PENeLOPE - Nc State Universityneutron.physics.ncsu.edu/LifetimeWorkshop/talks/Picker.pdf · PENeLOPE layout . 11 inner solenoids . protect center current . 13 outer solenoids . radial

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


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




• Status • Conclusions


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






2 m






2 m





• 28 superconducting coils • storage volume 400 dm3

2 m






• decay particle detector 20 dm2

detector for decay particles

2 m







2 m









neutron filling while magnet is off

2 m








He cryostat for superconductivity

lN2 shield heat radiation shield

vacuum vessel

neutron filling

2 m




• Blind analysis • Status • Conclusions


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





warm bore for central current

to avoid |B|=0



• absorbers to clean spectrum




vacuum vessel

neutron filling

2 m

n absorbing rings spectrum cleaning


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


Total potential for UCN:

High-field seekers (HFS)

Bnn ⋅−⋅= µzgmU

Technische Universität München High-field seekers


cooling of HFS by nearly 200 neV

Bnn ⋅−⋅= µzgmU

Technische Universität München Neutron distribution


• LFS and HFS are almost completely separated

• move absorber down during first phase of magnetic storage

Technische Universität München High-field seeker cleaning


• lifetime of HFS much longer than thought

⇒ move absorber down

Technische Universität München Neutron distribution


• 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]
















vacuum vessel

neutron filling

2 m

IC

zero field regions

Technische Universität München Spin flip suppression




warm bore for central current

to avoid |B|=0







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 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 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



• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring / decay particle detection • uniformity of detectors



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



• phase space evolution • marginal trapping • chaos • spin-flip losses • UCN heating • UCN detection • relative monitoring • uniformity/stability of detectors



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 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 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


• Change of contractor 2009 • Coil prototype test this year


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


• 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?




• Blind analysis • Status • Conclusions – almost...?


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


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




∆𝑧 = 10−17m, 𝑡 = 30s ∆𝑧 = 10−17m, 𝑡 = 0.7s




∆𝑧 = 10−17m, 𝑡 = 30s ∆𝑧 = 10−17m, 𝑡 = 30s




∆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


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


„UCN plug“

Technische Universität München Statistical experiment simulation

BNNN HFSMn

t

HFS

tt

LFS ++


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 ++


( ) 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 ++


( ) BNNN st

LFSs

ts

t

LFS +⋅⋅+

⋅+= 1064404-880 e125.0e10 e(t)

measured neutron lifetime for fixed absorber



• reduce HFS by factor of 20

BNNN HFSMn

t

HFS

tt

LFS ++


( ) BNNN st

LFSs

ts

t

LFS +⋅⋅⋅+

⋅+= − 10834404-880 e104.2e10 e(t)

measured neutron lifetime for lowered absorber




⇒ better, but not good enough

BNNN HFSMn

t

HFS

tt

LFS ++


measured neutron lifetime for lowered absorber





⇒ spin filter is needed ⇒ 90 % polarization is

enough

BNNN HFSMn

t

HFS

tt

LFS ++


measured neutron lifetime for lowered abs + spin filter

( ) BNNN st

LFSs

ts

t

LFS +⋅⋅⋅+

⋅+= − 10844404-880 e104.2e10 e(t)





⇒ spin filter is needed ⇒ 90 % polarization is

enough

BNNN HFSMn

t

HFS

tt

LFS ++


( ) 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

Documents

PENeLOPE - Nc State Universityneutron.physics.ncsu.edu/LifetimeWorkshop/talks/Picker.pdf · PENeLOPE layout . 11 inner solenoids . protect center current . 13 outer solenoids . radial