1. 11.09.2018 I Alexander Nass for the JEDI collaboration
Commissioning of the RF Wien filter for a first deuteron EDM measurement at COSY/Jülich
I Alexander Nass for the JEDI collaboration

2. Proof of principle experiment at COSY: („precursor experiment“)
Highest EDM sensitivity shall be achieved with a new type of machine:
An electrostatic storage ring, where:
Centripetal force produced primarily by electric fields
Electric field couples to EDM and provides required sensitivity (< 1028 e cm)
In this environment, magnetic fields mean evil (since 𝜇 is large)
Idea behind proof of principle experiment with novel RF Wien filter ( 𝐸 × 𝐵 ):
In magnetic machine, particle spins (protons, deuterons) precess about stable spin axis (≅ direction of magnetic fields in dipole magnets)
Use RF device operating on some harmonic of the spin precession frequency:
Phase lock between spin precession and device RF
Allows to accumulate EDM effect as functionof time in cycle (~ 1000 s)
Show that conventional storage ring usable for first direct EDM measurement
11. September 2018

3. Model calculation of EDM build-up with RF Wien filter
Ideal ring with deuterons at 𝑝 𝑑 =970 MeV/c:
𝐺=−0.143, 𝛾=1.126, 𝑓 𝑆 = 𝑓 𝑟𝑒𝑣 𝛾𝐺+ 𝐾 =0 ≈ kHz
Electric RF field integral assumed 1000 × 𝐸 𝑊𝐹 ∙𝑑𝑙 ≈2200 kV (w/o ferrites)
EDM accumulates in 𝑃 𝑦 (𝑡)∝ 𝑑 EDM
11. September 2018

4. The RF Wien filter
Waveguide design provides 𝐸 × 𝐵 by design.
Support for geodetics
Inner support
tube
Support structure
for electrodes RF
feedthrough
Ferrit cage
BPM
(Rogowski coil)
Beam pipe (CF 100)
Copper
electrodes
Ferrit cage
Mechanical
support
Vacuum vessel with
small angle rotator
Belt drive for rotation
Aim was to build the best possible device with respect to electromagnetic performance, mechanical tolerances, etc.
Device rotatable by in situ
Clamps for the Ferrit cage
~1 m
11. September 2018

5. Electromagnetic field simulations
Full-wave simulation with CST Microwave Studio
Each simulation required ~12 hours of computing time
Excellent cooperation with RWTH Aachen and ZEA / FZ Jülich
11. September 2018

6. Driving Circuit
Realization with load resistor and tunable elements
Maximum 4 × 1 kW power available
Adjustment of phase and relative amplitudes of E and B field
Different 𝐿𝑓 permit the use in the frequency range of 0.6−1.7 MHz
Current / voltage detectors 𝑈,𝐼 𝑖=1…9 used to monitor the system
Driving circuit used to power system and match it for zero Lorentz force
11. September 2018

7. Phase and impedance matching
Measured phase and impedance for 𝑓 WF =871 kHz
𝐸/𝐵 phase as function of 𝐶L and 𝐶T
Impedance 𝑍9 as function of 𝐶L and 𝐶T
𝑍 9 =79 Ω when matched to deuteron momentum of 970 MeV/c
11. September 2018

8. Control System
Control via LABVIEW. Feedback loops keep the system in optimal working condition. EPICS used to exchange data.
11. September 2018

9. Installation into COSY
Installed at COSY since April 2017.
11. September 2018

10. Lorentz force measurements
COSY BPMs measure beam position
Unmatched RF Wien filter excites beam at 𝑓 WF
Lock-In amplifiers are used to extract excitation from BPM signal
Signal is sent to EPICS
RF Wien filter is matched by minimizing the beam excitation
11. September 2018

11. Lorentz force measurements
Dependence on beam size and shape:
Normal COSY lattice
Matching point at 𝐶L = 6800 and 𝐶T = 4950,
where in addition phase between 𝐸 and 𝐵 field is zero.
11. September 2018

12. Lorentz force measurements
Dependence on beam size and shape:
COSY lattice with low-𝛽 section on
Same matching point at 𝐶L = 6800 and 𝐶T = 4950.
Excitations in unmatched case larger.
11. September 2018

13. Lorentz force measurements
Dependence on RF Wien filter frequency
629.4 kHz
871 kHz
Different matching points. Tuning with loop 2 and 3.
kHz
kHz
11. September 2018

14. Driven oscillations
Matched RF Wien filter in 90° position (radial B field):
Polarization is rotated in 𝑥𝑦 plane.
11. September 2018

15. COSY cycle for resonant build-up measurements:
RF Wien filter in 0° position (vertical 𝐵 field)
Beam preparation (injection, acceleration, bunching, cooling)
Switch off cooler, including toroid magnets
Rotation of spin into horizontal plane (RF solenoid)
Start spin tune feedback
set relative phase between RF-WF and spin precession
Switch on Siberian Snake
Power up RF Wien filter
Measure build-up 𝑃 𝑦 (𝑡)
11. September 2018

16. Resonant build-up
Rate of out-of-plane rotation angle 𝛼 as function of RF-WF phase.
Variation of the RF Wien filter rotation angle, Siberian snake off.
11. September 2018

17. Resonant build-up
Rate of out-of-plane rotation angle 𝛼 as function of RF-WF phase.
Variation of the spin angle by Siberian snake. RF Wien filter at 0°.
11. September 2018

18. Expectation for 𝑑= 10 −20 e cm in ideal COSY ring
Resonant build-up
Expectation for 𝑑= 10 −20 e cm in ideal COSY ring
11. September 2018

19. Expectation for 𝑑= 10 −18 e cm in ideal COSY ring
Resonant build-up
Expectation for 𝑑= 10 −18 e cm in ideal COSY ring
11. September 2018

20. Resonant build-up: Data from COSY
𝑑= 10 −20 e cm,
ideal COSY ring
𝟏𝟔 data points from last run
In upcoming run, produce map covering minimum
11. September 2018

21. Summary
RF Wien filter method together with spin tracking simulation is a powerful tool to:
Rotate spin in 𝑥𝑦 plane (in 90° mode)
Measure resonant EDM build-up of vertical polarization
Conduct a first EDM measurement with deuterons
Study imperfections of accelerator
Next steps:
Improve beam position monitors around RF Wien filter
Improvements to Siberian snake
First EDM measurement with deuterons (Nov./Dec. 2018)
11. September 2018