Patricia Aguar Bartolomé, Kurt Aulenbacher, Valery Tioukin, Jürgen Diefenbach Institut für Kernphysik, Universität Mainz PAVI’14, Syracuse, NY 17th July 2014 Patricia Aguar Bartolome - PAVI'14117/07/2014

 Physics Motivation  Polarized Atomic Hydrogen Target  Status of the Mainz Hydro-Møller Target  Beam Stabilization Test  Summary 2 Patricia Aguar Bartolome - PAVI'14 17/07/2014

Hydro-Møller PV Detector Goal: Low energy PV electron scattering experiments at MESA with systematic accuracy < 0.5% for beam polarization measurements 3 Patricia Aguar Bartolome - PAVI'14 MESA (Mainz Energy recovering Superconducting Accelerator) 17/07/2014

Compton Scattering: Accurate enough at E beam > 4GeV, but accuracy around 1% at low energies Not enough for PV-experiments Møller Scattering with ferromagnetic target Polarimetry Methods 4 Patricia Aguar Bartolome - PAVI'14 AdvantagesDisadvantages Beam energy independent  Low electron polarization ( ~ 8 % ) High analyzing power (~ 80%)  Target heating Beam current limited to 2-3 A 2 particles with final state high energies eliminates background  Levchuk effect ~ 1%  Systematic errors on target polarization ~ 2%  Low Pt Dead time 17/07/2014

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 5 Patricia Aguar Bartolome - PAVI'14 AdvantagesDisadvantages 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 P B /P B ≤ 0.5% Suitable for PV-experiments 17/07/2014

Magnetic field B splits H 1 ground state At B = 8T, sin ≈ 0.3% Mixing angle tan2 ≈ 0.05/B(T) 6 Mixture ~ 53% of and ~ 47% of, P e ~ 1-,  ~ 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 4 He H+H H 2 Gas density : cm- 3 17/07/2014

Dilution refrigerator and magnet shipped 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 7 Patricia Aguar Bartolome - PAVI'14 17/07/2014

New Dilution Refrigerator needs to be designed and produced!! Test superconducting solenoid 8 Patricia Aguar Bartolome - PAVI'14 17/07/2014

UVA Superconducting Solenoid Test 9 Patricia Aguar Bartolome - PAVI'14 Central 4.2K Current76.4 A Homogeneity /10mm DSV Inductance20.3H Voltage0.995V Clear Bore762 mm Overall Length304.8mm Outer Diameter167.64mm 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 17/07/2014

10 New cooling system set up design Patricia Aguar Bartolome - PAVI'14 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

11 New cooling system set up design Patricia Aguar Bartolome - PAVI'14 Copper Shields (T ~77K) 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

12 New cooling system set up design Patricia Aguar Bartolome - PAVI'14 Solenoid (T ~4K) 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

13 New cooling system set up design 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 Patricia Aguar Bartolome - PAVI'1417/07/2014 Courtesy of J.Bibo and D. Rodriguez

14Patricia 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 3 He and 4 He gas needed - Volumes of all parts inside the DR (separator, evaporator, still) and also pumps and lines - Produce new mixing chamber 15 Patricia Aguar Bartolome - PAVI'14 17/07/2014

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 ~ T 3 Preliminary design of the new Dilution Refrigerator 16 Patricia Aguar Bartolome - PAVI'14 17/07/2014

Preliminary design of the new Dilution Refrigerator 17 Patricia Aguar Bartolome - PAVI'14 ModuleReadyStatusRemarks & Problems Cryostat housingEnd 2014R&D Construction Cons. using Super-MLI Accurate positioning of solenoid Stage 1.10 KEnd 2014Development Construction HT-HE Pre-HE LT-HE Valves Stage 0.25 KEnd 2015R&D (Technologies not yet under control) Final-HE Mixing Chamber Film Burners Hydrogen feed systemEnd 2016R&DLiterature references Transition unit not ready Superconducting solenoid End 2014Test Detection systemR&DCollaboration? Pumping systemSummer 2016Not funded yet 3 He Still 4 He Evaporator 4 He Separator 4 He Pre-HE 3 He-FillingEnd 2016Not funded yetVolume = 200 l STP Target TestEnd /07/ K stage HE currently under construction in our Mechanical Workshop

18 Patricia Aguar Bartolome - PAVI'14 Requirements for the PV experiment at MESA 17/07/2014 P2 expected physics asymmetry < 50 ppb Beam energy ~ 150 MeV (external beam) P B /P B ≤ 0.5% Beam quality: Beam must be stabilized ( A i 0) Helicity correlations must be suppressed (A i 0) Beam parameters are correlated with helicity A i Noise on beam parameters (helicity un-correlated)  A i

19 Patricia Aguar Bartolome - PAVI'14 Beam stabilization and solenoid test set up Reliable 3T solenoid for first tests 17/07/2014

20 Patricia Aguar Bartolome - PAVI'14 Principle of beam stabilization 17/07/2014 Cavity monitors measure beam position (XYMOs) Steering magnets correct beam direction (WEDLs)

21 Patricia Aguar Bartolome - PAVI'14 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

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 22Patricia Aguar Bartolome - PAVI'1417/07/2014

BACKUP Patricia Aguar Bartolome - PAVI'142317/07/2014

24 Patricia Aguar Bartolome - PAVI'14 Planned Beam test setup 17/07/2014

25 Patricia Aguar Bartolome - PAVI'14 17/07/2014

26 Patricia Aguar Bartolome - PAVI'14 17/07/2014

Gas Lifetime in the Cell Loss 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 ~10 17 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) 27 Patricia Aguar Bartolome - PAVI'14 17/07/2014

Contamination and Depolarization of the Target Gas No Beam  Hydrogen molecules ~  High energy atomic states and <  Excited atomic states <  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 <  Depolarized ions and electrons contamination <  Contamination by excited atoms < Expected depolarization 28 Patricia Aguar Bartolome - PAVI'14 17/07/2014

Dynamic Equilibrium and Proton Polarization As a result, the cell contains predominantly In a dynamic equilibrium, P ~ 80 % in about 10 min. Patricia Aguar Bartolome - PAVI'142917/07/2014

Below 0.3K the dilution refrigerator has much higher cooling power Cooling power : 30 Patricia Aguar Bartolome - PAVI'14 17/07/2014