1. Siara Fabbri University of Manchester
Optimization of Degrader Integration, Beam Injection and B-field Measurements for Antiproton Experiments at CERN
Siara Fabbri
University of Manchester

2. ALPHA
ALPHA studies fundamental symmetries between matter and antimatter by making precise comparisons of hydrogen and antihydrogen.
ALPHA-g: tests the interaction of antimatter with gravitational fields.
In Jan. 2013, ALPHA placed the first experimental limits on the ratio of the gravitational and inertial masses of antihydrogen.
ALPHA-2: uses optical spectroscopy to measure the antihydrogen spectrum with high precision.
In Dec. 2016, ALPHA published the first observation of a spectral line in antihydrogen.
Components of ALPHA-2:
Antiprotons
Positrons
Antiproton Catching trap
Antihydrogen trap
Annihilation detector r5
FIG.1: A schematic view of the mixing trap and detectors.

3. Upgrade to Antiproton Decelerator: ELENA
In current setup, 99.9% of the antiprotons are lost due to the use of degrader foils needed to decelerate them down to around 5 keV.
ELENA will bring access to an entirely new range of experiments by drastically improving the number of antiprotons caught and delivering beams almost simultaneously to all four experiments. AD
AD with ELENA
Energy
5.3 MeV
100 keV
Number of Antiprotons
3*107
0.45*107
Bunch Length
200 ns
75 ns
Period/Run time
100 s / 8 hr
100s / 24 hr
FIG.1: A schematic of the new addition to the antiproton decelerator.

4. Antiproton Catching Trap
Penning-Malmberg Trap: uses a strong axial magnetic field for radial confinement and an electrostatic well for axial confinement.
FIG.1: An illustration of a typical Penning trap. (
Before entering the trap, the 5.3 MeV Antiprotons from AD are slowed down through a series of thin degrading foils.
Particles with energy below 5keV are caught, equating to <1% of incoming particles.
The trapped antiproton plasmas are subjected to electron cooling and evaporative cooling, until they are cold and dense enough for antihydrogen formation.
FIG.2: The antriproton catching trap in ALPHA-2.

5. I. Degrading
As many particles as possible need to be trapped in a 3T Penning-Malmberg trap using roughly 5kV axial potential depth.
Deceleration is done mostly using degrading foils.
Catching Trap
<1% at < 5keV
~5.3 MeV
Current Setup:
Antiprotons Al
30 um Al
10 um Be
50 um Be
165 um
100 keV
Proposed Setup:
Antiprotons
Al, Be or Polyimide
~1 um
Catching Trap

6. I. Degrading Choosing a material: Capture efficiency.
Induced divergence.
Induced longitudinal and transverse energy spread.
Cyclotron radius: beam must fit in catching trap of inner diameter ~40 mm.
Approach
SRIM
- Modify models in SRIM to include secondary electrons produced.
Input the output file from SRIM into GPT and determine optimal position of the degrader relative to the Catching Trap solenoid.
Geant4
Correct the models in Geant4 for the known systematic uncertainties at lower energy.
Fig.1: Percentage of antiprotons caught calculated with SRIM.

7. Future Work
Complete the upgrade of the degrading system for 100keV antiprotons.
Prototype a non-destructive beam counter for quantifying antiprotons extracted from the Catching Trap (CT).
Prototype non-destructive diagnostics for trapped plasma modes used to characterize particle temperature and perform in situ measurements of the magnetic fields.
Simulate and develop a technique for extracting antiprotons from a high magnetic field region to a low field Paul trap.