Cliff Surko* - UC San Diego: Department of...

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!


e+ - e- plasmasmaterials studies

antihydrogen

e+

p

Antimatterin our world

of Matter

medicinePET scan

galactic center


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−)


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


Antimatter Sources &Creating and Manipulating

Positron Plasmas


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)


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+


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


Trapping Antimatterthe Plasma Connection


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


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)


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


Commercial Positron Traps First Point Scientific, Inc. (R. G. Greaves)

Accumulator

source/moderator two-stage trap

(~ 250 K$/module)


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


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


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


• Dr. Keyes found himself able to control anti-matter.• He constructed a crude suit able to contain the stuff.• This allowed him to fire antimatter blasts, as well as a limited form of flying.

Positron - the cartoon character(Wikipedia)

PositronPositron

BUT WE HAVE COMPETION!


High Resolution Positron Beam

Gilbert et al., APL (1997)

Trap, cool and release:

High-resolution positron beam tunable from 50 meV upwards


(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


Physics with Antimatter

Positron-matter Interactions


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


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)


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


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


Positron Studies ofMaterials



Materials Analysis Using Positron Beams

Positrons provide new techniques and new informationnot available using e- beams.


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


Stable, Neutral Antimatter

Antihydrogen


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


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


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


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


Detect Antihydrogen Atoms Annihilating on the Electrodes

ATHENAAmoretti, Nature (2002)

Colde+

Hote+

Images of antiproton decays

Field-ionization detection too(ATRAP)


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


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


* 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


• 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


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


Many-ElectronMany-Positron System


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


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


-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+


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


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

Electron-PositronPlasmas


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

Larger Collectionsof Antimatter


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)


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)


• 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


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+


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