Petersburg

14 PENeLOPE procedure Filling with UCN storage field switched off 100 s

15 PENeLOPE procedure Filling with UCN storage field switched off 100 s Cleaning of spectrum 100 s absorber cuts UCN spectrum at the top

16 PENeLOPE marginally trapped neutrons Marginally trapped neutrons PENeLOPE trapping potential simulations by R. Picker

17 PENeLOPE marginally trapped neutrons Marginally trapped neutrons considerably long storage times remove by ringshaped absorber

18 PENeLOPE marginally trapped neutrons Marginally trapped neutrons considerably long storage times remove by ringshaped absorber Absorber efficiency confirmed in pre-experiment AbEx cryostat + material storage bottle movable absorber ring - titanium or polyethylene - cryogenic temperatures ucn marginally trapped neutrons ucn-detector reduced to 10 ppm no effect up to Δ τ n stat ~ 0.03 s

19 PENeLOPE procedure Filling with UCN storage field switched off 100 s Cleaning of spectrum 100 s absorber cuts UCN spectrum at the top Ramping of magnets 100 s low-field seekers are confined high-field seekers escape the magnetic trap good reflection properties of storage container

20 PENeLOPE UCN heating Ramping magnetic field trapping potential ~ 110 nev heating of UCN ~ 30 nev + absorber UCN energy window of ~ 60 nev simulations by R. Picker

21 PENeLOPE magnets CoTEX (Coil Test Experiment) test: maximum field and ramp rate two coils in series with different current direction I max = A, B ~ 6.8 T 855 mm

22 PENeLOPE magnets CoTEX (Coil Test Experiment) test: maximum field and ramp rate two coils in series with different current direction I max = A, B ~ 6.8 T 855 mm 73 %

23 PENeLOPE magnets FEM calculations done by Scientific Magnetics Scientific Magnetics: Quenches caused by mechanical instabilities G-10 (fiberglass epoxy) sheet bonded to alloy plate cannot stand the stresses (introduced mainly by thermal contraction)

24 PENeLOPE procedure Filling with UCN storage field switched off 100 s Cleaning of spectrum 100 s absorber cuts UCN spectrum at the top Ramping of magnets 100 s low-field seekers are confined high-field seekers escape the magnetic trap good reflection properties of storage container Storage phase detection of protons detection of depolarized neutrons s

25 PENeLOPE proton detection Extraction magnetic field shaping focussing coils detector area reduced by 20% detector storage coils field lines

26 PENeLOPE proton detection Extraction magnetic field shaping focussing coils detector area reduced by 20% no focussing coils: - simplified setup - extraction efficiency increases by 6% detector storage coils field lines

27 PENeLOPE proton detection Extraction magnetic field shaping electrical field to optimize extraction talk by B. Franke simulations by R.Picker / B.Franke

28 PENeLOPE proton detection Detection Restrictions high magnetic field cryogenic temperature large area (3000 cm 2 ) Possible solution 1 μm CsI on plastic light guide proton signal electron ec signal suppressed readout with LAAPD LAAPD 36 segments light guide 18 cm CsI layer

29 PENeLOPE proton detection Proof of principle high light-output of CsI at low temperatures LAAPD work at low temperatures 40-keV protons detected measurements by A.Müller light output t( (arb. units) channel num mber light outp put kev gamma 2000 from Co source CsI CsJ(Tl) + Quarz CsJ + Quarz CsI(Tl) Temperature K temperature ( C)

30 PENeLOPE proton detection Disadvantages of scintillator solution light output in large-scale detector? CsI is hygroscopic post-acceleration by ~ 40 kv necessary support by n p + e - + ν e E p < 780 ev

31 PENeLOPE proton detection Disadvantages of scintillator solution light output in large-scale detector? CsI is hygroscopic post-acceleration by ~ 40 kv necessary support by n p + e - + ν e E p < 780 ev Alternatives plastic scintillator thin foil (< 20 μm) glued on lightguide non-hygroscopic matches the refractive index of the lightguide HV installations still necessary

32 PENeLOPE proton detection Disadvantages of scintillator solution light output in large-scale detector? CsI is hygroscopic post-acceleration by ~ 40 kv necessary support by n p + e - + ν e E p < 780 ev Alternatives plastic scintillator thin foil (< 20 μm) glued on lightguide non-hygroscopic matches the refractive index of the lightguide HV installations still necessary microchannel plate detectors no post-acceleration needed d poor effective area ratio < 60% large cost (1 /mm 2 ) Tectra GmbH

33 PENeLOPE procedure Filling with UCN storage field switched off 100 s Cleaning of spectrum 100 s absorber cuts UCN spectrum at the top Ramping of magnets 100 s low-field seekers are confined high-field seekers escape the magnetic trap good reflection properties of storage container Storage phase detection of protons detection of depolarized neutrons s

34 PENeLOPE spin flip Zero-field suppression with racetrack coils nominal current 10kA : B > 2.8 mt Monte Carlo simulations by R. Picker

35 PENeLOPE spin flip Zero-field suppression with racetrack coils nominal current 10kA : B > 2.8 mt Monte Carlo simulations by R. Picker losses by spin-flip Δτ n < s

36 PENeLOPE losses on restgas Vacuum restrictions UCN losses by elastic (up-)scattering absorption Δτ (s) p(mbar)

37 PENeLOPE procedure Filling with UCN storage field switched off 100 s Cleaning of spectrum 100 s absorber cuts UCN spectrum at the top Ramping of magnets 100 s low-field seekers are confined high-field seekers escape the magnetic trap good reflection properties of storage container Storage phase detection of protons detection of depolarized neutrons Ramping down s 100 s emptying py and detection of surviving neutrons Stefan Materne 7 th`workshop on UCN & CN, `09 St.Petersburg

38 PENeLOPE precision goal Statistics PSI and FRM II sources ~ UCNs statistics (after 10 days) Δτ n ~ 0.07 s Δ τ n ~ 0.1 s n

39 PENeLOPE precision goal Statistics PSI and FRM II sources ~ UCNs statistics (after 10 days) Δτ n ~ 0.07 s and systematics spin-flip marginally trapped neutrons < s < 0.03 s Δ τ n ~ 0.1 s scattering on restgas < s proton detection efficiency!< 0.01 s every time dependant effect

40 PENeLOPE outlook A look into the future magnets funded by DFG detailed magnet design started will be finished first quarter 2010 incorporates new prototype test coil construction will start right after proton detector R&D enforced ILL this autumn proton detector tests storage volume coating tests

41 THANK YOU FOR YOUR ATTENTION!

42 PENeLOPE proton detection Simulation light output t 5000 photons, random direction simulations by A.Müller

43 PENeLOPE proton detection PENeLOPE LAAPD performance peak position of kev line from 55 Fe

44 PENeLOPE proton detection PENeLOPE paff Intensity [a.u.] 0,010 0,008 0,006 0,004 0,002 0, kev 12 kev 14 kev 16 kev 18 kev 20 kev 22 kev 24 kev 26 kev 28 kev 30 kev 32 kev Ekin[keV]

45 PENeLOPE scattering on restgas Elastic (up-) scattering UCN velocity τ -1 = σ * v UCN * n T cross section target density n = p (kt) -1 constant cross-section σ Η2 scatt= 2*80 barn convolution with Maxwell velocity distribution of target particles (K.-H. Beckurts, K. Wirtz, Neutron Physics, Springer, Berlin, 1964) σ(e( n n) = σ scatt β -2 π -1/2 ψ(β) ) β 2 = A E n (kt) -1 ψ(β) = 1 / 2 β exp(β 2 ) +(2β 2 +1) π 1/2 erf(β) UCN

46 PENeLOPE scattering on restgas Elastic (up-) scattering UCN velocity τ -1 = σ * v UCN * n T cross section target density n = p (kt) -1 constant cross-section σ Η2 scatt= 2*80 barn convolution with Maxwell velocity distribution of target particles (K.-H. Beckurts, K. Wirtz, Neutron Physics, Springer, Berlin, 1964) σ(e( n n) = σ scatt β -2 π -1/2 ψ(β) ) β 2 = A E n (kt) -1 ψ(β) = 1 / 2 β exp(β 2 ) +(2β 2 +1) π 1/2 erf(β) UCN Atchison et al. PRL 94, (2005)

47 PENeLOPE absorption on restgas Absorption UCN velocity τ -1 = σ * v UCN * n T cross section target density n = p (kt) -1 cross-section σ abs (v th = 2200 m / s ) = 0.3 barn (H); 1.9 barn (N) scale σ according to 1/v and average over Maxwell velocity distribution of restgas molecules <σ abs > = <σ th abs v th /v > = σ th abs v th <1/v> = 4 π σ th abs v th p/kt

48 PENeLOPE statistics UCN FRM II (rough estimation) UCN density ρ = Φ V t 0 - e ( t-t ) τ dt

49 PENeLOPE statistics UCN FRM II (rough estimation) flux Φ ~ s -1 ( 100 nev < E UCN < 160 nev) UCN density ρ = storage volume Φ V t 0 - e filling time ( t-t ) τ lifetime dt τ -1 = τ n -1 + τ losses -1 ~ 5 s τ -1 + τ -1 abs slits

50 PENeLOPE statistics UCN FRM II (rough estimation) flux Φ ~ s -1 ( 100 nev < E UCN < 160 nev) UCN density ρ = storage volume Φ V t 0 - e filling time ( t-t ) τ lifetime dt T d transmission over length d ½ τ -1 = τ n -1 + τ losses -1 ~ 5 s spin polarization τ abs -1 + τ slits -1 abs slits

51 PENeLOPE statistics UCN FRM II (rough estimation) t ( t-t ) Φ - UCN density ρ = e τ dt T V d ½ 0 #UCN Filling time t(sec)

52 PENeLOPE statistics UCN FRM II (rough estimation) Flux balance Φ = 1/4 ρ v Α ρ(t) V dρ/dτ d = Φ Φ = 1 / 4 vα (ρ 0 ρ(t)) φ ρ 0 A

53 PENeLOPE statistics UCN FRM II (rough estimation) Flux balance Φ = 1/4 ρ v Α φ ρ(t) ρ 0 A #UCN V dρ/dτ d = Φ Φ = 1 / 4 vα (ρ 0 ρ(t)) 1 /τ ρ V losses τ -1 = τ -1-1 n + τ abs Filling time t(sec)

54 PENeLOPE marginally trapped neutrons Marginally trapped neutrons removed by Absorber ABSORBER

55 PENeLOPE marginally trapped neutrons Polyethylene Absorber 120 RT Abs 751 mm RT Abs 551 mm RT Abs 351 mm lhe Abs 751 mm lhe Abs 551 mm lhe Abs 351 mm ln2 Abs 751 mm ln2 Abs 551 mm ln2 Abs 351 mm room temperature LHe (4K) LN 2 (77K) τ st [s] mm 551 mm 751 mm U height [mm]

56 PENeLOPE marginally trapped neutrons Proton extraction focusing coils no focusing coils

57 PENeLOPE magnets Test coils Temperature Lower coil sensors Upper coil sensors

58 PENeLOPE magnets Ramp rate 25A/s V

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