Spin Feedback System at COSY

Size: px

Start display at page:

Download "Spin Feedback System at COSY"

Derick Carson
5 years ago
Views:

1 Spin Feedback System at COSY Nils Hempelmann

2 Outline Electric Dipole Moments Spin Manipulation Feedback System Validation Using Vertical Spin Build-Up Wien Filter Method Nils Hempelmann Slide 2 24

3 Electric Dipoles and Fundamental Symmetries Nonzero electric dipole moment (EDM) of elementary particles violates CP-Symmetry H = µσ B dσ E T : H = µσ B + dσ E P : H = µσ B + dσ E Standard Model prediction: to e cm New physics? Nils Hempelmann Slide 3 24

4 Measurement Principle ds dt = d E + µ B Different methods proposed: E-field, B-field, combined Pictured: E-field only Signal is build-up of vertical polarization Nils Hempelmann Slide 4 24

5 Cooler Synchrotron - COSY From 300 MeV/c to 3300 MeV/c, protons or deuterons Circumference: 184 m Magnetic ring elements only To be used for EDM precursor experiments Nils Hempelmann Slide 5 24

6 Spin Precession Vertical magnetic field Vertical polarization is stable Horizontal polarization precesses Coherence time at COSY: 1000 s Nils Hempelmann Slide 6 24

7 Spin Manipulation y z P x Spin can be rotated by RF devices Comparable to NMR Frequency must be on resonance Solenoid rotates spin around beam axis (z), Wien filter around y-axis Nils Hempelmann Slide 7 24

8 Spin Resonance y P B x Resonance: Fixed phase relation between field and spin Spin precesses each turn Magnetic RF field must match this z Nils Hempelmann Slide 8 24

9 Spin Resonance y P B x Resonance: Fixed phase relation between field and spin Spin precesses each turn Magnetic RF field must match this z Nils Hempelmann Slide 8 24

10 Spin Resonance P y B x Resonance: Fixed phase relation between field and spin Spin precesses each turn Magnetic RF field must match this z Nils Hempelmann Slide 8 24

11 Spin Resonance y P B x Resonance: Fixed phase relation between field and spin Spin precesses each turn Magnetic RF field must match this z Nils Hempelmann Slide 8 24

12 Spin Resonance y P z B x Resonance: Fixed phase relation between field and spin Spin precesses each turn Magnetic RF field must match this Nils Hempelmann Slide 8 24

13 Spin Resonance y P x Resonance: Fixed phase relation between field and spin Spin precesses each turn Magnetic RF field must match this z B Nils Hempelmann Slide 8 24

14 Spin Resonance y z B P x Resonance: Fixed phase relation between field and spin Spin precesses each turn Magnetic RF field must match this Nils Hempelmann Slide 8 24

15 Spin Resonance y P B x Resonance: Fixed phase relation between field and spin Spin precesses each turn Magnetic RF field must match this z Nils Hempelmann Slide 8 24

16 Spin Resonance y P B x Resonance: Fixed phase relation between field and spin Spin precesses each turn Magnetic RF field must match this z Nils Hempelmann Slide 8 24

17 Why Feedback? Feedback system fixes phase between spin precession and solenoid frequency Need spin in phase with RF over 1000 s Would mean, f /f < if 80% drop in signal is accepted Solution: Adjust accelerator frequency to keep the spin phase fixed Nils Hempelmann Slide 9 24

18 Feedback System COSY beam COSY control frequency generator rf cavity phase determination solenoid stand-alone DAQ polarimeter Measure polarimeter events, COSY frequency and solenoid frequency using one time reference Measure phase difference between spin and solenoid Adjust COSY accelerator frequency to change the phase Tested with solenoid, Wien filter planned Nils Hempelmann Slide 10 24

19 Polarimetry Polarized beam causes asymmetry in count rate of elastic events Scattering angle 9 to 13 Measure asymmetry, e.g. N L N R N L +N R Horizontal polarization precesses faster than detector rate Nils Hempelmann Slide 11 24

20 Calculating Spin tune and In-Plane Polarization Spin tune ν s = f spin f COSY Gγ 0.16 Problem: only one detector event every 24 spin revolutions Solution: use time information to map all events to one period Spin tune can be measured to a precision of O(10 8 ) in 2 s (PRL 115, (2015)) Nils Hempelmann Slide 12 24

21 Phase and COSY Frequency Relative phase: ( ) φ = 2πf sol T 2πν s f COSY T = 2πn fsol f COSY ν s f COSY 750 khz, f spin 120 khz and f sol 871 khz: φ T rad = 7.7 f Hz s COSY Frequency can be adjusted in steps of 3.7 mhz corresponding to φ/ T ±30 mrad/s Nils Hempelmann Slide 13 24

22 Phase Over One Cycle Phase φ [rad] [rad] φ set meas Phase φ [Hz] f COSY (a) feedback off 3 (b) feedback on (c) 0.2 corrections time in cycle [s] Top: relative phase drifts without feedback Center: relative phase fixed over cycle with feedback Bottom: corrections to frequency Stable within σ = Nils Hempelmann Slide 14 24

23 Feedback in Spin Flip z φ B P y x Spin rotation depends on relative phase φ Maximum field when spin is parallel to beam: no effect Maximum field when spin is perpendicular to beam: maximum effect Use feedback to set relative phase Equivalently: Choose where spin points when RF field is at maximum Nils Hempelmann Slide 15 24

24 Feedback in Spin Flip z B y φ P x Spin rotation depends on relative phase φ Maximum field when spin is parallel to beam: no effect Maximum field when spin is perpendicular to beam: maximum effect Use feedback to set relative phase Equivalently: Choose where spin points when RF field is at maximum Nils Hempelmann Slide 15 24

25 Feedback in Spin Flip z B y φ x P Spin rotation depends on relative phase φ Maximum field when spin is parallel to beam: no effect Maximum field when spin is perpendicular to beam: maximum effect Use feedback to set relative phase Equivalently: Choose where spin points when RF field is at maximum Nils Hempelmann Slide 15 24

26 Feedback in Spin Flip z B y φ P x Spin rotation depends on relative phase φ Maximum field when spin is parallel to beam: no effect Maximum field when spin is perpendicular to beam: maximum effect Use feedback to set relative phase Equivalently: Choose where spin points when RF field is at maximum Nils Hempelmann Slide 15 24

27 Feedback in Spin Flip z B y P φ x Spin rotation depends on relative phase φ Maximum field when spin is parallel to beam: no effect Maximum field when spin is perpendicular to beam: maximum effect Use feedback to set relative phase Equivalently: Choose where spin points when RF field is at maximum Nils Hempelmann Slide 15 24

28 Feedback in Spin Flip P z B y φ x Spin rotation depends on relative phase φ Maximum field when spin is parallel to beam: no effect Maximum field when spin is perpendicular to beam: maximum effect Use feedback to set relative phase Equivalently: Choose where spin points when RF field is at maximum Nils Hempelmann Slide 15 24

29 Feedback in Spin Flip P z B y φ x Spin rotation depends on relative phase φ Maximum field when spin is parallel to beam: no effect Maximum field when spin is perpendicular to beam: maximum effect Use feedback to set relative phase Equivalently: Choose where spin points when RF field is at maximum Nils Hempelmann Slide 15 24

30 Feedback in Spin Flip P z B y φ x Spin rotation depends on relative phase φ Maximum field when spin is parallel to beam: no effect Maximum field when spin is perpendicular to beam: maximum effect Use feedback to set relative phase Equivalently: Choose where spin points when RF field is at maximum Nils Hempelmann Slide 15 24

31 Feedback in Spin Flip z φ B P y x Spin rotation depends on relative phase φ Maximum field when spin is parallel to beam: no effect Maximum field when spin is perpendicular to beam: maximum effect Use feedback to set relative phase Equivalently: Choose where spin points when RF field is at maximum Nils Hempelmann Slide 15 24

32 Vertical Spin Build-Up - I Solenoid Amplitude ε V ε H φ = 0.50 set π (a) 0.1 (b) (c) time in cycle t [s] Confirm that phase is fixed Solenoid is switched back on with active feedback system Polarization tilted into vertical direction at a speed proportional to sin φ Nils Hempelmann Slide 16 24

33 Vertical Spin Build-Up - II α [rad] Pos. Initial p V Neg. Initial p Fits V φ = 0.50 π set time in cycle t [s] Examine angle α = arctan ( pv p H ) Blue: positive initial polarization, Red: negative Increases at roughly constant rate Feedback stops when spin is vertical Nils Hempelmann Slide 17 24

34 Vertical Spin Build-Up - III [rad/turn] dα dn Angular Velocity Pos. Initial p V Neg. Initial p V Pos. Fit Neg. Fit φ 6 = φ + φ set det 0 α [rad/s] Slope of build-up has expected sinusoidal shape Independent from initial polarization Confirms that the feedback system works Nils Hempelmann Slide 18 24

EDM in Magnetic Rings Spin rotates rapidly (120 khz) around vertical axis EDM causes small up-down-oscillation of spin, no macroscopic build-up Limit

35 EDM in Magnetic Rings Spin rotates rapidly (120 khz) around vertical axis EDM causes small up-down-oscillation of spin, no macroscopic build-up Limit for muon EDM measured this way Not suitable for hadrons: G µ 10 3, G p 1.79, proportional to precession frequency Nils Hempelmann Slide 19 24

36 Wien Filter Method Radio frequency Wien filter rotates spin Causes net build-up of vertical polarization Nils Hempelmann Slide 20 24

37 Wien Filter Wien filter: E- and B-fields with zero Lorentz force No influence on trajectory at design velocity RF field: spin rotates about axis of magnetic field f lter = f COSY + f spin Nils Hempelmann Slide 21 24

38 Wien Filter Signal Top: vertical polarization without Wien filter Bottom: the same with Wien filter Broad band from rapid oscillation Source: PhD thesis M. Rosenthal Nils Hempelmann Slide 22 24

39 RF Wien Filter at COSY Frequency 100 khz to 2 MHz Rotatable 90 about beam axis Nils Hempelmann Slide 23 24

40 Conclusion Successfully tested spin feedback system Confirmed by direct measurement of relative phase and vertical build-up experiments Phase stable within σ = 12 Will be used with RF Wien Filter in precursor experiments Phase Locking the Spin Precession in a Storage Ring, Publication: Phys. Rev. Lett. 119, Nils Hempelmann Slide 24 24

POLARIMETRY FOR A STORAGE-RING ELECTRIC-DIPOLE-MOMENT MEASUREMENT MARIA ŻUREK FOR THE JEDI COLLABORATION

POLARIMETRY FOR A STORAGE-RING ELECTRIC-DIPOLE-MOMENT MEASUREMENT 8 JUNE 2018 MARIA ŻUREK FOR THE JEDI COLLABORATION MOTIVATION Barion Asymmetry Problem Barion Asymmetry Observation Standard Cosmological