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Transcript of Patricia Aguar Bartolomé, Kurt Aulenbacher, Valery Tioukin, Jürgen Diefenbach Institut für...
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
4Patricia Aguar Bartolome - PAVI'14
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
17/07/2014
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
5Patricia Aguar Bartolome - PAVI'14
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 Target
Magnetic field B splits H1 ground state
At B = 8T, sin q ≈ 0.3% Mixing angle tan2q ≈ 0.05/B(T)
6
Mixture ~ 53% of and ~ 47% of , Pe ~ 1-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
17/07/2014
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
7Patricia Aguar Bartolome - PAVI'1417/07/2014
Status of the Atomic Hydrogen Target
New Dilution Refrigerator needs to be designed and produced!!
Test superconducting solenoid
8Patricia Aguar Bartolome - PAVI'1417/07/2014
UVA Superconducting Solenoid Test
Status of the Atomic Hydrogen Target
9Patricia Aguar Bartolome - PAVI'14
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
17/07/2014
10
Status of the 8T Superconducting Magnet
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
Status of the 8T Superconducting Magnet
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
Status of the 8T Superconducting Magnet
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
Status of the 8T Superconducting Magnet
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
14
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
15Patricia Aguar Bartolome - PAVI'1417/07/2014
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 ~ T3
Status of the Atomic Hydrogen Target
Preliminary design of the new Dilution Refrigerator
16Patricia Aguar Bartolome - PAVI'1417/07/2014
Status of the Atomic Hydrogen Target
Preliminary design of the new Dilution Refrigerator
17Patricia Aguar Bartolome - PAVI'14
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
18Patricia 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)
• 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
19Patricia Aguar Bartolome - PAVI'14
Beam stabilization and solenoid test set up
Reliable 3T solenoid for first tests
17/07/2014
Beam Stabilization
20Patricia Aguar Bartolome - PAVI'14
Principle of beam stabilization
17/07/2014
• Cavity monitors measure beam position (XYMOs)
• Steering magnets correct beam direction (WEDLs)
Beam Stabilization
21Patricia 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
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
22Patricia Aguar Bartolome - PAVI'1417/07/2014
BACKUP
Patricia Aguar Bartolome - PAVI'14 2317/07/2014
Beam Stabilization
24Patricia Aguar Bartolome - PAVI'14
Planned Beam test setup
17/07/2014
Beam Stalilization
25Patricia Aguar Bartolome - PAVI'1417/07/2014
Beam Stalilization
26Patricia Aguar Bartolome - PAVI'1417/07/2014
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 ~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)
Polarized Atomic Hydrogen Target
27Patricia Aguar Bartolome - PAVI'1417/07/2014
Contamination and Depolarization of the Target Gas
No 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 Target
28Patricia Aguar Bartolome - PAVI'1417/07/2014
Polarized Atomic Hydrogen TargetDynamic Equilibrium and Proton Polarization
As a result, the cell contains predominantlyIn a dynamic equilibrium, P ~ 80 % in about 10 min.
Patricia Aguar Bartolome - PAVI'14 2917/07/2014
Below 0.3K the dilution refrigerator has much higher cooling power
Cooling power:
Physics Principles of the DR
30Patricia Aguar Bartolome - PAVI'1417/07/2014