Antiparticle Trapping for Antihydrogen Physics

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Mike Charlton, PhysicsSwansea UniversityUK
Antiparticle Trapping for Antihydrogen Physics
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Summary of the Talk

• Motivation for Antihydrogen Experiments
• Spectroscopic comparisons with H test of CPT
• Measurement of gravitational interaction of
  antimatter with matter
• Antiproton Production, Collection and
  Manipulation
• Moderation, capture, cooling (I), compression
  and cooling (II)
• Positron Production, Collection and Manipulation
• Moderation, accumulation, compression (I),
  transfer, compression (II) and diagnostics
• Antihydrogen Production
• Selected results from ATHENA
• ALPHA an Antihydrogen Trapping Experiment
• Recent progress
• Concluding Remarks

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Motivation for Antihydrogen Experiments
Antihydrogen Hydrogen ?
CPT Theorem (Based upon Lorentz Invariance,
spin-statistics and locality )
Some of the most precise tests of CPT
Relative precision
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Motivation for Antihydrogen Experiments
Antihydrogen Hydrogen ?
Gravity
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Antiprotons CERNs Accelerators
Accelerators   Schematic representation of the
cern accelerator complex without LHC

Accelerators   Schematic representation of the
cern accelerator complex without LHC

Accelerators   Schematic representation of the
cern accelerator complex without LHC

Accelerators   Schematic representation of the
cern accelerator complex without LHC

Machines Projects
Machines Projects
Machines Projects
Machines Projects
The Antiproton Decelerator
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Antiprotons the AD, Antiproton Decelerator
ALPHA
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Antiprotons Capture and Cooling
The trap walls were cooled to 15 K
ATHENA
Antiproton Capture Trap
Similar apparatus used currently in ALPHA method
originally devised by Gabrielse and co-workers
(PRL, 63, 1360 (1989))
To (or close to) the trap temperature
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Antiprotons Capture in ALPHA
Andresen et al., ALPHA collaboration
25k pbars
N.B. magnetic field difference
ALPHA will routinely stack up to 8 shots from the
AD or 2 x 105 pbars into mixing
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Antiprotons Compression in ALPHA
G. Andresen et al., Phys. Rev. Lett. 101 (2008)
203401
Tailor size of electron plasma to maximise the
fraction of cooled antiprotons tuned
empirically as it depends upon the AD output and
other experimental parameters
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Antiprotons ALPHA-Sympathetic Compression using
Electrons
Sympathetic compression of an antiproton cloud by
electrons
G. Andresen et al., Phys. Rev. Lett. 101 (2008)
203401
Typically use a fixed frequency rotating wall
technique at 10 MHz
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Antiprotons ALPHA Evaporative Cooling
Recently published Andresen et al. PRL (2010)
105 013003
23 K
9 K
19 K
325 K
1040 K
57 K
Typically (9 4) K is lowest achievable at the
lowest well available at which (6 1) of the
initial antiprotons remain
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Antiprotons ALPHA Evaporative Cooling
Recently published Andresen et al. PRL (2010)
105 013003
Rate equation model
Small annihilation term
Evaporation time constant
Heating term due to plasma expansion
a is related to the ratio of the barrier height
and the total (KEPE) energy of the particle in
the well. It is around eV/2kT ? for our
situation.
tev tcol?e? with tcol the antiproton-antiproton
collision time
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Antiprotons So far
Antiprotons into the AD at 3.5 GeV (3x107 from
1.5x1013 protons at 26 GeV) 100 s of cooling in
the AD to 5.3 MeV ejection in a 100 ns
burst Capture and electron cooling in a
Penning-Malmberg trap for 20 s (e
10-3) Stacking of up to 8 AD shots. Takes 1000
s for 2 x105 cold antiprotons Shuffle to 1 T
region. Recool and sympathetic radial compression
for about 60 s Evaporative cooling if desired to
very low temperatures. Takes 10 s Now ready
for mixing with positrons
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Positrons Accumulation ATHENA and ALPHA
Trap electrode voltages
Based upon the industry standard Solid-Ne
moderator UCSD Penning Malmberg buffer gas
trap
Distance along the trap
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Positrons Compression ALPHA
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Positrons Accumulation ATHENA and ALPHA
Open circles no rotating electric field Closed
circles rotating field applied
These data using the lazy approach fixed
rotating wall frequency during accumulation N2
gas only
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Positrons Compression ALPHA
Data are a projection of the rotationally
symmetric distribution
Rotating Wall (Dipolar) _at_ 600 kHz for entire
accumulation cycle
N2 only
N2 with CO2 cooling gas
No RW
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Positrons Transfer ATHENA and ALPHA
ATHENA positron transfer protocol time
variation of the electrode voltages
Dynamic recapture positron bounces
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Positrons Transfer and Compression II ATHENA
and ALPHA
Rotating Wall Frequency 15 MHz, Amplitude 3
V, m? 1
Amplifier saturation limit!
Positron stacking study in ATHENA
Rotating Wall compression n 2.6 x 1010 cm-3
achieved
Amoretti et al., PRL 91 55001 (2003) and Phys.
Plasmas, 10 3056 (2003) and Funakoshi et al., PRA
76 012713 (2007)
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Positron manipulation in the single particle
regime
Approximate position of the positron cloud
Swansea 2-stage positron accumulator uses
nitrogen buffer gas and SF6 as a cooling gas.
Incorporates 4-way segmented electrode for
rotating wall compression
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Positron manipulation in the single particle
regime
Radius of the positron cloud versus time after
switching on the rotating wall
At a fixed frequency fit an exponential plus a
constant to derive the compression rate.
Related to similar work by Greaves and Moxom,
Phys. Plasmas, 15 072304 (2008) where the
underlying mechanism for the transport was
attributed (tentatively) to bounce resonance
transport
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Positron manipulation in the single particle
regime
Curve is the theory for a harmonic trap with an
asymmetric oscillating dipole with buffer gas
cooling modelled by a Stokes-type
term. Developed by CA Isaac (Swansea)
Frequency response around the axial frequency
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Antihydrogen Production ATHENA
1. Fill positron well in mixing region with
75106 positrons allow them to cool to ambient
temperature (15 K) 2. Launch 104 antiprotons into
mixing region 3. Mixing time 190 sec - continuous
monitoring by detector 4. Repeat cycle every 5
minutes
For comparison hot mixing continuous RF
heating of positron cloud (suppression of
formation of antihydrogen)
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Antihydrogen Detection ATHENA

• Charged tracks to reconstruct antiproton
  annihilation vertex.
• Identify 511 keV photons from e-e-
  annihilations.
• Identify space and time coincidence of the two.

Two annihilation events from antihydrogen which
strikes the wall of the charged particle traps

• Compact (3 cm thick)
• Solid angle gt 70
• High granularity
• Operation at 140K, 3 T

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Antihydrogen Production ATHENA
Cold Mixing 103270 vertices, 7125 2x511keV
events
131 22 events
(or about 50,000 antihydrogen atoms made)
Antihydrogen suppressed
Hot Mixing Scaled (x1.6) to 165 mixing cycles.
No peak
Amoretti et al., Nature 419 456 (2002)
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Antihydrogen Selected results from ATHENA
ATHENA Vertex Z Distribution
Madsen et al., PRL 94 033403 (2005)
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Antihydrogen Selected results from ATHENA
Behaviour of antihydrogen annihilations versus
time
Example of use of plasma modes to monitor change
in plasma temperature
See Fujiwara et al., PRL 101 053401 (2008)
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Antihydrogen Selected results from ATHENA
P is important T-scaling parameter for Hbar
formation
See Fujiwara et al., PRL 101 053401 (2008)
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Antihydrogen Production Formation Processes

Radiative Three-body
Radiative Three-body Rate T
dependence T-0.6 T-4.5 Final state n lt
10 n gtgt 10 Stability (re-ionization) high l
ow Expected rates 10s Hz fast ???
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Antihydrogen Production Formation Processes
The TBR is a quasi-elastic encounter of 2
positrons in the vicinity of an antiproton.
Energy exchange kBTe, which will be the same
order of the binding energies. Thus, these are
very weakly bound states which are strongly
influenced by the ambient fields Electric and
magnetic fields of the Penning trap AND The
plasma self electric field
The combination of Er and Bz results in a
tangential drift speed, which to 2nd order is
given by
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ALPHA Collaboration 2009-10

• Antihydrogen Laser PHysics Apparatus

University of Aarhus G.B. Andresen, P.D. Bowe,
J.S. Hangst Auburn University F.
Robicheaux University of British Columbia W.N.
Hardy, S. Seif El Nasr University of Calgary T.
Friesen, R. Hydomako, R.I. Thompson University of
California, Berkeley M. Baquero-Ruiz, C. Bray,
S. Chapman, J. Fajans, A. Povilus, C. So, J.S.
Wurtele University of Liverpool P. Nolan, P.
Pusa NRCN, Negev E. Sarid Riken D. M. Silveira,
Y. Yamazaki Federal University of Rio de Janeiro
C.L. Cesar, R. Lambo Simon Fraser University
M.D. Ashkezari, M.E. Hayden York University,
Toronto S. Menary Swansea University W.
Bertsche, E. Butler, M. Charlton, A. Humphries,
S. Jonsell, L. V. Jørgensen, S.J. Kerrigan, N.
Madsen, D.P. van der Werf, D. Wilding ( and
Fysikum, University of Stockholm) University of
Tokyo R.S. Hayano TRIUMF M. C. Fujiwara, D.R.
Gill, L. Kurchaninov, K. Olchanski, A. Olin, J.W.
Storey
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ALPHA An Antihydrogen Trapping Experiment
Main Aim To superimpose a magnetic well neutral
trap onto an antihydrogen production and
detection apparatus. Thus, to trap antihydrogen
to promote spectroscopic comparisons with
hydrogen. Complexities are many including Effect
of neutral trap fields on stability of charged
particle clouds Detection involves pion
trajectory detection and vertex reconstruction
Cryogenic traps Laser access
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ALPHA An Antihydrogen Trapping Experiment
Ioffe-Pritchard Geometry
Solenoid field is the minimum in B
B
quadrupole winding
mirror coils
N.B. Well depth 0.7 K/T
Plasma lifetimes drastically reduced in the
presence of quadrupolar field
Based on Berkeley/Swansea results standard
quadrupole not a good idea field gradient
across charged plasmas is too great see Fajans
et al., Phys. Rev. Lett. 95 155001 (2005)
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ALPHA An Antihydrogen Trapping Experiment
Quadrupole
Magnetic field normalised to value at electrode
wall
Octupole
Radius in trap
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ALPHA An Antihydrogen Trapping Experiment
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ALPHA An Antihydrogen Trapping Experiment
Correlation of the field ionized signal with that
from annihilation on the wall of the trap
Physical cause of drop unclear, but it is caused
by the presence of the octupolar field
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ALPHA An Antihydrogen Trapping Experiment
Image of the Penning trap electrode
With the neutral trap off
With the neutral trap on
Projections along the magnetic field axis
N.B. extra features with the trap on
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ALPHA An Antihydrogen Trapping Experiment
Searching for trapped antihydrogen Shut off
magnetic minimum trap (1/e time 9
ms) Interrogate output of vertex detector in 30
ms time window after the shut off Apply cuts to
data to reject cosmic ray events
a) Antiproton annihilation
b) Cosmic ray
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ALPHA An Antihydrogen Trapping Experiment
We have observed a few events like this in the 30
ms time window, and distributed in the apparatus
in the way in which released antihydrogen would
be expected to behave.
Work is ongoing to assess systematic effects
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Concluding Remarks
Trapping antihydrogen is a lot harder than making
it! Great care has to be taken manipulating
plasmas to keep them cold enough. Many
manipulations on both the positrons and
antiprotons must be done to prepare them for
mixing. Our apparatus seems to work well, and
work is progressing .
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Acknowledgements
Members of the ATHENA collaboration Members of
the ALPHA collaboration Colleagues at Swansea UK
financial support from EPSRC AD staff and all
support from CERN