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Antimatter

Congratulations and Thanks Ron!

• Plasma Fusion Center, MIT

• Physics of Plasmas

• ‘95 Plasma Study

New Tools for Antimatter Studies Positron Plasmas and Trap-Based Beams*

Cliff Surko

James DanielsonToby WeberTom O’NeilMike Anderson

* Supported by NSF,DOE/NSF Partnership

Antimatter in our world

of Matter

Plasma Physicsenabling the study and use low-energy antimatter

PET scan

Fast electronics

Electron-positron PlasmasAntihydrogen

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p

Galactic center

The real reason we are making antihydrogen...

But the real reason we’re making antimatter …

NO!

Why Trap and Cool Antimatter?

Isolate interactions with matterAtomic/molecular physicsLaboratory astrophysicsDensity dependent processesPulsed, bright beams (e.g., plasma diagnostics, materials analysis)Antihydrogen production

Electron-positron plasmas BEC positronium

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A Near-Perfect “Antimatter Bottle” The Penning-Malmberg Trap

Angular Momentum

No torques Lz = is constant No expansion!

Single-componentplasma

B V V

(Malmberg & deGrassie ‘75; O’Neil ‘80)

JohnMalmberg

E x B plasmarotation

fE = cne/B

Buffer-Gas Positron Trap

Trap using a N2-CF4

gas mixture

Positrons cool to 300K

(25meV) in ~ 0.1s

Surko PRL ‘88; Murphy, PR ‘92

30%trapping efficiency

Buffer-gas Accumulator

Positron plasmaGas in

Positronsin

(flux ~ 1 pA)

Cryopumps

1.8 m

Trapping Antimatter

Goals

Long-term storage

High capacity

Cold, dense plasmas

Portable antimatter traps

Considerations

Space charge: 10 kV ~ 1011 e+/cm* Confinement at high plasma densities?Cooling cool ~ 0.2 s @ 5 tesla

* cylindrical plasma

Improve vacuum

Improve B-field

Computerized optimization

Improved trap StackingATHENA

Solid neon moderator

Year

trap

ped

posi

tron

s

UCSD

Multicell1x1012

Overview of Positron Trapping

• Increase positron storage capacity

• Plasma compression for lifetime anddensity control

• Extraction of finely focused beams

New Tools for Antimatter Physics

End View

D

RF ElectrodesDC Electrode

2Rp

Lp

L

Side View

Positron Plasma

Multicell Trap for Large Ntot*

Many “beaded rods” in parallel

Design Parameters

• B = 5T • n ~ 3x1010 cm-3

• Lp ~ 5 cm• Rp ~ 0.14 cm• T ~ 2 eV• Ntot ~ 1010 (1 cell)• c ~ 1 kV

Total number of cells ~ 100 Ntot ~ 1012

*Surko and Greaves, Radiation Physics and Chemistry (2003)

B

master cell2 banks of 19 storage cells

Multicell Positron Trap Electrodes

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Danielson, Phys. Plasmas (2006)

Autoresonant Diocotron-modeExcitation to Position

AzimuthalRadial

Danielson, Phys. Plasmas (2006)D/Rw ≥ 0.8

€

Df = Dof (1−

€

fD = fDo[1 - (D/Rw)2]-1

“Rotating-Wall” Compression of Positron Plasmas

• Compress radially using a rotating electric field.

• Good coupling over broad range of frequencies.

Applications:

- ‘infinite’ confinement times

- increase plasma density

- create bright antiparticle beams

(Huang, et al., Anderegg, et al., (Huang, et al., Anderegg, et al.,

Hollmann, et al., ‘95 - ‘00)Hollmann, et al., ‘95 - ‘00)

•Greaves and Surko, PRL (2000).Greaves and Surko, PRL (2000).

Radial density profiles from CCD images:*Radial density profiles from CCD images:*

B

weak-drive

strong-drive

TransitionRegion

Transition/bifurcation_________________________________________________

Danielson PRL (05); Phys. Pl. (06)

electronplasma

fE fRW

Hysteretic Behavior in fRW Characteristic of the Strong Drive Regime

Strong Drive Regime - above a critical VRW, fE fRW

ZeroFrequencyMode

Zero-Frequency-Mode (ZFM) Drag is Key to the DynamicsDependence on fRW

€

=ηfE

fRW − fE( )VRW2 −

β

fE

fE2

D2 + fE2

⎛

⎝ ⎜

⎞

⎠ ⎟− γ

δf0

fE − f0( )2

+ (δf0)2

drive drag ZFM drag

ZFM

Danielson, O’Neil, Surko, PRL, submitted

RW Compression in the Strong Drive Regime

• Good physical model of transitions, upper and lower fixed points.

• Now explore limits, high densities and low temperatures for applications

Brightness Enhancement Using Traps

• Rotating wall compressed plasma• Slow release creates beam narrower than plasma• RW and inward transport fill “hole” created by positron release

Danielson, APL (2007)

Beam Extraction

€

σ b (r) ≈ σ b 0 exp −r

2ρ b

⎛

⎝ ⎜

⎞

⎠ ⎟

2 ⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥

Small-beam limit:

Plasmaelectron plasma(10 s pulses)

Beam Widths vs Nb/N

€

ρb = 2λ D 1+e2Nb

LpT

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

12

....

__ numerical calc.

“Small beam” when:b/T = e2Nb/LpT< 1

What’s Next Some Near-term Goals

• Explore the density limits of RW compression

• Create a 1 meV positron beam

• Develop a multicell trap

Long-term challenge: a portable antimatter trap

For references see:

http://positrons.ucsd.edu/

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