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 Danielson Toby Weber Tom O’Neil Mike Anderson * Supported by NSF, DOE/NSF Partnership

Antimatter in our world of Matter Plasma Physics  enabling the study and use low-energy antimatter PET scan Fast electronics Electron-positron Plasmas Antihydrogen e+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 matter  Atomic/molecular physics  Laboratory astrophysics  Density dependent processes  Pulsed, bright beams (e.g., plasma diagnostics, materials analysis)  Antihydrogen production  Electron-positron plasmas  BEC positronium e+e+

A Near-Perfect “Antimatter Bottle” The Penning-Malmberg Trap Angular Momentum No torques L z = is constant No expansion! Single-component plasma B V V (Malmberg & deGrassie ‘75; O’Neil ‘80) John Malmberg E x B plasma rotation f E = cne/B

Buffer-Gas Positron Trap  Trap using a N 2 -CF 4 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 Positrons in (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  ~ e + /cm* Confinement at high plasma densities? Cooling  cool ~ tesla * cylindrical plasma

Improve vacuum Improve B-field Computerized optimization Improved trap Stacking ATHENA Solid neon moderator Year trapped positrons UCSD Multicell 1x10 12 Overview of Positron Trapping

Increase positron storage capacity Plasma compression for lifetime and density control Extraction of finely focused beams New Tools for Antimatter Physics

End View D RF Electrodes DC Electrode 2R p LpLp L Side View Positron Plasma Multicell Trap for Large N tot * Many “beaded rods” in parallel Design Parameters B = 5T n ~ 3x10 10 cm -3 L p ~ 5 cm R p ~ 0.14 cm T ~ 2 eV N tot ~ (1 cell)  c ~ 1 kV Total number of cells ~ 100 N tot ~ *Surko and Greaves, Radiation Physics and Chemistry (2003) B

master cell 2 banks of 19 storage cells Multicell Positron Trap Electrodes e+e+ Danielson, Phys. Plasmas (2006)

Autoresonant Diocotron-mode Excitation to Position Azimuthal Radial Danielson, Phys. Plasmas (2006) D/R w ≥ 0.8 f D = f Do [1 - (D/R w ) 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., Hollmann, et al., ‘95 - ‘00) Greaves and Surko, PRL (2000).Greaves and Surko, PRL (2000). Radial density profiles from CCD images:* B

weak- drive strong- drive Transition Region Transition/bifurcation _________________________________________________ Danielson PRL (05); Phys. Pl. (06) electron plasma f E  f RW

Hysteretic Behavior in f RW Characteristic of the Strong Drive Regime Strong Drive Regime - above a critical V RW, f E f RW Zero Frequency Mode

Zero-Frequency-Mode (ZFM) Drag is Key to the Dynamics Dependence on f RW 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 Small-beam limit: Plasma electron plasma (10  s pulses)

Beam Widths vs N b /N.... __ numerical calc. “Small beam” when:  b /T = e 2 N b /L p T< 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: e+e+