The ultracold neutron facility Bernhard Lauss at the Paul Scherrer - - PowerPoint PPT Presentation

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The ultracold neutron facility Bernhard Lauss at the Paul Scherrer - - PowerPoint PPT Presentation

Nov 18, 2022 377 likes •680 views

The ultracold neutron source at the Paul Scherrer Institute The ultracold neutron facility Bernhard Lauss at the Paul Scherrer Institute Paul Scherrer Institute on behalf of the UCN team Wor orkshop: : Pro Probing fun undamental l

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Bernhard Lauss UCN-2016@Mainz 1

The ultracold neutron source at the Paul Scherrer Institute

Bernhard Lauss

Paul Scherrer Institute

  • n behalf of the UCN team

Wor

  • rkshop:

: Pro Probing fun undamental l Sym Symmetries and and Int ntereactions wit with UCN UCN

The ultracold neutron facility at the Paul Scherrer Institute

Bernhard Lauss Paul Scherrer Institute

  • n behalf of the PSI UCN team

International Workshop: Probing fundamental symmetries and interactions with UCN April 11 - 15, 2016 Mainz, Waldthausen Castle

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Bernhard Lauss UCN-2016@Mainz 2

SLS:  600 MeV p cyclotron p beam current: 2.2 mA 1.3 MW: m, p SINQ: n Proton cyclotron for medical application: p

UCN: n

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Bernhard Lauss UCN-2016@Mainz 3

High Intensity Proton Accelerator (HIPA) complex

UCN Source Proton Accelerator 590 MeV Cyclotron 2.2 mA beam current

nEDM

Talk by Vira Bondar

2 experimental areas / 3 beamlines

kicker to UCN

SINQ

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Bernhard Lauss UCN-2016@Mainz 4

Sketch of the PSI UCN Source:

  • ur strategy: check and understand every step from

neutron production to UCN detection pulsed 1.3 MW p-beam 590 MeV, 2.2 mA, 1% duty cycle spallation target (Pb/Zr) (~ 8 neutrons/proton) heavy water moderator → thermal neutrons 3.6m3 D2O cold UCN-converter 5 kg solid D2 at 5 K

7 m

DLC coated UCN storage vessel height 2.5 m, ~ 2 m3 UCN guides towards experimental areas 8.6m(S) / 6.9m(W) cryo-pump

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Bernhard Lauss UCN-2016@Mainz 5

1000 2000 3000 1 10 100 1000 10000

Counts Time (100ms)

Characterization of UCN output with Cascade detector at beam-port

200 400 600 1 10 100 1000 10000

Counts Time (100ms) filling of storage vessel pilot pulse 7ms closing shutter emptying storage vessel up to 2.8 x107 UCN/pulse

typical exp. filling time <30s

Counts / 0.1 s

re-opening shutter

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Bernhard Lauss UCN-2016@Mainz 6

UCN operations 2011 - 2015

2015: full proton beam operation period (May - Dec.) ~ 200 days  58'000 pulses total of ~140 days with UCN available in 2015  124 nEDM data taking days

plot cortesy B.Blau

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Bernhard Lauss UCN-2016@Mainz 7

UCN operations in 2015

increasing duty cycle 2040mA

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20 40 60 3.2s 5.4 s 8.0s period 300s

West-1 West-2 x40 nEDM after storage - scaled

not measured with best D2 conditions and both beamlines open

increasing duty cycle 2040mA  60mA in 2016 change pulse length or frequency

plot cortesy D.Ries

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Bernhard Lauss UCN-2016@Mainz 9

UCN monitoring over entire operating period using nEDM detector

Measurement of the total UCN counts (spin-up and - down) after 180s of storage in the nEDM precession chamber Main features:

  • operation / failsafe
  • continuous UCN output

increase over operating period

  • UCN output decrease
  • ver short time and regain
  • f UCN output after

conditioning

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Bernhard Lauss UCN-2016@Mainz 10

Sketching preparation of solid deuterium

  • condensation
  • conversion
  • transfer
  • solidification in mod. vessel

5K 19K 300K 5K

Oxisorb

10m

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Bernhard Lauss UCN-2016@Mainz 11

solid D2 vessel

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Bernhard Lauss UCN-2016@Mainz 12

LANL / C.Morris et al, Phys.Rev.Lett.89(2002)2 72501

UCN lifetime in D2 (ms)

Raman spectroscopy

2014 cpara = 0.007± 0.004 2015 (preliminary) cPara = 0.007 +- 0.003 consistent value with 2014

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Bernhard Lauss UCN-2016@Mainz 13

4 h conditioning

higher UCN output  faster rate decrease

  • not a single exponential
  • regain of UCN output always worked

short D2 conditioning to regain UCN intensity decrease while operating

pressure measured in moderator vessel above solid D2

time

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Bernhard Lauss UCN-2016@Mainz 14

see pr presenta ntatio tion by Ek Ekaterina erina Korob robkina kina tomor

  • rrow

row

Hypothesis 1 "frost": layers of reflective interfaces with VF(D2) could result in strong elastic scattering in all directions for thicknesses > l(UCN) but UCN output slightly increases after conditioning points towards additional annealing of bulk. Hypothesis 2 "micro-defects": small cracks and defects in the bulk D2 also in the top region where UCN originate.

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Bernhard Lauss UCN-2016@Mainz 15

high (2.4mA) proton beam current day

  • UCN intensity increase

linear with proton beam current

  • at this pulse sequence

(4.1s every 300s) the UCN intensity decreased faster at 2.4 mA in comparison to 2.2 mA standard operating current

  • slower decrease rate

was regained with lower beam current  this hints at a beam power dependent effect

  • n the UCN output
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Bernhard Lauss UCN-2016@Mainz 16

Increasing proton pulse length: 5.4s to 8s

after 4h conditioning full regain

  • f UCN output

 conditioning works also when solid D2 deteriorated with 8s long pulses a different slope in UCN intensity decrease is visible p, r) shutter W-1 closed - open

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Bernhard Lauss UCN-2016@Mainz 17

Increasing proton pulse length: 5.4s to 8s D2 vapor pressure shows cooling works also fine at higher duty cycle

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Bernhard Lauss UCN-2016@Mainz 18

Check of various sub-systems

  • f the UCN source
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Bernhard Lauss UCN-2016@Mainz 19

Confirmation of target assembly, proton beam and neutron flux

7m

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Bernhard Lauss UCN-2016@Mainz 20

Cold neutron flux from MCNP simulation and experimental determination via tritium activation

Calculated history of tritium inventory in the source D2

capture cross-section depends on neutron energy  T content is sensitive to neutron energy spectrum

  • determine T/D in gas D2 via AMS

and

  • T/D in D2O produced via fuel cell
  • > up to now only rough agremeent between the two

methods (AMS might be complicated)

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Bernhard Lauss UCN-2016@Mainz 21

UCN guides with high transmission

sD2 1W 2W

neutron guides 180 mm inner diameter

stainless steel 1S glass

longest single pieces

nEDM

  • about 8m length each to each port
  • about 10m2 NiMo coated guide surface
  • guide volume ~3900 liter
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UCN transmission measured at PF2 (ILL) before mounting

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Bernhard Lauss UCN-2016@Mainz 23

UCN Ping-Pong to test transport in guides, storage vessel, windows

D1 D2

storage W-1 W-2

magnet

Total Guide length: about 16m preliminary

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Bernhard Lauss UCN-2016@Mainz 24

Ping Pong - UCN arrival times: simulation matches measurement

 full simulation reproduces measurements rather well working on further improvements  no 'big' unknowns in storage vessel or guides preliminary

small count rate difference

  • bserved between 5 T and 2 T

setting  En < 180 neV

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Bernhard Lauss UCN-2016@Mainz 25

A 'calibrated' source of UCN UCN production in solid thin-film D2

D2 fills with gas  exact D2 mass known (p,T)  freeze to make a solid thin-film D2 source 3 - 250 gram targets  thicknesses up to a few mm  no UCN losses occurring within the solid D2 (lifetime is long enough that UCN exit also after multiple scattering)

  • established thermal flux
  • (soon established) cold flux
  • established UCN production cross-section from

Golub/Boenig 1983, Yu/Malik/Golub 1985 Atchison et al, PRC71, 2005 Atchison et al, PRL99, 2007

  • established UCN transport to detector above

the SV shutter (Ping Pong)  check UCN extraction and transport below SV shutter via thin film measurement

100

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Solid thin-film D2

linear mass dependence found for similar solid D2 preparation 2015 data > 100 g : remelting improves UCN output also in thin films !

plots cortesy D.Ries

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Bernhard Lauss UCN-2016@Mainz 27

Plans for 2016

  • startup of proton accelerator and UCN source beginning of May
  • in 2016: main priority - deliver high UCN intensity to nEDM

experiment

  • improve D2 conditioning - is faster conditioning possible ?
  • increase to 3% duty cycle
  • further understanding of all parts of the source
  • study further improvement possibilities for UCN output
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Bernhard Lauss UCN-2016@Mainz 28

tha hank nk you

  • u

UCN physics group at PSI many thanks to Dieter Ries for his work and many plots I could show, which are part of his PhD work.