1. BEAMLINE MAGNETS FOR ALPHA-G
MARK JOHNSON
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2. OUTLINE A Brief Introduction to ALPHA Summary of the ALPHA-II Beamline
The ALPHA-G Beamline
Proposed layout
Modelling in OPERA 18
Particle Tracking Simulations
Current and Future Challenges
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3. THE ALPHA EXPERIMENT Based at CERN’s Antiproton Decelerator facility
ALPHA-II aims to perform low-energy tests of CPT symmetry using stable trapped antihydrogen:
Measurements of the H spectrum [1]
Tests of charge neutrality [2]
Antimatter gravitation experiments [3]
ALPHA-G is a proposed extension to ALPHA-II for greatly improved gravitational experiments
Current design aims for a precision ± 1% measurement of 𝑔
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4. TRAPPED ANTIHYDROGEN [4]
Three Penning-Malmberg traps in series:
Catching Trap for p capture
Atom Trap for autoresonant mixing of charged plasmas
Accumulator for e +
Magnetic minimum superimposed over the central Atom Trap
Annihilation vertex detector enclosing the Atom Trap
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5. CERN
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6. THE ALPHA-II BEAMLINE 𝐵 Catching Trap CT T2 T3 Atom Trap AT T4
B Gauss
s [cm]
Upstream
Downstream
Catching Trap CT T2 T3
Atom Trap AT T4
Accumulator 𝐵
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7. THE ALPHA-G CONCEPT
A highly simplified sketch of the proposed upstream beamline:
Vertical Solenoid
(2.6 m)
~ 4 m
Catching Trap CT T2 T3
Atom Trap AT
Interconnect
Beamline Modules × 3
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8. AN UNCONVENTIONAL BEAMLINE
The ALPHA-II ‘beamline’ has several unusual features:
Low energy plasmas can be held in place by a static potential (temporarily)
Techniques for the cooling and manipulation of p and e +
Plasmas are confined radially using solenoids, not quadrupole magnets! Cyclotron motion causes radial expansion in low fields
The proposed ALPHA-G beamline includes a sharp 90° bend into a new vertical trapping region
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9. FULL BEAMLINE MODEL
Small-bore solenoid: Stray field reduction without full FEA field analysis
Beamline Modules × 3
Accumulator
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10. THE INTERCONNECT SECTION
Crossed Solenoids generate a dipole component - without obstructing the p or e + beamlines
Steering coils allow adjustment of transverse p trajectories
Additional magnet pairs compensate for vertical solenoid fringe fields
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11. FIELDS ALONG THE BEAMLINE
Beamline Modules
Interconnect
External Solenoid
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12. EARLY PARTICLE TRACKING
Modelled the ALPHA-G beamline, in full, from the beamline modules onwards
Used the OPERA 18 postprocessor for:
An electromagnetic field solver (TOSCA 3D)
A simple Lorentz solver Higher-order effects on the internal plasma structure are currently neglected
Several thousand p can independently be propagated through the beamline forming a distribution in the vertical trap
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13. EARLY PARTICLE TRACKING
Initial
Final
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14. OFFSET CORRECTION Crossed Solenoids 𝐽 0 =650 A cm 2 Offset in 𝑥 ′
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15. PARTICLE TRACKING
Final
Initial
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16. INTERCONNECT STEERING
Before 𝑦 ′ offset correction
Outline shows DNCF100 cross IR
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17. INTERCONNECT STEERING
After 𝑦 ′ offset correction
Outline shows DNCF100 cross IR
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18. FUTURE WORK
Evidently, the magnets in the interconnect region need to be re-optimised to avoid beam losses
The cause of the strange 𝑥 ′ offset within the vertical trap remains unknown
Stray fields could nudge particles off-axis early in their trajectories
Leads to runaway growth of transverse displacements
Tracking of a more realistic plasma including higher-order collective effects
Full characterization of stray field gradients within the vertical trap
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19. THANKS FOR LISTENING! References:
[1] Resonant Quantum Transitions In Trapped Antihydrogen Atoms
C. Amole et al. (ALPHA Collaboration), Nature 483, 439 (2012)
[2] An Experimental Limit On The Charge Of Antihydrogen
C. Amole et al. (ALPHA Collaboration), Nature Communications 5, 3955 (2014)
[3] Description And First Application Of A New Technique To Measure The Gravitational Mass Of Antihydrogen
C. Amole et al. (ALPHA Collaboration), Nature Communications 4, 1785 (2013)