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Technische Universität München
PENeLOPE (Precision Experiment on the Neutron Lifetime Operating on Proton Extraction) D. Gaisbauera, W. Gebauera, E. Gutsmiedla, F. Haasa, F.J. Hartmanna, M. Losekamma, D. Margiottaa, S. Maternea, J. Nitschkea, S. Paula, R. Pickerb, D. Renkera, T. Pöschla, S. Rittc, W. Schreyera, A. Senfta, D. Steffena, R. Stoeplera, C. Tietzea, F. Wiesta aTechnische Universität München, Physik Department, Germany bCalifornia Institute of Technology, Pasadena, USA cPaul Scherrer Institut, CH-5323 Villigen, Switzerland
Technische Universität München Outline
• short history • PENeLOPE design • hot topics
• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring • uniformity of detectors
• Status • Conclusions
10.11.2012 2 Physik Department E18
Technische Universität München
rSolenoid = 10 cm, zSolenoid = ± 50 cm, .
History of the experiment
• idea came to Munich with S. Paul in 1997
• different topologies were studied:
– Ioffe type trap: current bars dodekapol + 2 solenoids
– U shaped multipole – ca 2001: large permanent magnet
trap, multipole in z-direction
Physik Department E18 3
perm. magnets
iron
Technische Universität München History of the experiment
• idea came to Munich with S. Paul in 1997
• different topologies were studied:
– Ioffe type trap: current bars dodekapol + 2 solenoids
– U shaped multipole – ca 2001: large permanent magnet
trap, multipole in z-direction
• 2003: superconducting multipole in z-direction, 2 nested cylinders
1.2
m
Technische Universität München Outline
• short history • PENeLOPE design • hot topics
• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring • uniformity of detectors
• Status • Conclusions
10.11.2012 5 Physik Department E18
Technische Universität München PENeLOPE layout
11 inner solenoids protect center current
13 outer solenoids radial confinement
4 bottom solenoids lower confinement
• 28 superconducting coils
2 m
Precision Experiment on Neutron Lifetime Operating with Proton Extraction
Technische Universität München PENeLOPE layout
11 inner solenoids protect center current
13 outer solenoids radial confinement
4 bottom solenoids lower confinement
• 28 superconducting coils
2 m
Technische Universität München PENeLOPE layout
11 inner solenoids protect center current
13 outer solenoids radial confinement
4 bottom solenoids lower confinement
• 28 superconducting coils
2 m
Technische Universität München PENeLOPE layout
11 inner solenoids protect center current
13 outer solenoids radial confinement
4 bottom solenoids lower confinement
• 28 superconducting coils • storage volume 400 dm3
2 m
Technische Universität München PENeLOPE layout
11 inner solenoids protect center current
13 outer solenoids radial confinement
4 bottom solenoids lower confinement
• 28 superconducting coils • storage volume 400 dm3
• decay particle detector 20 dm2
detector for decay particles
2 m
Technische Universität München PENeLOPE layout
11 inner solenoids protect center current
13 outer solenoids radial confinement
4 bottom solenoids lower confinement
• 28 superconducting coils • storage volume 400 dm3
• decay particle detector 20 dm2
2 m
detector for decay particles
Technische Universität München PENeLOPE layout
11 inner solenoids protect center current
13 outer solenoids radial confinement
4 bottom solenoids lower confinement
• 28 superconducting coils • storage volume 400 dm3
• decay particle detector 20 dm2
detector for decay particles
neutron filling while magnet is off
2 m
Technische Universität München PENeLOPE layout
11 inner solenoids protect center current
13 outer solenoids radial confinement
4 bottom solenoids lower confinement
• 28 superconducting coils • storage volume 400 dm3
• decay particle detector 20 dm2
detector for decay particles
He cryostat for superconductivity
lN2 shield heat radiation shield
vacuum vessel
neutron filling
2 m
Technische Universität München Outline
• short history • PENeLOPE design • hot topics
• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring • uniformity of detectors
• Blind analysis • Status • Conclusions
10.11.2012 14 Physik Department E18
Technische Universität München Phase space evolution
• UCN are filled in while magnet is off • material storage period >150 s
– 3 wall bounces per second – assuming 5 % diffuse reflection – probability of non diffuse storage < 10-13
⇒ phase space is randomized
• then the magnets are ramped and the phase space goes crazy...
Technische Universität München Ramping from 0 to full current
Low-field seekers Bnn ⋅+⋅= µzgmU
Technische Universität München Low-field seeker (LFS) heating
Bnn ⋅+⋅= µzgmU
© Wolfgang Schreyer
heating of LFS by around 30 neV
trap depth
absorber
Technische Universität München PENeLOPE layout
11 inner solenoids protect center current
13 outer solenoids radial confinement
4 bottom solenoids lower confinement
warm bore for central current
to avoid |B|=0
• 28 superconducting coils • storage volume 400 dm3
• decay particle detector 20 dm2
• absorbers to clean spectrum
detector for decay particles
He cryostat for superconductivity
lN2 shield heat radiation shield
vacuum vessel
neutron filling
2 m
n absorbing rings spectrum cleaning
Technische Universität München
abso
rber
Spectrum cleaning
• pre-experiment AbEx proved absorber principle
• efficient cleaning to keep high statistics: – long storage lifetime for
trapped UCN – short storage lifetime for
marginally trapped UCN
UCN storage and
absorber experiment AbEx @ ILL 2006/2007
abso
rber
1.2
m
Technische Universität München
Total potential for UCN:
High-field seekers (HFS)
Bnn ⋅−⋅= µzgmU
Technische Universität München High-field seekers
© Wolfgang Schreyer
cooling of HFS by nearly 200 neV
Bnn ⋅−⋅= µzgmU
Technische Universität München Neutron distribution
© Wolfgang Schreyer
• LFS and HFS are almost completely separated
• move absorber down during first phase of magnetic storage
Technische Universität München High-field seeker cleaning
© Wolfgang Schreyer
• lifetime of HFS much longer than thought
⇒ move absorber down
Technische Universität München Neutron distribution
© Wolfgang Schreyer
• LFS and HFS are almost completely separated
• move absorber down • need 80 % polarized UCN
beam time at ILL 2013
Technische Universität München Experiment phases (1) Magnet off, filling in neutrons
(200 s) (2) spectrum cleaning
(160 s) (3) ramping up magnet
(50-200 s) (4) cleaning high-field seekers
(ca 100 s)
E: 0-115 neV magnets on filling tube closed detector open
low- and high-field seekers
det z
[m]
r [m]
Technische Universität München Outline
• short history • PENeLOPE design • hot topics
• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring • uniformity of detectors
• Blind analysis • Status • Conclusions
10.11.2012 26 Physik Department E18
Technische Universität München PENeLOPE layout
11 inner solenoids protect center current
13 outer solenoids radial confinement
4 bottom solenoids lower confinement
• 28 superconducting coils • storage volume 400 dm3
• decay particle detector 20 dm2
• absorbers to clean spectrum
detector for decay particles
He cryostat for superconductivity
lN2 shield heat radiation shield
vacuum vessel
neutron filling
2 m
IC
zero field regions
Technische Universität München Spin flip suppression
11 inner solenoids protect center current
13 outer solenoids radial confinement
4 bottom solenoids lower confinement
warm bore for central current
to avoid |B|=0
• 28 superconducting coils • storage volume 400 dm3
• decay particle detector 20 dm2
• absorbers to clean spectrum
detector for decay particles
He cryostat for superconductivity
lN2 shield heat radiation shield
vacuum vessel
neutron filling
2 m
IC 𝜔𝐿 ≫�̇��𝑈𝑈𝑈𝑩
Technische Universität München Spin flip suppression
• spin flip: – systematic studies possible varying the central current – around 2-3 % of dep. UCN reach UCN detector MC simulations: – spin-flip loss time τSF > 109 s – systematic effect: ∆τn < 0.01 s
S. Materne, R.P. et al., NIM A 611, (2009).
d𝑺d𝑡
= 𝝎 × 𝑩
Technische Universität München Outline
• short history • PENeLOPE design • hot topics
• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring • uniformity of detectors
• Blind analysis • Status • Conclusions
10.11.2012 30 Physik Department E18
Technische Universität München UCN heating
??? vibrations
microphonics
clusters
field ripple
normal modes
acoustics
quasi-elastic scattering
my opinion: to many unknowns to make reliable predictions, need to check experimentally
Technische Universität München Outline
• short history • PENeLOPE design • hot topics
• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring • uniformity of detectors
• Blind analysis • Status • Conclusions
10.11.2012 32 Physik Department E18
Technische Universität München Cascade-U detector
• commercially available development of Uni Heidelberg
• 100 x 100 mm2
• efficiency 90 % • rate capability 107 n/s • no gamma background (low Z) • integrated electronics
Ar/CO2
http://n-cdt.com/assets/CASCADE-U-100-Detector-System.pdf
Technische Universität München Outline
• short history • PENeLOPE design • hot topics
• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring / decay particle detection • uniformity of detectors
• Blind analysis • Status • Conclusions
10.11.2012 34 Physik Department E18
Technische Universität München Electrons or protons ???
35
𝐸𝑝 < 750 𝑒𝑒 𝐸𝑒 < 780 𝑘𝑒𝑒
⇒ electrostatic manipulation of p possible ⇒ detector on HV ⇒ electrons are repelled by magnetic mirror effect
30 kV
Electrons protons
collection efficiency: 35 % 70 %
z [m
]
r [m]
Technische Universität München Particle detection
• requirements on proton detector – low energy < 30 keV – low temperature < 77 K – large area > 0.2 m2
– strong magnetic field > 0.5 T – high vacuum < 2 x 10-8 mbar – affordable << magnet costs
• various concepts were explored – thin pure CsI + APD columnar structure – bulk CsI + APC light at APD marginal – gas detector gas diffusion to high – MCPs not stable enough – direct APD detection bingo! – bulk CsI + SiPM very hip these days, under investigation
Technische Universität München Avalanche Photodiodes
15.03.2012
• Reverse-biased p-n-junction • Primary photo electron
accelerated in electric field and multiplied in an avalanche
• large gain, but proportional • Operable at large magnetic field
and low temperature (~77K)
37
5 mm
Technische Universität München APD as direct Proton Sensor
15.03.2012 38
• several hundreds of electron-hole pairs are produced • illumination with 30 keV protons from “paff”-accelerator at 77K
© Christian Tietze
Technische Universität München APD as direct Proton Sensor
15.03.2012 39
• several hundreds of electron-hole pairs are produced • illumination with 30 keV protons from “paff”-accelerator • even 5 keV protons can be observed • costs are pretty steep • >1000 channels
© Christian Tietze
Technische Universität München Outline
• short history • PENeLOPE design • hot topics
• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring • uniformity/stability of detectors
• Blind analysis • Status • Conclusions
10.11.2012 40 Physik Department E18
Technische Universität München Detector uniformity/stability
• proton flux is not constant over the detector area
• 2000 individual APDs make gain control and stabilization mandatory
• grouping APDs for similar bias voltage
• LED system or in-situ radioactive source
Technische Universität München Outline
• short history • PENeLOPE design • hot topics
• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring • uniformity of detectors
• Blind analysis • Status • Conclusions
10.11.2012 42 Physik Department E18
Technische Universität München Blind Analysis
Proton detection • real raw ADC data will be
recorded and stored • signal shape analysis:
pulse height is determined and timing info scaled (blinded) in software and stored
• this reduced data is used for analysis
Pro • raw data is unspoiled Con • some honor code is
necessary
UCN detection • ideal storage times will be
determined with real data during commisioning phase
• for physics run, storage times will be randomized around ideal ones
• Markov chains could be used Pro • if storage times were fixed, a
human analyzer would remember them
Con • slight loss of statistical
efficiency possible
Technische Universität München Outline
• short history • PENeLOPE design • hot topics
• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring • uniformity of detectors
• Blind analysis • Status • Conclusions
10.11.2012 44 Physik Department E18
Technische Universität München Status
• 2004 - physics solution for magnet found • 2007 - first prototype coil tested: partial failure... • after further setbacks: change of contractor 2009
Technische Universität München Coil revision 2010
- topology unchanged - bigger coil distances - less coils 44 ⇒ 28 - max. field in conductor 6.1 ⇒ 5.5 T
- storage potential 74 ⇒ 115 neV - proton collection 70 ⇒ 68 % - detector size 0.3 ⇒ 0.23 m2
- central current in warm bore
6 T 5.5 T 5 T 4.5 T
4 T 3.5 T 3 T 2.38 T
5.6 T 5 T
4 T
3 T
2 T
1 T 0 T
old new
Technische Universität München Status
• Change of contractor 2009 • Coil prototype test this year
Technische Universität München
3 m
Coil test facility
• New test facility “CoTEx 2.0“ to train and test all coils
• He liquefier + 36 kW power supply
1.7 m
Technische Universität München Coil test facility
• New test facility “CoTEx 2.0“ to train and test all coils
• He liquefier + 36 kW power supply
• First prototype coil exceeded nominal current by 20 %
• if coils are not treated gently ⇒ retraining
56 cm
Technische Universität München Status
• Change of contractor 2009 • Coil prototype test successful • Final engineering (incl workshop drawings) finishing 2012 • first-of-series coils shall ship this year • commissioning 2014 ?!? where?
Technische Universität München Outline
• short history • PENeLOPE design • hot topics
• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring • uniformity of detectors
• Blind analysis • Status • Conclusions – almost...?
10.11.2012 51 Physik Department E18
Technische Universität München Not touched...
• very nice, versatile UCN MC code n,p,e,spin tracking, 8th order Runge-Kutta, CAD import
• imperfections in mag. trap coil winding causes bumps, which are relevant
• rest gas interaction < 10-8 mbar needed for ∆τn<0.1 s
• statistics 30 days of beamtime for ∆τn<0.1 s
Technische Universität München
use MC simulations to learn about all possible effects in the experiment first
optimize it so that zero to minimal corrections (possibly through MC) are necessary
but many systematical studies needed for a credible 0.1 s measurement
new high-density (large flux) UCN sources desperately needed (37 days for 0.1 s statistical if FRM2 projections hold)
if new sources will not deliver, probing all possible systematics almost impossible
PENeLOPE conclusions
low-field seekers, high-field seekers, protons, electrons during storage period in PENeLOPE (r-z projection)
z r
Technische Universität München Statistics
source flux (FRMII) 107 UCN/s
energy window 70 neV
polarized UCN in trap (results full MC including source, guides, slits etc)
107 UCN
proton collection/detection efficiency 60 % / 40 %
neutron collection/detection efficiency 70 % / 90 %
material storage lifetime 350 s
filling / cleaning / ramping / HFS cleaning time
200 s / 200 s / 100 s / 160 s
storage times 1000 s / 3000 s / 5000 s / 8000 s
# of cycles necessary to reach 0.1 s in both detection schemes
610
time necessary 37 days
⇒ BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
NLFS: number of low field seekers - fM: fraction of marginal UCN - τn: beta decay lifetime -τM: storage lifetime of marginal UCN NHFS: number of high-field seekers - τHFS: storage lifetime of HFS - B: const background
Technische Universität München Chaos in the (magnetic) house?
10.11.2012 Physik Department E18 55
Instability of UCN tracks – physics or numerics?
∆𝑧 = 10−17m, 𝑡 = 30s ∆𝑧 = 10−17m, 𝑡 = 0.7s
Technische Universität München Chaos in the (magnetic) house?
10.11.2012 Physik Department E18 56
Instability of UCN tracks – physics or numerics?
∆𝑧 = 10−17m, 𝑡 = 30s ∆𝑧 = 10−17m, 𝑡 = 0.7s
Technische Universität München Chaos in the (magnetic) house?
10.11.2012 Physik Department E18 57
Instability of UCN tracks – physics or numerics?
∆𝑧 = 10−17m, 𝑡 = 30s ∆𝑧 = 10−17m, 𝑡 = 30s
Technische Universität München Chaos in the (magnetic) house?
10.11.2012 Physik Department E18 58
Instability of UCN tracks – physics or numerics?
∆𝑧 = 10−17m, 𝑡 = 30s
⇒
Technische Universität München Rest gas interaction
• rest gas interaction: – for efficient proton collection: p < 10-7 mbar – n absorption (nitrogen) and upscattering (hydrogen): p < 3 · 10-8 mbar – mass spectrometry to examine partial pressures
H2 partial pressure
⇒
Technische Universität München Experiment phases (1) Magnet off, filling in polarized
neutrons (200 s)
storage volume
UC
N guide
r-z plot x-y-z plot
detector for decay particles
n absorbing rings spectrum cleaning
Technische Universität München Experiment phases (1) Magnet off, filling in neutrons
(200 s) (2) spectrum cleaning
(160 s) (3) ramping up magnet
(50-200 s) (4) cleaning high-field seekers
(ca 100 s) (5) neutron storage, counting
of protons and depolarised UCN (up to 8000 s)
E: 0-115 neV magnets on filling tube closed detector open protons: 106 x slower electron: 109 x slower
low-field seekers, high-field seekers, protons, electrons
Technische Universität München Exp. phases: 5 - ramp-down, UCN counting
(1) Magnet off, filling in neutrons (100 s)
(2) spectrum cleaning (160 s)
(3) ramping up magnet (50-200 s)
(4) cleaning high-field seekers (ca 100 s)
(5) neutron storage, counting of protons and depolarised UCN (up to 3000 s)
(6) ramping down magnet (50-200 s)
(7) UCN counting (250 s)
neutron counting collection efficiency around 75 %
E: 0-108 neV ramping down in 10 s filling tube closed detector open
storage volume
UC
N guide
Technische Universität München Systematic effects
• spin flip: – around 5 % of dep. UCN reach UCN detector – spin-flip lifetime τSF > 109 s systematic effect: ∆τn < 0.01 s
• UCN energy distribution – proton collection efficiency is space- and energy dependent – time-evolving effects may change efficiencies – not expected, but may be examined through energy shaping:
• absorber movable • magnetic trap depth adjustable • “U” before experiment
Technische Universität München AbEx Design
energy selector (rotatable“U” tube)
UCN detector (3He)
UCN Absorber (Polyethylen & titanium)
n-storage vessel (He cryostat) (electropolished stainless steel)
Is our absorber design capable of removing high energy neutrons
sufficently?
⇒ test of different absorber materials down to temperatures of 10 K ⇒ energie selective measurement
UCN valves
10.11.2012 Physik Department E18 64
„UCN plug“
Technische Universität München Statistical experiment simulation
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
NLFS: number of low field seekers fM: fraction of marginal UCN τn: beta decay lifetime τM: storage lifetime of marginal UCN NHFS: number of high-field seekers τHFS: storage lifetime of HFS B: const background
Technische Universität München High-field seeker cleaning II
• influence of waiting time on measured lifetime???
• proton detector sees lower storage time of high-field seekers
• Why not neutron detector?
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
( ) BNNN st
LFSs
ts
t
LFS +⋅⋅+
⋅+= 1064404-880 e125.0e10 e(t)
measured neutron lifetime for fixed absorber
NLFS: number of low field seekers fM: fraction of marginal UCN τn: beta decay lifetime τM: storage lifetime of marginal UCN NHFS: number of high-field seekers τHFS: storage lifetime of HFS B: const background
Technische Universität München High-field seeker cleaning III
• lower absorber during first seconds of storage time
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
( ) BNNN st
LFSs
ts
t
LFS +⋅⋅+
⋅+= 1064404-880 e125.0e10 e(t)
measured neutron lifetime for fixed absorber
Technische Universität München High-field seeker cleaning III
• lower absorber during first seconds of storage time
• reduce HFS by factor of 20
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
( ) BNNN st
LFSs
ts
t
LFS +⋅⋅⋅+
⋅+= − 10834404-880 e104.2e10 e(t)
measured neutron lifetime for lowered absorber
Technische Universität München High-field seeker cleaning III
• lower absorber during first seconds of storage time
• reduce HFS by factor of 20
⇒ better, but not good enough
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
measured neutron lifetime for lowered absorber
Technische Universität München High-field seeker cleaning III
• lower absorber during first seconds of storage time
• reduce HFS by factor of 20
⇒ better, but not good enough
⇒ spin filter is needed ⇒ 90 % polarization is
enough
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
measured neutron lifetime for lowered abs + spin filter
( ) BNNN st
LFSs
ts
t
LFS +⋅⋅⋅+
⋅+= − 10844404-880 e104.2e10 e(t)
Technische Universität München High-field seeker cleaning III
• lower absorber during first seconds of storage time
• reduce HFS by factor of 20
⇒ better, but not good enough
⇒ spin filter is needed ⇒ 90 % polarization is
enough
BNNN HFSMn
t
HFS
tt
LFS ++
⋅+= τττ eef )ef-(1(t) MM
( ) BNNN st
LFSs
ts
t
LFS +⋅⋅⋅+
⋅+= − 10844404-880 e104.2e10 e(t)
measured neutron lifetime for lowered abs + spin filter
Technische Universität München Coil bumpiness... consequences
© Wolfgang
⇒
Technische Universität München Heating and cooling
© Wolfgang
LFS
HFS