Polarized

3

He target based on an

ex situ polarizer

Bill Hersman University of New Hampshire and Xemed LLC David W. Watt Xemed LLC FCOI Disclosure: Prof. Hersman has a financial interest in Xemed LLC

Overview

• • • • • •

Rationale and goals

– reaching high

p 2 L

Our approach

– Remote large-scale polarizer, high density target, mechanical gas transfer

Zeppelin-3 implementation Measured performance Plans for Zeppelin-4 Recommendation

Rationale: Paradigm shift: ex situ pumping

• • • • • • Provide high luminosity by exposing a very dense 3 He target to the full beam current. –

p 2 L

is maximized when beam adds a depolarization factor of 50%.

Provide large spin-up rates by exposing a huge number of 3 He atoms to polarized alkali atoms. Requires laser power.

Provide high transfer rates between pump cell and target cell using a mechanical pump Also achieves isolation from radiation and field gradients Originally proposed in 2008 Expectation of

p 2 L

enhancement factor of ~50

Our approach

• • • • • • Place a large 8.5L thin-walled aluminosilicate pumping cell, multi zone thermal bath, and NMR coil inside a pressure vessel.

Pressurize to up to 10-20atm Immerse in a 24g solenoidal magnetic field Illuminate 5:1 hybrid alkali mix with a 2.5kW-4kW high-power wavelength locked spectrally-narrowed external cavity laser Zeppelin-3 is our third generation 3He polarizer built with this technology Transfer gas at up to 22 slpm with an industrial-scale diaphragm pump with non-ferrous wetted surfaces Polarized 3 He would interact with the beam in a pressurized, cryogenically cooled, vertical (transverse) flow, thin-windowed, aluminum target cell

Pumping cell: optical windows

• •

Hand blown:

– Prior studies found that cells with the best polarization had fully blown surfaces – Examination of blown windows reveals most thickness variations are azimuthally symmetric – We mapped deflections of hundreds of point beams, inverted, fit to twelfth-order polynomial – Custom lens corrected dominant aberrations

Machine polished:

– Using a melt shop, we produced a custom-melt 4” diameter GE180 ingot – – – Sliced into 1.5mm thicknesses; polished surfaces Selected wafers based on minimum bubbles Blown into a conformal dome Hand-blown window with illumination pattern GE180 ingot from Nor Cal Inc.

Pumping cell: fabrication

• • • Cylindrical barrel pumping cell measures 9.5cm inner diameter by 120cm long, 8.5 liters interior volume.

Valved capillary for gas transfer (currently only one is implemented for neutron analyzer filling) Blown port for distillation of alkali into the cell, permanently sealed.

Mike Souza, Princeton Glassblowing prepares a GE180 barrel end with GE180 domed window Aaron Kirchoff of NIST produced “Titan” fully from GE180

Pumping cell: preparations and filling

• • • Distillation #1: 1-5 g of rubidium and 5-25 g potassium are distilled separately in two stages into charging ampule at low temperature (200 o C for Rb, 280 o C for K).

Cell Bakeout: Pyrex retort is attached to cell, sealed with a Teflon cap, baked with a retort temperature of 350 o C and a cell temperature of 450 o C under UHV for ~ 1 week.

Alkali charging: Purified alkali mixture driven into the retort under flow of UHP N 2 . The mixture is then distilled into the cell at 260 o C.

1-5 g Rb Breakseal 5-25 g K Charging Ampule

Thermal Bath

• • • Cell operates at an angle to drive buoyant convection Flowing silicone oil delivers heat during warm up, removes heat during operation Provides independent control over three thermal zones – Lower 72% of the barrel is the hot-polarization zone, most of the laser power is absorbed here – Upper 28% of the barrel is maintained at a lower temperature, less alkali vapor, less laser absorption.

– Bottom window zone (and perimeter) is controlled electrically, establishes local alkali density • An opening is maintained for NMR coil and RF flux return All polarizer services are fed through the top flange Cell in encased in custom aluminum extrusion that serves as a dual zone thermal bath

A: Lasers, total of 4 B: External cavity C: Step mirrors D: Grating E: Beam shaping optics F: Combining prism G: Diffuser/ waveplate H: Main collimator E: Exit optic

Laser

Specifications:

Power Wavelength 2.7kW Locking efficiency Spectral width Beam divergence (2.12kW circular aperture) 794.8nm

75% 0.6nm

3x6mrad

Initial laser performance

Four 12 bar lasers (foreground) combining their outputs into a single 10 cm diameter beam (center).

Wavelength locked beam @2.7kW

16 14 12 10 8 6 4 2 0 792 793 794 795 Wavelength (nm) 796 797 798

Less-than-optimal components decommissioned from other projects cause beam inhomogeneities 3000 2500 2000 1500 1000 500 0 48 Bar exit beam, and 1m downstream with diffuser.

Divergence ~3x6 mrad (hor x vert.) 0

Power 0.6 nm narrowed laser (max = 110A)

20 40 60

current (A)

80 100

3

He Polarizer: Zeppelin-3

• 8.5L Cell cartridge • • • • • • pressure vessel, laser path, thermal bath, electronics control system diagnostics • Assembly/Operation

Performance: cell testing

Name Souza 1 Souza 1 Souza 2 Kirchoff Souza 3 Materials

Corning 1720 GE180 GE 180 GE 180

Test Dates

Jan April 2012 11/13 3/14 5/14 6/14 7/14 8/14

Alkali Ratio Optimal Temp ( o C) Density (amagat)

10:1 (10 g total) 220/200 1

T1 , Min (hrs)

3 4 5:1 (5 g total) 5:1 (10 g total) 5:1 (10 g total) 210/180 205/180 205/180 1 1 4 *4

Souza 3

2 --

T1, Max (hrs)

8 8 1.8

7

Remarks

Cell was refurbished due to O 2 contamination.

Cell was refurbished due to O 2 contamination Switched B 0 orientation **10.

5 *T1 changed during solenoid loss of Power.

**After intensive degaussing 12.5

Performance: cell spinup

Polarizer Testing Run times of up to 60 hours Studied effect of tilt angle, wall temperature Laser power up to 1800 W Internal NMR Measurement Probe: 30 mm dia multilayer surface coil Calibrated with in situ water phantom Corrected for changes in coil Q with temperature External NMR Measurement Short cylindrical coil surrounding sample bulb Calibrated with water sample in identical bulb Good SNR in calibration He-3 removed from polarizer through wire-wound PFA transfer line and PFA gas manifold.

Polarization agreed with in situ measurement within 2 % (external measurement was slightly higher).

Results Polarizations up to 59 % with 6 hr rise time.

Best results with polarizer tilt ~15 o from horizontal Average gas temperature ~230 o C. 1800 W laser power, ~1 nm spectral width

Non-ferrous Diaphragm Pump

• • • • • • Piston-driven hydraulic compression Nominal 30 cps Compression ratio ~6.5

Two pumps ordered Low pressure: 50 torr to 150 psi 150psi to 1000 psi @ 22 SLM • • • • • PEEK valves Titanium head 6AL4V Three-layer diaphragm Phosphor-bronze wetted Delivered February, 2012

• • • •

Gas Circulation Hardware

Two non-ferrous diaphragm compressors – – Low pressure system : 50  10,000 torr High Pressure (10  70 bar) – Low pressure system showed <2% polarization loss per cycle in continuous circulation Transfer lines: Wire-wound PFA tubing with internal field ~4 G.

Polarized Gas Handling Manifold-PFA block with Pneumatic PTFE valves.

Return gas purifier-Rb metal followed by LN2 trap to capture residual O 2 , H 2 O, and other impurities.

High Pressure Compressor Inlet to Analyzer Rubidium Trap c. LN2 Trap

Plan for Zeppelin-4: laser

Change feedback scheme from: – Low-efficiency grating feeds back small portion, each emitter occupies grating area To: – High efficiency grating feeds back all power, emitters share grating area – Increase magnification factor ~10 to reduce laser linewidth <50pm – Increase power capability to 3-4 kW 4000 3500 3000 2500 2000 1500 1000

intensity Nlight 1 bar laser narrowed x38 cavity (~center 5 emitters) ~ 10*4.4*0.353=16 pm

500 0

pixel #; 4.4 microns/pixel; 0.353 pm/micron

Linewidth as low as 0.016nm demonstrated for few emitters Output beams 50% 33% 25% 20% Lasers contribute equal power to a single external cavity, draw equal portions back for wavelength locking to/from external cavity

Plan for Zeppelin-4: cell

• Cell trials to include: – New monolithic aluminosilicate cells, – – sol-gel coating existing short-lifetime aluminosilicate cells, and sol-gel coating new borosilicate cells Motorized rig for rotating glassware to distribute sol-gel uniformly over inner surface Sol-gel coated borosilicate cell 10cm in diameter with surface coil attached for measuring polarization lifetime

Plan for Zeppelin-4: infrastructure

• • Change pressure vessel from: – Aluminum pressure vessel (unrated) inside a solenoid surrounded by flux return steel to: – – Engineer-stamped and rated steel pressure vessel Steel vessel also serves as magnetic flux return – – Solenoid relocated to fit inside pressure vessel Greater isolation from ambient fields, including earth’s field – Steel e Change thermal system from: – Two heat/cool oil systems, two electrical window heaters to: – Three zone direct electrical heat, oil systems provide for heat removal only Heat Spreader Graphite Heater Insulation Cooling Plate

laser power (W) 3He gas density (Pump) dipole relaxation (Pump) 3He gas temperature (target) 3He gas pressure (Target) 3He gas density (target) Loschmidt (cm-3) thickness (cm-2) dipole relaxation (Target) beam current (uA) e beam number density Luminosity depolarization const (loss/dilution) pump cell T1 pump cell X-factor spin up rate pump volume pump 3He (STP cc) number of 3He pump atoms moles 3He pump atoms 3He polarized per second 3He polarized moles per hour target radius target length target volume target 3He volume (STP cc) total volume 3He volume (STP cc) 3He atoms (pump+target) pressure related T1 polarization (bench) beam related T1 (entire volume) beam related T1 (target cell volume) beam depolarization rate (atoms) polarization (in beam) luminosity figure of merit ratio existing eva 180 7.66

97.1279373

297 new existing polarizer 3000 12 62 170 K 10 10.0

2.69E+19 1.07E+22 74.4

15 69 120.5

2.69E+19 1.30E+23 6.17 hrs 65 176.4 psia 1014.3 psia 1772.04 psia 12.05

1.60E-19 9.38E+13 1.01E+36 0.0025

33 0.5

7.1

1.60E-19 4.06E+14 s-1 5.26E+37 7.68E-04 11 0.3

5 1.292

1.42

230 1760.63

4.73E+22 0.0786

1.85E+18 0.0111

0.93

40 108.69

1086.87

338.53

2847.50

7.65E+22 77.40

55.9% 26.6667

8500 102000 102000.00 STP cc 2.74E+24 4.5527

1.52E+20 0.9105

0.8

40 57.9

82.27

80.42 cc 9694.97 STP cc 8580.42

111694.97

3.00E+24 39.2257

6.42 hrs 54.5% 20.0244

1.33171

10.1784

5.31E+16 48.7% 60 14.21

1.7381

2.78E+18 48.0% 3134.2235

721.05

50.73

104.286 minutes 52.2371

p2L 2.39E+35 1.21E+37 50.7 ratio

Implications for a polarized 3He target

• • • • • • Compares new paradigm with old performance (not projected improvements) Likely cell design is aluminum, transverse flow, cryogen cooled Beam current and target density insufficient to maximize

p 2 L

Roughly 7% beam-related 3He depolarization Assumptions can be adjusted (cell, target; temperature and pressure) Approximate improvement factor of 50

Funding and timeline

• Polarizer funding renewed April 2015 by the DOE SBIR program to develop a filling station for large-angle neutron spin filters • • • Two year timeline with $500K/yr, total budget of $1M Zeppelin-4 will be demonstrated on-site at Oak Ridge in January 2017 Could also visit Jlab • But… Single capillary for gas entry/exit; not suitable for flow-through circulating Jlab target testing

Recommendations

1.

2.

Borrow Zeppelin-3 for tests. Commission assembly of a copy of Zeppelin-4 with two capillaries, inlet and exit, for flow through operation. Delivery May 2017.