cliff surko* - uc san diego: department of...
TRANSCRIPT
Plasmas as Drivers for Science with Antimatter
Cliff Surko*
* Supported by the U. S. DoE, NSF and DTRA
University of CaliforniaSan Diego
Plenary review talk, APS Plasma Physics Division, Chicago IL, Nov. 9, 2010
Positron
Picture credit: AIP Emilio Segrè Visual Archives
Proc. R. Soc. (London) A 118 351-361 (1928)
Proc. R. Soc. (London) A 117 610-612 (1928)
Dirac equation: “anti-electrons” (1928)
C. M. Surko, DPP, Nov. 9, 2010
But gamma-ray observations => antimatter in our universe ~ zip!
Quantum Field Theories aresymmetric: matter <=> antimatter
We live in a matter world and we don’t know why
This talk: Creating and using antimatter in science and technology
Plasma Science is the Driver!
C. M. Surko, DPP, Nov. 9, 2010
e+ - e- plasmasmaterials studies
antihydrogen
e+
p
Antimatterin our world
of Matter
medicinePET scan
galactic center
C. M. Surko, DPP, Nov. 9, 2010
The Mirror World of Matter andAntimatterAntimatterpositron positron ↔ electronantiproton antiproton ↔ proton
Positronse- + e+ => gamma rays 2γ* (S = 0) or 3γ (S = 1)
(2γ decay: εγ = mec2 = 511 keV)Positronium atom (e+e−): EB = 6.8 eV
τs=0 = 120 ps; τs=1 = 140 ns
Antiprotonsp + p => shower of pions (π0, π+, π−)
C. M. Surko, DPP, Nov. 9, 2010
Outline
Focus on low-energy antimatter: Omits laser-producedrelativistic positron plasmas [e.g., H. Chen, et al., PRL 2010)]
Creation and Manipulation of Antimatter Plasmas
Future Antimatter Traps
Antihydrogenstable neutralantimatter
Positron binding to atoms and molecules
Positron studies of materials
e+ − matter interactions
Bose-condensed positronium
Electron-positron plasmase+ - e-
many bodysystem
Physics with Antimatter
C. M. Surko, DPP, Nov. 9, 2010
Sources of e+and pPositrons (energies ~ 10 - 500 keV) Radioisotopes (18F, 58Co, 22Na)
(portable, or reactor-based)
Electron accelerators (e.g., LINACs) (ε ≥ 2mec2 = 1 MeV)
Antiprotons (energies ~ GeV) Particle accelerators (CERN, Fermilab) (fast protons: εp ≥ 6mpc2 ∼ 5.6 GeV)
C. M. Surko, DPP, Nov. 9, 2010
Focus on Slow PositronsUse “moderators” 100’s of keV → ~ 1 eV
Neon efficiency ε ~ 1%
50 mCi 22Na ~ 107 slow e+/s (1 pA)
Some metals are moderators tooW, Ta, Pt (ε ~ 0.1 %)
slow positronbeam (E ~ 1eV)
22Nae+ source
coppersolid neon(~ 7.2 K)
B
fast e+
C. M. Surko, DPP, Nov. 9, 2010
FRM II reactor, Munich
Intense Reactor-Based Positron Beam
C. Hugenschmidt, U. Munich
Beam 7 mm FWHM, in 60 G
9.0 x 108 e+/s (~ 100 pA)
platinum moderator
Reactor core
γ
γ
γ
C. M. Surko, DPP, Nov. 9, 2010
A Near-Perfect “Antimatter Bottle” the Penning-Malmberg Trap
Canonical angular momentum
No torques ⇒ is constant. No expansion!
Thermal equilibrium rigid rotor
single-componentplasma
B V V
(Malmberg & deGrassie ‘75; O’Neil ‘80)
!
Ef = cne /B
plasma rotates:
V(z)z
C. M. Surko, DPP, Nov. 9, 2010
Buffer-Gas Positron Trap
Surko PRL ‘88; Murphy, PR ‘92
♦ Trap using a N2-CF4 gas mixture
♦ Positrons cool to 300K (25meV) in ~ 0.1s
30% trapping efficiency
Early positron trapping efforts: Gordon et al., (LLNL) ‘60 (Mirror) Schwinberg, et al., ‘81 (Penning trap)
C. M. Surko, DPP, Nov. 9, 2010
Buffer-gas Positron Accumulator
positron plasmagas in
positronsin
cryopumps
1.8 m
Similardevices in: Australia China Europe Russia CERN (3)
UCSD
B = 0.15 T
C. M. Surko, DPP, Nov. 9, 2010
Commercial Positron Traps First Point Scientific, Inc. (R. G. Greaves)
Accumulator
source/moderator two-stage trap
(~ 250 K$/module)
C. M. Surko, DPP, Nov. 9, 2010
50cm
120cm
• B = 5T
• T as low as 10 - 30 K
• P ≤ 10-10 torr
• τc = 0.16 s
High-field PositronTraps =>
cyclotron cooling
Particles cool by cyclotronradiation τc ∝ B-2
Also laser cooling using Be+: Jelenkovic et al, PRA ‘03
C. M. Surko, DPP, Nov. 9, 2010
Compression with Rotating Electric Fields
Vconf Vconf
segmented electrodephased for mθ = 1
“The Rotating Wall Technique”
V = VRW cos[(2πfRW) t + φ]
ERW ff >compression for
(Huang, et al., (Huang, et al., AndereggAnderegg, et al., , et al., HollmannHollmann, et al.,, et al., Greaves et al., Danielson et al., 1997 - 2007Greaves et al., Danielson et al., 1997 - 2007))C. M. Surko, DPP, Nov. 9, 2010
Rotating-wall compression- strong drive regime
Attracting fixed point
Danielson et al., PRL ‘05, ‘07,Phys. Plasmas, ‘06
“flat-top”
high-density rigid-rotor
fRW = 6.4 MHz
Convenient tool: one knob tunes densityOpen question: what is the density limit −
Zero-frequency Modes (ZFM)?
ZFM
data with test electron plasmas
!
Ef = cne /B "RWf
C. M. Surko, DPP, Nov. 9, 2010
Positron Plasma Parameters
Magnetic field 10-2 – 5 teslaNumber 104 - 109
Density 105 - 1010 cm-3
Space charge 0.001 - 100 eVTemperature 10-3 – 1 eVPlasma length 1 – 30 cmPlasma radius 0.5 – 10 mmDebye length 10−2 − 1 mmConfinement time 102 – 105 s
Gilbert ‘97
Diagnostics: modes to measure N, n, T, & aspect ratio 2D CCD images
Trivelpiece-Gould modes*
mz mz mz
Dubin‘93; Tinkle ‘94
frequency
C. M. Surko, DPP, Nov. 9, 2010
• Dr. Keyes found himself able to control anti-matter.• He constructed a crude suit able to contain the stuff.• This allowed him to fire anti- matter blasts, as well as a limited form of flying.
Positron - the cartoon character(Wikipedia)
PositronPositron
BUT WE HAVE COMPETION!
C. M. Surko, DPP, Nov. 9, 2010
High Resolution Positron Beam
Gilbert et al., APL (1997)
Trap, cool and release:
High-resolution positron beam tunable from 50 meV upwards
C. M. Surko, DPP, Nov. 9, 2010
(data withtest electron plasmas)
Tailored Positron Beams
Cryogenic plasmas and RW compressionfor low T and high n yield small beams
Δt ~ 6 µs
Danielson, APL ‘07Weber, PP ‘08, ‘09 ar
eal d
ensi
ty (1
010 c
m-2
)
with RWcompressionD = 100 µ
!
D" # T /n
extracted beam
T = 0.1 eV
C. M. Surko, DPP, Nov. 9, 2010
Positron Annihilation on Molecules - Anomalously LargeA mystery for 5 decades
* annihilation with thermal positrons at 300 K
Molecule Γm/ ΓD*
methane (CH4) 14butane (C4H10) 330octane (C8H18) 9000
ΓD ≡ annihilation rate using Dirac annihilaiton rate for free electrons
simplecollisionmodel
Γm >> ΓD for molecules ??, but Γm ~ ΓD for atoms
Γm ≡ measured annihilation rate
C. M. Surko, DPP, Nov. 9, 2010
energy (eV)
0.0 0.1 0.2 0.3 0.4 0.5
Ze
ff
0
10000
20000ButaneButane
(C4H10)
Gilbert, et al., PRL (02)Barnes, et al., PR (03)positron energy, ε (eV)
!
m"
D"
300
Energy Resolved Annihilation Ratefor Butane (C4H10)
C-H stretch modes
— vibrational modes (10 meV width)
Positrons bind to molecules, andCan measure binding energies
Peaks shifted by binding energy ΔΕΒ
ε + ΔEB = Evib
alkanes
600butane(C4H10)
C. M. Surko, DPP, Nov. 9, 2010
Bound Positron Wave Functions for Alkanes
Gribakin and Lee, EPJ ‘08
C14H30C14H30
C8H18
!
" = Ai
i=1
N
#e$% r$R
i
r $Ri
C14H30
ΔEB = 260 meV
C4H10
ΔEB = 35 meV
alkanes
ΔEB increases with molecular size
bound positronwave functions
C. M. Surko, DPP, Nov. 9, 2010
Positron Interactions with Atoms and Molecules
• Positrons bind to molecules − likely bind to atoms too, but no experiments• For similar ions, positron binding
~ 10 - 100 larger than for electrons• Theoretical comparisons for ΔEb beginning
Gribakin, Young, Surko Rev. Mod. Phys. ‘10
C. M. Surko, DPP, Nov. 9, 2010
Materials Analysis Using Positron Beams
Positrons provide new techniques and new informationnot available using e- beams.
C. M. Surko, DPP, Nov. 9, 2010
Plasma challenges for materials studies: more intense positron beams
microbeams short pulses for lifetime spectroscopy
Munich reactor-beam datasub-monolayer sensitivity
electronimpact2 keVcopper
surfacepositron
annihilation20 eV
Mayer, et al., Surf. Sci., ‘10
Ecv
Positron-induced Auger-electron Spectroscopymake a core hole, then filled in a 2-electron transition
Ecv
Ecv
core
valence
E
1 2
C. M. Surko, DPP, Nov. 9, 2010
Would like totest all particle
sectors
Precision
Test gravity too −force of matter on
antimatter
(e/m)
(H)?
Some Tests of CPT
possible
Precision
Why Study Antihydrogen
C. M. Surko, DPP, Nov. 9, 2010
Antihydrogen Experiments at CERN
ATRAP, ATHENA (≤ 2005), ALPHA* (2005 →)
Antihydrogen trapping for spectroscopy
ASACUSAAntihydrogen beam for microwave spectroscopy
AEGIS*Antihydrogen beam for gravity tests
* Some members part of ATHENAC. M. Surko, DPP, Nov. 9, 2010
ASACUSA
ATHENA
ATRAP
100
Sto
chast
ic C
oolin
gElectron Cooling
Antiproton
Production
1
Injection at 3.5 GeV/c2
Deceleration and
Cooling
(3.5 - 0.1 GeV/c)
3
Extraction
( 2x107 in 200 ns)
4
From PS:
1.5x1013 protons/bunch, 26 GeV/c
20 m
Low-energy AntiprotonsThe CERN Antiproton Decelerator (AD)
to 5 MeV
ALPHAATHENA/ALPHA
ASACUSA
ATRAP
2 - 4 x 107 in 200 ns
C. M. Surko, DPP, Nov. 9, 2010
Antiproton Catching & Cooling*
Degrader
Solenoid - B = 3 Tesla
e-
Antiprotons
Cold electron cloud
[cooled by Synchtrotron Radiation, ! ~ 0.4s]
t = 0 s
a) Degrading
b) Reflecting
Potential
99.9% lost
0.1%
t = 200 ns
Potentialt = 500 ns
E<5kV
c) Trapping
Potentialt ~ 20 s
c) Cooling
[through Coulomb interaction]
~ 10,000 antiprotons per AD pulseATHENA/ALPHA Gabrielse, PRL ‘86C. M. Surko, DPP, Nov. 9, 2010
Antihydrogen Production(one scenario)
~ 108 positrons
Launch ~ 104 antiprotons into mixing region
Mixing time 190 sec
Repeat cycle every 5 minutes
Nested Penning traps
0 2 4 6 8 10 12-50
-100
-75
-125
Length (cm)
antiprotons
B
ATHENA/ALPHA (pre-2007)
p, e+ plasmastrapped, cooled,RW-compresed
ATRAP similar
C. M. Surko, DPP, Nov. 9, 2010
Antihydrogen Formation Mechanisms
Rate ~10’s Hz very fast
Rate Tp dep.* Tp-0.6 Tp
-4.5
Final state tightly bound weakly bound, Eb ~ kTp
Radiative Three-body
+
!hHpe +"++ +++
+!++ eHpee
* equilibrium assumed - experiments are typically non-equilibrium
C. M. Surko, DPP, Nov. 9, 2010
Detect Antihydrogen Atoms Annihilating on the Electrodes
ATHENAAmoretti, Nature (2002)
Colde+
Hote+
Images of antiproton decays
Field-ionization detection too(ATRAP)
C. M. Surko, DPP, Nov. 9, 2010
Antihydrogen Trappingminimum-B trap
!
U = "v µ #
v
B
Ioffe-Pritchard geometry
B
quadrupole winding mirror coils
Plasma lifetimes drastically reduced in thepresence of quadrupolar field so use octopole*
Well depth ~ 0.6 K
* ALPHA - Fajans, PRL ‘05 Andresen, PRL ‘07C. M. Surko, DPP, Nov. 9, 2010
In p cooling with e-, there can be extensive centrifugal separation
p
e-B
Andresen PRL 08Kuroda PRL 08Gabrielse PRL 10
Antihydrogen ProductionMany Physics Challenges
Two examples:
The weakly bound atoms in a strong B field are“guiding center (GC) atoms” Many dynamical regimes Can be either high-field or low-field seekers
Glinsky PF 91, Robicheaux PRA 04, Bass PP ‘09 Most processes are non-equilibrium
C. M. Surko, DPP, Nov. 9, 2010
annihilationdetector
octupole
mirror coils
electrodes
* ALPHA collaboration Andresen, Phys. Lett. B, in press, Nov. 2010
+ data Oct. - Nov. 2009
Search for Trapped Antihydrogen*+
• six events are consistent with trapped antihydrogen however cannot yet rule out that the signal could be due to (hot) mirror-trapped
!
p
• launch ~ 5 x 104 into ~ 2 x 106 positrons (212 cycles)• hold 130 ms then shut off min-B trap in 9 ms!
!
p
C. M. Surko, DPP, Nov. 9, 2010
* ALPHA collaboration, Andresen, Phys. Lett. B, in press, Nov. 2010
Search for Trapped Antihydrogen*
50%
tim
e (m
s)
z (cm)
simulatedlocations mirror-
trapped
simulatedlocations
!
H !
p
events
99%
• Six events resolved in space and time• Simulate and signals• Data favor interpretation
!
H
!
p
!
H
C. M. Surko, DPP, Nov. 9, 2010
• Experiments appear to be close to
trapping antihydrogen
• Focus will continue to be on the efficient
production of trappable antihydrogen atoms
and efficient methods to trap them
Antihydrogen Production and TrappingSummary
C. M. Surko, DPP, Nov. 9, 2010
frequencymeasurements
laser spectroscopy
need ~ 102 trapped for a 10-11 measurement
!
H
Long-term goal: spectroscopic tests of symmetry
1s-2s two 1s-2s two--photon spectroscopyphoton spectroscopy
• Doppler effect cancels
Hansch, PRL ‘00
hydrogen
C. M. Surko, DPP, Nov. 9, 2010
The Electron-Positron Phase Diagram
Yabu, NIMB ‘04
8 x 103 K
T ~ 7 x 104 K
nnMott~ 3 x 1022 cm-3
e+ - e- plasma
(BEC ≡ Bose-Einstein condensate)
e+ - e- liquidnormal /supercond.
Ps2 gas
Ps BECPs BEC
Psgas
Ps BEC
C. M. Surko, DPP, Nov. 9, 2010
Bose-Einstein Condensation (BEC) of Positronium Atoms (Ps)
a quantum many-body e+ − e- system
Small mass => 10 K, λDeBroglie ~ 30 nm, nBEC ~ 3 x 1017 cm-3
Low density quantum fluid ⇒ Ps atom interferometer, γ-ray laser ...Ps - Ps Interactions
Long-lived Ps states (~ 140 ns)S = 1, m ±1 (Ps↑↓)
Ps↑ + Ps↓ => Ps2 + Eb (.42 eV) => 2 Ps→ + Eh (1meV)
Ps↑ + Ps↑ => long lived - can form a BEC
short lived states
C. M. Surko, DPP, Nov. 9, 2010
-20 -10 0 10 20 30 40 50
-120
-80
-40
0
-8
-6
-4
-2
0
Buncher onBuncher off
PM
T o
utp
ut
(mV
)
PM
T o
utp
ut
(mV
)
time (ns)
pulsed magnet coil
beam from accumulator
phosphor screen
targetaccelerator
high voltage buncher
Final Stages of the Quantum Ps Gas Experiment
Implant e+ inporous silicad ~ 10 nm
D. Cassidy, A. Mills,U. California, Riverside
Use rotatingwall to adjustareal density, n2D
B = 2.3 T
spin-aligned e+
C. M. Surko, DPP, Nov. 9, 2010
28% alignedm = 1 Ps atoms
22Na source => S = 1 spin- polarized Ps gasrequired for Ps BEC
At high densities, only S = 1, m = 1 remain
Cassidy, PRL ‘10
Buffer-gas Traps Preserve Positron Spin Polarization- critical for the BEC Ps experiment
0 2 4 6 8 100.0
0.2
0.4
0.6
0.8
1.0
0
20
40
60
80
100
P m=1
(%)
Q
Beam areal density ( 1010 cm-2) areal density, n2D (1010 cm-2)
!
Q " df / df ( 2Dn = 0)
Delayed annihilation fraction, fd (150 ≥ t ≥ 50 ns)
norm
aliz
ed d
elay
ed fr
actio
n, Q
Ps2 formation
C. M. Surko, DPP, Nov. 9, 2010
Bose-Condensation of Positronium
• Produced Ps2 molecules & spin-polarized e+
• In progress - higher densities lower-T Ps for BEC– Accelerator-based intense positron source and multicell trap– Remoderate beam for higher areal density– Laser-cool the Ps
• Goals– BEC Ps– Stimulated γ annihilation?
D. Cassidy, A. Mills, et al.C. M. Surko, DPP, Nov. 9, 2010
ClassicalElectron-Positron (“Pair”) Plasmas
Nonlinear phenomena for T+= T− and n+ = n− • Heavily damped acoustic mode
• Faraday rotation absent • Three-wave decay processes absent* • Very strong nonlinear growth and damping processes*
* Tsytovich & Wharton, Comm. on Pl. Phys. (1978)
Relativistic e− - e+ plasmas • Astrophysical relevance
Complementary workon pair-ion plasmas (e.g.,C60
±)C. M. Surko, DPP, Nov. 9, 2010
1 m
Columbia Non-neutral Torus a stellarator for electron-positron plasmas
• Advantages• Can confine e+ & e-
at arbitrary degrees of neutralization
•Status and plans• ≥ 50 ms confinement achieved
for electron plasmas• Plan e+ injection via (< 10 µs)
electrostatic perturbations• Need ~ 1011 - 1012 e+
− use a “multicell-trap”
T. Sunn Pedersen et al., PRL, ‘02; JPB ‘03 Other possible confinement schemes:Penning/Paul trapMagnetic mirrorC. M. Surko, DPP, Nov. 9, 2010
Future of Trapping Antimatter
GoalsHigh capacityLong-term storagePortable antimatter traps?
* cylindrical plasma
Major technical issueSpace charge becomes large
(e.g., 1011 e+/cm ~ 10 kV)* → breakdown, heating, .....
(Brillouin limit, n = B2/8πmc2, not yet a problem)
C. M. Surko, DPP, Nov. 9, 2010
Improve vacuum
Improve B-field
Computerized optimization
Improved trapATHENA
Solid neon moderator
Year
trapp
ed p
ositr
ons Single cell
N ~ 1010
V ~ 1kV
MulticellN > 1012
Positron Traping − the Long View
1 meV
1 eV
1 keV
100 keV
10 meV
100 meV
10 eV
100 eV
10 keV
plasma space charge
30 - 100 mCi 22Na sources C. M. Surko, DPP, Nov. 9, 2010
Solution: Shield Parallel Cells with Copper Electrodes− a multicell trap for 1012 positrons*
3 banks of 7 cells (21 cells, total), with 5 x 1010 e+ each1 kV confinement potentials & RW compressionMove plasma across B with “autoresonant Diocotron mode”+
e+ in1 m
B
Modular design so larger traps are possible * Surko, JRCP ‘03 Danielson, PP ‘06+ Fajans et al., ‘99 - ‘01C. M. Surko, DPP, Nov. 9, 2010
Antimatter in the Laboratory
Plasma-Driven Progress and Opportunities
• Fundamental questions (e.g., matter/antimatter asymmetries) with antihydrogen
• Antimatter plasmas & BEC Ps
• Technological applications (e.g., materials studies)
C. M. Surko, DPP, Nov. 9, 2010
• Rotating Wall compression and cyclotron cooling
– Higher densites and colder temperatures?
• Antihydrogen
– Efficient ways to cool and trap the atoms
• Electron-positron plasmas and Ps BECs
– Effective and efficient ways to create them?
Outstanding Challenges
C. M. Surko, DPP, Nov. 9, 2010
Thanks to my collaborators and those providing material for this talk:L. Barnes, D. Cassidy, C. Cesar, M. Charlton, J. Danielson, D. Dubin, E.Butler, J. Fajans, M. Fujiwara, R. Greaves, G. Gribakin, C. Hugenschmidt,M. Leventhal, J. Marler, T. O’Neil, A. Mills, Al Pasner, T. Pedersen, F..Robicheaux, J. Sullivan, M. Tinkle, T. Weber, A. Weiss, and J. Young
Thanks too for support from DoE, NSF and DTRA
For references and linksto other work see:
positrons.ucsd.edu/
e+
C. M. Surko, DPP, Nov. 9, 2010