Neutron Electric Dipole Moment 1.D. Beck (Intro) 2.S. Williamson (He3 Services construction and testing) 3.L. Yang (Light collection) with J. Blackburn, J. Nicholson, T. Rao, S. Sharma, P. Sobel, E. Thorsland

Status l Ongoing development project l Currently in year 2(of 4) of “Critical Component Demonstration” phase  Successful completion of Critical R&D phase in Dec  Continued Annual Reviews, Technical Review Committee meetings  15 critical component activities  GOAL: reduce risk, build from inside out l Equipment funding from NSF for He3 Services (UIUC), Magnet Systems (Caltech) at ~$1.4M/year l Equipment funding from DOE for Central Detector System, Cryogenics, Neutronics at ~$1.8M/year Lessons learned  modified design He3 services Central Detector 2

l Measure neutron precession frequency in NMR-style experiment Experiment Overview Concept: Golub and Lamoreaux, Phys. Rep. 237 (1994) 1 Measurement cell cutaway HV Ground Measurement Cells (7.6x10x40 cm) B E Scintillation signal (B/40) h =2(  B  dE)  (n + 3 He) ~ 0,  (n + 3 He) ~ 2 Mbarns l 3 He co-magnetometer 3

Experiment Statistics Incident neutron fluence  cold ~ 3x10 8 n/s:  ~ 0.3 Å FWHM UCN density at beginning of measurement n UCN ~ 100 cm -3 Polarized 3 He densityn 3 ~ cm -3, n 3 /n 4 ~ 5x Cell volumex·y·z = 7.6·10·40 cm 3 = 3100 cm 3 Holding fieldB 0 ~ 30 mG x Electric fieldE 0 ~ 50 kV/cm x Precession frequenciesf n ~ 100 Hz, |f n – f 3 | ~ 9 Hz Operating temperatureT op = 0.45 K Refrigeration~ K Official sensitivity (3 years)  d = 3-5x e·cm (90% CL) 4

nEDM Activities l UIUC responsible for “ 3 He Systems”  Getting the polarized 3 He both in and out Source is existing Atomic Beam Source Use “heat flush” to remove ( 3 He transported using phonons)  3 He enters some distance from measurement cells  plumbing including valves, etc. l He3 Services Critical Component Demonstration activities (Williamson)  Dilution Refrigerator  Injection System  Purification System l WLS fiber light system readout (Yang) Atomic Beam Source to Central Detector He3 Services System Dilution Refrigerator Injection system Purification system 5

nEDM Activities in Support (DHB) 1. Theory of transport coefficients of dilute solutions of 3 He in superfluid 4 He (heat flush)  Baym, Beck and Pethick Phys. Rev. B 88, (2013) ; JLTP 178 (2015) 200, and to be published 2. Design and performance of magnetic shielding for nEDM experiments (with TUM)  I. Altarev, et al. Rev. Sci. Instrum. 85, (2014) 3. Possible test nEDM experiment at ILL (Illinois student?)  CryoEDM cancelled at ILL 4. Development of external atomic vapor magnetometry for TUM experiment  Require array of magnetometers  Proof of principle of all-optical vector magnetometry (B. Patton, et al. PRL 113 (2014) ) 5. Development of cryogenic NV-diamond magnetic and electric field sensor  STTR DE-SC with Southwest Sciences & Sarvagya Sharma 6

l Introduction l Injection system  Film-burner test  The InjVol/IV1 conductance test  Radiation heat-load test l Purification system  Heat-flush test l Dilution refrigerator Steve Williamson Helium-3 Services 7

Polarized 3 He in l The experiment relies on efficient…  injection of polarized 3 He into isotopically purified 4 He  transport of the polarized 3 He to the measurement volumes  maintenance of polarization during the measurement  removal of unpolarized 3 He when a precession measurement is complete. Inject 3 He and n Move 3 He to Measurement Cell Measure Remove Unpolarized 3 He 8

Where are we? Critical Component Demonstration (CCD) l A working dilution refrigerator meeting the operational and material requirements l Critical components for the injection and purification systems individually tested at operating temperature l All testing, including full He3 services cryostat, at UIUC 2014 Pre FY12 Critical Component Demonstration Large Scale Integration Conventional Components R&D Data Collection Assembly and Commissioning … Helium-3 Services (He3S) CCD Goals 9

Injection System ABS Film- burner InjVol IV1 InjVol valve l Prepares polarized 3 He in isotopically purified 4 He for transport to the measurement cells. l Some of the CCD challenges :  Control superfluid film from bulk LHe in InjVol.  Cooling InjVol and IV1 Plastic (no metal), no sinter InjVol is coldest point in He3S (300 mK) IV1 must come to equilibrium quickly  Thermal isolation and seal of InjVol valve 10

l Evaporation of film into beam line must be prevented  Produces large heat load to injection volume (HeVAC)  4 He gas can block the beam ( 3 He- 4 He atomic scattering) l Film-burner concept  Evaporate the film with a heater.  Then re-condense it where … cooling is efficient and gas conductance to beam line is low Film-burner Heater Injection Volume LHe, T= 0.3 K Film- burner Assembly Baffle Beam line from Atomic Beam Source To IV1 and the rest of the experiment Superfluid Film Control 11

l Detect film (or its absence) to measure required heater power l Measure atomic “beam” transmission to be sure vapor is trapped. Superfluid Film Control Test Film- burner Heater Upper film sensor (dry if FB works) Thermal Link Dilution Refrigerator Mixing Chamber NTD Ge Bolometer LHe, T= 0.3 K Source ROX Injection volume assembly Film-burner Top flange assembly 12

l Detect film (or its absence) to measure required heater power l Measure atomic “beam” transmission to be sure vapor is trapped. Superfluid Film Control Test Injection volume assembly Film-burner Top flange assembly Mixing chamber of Silvera DR (Harvard) Film-burner assembly Injection volume assembly Top flange assembly 13

Transmission at K 14

Transmission at K 15

The InjVol/IV1 Conductance Test l The results:  Slope of each  T vs P curve is thermal resistivity  Extrapolates, for real geometry, to ~0.9 mW at T fridge = 250 mK l But what will the actual heat load be? Stainless outer wall Top flange bolted to MC 19.3 mm OD, 77 µm wall Kapton inner wall Heater bobbin LHe here Silver sinter ~11 cm Bottom flange assembly showing Kapton tube  T vs. Inside Heater Power l The problem:  Plastic injection volume (InjVol) and IV1 must be cooled to 0.3 K.  No metal or sinter allowed on InjVol  What is the maximum power that can be removed through the walls? l The test:  Double-walled volume; LHe thermal link to DR.  Temperature sensors in both volumes  Inner wall of seamless Kapton tubing  Heat inner volume  Measure  T vs heater power 16

Radiation Heat Load Test l Most of the InjVol heat load is from 300 K thermal radiation l Estimate is too uncertain  COMSOL FEA: mW  Ray-trace: 0.42 mW l A test would be prudent:  Simple geometry, an “upper limit” for the beam line. 1.Pull copper plug to 300K. 2.Measure absorber temperature (with radiation). 3.Push copper plug to thermally connect at 4.2K. 4.Adjust absorber heater to obtain the temperature of step 2. l Results  First test at ~15K  0.45 mW for the real geometry.  More analysis of this test is necessary.  Repeat test at lower temperature. ~115 cm Absorber Copper plug Radiation test insert (for standard LHe storage dewar) 17

Purification System l Removes depolarized 3 He from measurement cells; provides isotopically pure 4 He l CCD activities:  Heat-flush test New capacitor ( 3 He density sensor) design to be tested in early 2015  Adjustable Thermal Link (ATL) With greater DR cooling power, may be unnecessary Analysis in progress  Sequestration Volume (SV) Is 3 He dumped with bulk 4 He?  test SV ATLs 18

The Heat-flush Test l The concept:  Measure heat flush on “reasonably large” scale  Compare to theory (Baym, Beck, and Pethick)  Apply theory to the “real experiment” design l The test:  Use osmotic pressure to measure X100 concentration change For natural He, 0.45K, X100 concentration change, ΔP = Torr  Capacitive pressure sensor 0.5” diameter 25  m-thick Kapton diaphragm deflects by 0.57  m With 25  m gap, capacitance changes from to pF (0.77%) Heat-flush test assembly Section view of capacitive pressure sensor Solid electrode (diaphragm not visible on this scale) Superleak (not shown) 19

Dilution Refrigerator l Some characteristics  Magnetic field gradient specs  only non-magnetic materials allowed.  Close coupling with He3S  Hybrid operation as 3 He evaporation fridge  Optimized to run at 85 mW of cooling power (30% reserve) at ~200 mK l Ultimately 2 DRs are needed (one for He3S, one for CDS) l Build first DR for He3S  DR test bed at UIUC “barn” Space for large equipment LHe from UIUC Physics liquefier Helium recovery infrastructure Close to NPL technical support  DR will be critical to He3S component testing during last year of CCD CAD Model of the DR Test Stand setup in the NPL High Bay Area 20

Dilution Refrigerator CCD Activities l DR test-bed, 3 He gas panel, slow control, cryostat, helium supply Dewar and transfer line, He gas recovery, DR “Insert”  Substantial amount of commercial purchasing complete  Cryostat leak checked, fabrication tasks beginning l Low-temperature 3 He circulation components (the still, mixing chamber, heat exchangers, impedances)  Technically challenging  multiple prototypes l Testing The DR test-stand setup begins to take shape in the High Bay Area 21

In the next 3 years… l A working dilution refrigerator meeting the operational and material requirements  Used during last year for He3S component testing l Critical components for the injection and purification systems individually tested at operating temperature  Focus on most uncertain components first  The rest of the parts and assembly-level testing in the post-CCD phase 22

Measuring Neutron Precession using Helium Scintillation Neutron precesses at a slight different frequency than 3 He, ~ 10%. Neutron absorption on 3 He is highly spin dependent. Reaction products of n+ 3 He→p+T generates UV scintillation (80 nm) in LHe. The UV photons are down-converted before detection. Spin dependent n - 3 He absorption reaction measures the difference in precession frequencies between neutron and 3 He. L. Yang, UIUC 23

nEDM Light Collection R&D l Optimize the light collection using simulation given other system constraints on HV, magnetic field, neutron activation, etc. l Demonstrate the efficiency of the photon detection system with a full scale prototype. An early conceptual design of light collection system 24

Full Scale Test Apparatus A full scale prototype was constructed at ORNL to test light collection Detection efficiency of 80 nm scintillation light significantly lower than expected. Collection of UV photons from LED agree with expectation. Suspect that some down- converted blue photons are not trapped in the cell wall. 25

Alternative Detection Scheme Adding wavelength shifting fibers at the outside the cell wall significantly increased the light detection efficiency. Supports the model of reduced optical capture efficiency for blue photons. 26

Light Collection Simulation Light Guide, PMTs WLS fiber, SiPMs UIUC and Miss. State are collaborating on the development of GEANT4 simulation of the light collection. Use the experimental data and simulation to better understand the UV photon down-conversion process and light propagation. In the process of determining unknown parameters. 27

SiPM Testing Silicon photomultipliers (SiPMs) offer better quantum efficiency and distinct P.E. peaks. KETEK evaluation package stopped working at 110 K. UIUC is developing a front end readout package. KETEK SiPM Preamp Box Synergy with nEXO readout electronics R&D (Yang) and sPHENIX EMCal detector R&D (Sickles). 28

Future Light Collection R&D at UIUC Refine the light simulation and optimize WLS fiber readout. –Improve detector energy resolution to reduce background events from beta decay and environmental gammas. –Develop position reconstruction capability with fiber readout, a new handle on background reduction and systematics studies. Develop full scale readout with SiPMs –Low noise front end readout –Mechanical and thermal design for the SiPM system –Upgrade the DAQ to handle a large number of channels. 29

nEDM Summary l In demonstration/construction phase “CCD”  Strategy is still “design-build-test”, repeat as necessary  Build internal (less expensive) components first; beamline, large cryostats, magnetic shielding, infrastructure (more expensive) later l UIUC responsible for 1.He3 services: getting polarized 3 He to measurement cells, removing (de-)polarized 3 He Dilution refrigerator construction Injection volume prototype (film burner, vessel, radiation heat Heat flush test (demonstrate feasibility, compare to Need for postdoc to help manage and execute parallel activities 2.Fiberized light collection development (with ORNL, Miss. State) Synergy with development for nEXO 30