Philip Harris CryoEDM at ILL. P. Harris ORNL, 11 Oct 2012 Overview Motivation, history and technique...
Transcript of Philip Harris CryoEDM at ILL. P. Harris ORNL, 11 Oct 2012 Overview Motivation, history and technique...
P. HarrisORNL, 11 Oct 2012
Overview
Motivation, history and technique CryoEDM: Current status Upgrade Systematic errors Timeline Conclusion
P. HarrisORNL, 11 Oct 2012
CryoEDM Collaboration
C. Baker, S. Balashov, A. Cottle, V. Francis, P. Geltenbort, M. George, K. Green, M. van der Grinten, M. Hardiman, P. Harris, S. Henry, P. Iaydjiev, S. Ingleby, S. Ivanov, K. Katsika, A. Khazov, H. Kraus, A. Lynch, J.M. Pendlebury, M. Pipe, M. Raso-Barnett, D. Shiers, P. Smith, M. Tucker, I. Wardell, H. Yoshiki, D. Wark, D. van der Werf
P. HarrisORNL, 11 Oct 2012
Electric Dipole Moments
EDMs are P, T odd Complementary study of
CPv Constrains models of new
physics
E +
P. HarrisORNL, 11 Oct 2012
Measurement principle
() – () = – 4 E d/ h
with appropriate compensation for any changes in B during measurement period.
B0 E<Sz> = + h/2
<Sz> = - h/2
h(0) h() h()
B0 B0 E
Use NMR on ultracold neutrons in B, E fields.
P. HarrisORNL, 11 Oct 2012
Ramsey method of Separated Oscillating Fields
4.
3.
2.
1.
Free precession...
Apply /2 spin-flip pulse...
“Spin up” neutron...
Second /2 spin-flip pulse
130 s
2 s
2 s
29.7 29.8 29.9 30.0 30.1
10000
12000
14000
16000
18000
20000
22000
24000
xx
x = working pointsResonant freq.
xx
Spi
n-U
p N
eutr
on C
ount
s
Applied Frequency (Hz)
P. HarrisORNL, 11 Oct 2012
UCN production in liquid helium
1.03 meV (11 K) neutrons downscatter by emission of phonon in liquid helium at 0.5 K
Upscattering suppressed: Boltzmann factor e-E/kT means not many 11 K phonons present
Observed: C.A.Baker et al., Phys.Lett. A308 67-74 (2002)
n = 8.9 Å; E = 1.03 meV
Landau-Feynman dispersion curve for 4He excitations
Dispersion curve for free neutrons
R. Golub and J.M. Pendlebury Phys. Lett. 53A (1975), Phys. Lett. 62A (1977)
P. HarrisORNL, 11 Oct 2012
CryoEDM overviewNeutron beam input
Transfer section
Cryogenic Ramsey chamber
P. HarrisORNL, 11 Oct 2012
Sensitivity
•Successfully produced, transported, stored UCN, but need
to reduce losses
•Successfully produced, transported, stored UCN, but need
to reduce losses
•Successfully applied 10 kV/cm (same as previous expt); aiming for 20-30
kV/cm
•Successfully applied 10 kV/cm (same as previous expt); aiming for 20-30
kV/cm
•Achieved 60% polarisation in source,
but must improve
•Achieved 60% polarisation in source,
but must improve
•RT-edm: 130 s. So far we have 62 s cell storage
time.
•RT-edm: 130 s. So far we have 62 s cell storage
time.
P. HarrisORNL, 11 Oct 2012
Neutron numbers• Anticipated production rate 1.4 /cc/s• Aperture mask x 0.44• Entrance window scattering x 0.8• Beam attenuation x 0.72• Source storage lifetime 91 s• Incomplete source filling (200 s): x
0.89
Gives expected density in source: 30/ccSource volume 10.5 litres.
P. HarrisORNL, 11 Oct 2012
Neutron numbers• Measurement has been somewhat
indirect (neutrons taking convoluted paths to detectors) but it appears that we are currently down a factor of ~4: Under investigation
• Alignment/divergence issue?• Spectrum affected by upstream
instruments?
P. HarrisORNL, 11 Oct 2012
Neutron numbers• Guides and valves not yet optimal. • Ramsey chambers: first attempt
yielded storage time 60 s. For next time, improved cleaning; also bakeout.
• What is limiting storage lifetimes in source and cells...?
P. HarrisORNL, 11 Oct 2012
Electric field
See talk by M. Hardiman Latest feedthru installed designed
for 30 kV (6.7 kV/cm); it was run up to 45 kV (10 kV/cm).
We know how to design feed up to ~80 kV, and possibly up to ~150 kV, but...
... will need mild pressurisation of He.
P. HarrisORNL, 11 Oct 2012
Detectors Solid-state detectors
developed for use in LHe Thin surface film of 6LiF: n +
6Li + 3H; 82% efficient Fe layer for spin analysis Currently, peak hidden
under background pulse-shape discrimination
Now moving to detector with 10x area, to cover entire guide
C.A.Baker et al., NIM A487
511-520 (2002)
P. HarrisORNL, 11 Oct 2012
Detection of polarised UCN
Observed ~60% polarised downscattered neutrons Should be able to improve on this - Upcoming
measurement of source polarisation
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T1
Longitudinal polarisation T1 is fairly straightforward to hold: field mustn’t change too fast for precession to follow
Issues last time with superconducting material around source/guide region...
Need to watch also sensitive area at entrance to shields, where field is low
P. HarrisORNL, 11 Oct 2012
T2 Transverse polarisation T2 is more delicate.
Depends largely on variation of Bz within trap volume – causes dephasing: goes as
We are aiming for ~1 nT across the bottle Currently in commissioning phase. SS
plates at end of superfluid containment vessel (SCV) distort field. Modelling suggests that with correction coils we can reach T2 ~ 30 s with current SCV.
Working on non-magnetic SCV.
P. HarrisORNL, 11 Oct 2012
Sensitivity summary: Current
Room-temperature expt final sensitivity ~2E-25 ecm/day Took 12 years of incremental developments from known
technology Systematics limited (geometric phase effect)
We can come within factor 4-5 of this in 2013 by increasing detector area x10: technology now proved refurbishing damaged detector-valve: in hand applying ~70 kV (previously ~40 kV): should be
straightforward opening beam aperture from 43 to 50 mm: depends on
radiation levels retaining polarisation: superconducting material has been
removed
There may be additional improvements beyond this peak above background (detector improvement) Polarisation to 60% or more (improved guide field) Increasing cell storage lifetime (insulator bakeout)
(we will achieve these by 2014)
P. HarrisORNL, 11 Oct 2012
Shutdown, move to new beamline
Mid-2013: Have to vacate current location. ILL to shut down for a year; we move to new dedicated beamline.New beam 4x more intense; and dedicatedDue to become operational mid-2014Beam must then be characterised (9A flux, divergence, stability, polarisation) We will then have access to the area (late 2014) to move our apparatus into it.
P. HarrisORNL, 11 Oct 2012
Upgrade 2013-15 Not yet fully costed Major upgrade to experiment:
Cryogenics design changes: Pressurise the liquid helium: increase E field x 2-3
Upgrade to back-to-back cells (or possibly 4 cells) 2 x neutrons Cancellation of some systematic effects
Installation of inner superconducting magnetic shield
B-field stability improves x500, for systematics Construction of non-magnetic SCV
Improves depolarisation: better T2 Overcome geometric-phase systematic error
Net result: Order of magnitude improvement in sensitivity Commensurate improvement in systematics
P. HarrisORNL, 11 Oct 2012
Systematics: General Systematics minimised by highly
symmetric data taking: B and E field reversals Alternating either side and
above/below middle of central Ramsey fringe
Upgrade: opposite E in adjacent cells Possibly also neutron magnetometers
in adjacent (outer) cells, for 4-cell system
P. HarrisORNL, 11 Oct 2012
Systematics: B field fluctuations At present, Pb shield too short: flux lines
clip coil end, inducing current in whole coil
Introduces common-mode noise, limiting sensitivity to 1E-27 e.cm
Figure: JMP
P. HarrisORNL, 11 Oct 2012
Systematics: B field fluctuations We plan to add an inner
superconducting shield. Scale model work in lab (MH) suggests that this can bring increased shielding factor ~500.
Figure: JMP
ISS
P. HarrisORNL, 11 Oct 2012
Systematics: B field fluctuations Can also (or instead) add Pb end caps,
calculated to give factor ~250 improvement
Figure: JMP
P. HarrisORNL, 11 Oct 2012Br
Br
Bnet
Bnet
Bv
Bv
Bv
Bnet
Bnet
... so particlesees additionalrotating field
Frequency shift E
Looks likean EDM, butscales withdB/dz
Bottle(top view)
Systematics: Geometric phase
P. HarrisORNL, 11 Oct 2012
Systematics: Geometric phase For neutrons,
Scales as 1/B2; increase B 5x to obtain factor 25 protection
<1 nT/m 3E-29 e.cm
P. HarrisORNL, 11 Oct 2012
Systematics: E x v
Translational: Vibrations may warm UCN, cause CM to rise
~1 mm in 300 s 3E-6 m/s If E, B misaligned 0.05 rad., gives 2E-29 e.cm
Rotational: Net rotation damped quickly (~1 s): matt walls Delay before NMR pulses allows rotation to die
away Neutrons enter E-field cells centred
horizontally; no preferred rotation Below 1E-29 e.cm
P. HarrisORNL, 11 Oct 2012
Systematics: 2nd order E x v
Perpendicular component, adds in quadrature to B.
Prop. to E2; gives signal if E reversal is asymmetric
Cancellations (back-to-back cells; B reversals) reduce effect to < 3E-29 e.cm
P. HarrisORNL, 11 Oct 2012
Systematics: metal hysterisis
Room-temp expt: Pickup in B coil from E field reversals; return flux causes hysterisis in metal
Coil here is SC, not power-supply driven
Inner shield is SC also Small effect from trim coils,
enhanced by any misalignments Net estimate < 1E-30 e.cm
P. HarrisORNL, 11 Oct 2012
Systematics: E induced cell movement
Electrostatic forces of order 1 N; E2
Asymmetry perhaps ~1% of this Radial gradients of order 3 nT/m Must keep radial displacement on E
reversal symmetric to ~ 0.01 m Cancellation with double cell Symmetric voltages to ~2% Net effect < 1E-28 e.cm
P. HarrisORNL, 11 Oct 2012
Systematics: Leakage currents
Azimuthal current components generate axial contributions to B
Cancellation in adjacent cells Conservative estimate: 1 nA 5E-
29 e.cm In reality LHe should keep currents
much below this? New source of current: ionisation
from UCN decay electrons (10-100 pA?, but preferentially axial)
P. HarrisORNL, 11 Oct 2012
Systematics: HV supply contamination
HV circuit isolated as far as possible to minimise earth contamination. Feedback line far from cells. Separate computer control.
10 kHz ripple on HV line can “pull” resonant freq. Estimate 1E-30 e.cm
Likewise 50 Hz ripple: estimate ~1E-29 e.cm
Directly generated AC B fields negligible
P. HarrisORNL, 11 Oct 2012
Systematics: Summary
Effect Size (e.cm)
B fluctuations 1 x 10-30
Geometric phase 3 x 10-29
Exv translational 2 x 10-29
Exv rotational 1 x 10-29
Exv 2nd order 3 x 10-29
metal hysterisis 1 x 10-30
E-induced cell movement 1 x 10-28
Leakage currents 5 x 10-29
HV line contamination 1 x 10-29
P. HarrisORNL, 11 Oct 2012
Sensitivity timelineDate Item factor ecm/year
Comment
2002RT-edm 1.7E-26 Baseline
2010CryoEDM commission 1.7E-24
2012Large-area detector 3.5 4.9E-25 Proven
2012HV to 70 kV 1.6 3.1E-25 OK to 50 kV, lab tests suggest should work at 70 kV
2012Repair detector valve 1.3 2.5E-25 Repair – should be fine
2012Polarisation 60% 1.5 1.7E-25 Seen in source. Should transfer ok to cells.
2012Aperture to 50 mm 1.2 1.4E-25 Will increase radiation levels slightly, but should be ok
2013Ramsey time to 60 s 1.8 7.7E-26 Requires change of SCV baseplates
2013See alpha peak 1.4 5.5E-26 Quite likely by 2012, but we do not count on it by then
2014New beam 2.0 2.7E-26 ILL produced this estimate
2014Recover missing input flux?
2.2 1.2E-26Depends on geometry match to new beam.
2014Improve cell storage lifetime to 100 s
1.5 8.3E-27Not guaranteed, but haven't yet tried most obvious solutions (e.g. bakeout), so improvement likely
2014Match aperture to beam
1.3 6.4E-27Likely
2015HV to 135 kV 1.9 3.3E-27 Requires pressurisation. Lab tests show this is realistic.
2015Four-cell system 1.4 2.3E-27 Guaranteed part of upgrade
2015Polarisation to 90% 1.5 1.6E-27 No known reason why not
2013-15 Inner supercond. shield Lab tests on scale model shows factor 500
2013-15 Cryogenics Included in upgrade
2013-15 Non-magnetic SCV Included in upgrade
P. HarrisORNL, 11 Oct 2012
New collaborators
Swansea is interested in joining us soon.
There is still plenty of room for new collaborators! Grants panel would like to see us recruiting from overseas.