111 antimatter. congratulations and thanks ron! plasma fusion center, mit physics of plasmas ‘95...
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111
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
e+
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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