the aegis experiment · the first experiment planned in aegis to probe the validity of the weak...
TRANSCRIPT
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Andreas Knecht / CERN
on behalf of the AEgIS collaboration
LEAP 2013, 10/6/2013
The AEgIS Experiment
Measuring the Gravitational Interaction of Antimatter
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Andreas Knecht LEAP 2013, 10/6/2013
AEgIS Collaboration
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University of Oslo and University of Bergen, NorwayCERN, Switzerland
INFN Genova, ItalyINFN Bologna, Italy
Kirchhoff Institute of Physics, Heidelberg, Germany
Max-Planck-Insitut für Kernphysik Heidelberg, Germany
INFN, Università degli Studi andPolitecnico Milano, Italy
INFN Pavia-Brescia, Italy
INR Moscow, Russia
Université Claude Bernard, Lyon, France
Czech Technical University,Prague, Czech Republic
INFN Padova-Trento, Italy
ETH Zurich, Switzerland
Laboratoire Aimé Cotton, Orsay, France
University College, London, United Kingdom
Stefan Meyer Institut, Vienna, Austria
University of Bern, Switzerland
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Andreas Knecht LEAP 2013, 10/6/2013
Motivation
First direct test of the Weak Equivalence Principle involving antimatterDirect tests so far only for matter systemsValidity for antimatter inferred from heavily debated indirect argumentsTheory could accommodate differences (e. g. through potential including gravivector and graviscalar)
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Nieto and Goldman, Phys. Rep. 205, 221 (1991)Amole et al., Nat. Comm. 4:1785 (2013)
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Andreas Knecht LEAP 2013, 10/6/2013
Motivation
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And quite generally:Experimental test of the gravitational interaction in a new sector - one for the textbooks (and for the public)!
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Andreas Knecht LEAP 2013, 10/6/2013
AEgIS Experimental Goal
Primary goal:Measurement of gravitational acceleration g for antihydrogen with 1% accuracy
Secondary goals:Spectroscopy of antihydrogenStudy of Rydberg atomsPositronium physics: formation, excitation, spectroscopy
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Figure 3.5: Schematic view of the AEGIS Moiré deflectometer (not to scale). The cylinders represent theelectrodes of the trap for charged particles in which the antihydrogen will be produced. The first cloudrepresents the antihydrogen before the acceleration and the second one the cloud at the time t0 when theaccelerating electric field is switched o↵. The two gratings and the detector are shown.
3.5 The first AEGIS gravity measurement: a classical Moirédeflectometer coupled to a position sensitive detector
The first experiment planned in AEGIS to probe the validity of the weak equivalence principle for anti-hydrogen is the g measurement with a classical Moiré deflectometer. Such an apparatus was built andoperated by M. K. Oberthaler et al., in 1996 [64] and we are proposing an upgraded design of it (M. K.Oberthaler is member of AEGIS).
A classical deflectometer is usually made of three gratings, but the slit widths are su�ciently largethat di↵raction can be neglected. Referring to relation 3.5 for L = 0.1 m, a = 40 µm and for L = 1m, a = 120 µm. As already anticipated, the motion of the atoms in the Moiré deflectometer is purelyclassical. The presence of the first two gratings at distance L produces a periodical structure in thenumber of the atoms N(x) arriving at distance L from the second grating. Here x is the coordinate inthe direction of the gravity force. In the experiment described in [64] the atomic density modulation wasdetected, as in the case of the interferometer experiments, by using the third grating as filter: the thirdgrating is moved in the vertical direction by a fraction �x of the grating period and the total number ofatoms passing through is detected vs �x.The number of atoms N(�x) is a periodical function of �x with period keff = 2⇡/a.The comparison of N(�x) with and without including the gravity force shows that the fall of the atoms
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Produce ultra cold antiprotonsForm positronium by interaction of positrons with a porous target (pulsed)Laser excite Ps to get Rydberg Ps (pulsed)Form Rydberg cold antihydrogen (pulsed) byStark accelerate the antihydrogen with inhomogeneous electric fields
→ Pulsed production of a cold beam of antihydrogen
Measure the gravitational accelerationin a classical moiré deflectometer
Andreas Knecht LEAP 2013, 10/6/2013
AEgIS Experimental Strategy
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Chapter 4
Antihydrogen production by chargeexchange
The production of antihydrogen in AEGIS is based on the charge exchange reaction between antiprotonsand Rydberg positronium
Ps⇤ + p! H⇤ + e� (4.1)
The use of this reaction was proposed some time ago [150] and recently demonstrated by the ATRAPcollaboration [91]. The method by which the antihydrogen production will be implemented in AEGIShowever significantly di↵ers from that of ATRAP.
Charge exchange reactions between Rydberg atoms and ions are largely studied in atomic physics:we only recall here the main physical features of this process.
The main reasons that make this reaction interesting for the AEGIS design are
• the large cross section which is of the order of a0n4 where a0 = 0.05 nm is the Bohr radius and nis the principal quantum number of the Ps;
• the expected distribution of the quantum states of the produced antihydrogen. The antiatomsare produced in Rydberg states with a predictable state population strictly related to that of theincoming positronium. The range of final quantum states is reasonably narrow. Thanks to thesensitivity to electric field gradients of these Rydberg atoms a beam can be formed by acceleratingthe atoms with a time dependent inhomogeneous electric field.
• the possibility to experimentally implement the reaction in such a way that very cold antihydrogencan be produced. To maximize the e�ciency in the use of the antihydrogen and the quality of thebeam it is in fact important that the transverse velocity be as low as possible.
In order to best understand the formation process under the experimental conditions of AEGIS, andin order to optimize the production rate of useful antihydrogen atoms, we have implemented a completecalculation of the charge exchange process using a classical trajectories Monte Carlo (section 4.2).
4.1 Kinematics
The conservation of energy and momentum in the charge exchange reaction sets the constraints on theminimum energy of the resulting antihydrogen. Figure 4.1 defines the coordinate system: we call xp thedirection of the antiproton velocity before the recombination; ✓Ps the angle between the positroniumand antiproton velocity and ✓H the angle formed by the emerging antihydrogen velocity and the xp axis.After some calculations it is straightforward to find that the antihydrogen velocity v2H in the laboratoryreference satisfies
v2H
+ v2p + 2✓
me+mp
◆2v2Ps � 4
me+mp
vHvPscos(✓H � ✓Ps)� 2vpvPscos(✓Ps)� 2me+mp
Q
mp= 0 (4.2)
AEGIS collaboration
Storry et al., PRL 93, 263401 (2004)Vliegen and Merkt, J. Phys. B: At. Mol. Opt. Phys. 39, L241 (2006)
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Andreas Knecht LEAP 2013, 10/6/2013
Antihydrogen Formation
Positronium charge exchange technique:Large cross-section, scales as n4Narrow and defined final state distributionAntihydrogen production from antiprotons at rest
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grating 1 grating 2
position-sensitivedetector
L Latomicbeam
Ps
laser excitation
antiproton trap
positronium converter
e+
Ps
Ps*Ps*
H*
H*H beamH*
accelerating electric field
Schematic overview
Physics goals: measurement of the gravitational interaction betweenmatter and antimatter, H spectroscopy, ...
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Schematic overview
Chapter 4
Antihydrogen production by chargeexchange
The production of antihydrogen in AEGIS is based on the charge exchange reaction between antiprotonsand Rydberg positronium
Ps⇤ + p! H⇤ + e� (4.1)
The use of this reaction was proposed some time ago [150] and recently demonstrated by the ATRAPcollaboration [91]. The method by which the antihydrogen production will be implemented in AEGIShowever significantly di↵ers from that of ATRAP.
Charge exchange reactions between Rydberg atoms and ions are largely studied in atomic physics:we only recall here the main physical features of this process.
The main reasons that make this reaction interesting for the AEGIS design are
• the large cross section which is of the order of a0n4 where a0 = 0.05 nm is the Bohr radius and nis the principal quantum number of the Ps;
• the expected distribution of the quantum states of the produced antihydrogen. The antiatomsare produced in Rydberg states with a predictable state population strictly related to that of theincoming positronium. The range of final quantum states is reasonably narrow. Thanks to thesensitivity to electric field gradients of these Rydberg atoms a beam can be formed by acceleratingthe atoms with a time dependent inhomogeneous electric field.
• the possibility to experimentally implement the reaction in such a way that very cold antihydrogencan be produced. To maximize the e�ciency in the use of the antihydrogen and the quality of thebeam it is in fact important that the transverse velocity be as low as possible.
In order to best understand the formation process under the experimental conditions of AEGIS, andin order to optimize the production rate of useful antihydrogen atoms, we have implemented a completecalculation of the charge exchange process using a classical trajectories Monte Carlo (section 4.2).
4.1 Kinematics
The conservation of energy and momentum in the charge exchange reaction sets the constraints on theminimum energy of the resulting antihydrogen. Figure 4.1 defines the coordinate system: we call xp thedirection of the antiproton velocity before the recombination; ✓Ps the angle between the positroniumand antiproton velocity and ✓H the angle formed by the emerging antihydrogen velocity and the xp axis.After some calculations it is straightforward to find that the antihydrogen velocity v2H in the laboratoryreference satisfies
v2H
+ v2p + 2✓
me+mp
◆2v2Ps � 4
me+mp
vHvPscos(✓H � ✓Ps)� 2vpvPscos(✓Ps)� 2me+mp
Q
mp= 0 (4.2)
AEGIS collaboration
Figure 4.4: Mean value of the principal quantum number nH of the produced Has a function of the initialnPs state. Di↵erent conditions are evaluated:⌅ fixed lPs,• mixed lPs [0;n-1]N lPs = 2 with di↵erent values of kv
n(H)0 10 20 30 40 50 60 70 80
prob
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
n (H) distribution
l (H)0 10 20 30 40 50 60 70
prob
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
l (H) distribution
k (H)-100-80 -60 -40 -20 0 20 40 60 80
prob
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
0.0016
0.0018
0.002
k (H) distribution
Figure 4.5: Distribution of final states obtained with 3000 anti-hydrogen atoms; from left to right, thethree plots show the distribution of nH , lH and kH . The initial state of the positronium used to simulatethe charge exchange process was: nPs = 35 and lPs = 2.
35
nPs = 35
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Andreas Knecht LEAP 2013, 10/6/2013
Moiré Deflectometer
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grating 1 grating 2
position-sensitivedetector
L Latomicbeam
Ps
laser excitation
antiproton trap
positronium converter
e+
Ps
Ps*Ps*
H*
H*H beamH*
accelerating electric field
Schematic overview
Physics goals: measurement of the gravitational interaction betweenmatter and antimatter, H spectroscopy, ...
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Schematic overview
x
GratingGratingunitsunits
v =600 m/s
v =250 m/s
δ = ―gt²a
with gravity
Gravitational deflection & Moiré deflectometer
Classical deflectometer (shadow mask)Third grating replaced by position-sensitivedetector
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Andreas Knecht LEAP 2013, 10/6/2013
Moiré Deflectometer
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time (s)0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016 0.0018 0.002 0.0022
Phas
e (ra
d)
0
0.5
1
1.5
2
2.5
3
With Real Detector resolution
0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016 0.0018 0.002 0.0022
0
0.5
1
1.5
2
2.5
3
With Infinite Detector resolution
Figure 3.14: Phase shift as a function of the time-of-flightp
< T 2 >(sec) between the two gratings of theMoiré interferometer. Top plot: assuming a 10µm detector resolution; Bottom plot: assuming perfectdetector resolution.
A proper magnetic shielding has to be designed around the grating system. Again, atoms in thefundamental state are preferred over Rydberg states with high m.
• Systematic errors can be controlled by comparison of the gravity induced shift with that obtainedwhen taking data with the gratings rotated by 900 degrees. In this case the e↵ect of gravity iscanceled.
• The design of the deflectometer can still be optimized: it is possible that having the same openingfraction in the two gratings is not the optimum solution.
• to cross-check our results, we are evaluating the possibility of carrying out the charge symmetricexperiment (producing hydrogen atoms, rather than antihydrogen atoms, by using protons, ratherthan antiprotons), but this requires enhancing the position sensitive detector with a scheme thatcan ionize ground state Hydrogen atoms.
3.6 Additional measurements with the antihydrogen beam
The availability of a beam of antihydrogen o↵ers the possibility to perform additional measurementsaiming to study antihydrogen properties. We simply mention here the possibility to perform Rydberg
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Phase shift as a function of time (velocity of antihydrogen) gives gravitational acceleration: Δz ~ gt2
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Andreas Knecht LEAP 2013, 10/6/2013
Experimental Apparatus
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p from AD_
Positron accumulator5T magnet 1T magnet
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Layout of the zone
Andreas Knecht LEAP 2013, 10/6/2013
Location
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Andreas Knecht LEAP 2013, 10/6/2013
Experimental Installation
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Zone early 2011 Zone late 2012
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Andreas Knecht LEAP 2013, 10/6/2013
5T Catching Traps
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HV
HV
HV
1
2
3
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Andreas Knecht LEAP 2013, 10/6/2013
1T Formation Traps
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Andreas Knecht LEAP 2013, 10/6/2013
Central Antihydrogen Detector
Scintillating fibre detector operating at 4K800 channels readout by SiPM200 MHz readout detecting hit pattern
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Andreas Knecht LEAP 2013, 10/6/2013
Positron System
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800 MBq 22Na sourceSolid neon moderator
Positron trap
Positron accumulatorBuffer gas cooling
Pulsed transfer line ~0.1T
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Andreas Knecht LEAP 2013, 10/6/2013
Positron System
Ongoing work to increase rates and efficiencies
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Number of stored e+ and lifetime
0 200 400 600 800
0 20 40 60 80 100 120
Time (s)
Lifetime = 29+/-2 sfill time = 120 s
7-8 106 e+
3 106 e+ Lifetime = 12+/-1 sfill time = 38 s
5 106 e+
6 106 e+
coun
ts (a
.u.)
Pulse number
Lifetime = 25+/-2 sfill time = 100 s
1 pulse from trap 5-6 104 e+
Dump intensity 7-8 106 e+
Lifetime ~30 s
Fill time ~120 s
5-6 x 104 e+ from trap
Conclusion
M o d e r a t i o n - Tr a n s p o r t efficiency ~ 2.5 10-2
Spot dimension 4-5 mm
Spot dimension 1-2 mm
Trapping-dumping efficiency ~ 0.14
Permanent diagnostic systems tested and calibrated
e+
Dump intensity 7-8 106
Lifetime ~30 s
Fill time ~120 s Transport efficiency ~80-90 %
Improvements for increasing the accumulator dump intensity (aim 108) Improvements for optimization of the beam transport and diagnostic in 5 T region
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Andreas Knecht LEAP 2013, 10/6/2013
Commissioning Results
Trapping, cooling
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Trapping voltage [kV]1 2 3 4 5 6 7 8 9
]5A
ntip
roto
ns c
augh
t [ x
10
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Antiproton catching vs applied high voltage
Antiproton cooling time [s]0 5 10 15 20 25 30 35 40
Col
d / h
ot a
ntip
roto
n fr
actio
n
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Cold and hot antiproton fractions vs. electron cooling time
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Andreas Knecht LEAP 2013, 10/6/2013
Commissioning Results
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Lifetime ~500 s
Storing
sec0 50 100 150 200 250 300
Tra
pped
ant
ipro
tons
0
20
40
60
80
100
120
140
310×
Hot antiprotons storage time9 KV
Cold antiproton storage
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Andreas Knecht LEAP 2013, 10/6/2013
Commissioning Results
Manipulations
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Andreas Knecht LEAP 2013, 10/6/2013
Commissioning Results
Positron transfers through transfer line and 5T into 1T magnet
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Extraction pulsefrom accumulator
Scintillator pulsesfrom positron annihilation in 1T
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Andreas Knecht LEAP 2013, 10/6/2013
Detector Tests
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Parasitic tests:
Silicon detectors (strip, pixel) MCP Emulsions
Explore different candidate technologies for the (downstream) antihydrogen detector
See poster by O. Karamyshev
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Andreas Knecht LEAP 2013, 10/6/2013
Silicon Detectors
3D pixel sensor designed for the ATLAS upgradeAlso tested: strip sensor, Mimotera
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+ Installation of the detector in the six cross chamber
3D pixel detector mounted on the flange
p_
-
[MeV]totE
Prob
abilit
y
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14 FTFChipsData
[MeV]totE0 5 10 15 20 25 30
DAT
A/N
SIM
N 0
1
2
Analyses andresults on the
MIMOTERA data
A. Gligorova,N. Pacifico,G. Bonomi,C. Riccardi,A. Magnani,H. Sandaker,M. Caccia
Short reminder ofthe MIMOTERAdetectorInstallation in testbeam in May-June2012Features of theMIMOTERA
Analyses andResultsCalibrationSignal and NoiseClustering AlgorithmPotential BackgroundSourceTracks produced byannihilation productsComparison betweenMonte Carlo models(CHIPS and FTF)and data
Conclusions
ClusteringI Clustering was performed after applying the above
mentioned cut on the single pixels.I Clusters were defined as conglomerates of pixels
neighbouring in the horizontal, vertical and diagonaldirection.
I To avoid overlapping of clusters, only frames with apixel occupancy < 10% and less than 150 clusters perframe were accepted for analysis.
Energy [keV]1 10210 310 410
Cou
nts
210
310
410
510
Raw signalNoiseNoise subtracted
Distribution of the signal in single pixelsafter subtraction of the noise fitted witha normal distribution.
X0 20 40 60 80 100
Y
0
20
40
60
80
100
0
1000
2000
3000
4000
5000
6000
7000
Sample of a triggered frame afterapplying the noise cut
Andreas Knecht LEAP 2013, 10/6/2013
Mimotera Detector
112 x 112 silicon pixel detector, 153 μm x 153 μm, 15 μm active depth
Detailed comparison of data vs simulation
Test of Monte Carlo treatment of antiproton annihilations on bare silicon
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Publication forthcoming!
Preliminary
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Andreas Knecht LEAP 2013, 10/6/2013
Emulsions
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Exposure of emulsionDevelopment in dark roomScanning on automated microscopes
Offline track and vertex finding algorithms1 μm vertex resolution
See talk by J. StoreyFriday @ 9:55 am
Glass%base%1%mm%
Emulsion)layer))(50)micron))
Focus&
an#proton(
Base (glass or plastic)(several 100 μm)
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Andreas Knecht LEAP 2013, 10/6/2013
First Test of Moiré Deflectometer
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Mini-Deflectometer
CERN 2013: Philippe Bräunig
emul
sion
deflectometer (353 hits)
reference grating (296 hits)
• ~100keV antiprotons• 7 hours exposure time• deflectometer and emulsion in the OVC• no seperation foil
~100 keV antiprotons7 hour exposureBare emulsion behind deflectometer
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Andreas Knecht LEAP 2013, 10/6/2013
First Test of Moiré Deflectometer
Antiproton fringes observed
Alignment of gratings using light and single grating
Promising results!
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Publication forthcoming!
Rotation (rad)-0.03 -0.02 -0.01 0 0.01 0.02 0.03
Perio
d39
39.2
39.4
39.6
39.8
40
40.2
40.4
40.6
40.8
20
40
60
80
100
Cross-correlation method
Preliminary
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Andreas Knecht LEAP 2013, 10/6/2013
Conclusions and Outlook
Installation of apparatus largely completed and commissioned
Parasitic measurements essential in converging to an optimal deflectometer/detector layout
Next steps:Install proton source, hydrogen detectorCommission Rydberg positronium formationWork on hydrogen formation/characterization
Goal: Be ready for antihydrogen beam formation in summer 2014!
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Andreas Knecht LEAP 2013, 10/6/2013
Backup
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Positronium target - parameters
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Ultracold antiprotons
Antiprotons in the trap cannot be directly cooled to 100 mK
Cool antiprotons by collisions with a partner particle stored in the same trap that can be cooled
e- antiproton
L C
electronsResistive cooling with a resonant tuned circuit + radiation cooling
Laser cooling of La_
Ultimate temperature: 240 nK
Negative ions: La-
A demonstration of laser cooling of negative ions is needed Experiment in progress at MPI (members of AEGIS)
antiprotonsEmbedded electron cooling, adiabatic cooling, evaporative cooling, ...
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Harmonic Generator
n=1 → n=3 205 nm Transition saturation energy: ~2 µJ
n=3 → Rydberg 1650-1700 nm Transition saturation energy: ~0.2 mJ
Nd:YAG 1064 nm
650 mJ, 5 ns
4th
2nd
1st
OPG
OPG + OPA SUM
OPA
894 nm
1650-1700 nm
266 nm
532 nm
1064 nm
Laser source and harmonic generator: Tender will start within December 2010 (?) Expected arrive in March - April 2011 Goal of the apparatus:
About 10 times the saturation energy
Rydberg excitation via a simultaneous two step incoherent process: 1 → 3 → Rydberg (wavelengths: 205 nm and 1650 - 1700 nm)
Main effects of level broadening: 1 → 3: Doppler effect (~0.04 nm) due to velocity distribution of Ps3 → Rydberg: Motional Stark effect (makes a quasi-continuum from n=17, each level is broadened to many nm) due to Ps movement in a strong B field
Lasers
components delivered in April 2011(pumping laser delivered in autumn 2011)
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Laser system: power tests
required level = 2μJ required level = 200μJ
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Moiré deflectometer: first tests
SolidWorks StudentenlizenzNur für akademische Zwecke
Faraday cup(detects integral
of incomingatom beam)
smalldistance
for highercontrast
small prototypegrating structures
loadingflange
last gratingis used to scanfringe pattern
v1
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Moiré deflectometer: 6” (full size) grating prototype