1. ASACUSA Status and Outlook: antihydrogen
Towards the production of an antihydrogen beam
N. Kuroda, S. Ulmer, D.J. Murtagh, Simon Van Gorp, M. Corradini, M. Diermaier, M. Leali, C. Malbrunot, V. Mascagna, O. Massiczek, K. Michishio, A. Mohri, H. Nagahama, Y. Nagashima, Y. Nagata, M. Otsuka, B. Radics, C. Sauerzopf, K. Suzuki, M. Tajima, H. A. Torii, L. Venturelli, B. Wünschek, N. Zurlo, H. Higaki, Y. Kanai, E. Lodi-Rizzini, Y. Matsuda, E. Widmann, and Y. Yamazaki

2. Overview Introduction to the ASACUSA-Cusp experiment
Antiproton trap (MUSASHI)
Positron trap
Cusp Trap
Results from 2012
Towards a beam of antihydrogen

3. Acronyms Pt1
ASACUSA : Atomic Spectroscopy And Collisions Using Slow Antiprotons

4. Motivation
Antihydrogen is the simplest antiatom consisting of an antiproton ( H ) and a positron ( e + )
A sample of antihydrogen amenable to spectroscopic investigation would allow comparisons to be made with hydrogen atoms. Resulting in a high precision test of CPT symmetry.
The ASUACUSA-Cusp experiment aims to perform high precision spectroscopy of the ground state hyperfine structure of antihydrogen.

5. Spectroscopy Method Rabi-like beam spectroscopy1,2
Rabi, I. I., Kellogg, J. M. B. & Zacharias, J. R. Phys. Rev. 46, 157–163 (1934).
A. Mohri and Y. Yamazaki, Europhys. Lett. 63 (2003) 207 [2] Y. Enomoto et al., Phys.Rev.Lett. 105 (2010)

6. The ASACUSA Cusp experiment
Positron Trap
Cusp Trap
Antiproton Trap
Hbar detector
RFQD

7. The ASACUSA Cusp Experiment
Antiproton trap
For storage of antiprotons from the AD ring
Positron accumulator
Production and storage of positrons
Cusp trap
Antihydrogen production and focusing p
Positron accumulator
Cusp trap
Antiproton trap
Kuroda, N., S. Ulmer, D. J. Murtagh, S. Van Gorp, Y. Nagata, M. Diermaier, S. Federmann, et al. Nature Communications 5 (2014).

8. AD & RFQD The AD cycles every 100s
3.5GeV/c antiprotons are cooled to 100MeV/c (5.3MeV) and extracted to experimental zones
Of the order 10 million antiprotons per cycle
The RFQD further reduced the antiproton energy from 5.3MeV to 115keV

9. Acronyms Pt2
MUSASHI : Monoenergetic Ultra-Slow Antiproton Source for High-precision Investigation

10. Antiproton Trap - MUSASHI
MRE
antiprotons
Extraction Electrodes
Electrodes are cooled to ~10K via contact with cold-bore (4-6K)
Vacuum < 10 −12 Torr
Superconducting solenoid provides 2.5T B field

11. Antiproton Trap - MUSASHI
Degrader foil reduces incoming antiproton energy to ~10keV
Catching bias ~-13kV
Antiprotons are cooled with ~3× electrons
A rotating wall electric field is superimposed on the trap ring electrodes to control the antiproton density
1-2 million antiprotons are trapped per AD cycle
Antiprotons can be extracted with eV energies.
Cyclotron cooling T~1s for electrons.

12. Positron Accumulation
Before the 2012 antiproton beam was delivered, significant improvements were made to the ASACUSA-Cusp positron accumulator.
The compact gas cell reported previously1 was extended and the tungsten mesh moderators replaced.
1. Imao, H., K. Michishio, Y. Kanai, N. Kuroda, Y. Enomoto, H. Higaki, K. Kira, et al. J. Phy: Conf. Ser. 225, no. 1 (2010)

13. Positron Beam Producion
Positrons are produced by the decay of a 22Na source in conjunction with a moderator
The W foil moderators used in previous experimental runs were replaced with a solid Ne ice grown onto a conical aperture in front of the source window.
This was expected to increase the beam intensity by an order of magnitude.

14. Positron Trap

15. Positron Trap M1
M14 G4 G3 G2 G1
This new gas cell was expected to improve the trapping efficiency by a factor of 2-3

16. Positron Trap Approximately 1e6 positrons were accumulated in 15s
Lifetime ~ 13s
Predicted lifetime >100s
Problem with :
Electronic Noise
Ground Loops

17. Transfer to the Cusp
Positrons must be transferred into the Cusp trap, this process is repeated multiple times to accumulate ~30 million positrons in the cusp trap
Whilst positrons are stored in the Cusp trap a rotating wall electric field is applied to compress the cloud e+
Positron trap
Cusp trap

18. Positron Storage in the Cusp Trap
The maximum number transferred to the cusp in 2012 was 60 million
Antihydrogen experiments typically used 30 million positrons compressed to 1mm in the mixing potential 𝜌~1× 10 14

19. The Cusp Trap
MCP
MRE
antiprotons
Thermal Shield
Thermal Shield
SC Magnet in anti-Helmholtz configuration i.e. a cusped field (Bmax ~2.7T)
Cold-bore T~10K
MRE T~15K

20. The Cusp Trap
To observe a high polarization fraction (and focusing of the beam) cold antihydrogen is required
For 3K antihydrogen the number exiting the Cusp trap should be enhanced by a factor of 50 above a solid angle consideration.

21. Antihydrogen Production
3e5 antiprotons injected from MUSASHI
3e7 positrons stored in the cusp trap
420kHz RF is injected onto one of the Cusp trap MRE electrodes to prolong antihydrogen formation

22. Field Ionization detection method
No RF
420KHz

23. Detection Field free region
Cusp Trap
Production region
Detector
2.7m
Field free region
BGO Crystal inside vacuum tube (OD=10cm t=5mm)
5 plastic scintillators surrounding BGO (t=10mm, SA~2pi)
Coincidence between 2 plastic scintillators for background discrimination
Background reduced by factor of ~1000
Signal reduced by a factor of 2
-400V (94 V/cm)  n>43 are ionized
-2000V (452 V/cm) n>29 are ionized

24. Results Field ionisation filter -400V (n<43)
Background measured by replacing positrons with electrons
Energy deposited in the BGO crystal for events with double coincidences from the 5 plastic scintillators detectors.
Kuroda, N., S. Ulmer, D. J. Murtagh, S. Van Gorp, Y. Nagata, M. Diermaier, S. Federmann, et al. Nature Communications 5 (2014).

25. Results Top plot shows number of counts with background subtracted
Bottom plot shows the number of counts corrected for the energy dependant detection efficiency predicted by GEANT 4 simulation.
25h-1 n<43
16h-1 n<29
Kuroda, N., S. Ulmer, D. J. Murtagh, S. Van Gorp, Y. Nagata, M. Diermaier, S. Federmann, et al. Nature Communications 5 (2014).

26. Outlook
After the 2012 antiproton run CERN shutdown the accelerator chain to upgrade the LHC
Work began to improve parts of the ASACUSA-Cusp experiment.
Further improvements to the positron accumulator
Adiabatic transport of pbar from MUSASHI to the Cusp trap
New Cusp trap magnet

27. Positron Accumulation 2014
B field increase to 1T from 0.3T
Filters installed into the vacuum system
Lifetime ~100s

28. Adiabatic transport 153.7±0.3 eV 145±2 eV 3.2±0.5 eV 24±2 eV
before transport
after transport
Mean
153.7±0.3 eV
145±2 eV
Sigma
3.2±0.5 eV
24±2 eV
before transport
after transport
Mean
16.2±0.4 eV
11.4±0.8 eV
Sigma
2.3±0.5 eV
3.7±0.7 eV
By decreasing the injection energy of protons and adding pulse coils, the energy spread of the protons was improved by a factor of ～6.

29. Double Cusp Magnet
Improved focusing at higher T  enhancement of beam over solid angle.

30. Outlook
Radics, B., D. J. Murtagh, Y. Yamazaki, and F. Robicheaux. Physical Review A 90, no. 3 (2014)

31. Conclusion
During 2012 antihydrogen was observed 2.7m away from the production region.
No evidence for focusing of antihydrogen with the Cusp trap  too energetic?
Improvements during LS1 may increase the ‘beam’ intensity

32. ASACUSA Cusp team in 2012