Patricia Aguar Bartolomé , Kurt Aulenbacher , Valery Tioukin , Jürgen Diefenbach

Patricia Aguar Bartolomé, Kurt Aulenbacher, Valery Tioukin, Jürgen DiefenbachInstitut für Kernphysik, Universität Mainz

PAVI’14, Syracuse, NY17th July 2014

Møller Polarimetry with Polarized

Atomic Hydrogen at MESA

Patricia Aguar Bartolome - PAVI'14 117/07/2014

Physics Motivation

Polarized Atomic Hydrogen Target

Status of the Mainz Hydro-Møller Target

Beam Stabilization Test

Summary

Outline

2Patricia Aguar Bartolome - PAVI'1417/07/2014

Physics Motivation

Hydro-Møller

PV Detector

Goal: Low energy PV electron scattering experiments at MESA with systematic accuracy < 0.5% for beam polarization measurements

3Patricia Aguar Bartolome - PAVI'14

MESA (Mainz Energy recovering Superconducting Accelerator)

17/07/2014

Physics Motivation

• Compton Scattering: Accurate enough at Ebeam > 4GeV, but accuracy around 1% at low energies Not enough for PV-experiments • Møller Scattering with ferromagnetic target

Polarimetry Methods


Advantages Disadvantages Beam energy independent Low electron polarization (~ 8 %)

High analyzing power (~ 80%) Target heating Beam current limited to 2-3 mA

2 particles with final state high energies eliminates background

Levchuk effect ~ 1%

Systematic errors on target polarization ~ 2%

Low Pt Dead time

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Physics Motivation

• Møller Scattering with polarized atomic hydrogen gas, stored in a ultra-cold magnetic trap E.Chudakov and V.Luppov IEEE Trans. on Nucl. Sc., 51, 1533 (2004)

Polarimetry Methods


Advantages Disadvantages

100% electron polarization Technical complexity of the target R&D needed

High beam currents allowed Continuous measurement

Contamination and depolarization effects of the target gas w/o beam

Very small error on polarization

No Levchuk effect

No dead time

Expected DPB/PB ≤ 0.5% Suitable for PV-experiments

17/07/2014

Polarized Atomic Hydrogen TargetMagnetic field B splits H1 ground state

At B = 8T, sinq ≈ 0.3% Mixing angle tan2q ≈ 0.05/B(T)

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Mixture ~ 53% of and ~ 47% of , Pe ~ 1-d, d ~ 10-5

Patricia Aguar Bartolome - PAVI'14

Storage Cell

• In a field gradient a force

Pulls , into the strong field Repels , out of the strong field

• recombination (releasing ~ 4.5 eV) higher at low T cell walls coated with ~50nm superfluid 4He

H+H H2

• Gas density: cm-3

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15103

Dilution Refrigerator and Magnet

Dilution refrigerator and magnetshipped from UVA to Mainz

T=300mK of the atomic trap can be reached using a Dilution Refrigerator and the requiered B=8T using a superconducting solenoid


Status of the Atomic Hydrogen TargetNew Dilution Refrigerator needs to be designed and produced!!

Test superconducting solenoid


UVA Superconducting Solenoid Test

Status of the Atomic Hydrogen Target


Central Field 8T @ 4.2K

Current 76.4 A

Homogeneity 1.10-5/10mm DSV

Inductance 20.3H

Voltage 0.995V

Clear Bore 762 mm

Overall Length 304.8mm

Outer Diameter 167.64mm

• 8 thermo sensors (4 Pt-100, Pt-1000, Si-Diode, 2 Cernox) placed in different points of the solenoid

• Several tests with Nitrogen (T~77K) were successfully performed

• Infeasible Helium (T~4K) test due to the appearance of a big leakrate

• New cooling set up for the solenoid needs to be designed and produced

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Status of the 8T Superconducting MagnetNew cooling system set up design


Vacuum Vessel

• Most of the new cooling system components currently under construction

• Estimated time to assemble the new set up ~ August • Cooling down of the magnet with Helium ~ September

17/07/2014

Courtesy of J.Bibo and D. Rodriguez

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Copper Shields(T ~77K)



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Solenoid(T~4K)



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Patricia Aguar Bartolome - PAVI'1417/07/2014


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Status of the 8T Superconducting Magnet

Patricia Aguar Bartolome - PAVI'1417/07/2014

Preliminary design of the new Dilution Refrigerator

General considerations

• Low temperature (T=300mK) and high cooling power (Q=75-100mW)

• Optimization by a careful calculation: - Heat exchangers - Pressure drop in the pumping lines - Condensation of the mixture - Amount of 3He and 4He gas needed - Volumes of all parts inside the DR (separator, evaporator, still) and also pumps and lines - Produce new mixing chamber

Status of the Atomic Hydrogen Target


Heat Exchangers (HE)

Design of the HE is of major importance. The important parameters are: 1. Small volume to reach the equilibrium temperature very fast 2. Small thermal resistance between the streams to get good temperature equilibrium between them

Imperfections and impurities can influence the transport of heat

Thermal boundary resistance between helium and the HE material at T<1K Kapitza resistance ~ T3

Status of the Atomic Hydrogen TargetPreliminary design of the new Dilution Refrigerator


Status of the Atomic Hydrogen TargetPreliminary design of the new Dilution Refrigerator


Module Ready Status Remarks & Problems

Cryostat housing End 2014 R&D Construction

Cons. using Super-MLIAccurate positioning of

solenoid

Stage 1.10 K End 2014 Development Construction

HT-HEPre-HELT-HEValves

Stage 0.25 K End 2015 R&D(Technologies not yet

under control)

Final-HEMixing Chamber

Film Burners

Hydrogen feed system End 2016 R&D Literature references Transition unit not ready

Superconducting solenoid

End 2014 Test

Detection system R&D Collaboration?

Pumping system Summer 2016 Not funded yet 3He Still4He Evaporator4He Separator

4He Pre-HE3He-Filling End 2016 Not funded yet Volume = 200 l STP

Target Test End 2017

17/07/2014

1.1K stage HE currently under construction in our Mechanical Workshop

Beam Stabilization for PV experiments


Requirements for the PV experiment at MESA

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• P2 expected physics asymmetry < 50 ppb

• Beam energy ~ 150 MeV (external beam)

• DPB/PB ≤ 0.5%

• Beam quality:

• Beam must be stabilized (DAi 0)

• Helicity correlations must be suppressed (Ai 0)

• Beam parameters are correlated with helicity Ai

• Noise on beam parameters (helicity un-correlated) DAi

Beam Stabilization


Beam stabilization and solenoid test set up

Reliable 3T solenoid for first tests

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Beam Stabilization


Principle of beam stabilization

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• Cavity monitors measure beam position (XYMOs)

• Steering magnets correct beam direction (WEDLs)

Beam Stabilization


Beam tests with solenoid

• Use an available 3T superconducting solenoid• Gain experience steering <200 MeV beam through a superconducting solenoid• Operate beam position/angle stabilization across the solenoid

• Most realistic test of polarimetry+beam stabilization for P2 possible before MESA is in operation

17/07/2014

Summary/Outlook• PV electron scattering experiments at MESA are planned systematic accuracy of < 0.5% for the beam polaization measurements

• Atomic Hydrogen gas, stored in a ultra-cold magnetic trap can provide this accuracy

• A solenoid and a dilution refrigerator were shipped from the University of Virginia to Mainz

• New cooling down setup of the solenoid and new DR design and production is in progress

• Production of a new mixing chamber and a atomic hydrogen dissociator is also required

• Beam stabilization test is planned within the next year


BACKUP


Beam Stabilization


Planned Beam test setup

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Beam Stalilization


Gas Lifetime in the CellLoss of hydrogen atoms from the cell due to:

• Thermal escape through the magnetic field gradient dominates at T > 0.55 K • Recombination in the gas volume negligible up to densities of ~1017 cm-3

• Recombination in the cell surface constant feeding the cell with atomic hydrogen

E.Chudakov and V.Luppov IEEE Trans. on Nucl. Sc., 51, 1533 (2004)



Contamination and Depolarization of the Target GasNo Beam

Hydrogen molecules ~ 10-5

High energy atomic states and < 10-16 Excited atomic states < 10-5

Helium and residual gas < 0.1% empty target measurement with the beam

Beam Impact

Depolarization by beam generated RF field Gas heating by beam ionization losses < 10-10 Depolarized ions and electrons contamination < 10-5

Contamination by excited atoms < 10-5

Expected depolarization



Polarized Atomic Hydrogen TargetDynamic Equilibrium and Proton Polarization

As a result, the cell contains predominantlyIn a dynamic equilibrium, P ~ 80 % in about 10 min.


Below 0.3K the dilution refrigerator has much higher cooling power

Cooling power:

Physics Principles of the DR


Patricia Aguar Bartolomé , Kurt Aulenbacher , Valery Tioukin , Jürgen Diefenbach

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