Plenary review talk, APS Plasma Physics Division, Chicago IL, Nov. 9, Plasmas as Drivers for Science with Antimatter.

Transcription

1 Plenary review talk, APS Plasma Physics Division, Chicago IL, Nov. 9, 2010 Plasmas as Drivers for Science with Antimatter Cliff Surko* University of California San Diego * Supported by the U. S. DoE, NSF and DTRA

2 Positron Proc. R. Soc. (London) A (1928) Picture credit: AIP Emilio Segrè Visual Archives Proc. R. Soc. (London) A (1928) Dirac equation: anti-electrons (1928)

3 Quantum Field Theories are symmetric: matter <=> antimatter But gamma-ray observations => antimatter in our universe ~ zip! 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!

4 p e + materials studies antihydrogen Antimatter in our world of Matter e + - e - plasmas medicine PET scan galactic center

5 The Mirror World of Matter and Antimatter positron electron antiproton proton Positrons e - + e + => gamma rays 2γ * (S = 0) or 3γ (S = 1) (2γ decay: ε γ = m e c 2 = 511 kev) Positronium atom (e + e ): E B = 6.8 ev τ s=0 = 120 ps; τ s=1 = 140 ns Antiprotons p + p => shower of pions (π 0, π +, π )

6 Outline Creation and Manipulation of Antimatter Plasmas e + matter interactions stable neutral antimatter e + - e - many body system Physics with Antimatter Positron binding to atoms and molecules Positron studies of materials Antihydrogen Bose-condensed positronium Electron-positron plasmas Future Antimatter Traps Focus on low-energy antimatter: Omits laser-produced relativistic positron plasmas [e.g., H. Chen, et al., PRL 2010)]

7 Antimatter Sources & Creating and Manipulating Positron Plasmas

8 Sources of e + and p Positrons (energies ~ kev) Radioisotopes ( 18 F, 58 Co, 22 Na) (portable, or reactor-based) Electron accelerators (e.g., LINACs) (ε 2m e c 2 = 1 MeV) Antiprotons (energies ~ GeV) Particle accelerators (CERN, Fermilab) (fast protons: ε p 6m p c GeV)

9 Focus on Slow Positrons Use moderators 100 s of kev ~ 1 ev copper solid neon (~ 7.2 K) 22 Na e + source fast e + B slow positron beam (E ~ 1eV) Neon efficiency ε ~ 1% 50 mci 22 Na ~ 10 7 slow e + /s (1 pa) Some metals are moderators too W, Ta, Pt (ε ~ 0.1 %)

10 Intense Reactor-Based Positron Beam FRM II reactor, Munich Reactor core γ γ γ platinum moderator Beam 7 mm FWHM, in 60 G 9.0 x 10 8 e + /s (~ 100 pa) C. Hugenschmidt, U. Munich

11 Trapping Antimatter the Plasma Connection

12 A Near-Perfect Antimatter Bottle the Penning-Malmberg Trap V B V plasma rotates: f E = cne /B V(z) z single-component plasma Canonical angular momentum No torques is constant. No expansion! Thermal equilibrium rigid rotor (Malmberg & degrassie 75; O Neil 80)

13 Buffer-Gas Positron Trap Trap using a N 2 -CF 4 gas mixture Positrons cool to 300K (25meV) in ~ 0.1s 30% trapping efficiency Surko PRL 88; Murphy, PR 92 Early positron trapping efforts: Gordon et al., (LLNL) 60 (Mirror) Schwinberg, et al., 81 (Penning trap)

14 Buffer-gas Positron Accumulator gas in positrons in 1.8 m positron plasma B = 0.15 T UCSD cryopumps Similar devices in: Australia China Europe Russia CERN (3)

15 Commercial Positron Traps First Point Scientific, Inc. (R. G. Greaves) Accumulator (~ 250 K$/module) source/moderator two-stage trap

16 High-field Positron Traps => cyclotron cooling 120cm B = 5T T as low as K P torr τ c = 0.16 s Particles cool by cyclotron radiation τ c B -2 Also laser cooling using Be + : Jelenkovic et al, PRA 03 50cm

17 Compression with Rotating Electric Fields The Rotating Wall Technique V conf V conf segmented electrode phased for m θ = 1 compression for f RW > f E V = V RW cos[(2πf RW ) t + φ] (Huang, et al., Anderegg,, et al., Hollmann,, et al., Greaves et al., Danielson et al., )

18 Rotating-wall compression - strong drive regime Attracting fixed point f E = cne /B " f RW high-density rigid-rotor f RW = 6.4 MHz flat-top ZFM Convenient tool: one knob tunes density Open question: what is the density limit Zero-frequency Modes (ZFM)? data with test electron plasmas Danielson et al., PRL 05, 07, Phys. Plasmas, 06

19 Positron Plasma Parameters Magnetic field tesla Number Density cm -3 Space charge ev Temperature ev Plasma length 1 30 cm Plasma radius mm Debye length mm Confinement time s Trivelpiece-Gould modes* m z mz m z frequency Dubin 93; Tinkle 94 Diagnostics: modes to measure N, n, T, & aspect ratio 2D CCD images Gilbert 97

20 BUT WE HAVE COMPETION! Positron - the cartoon character (Wikipedia) 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

21 High Resolution Positron Beam Trap, cool and release: High-resolution positron beam tunable from 50 mev upwards Gilbert et al., APL (1997)

22 Tailored Positron Beams Δt ~ 6 µs " D # T /n Cryogenic plasmas and RW compression for low T and high n yield small beams Danielson, APL 07 Weber, PP 08, 09 (data with test electron plasmas) areal density (10 10 cm -2 ) T = 0.1 ev with RW compression D = 100 µ extracted beam

23 Physics with Antimatter Positron-matter Interactions

24 Positron Annihilation on Molecules - Anomalously Large A mystery for 5 decades simple collision model Γ m measured annihilation rate Γ D annihilation rate using Dirac annihilaiton rate for free electrons Molecule Γ m / Γ D * methane (CH 4 ) 14 butane (C 4 H 10 ) 330 octane (C 8 H 18 ) 9000 Γ m >> Γ D for molecules??, but Γ m ~ Γ D for atoms * annihilation with thermal positrons at 300 K

25 Energy Resolved Annihilation Rate for Butane (C 4 H 10 ) " m " D butane Butane (C 4 H 10 ) C-H stretch modes Peaks shifted by binding energy ΔΕ Β ε + ΔE B = E vib positron energy, ε (ev) energy (ev) vibrational modes (10 mev width) Gilbert, et al., PRL (02) Barnes, et al., PR (03) alkanes Positrons bind to molecules, and Can measure binding energies

26 Bound Positron Wave Functions for Alkanes ΔE B increases with molecular size N " = # A e$% r$r i i r $ R i i=1 ΔE B = 35 mev ΔE B = 260 mev C 4 H 10 C 8 HC H 30 C 14 H 30 C 14 H 30 bound positron wave functions Gribakin and Lee, EPJ 08 alkanes

27 Positron Interactions with Atoms and Molecules Positrons bind to molecules likely bind to atoms too, but no experiments For similar ions, positron binding ~ larger than for electrons Theoretical comparisons for ΔE b beginning Gribakin, Young, Surko Rev. Mod. Phys. 10

28 Positron Studies of Materials

29 Materials Analysis Using Positron Beams Positrons provide new techniques and new information not available using e - beams.

30 Positron-induced Auger-electron Spectroscopy make a core hole, then filled in a 2-electron transition E cv valence E cv copper surface electron impact 2 kev positron annihilation 20 ev E core E cv 1 2 Munich reactor-beam data sub-monolayer sensitivity Plasma challenges for materials studies: more intense positron beams microbeams short pulses for lifetime spectroscopy Mayer, et al., Surf. Sci., 10

31 Stable, Neutral Antimatter Antihydrogen

32 Why Study Antihydrogen Some Tests of CPT (e/m) Would like to test all particle sectors? (H) Precision possible Test gravity too force of matter on antimatter

33 Antihydrogen Experiments at CERN ATRAP, ATHENA ( 2005), ALPHA* (2005 ) Antihydrogen trapping for spectroscopy ASACUSA Antihydrogen beam for microwave spectroscopy AEGIS* Antihydrogen beam for gravity tests * Some members part of ATHENA

34 Low-energy Antiprotons The CERN Antiproton Decelerator (AD) From PS: 1.5x10 13 protons/bunch, 26 GeV/c 1 Antiproton Production 2 Injection at 3.5 GeV/c 4 Extraction 2-4 ( 2x107 x 10 7 in 200 ns) ns ATRAP ATRAP 3 Deceleration and Cooling to 5 MeV ( GeV/c) Stochastic Cooling ASACUSA ASACUSA ATHENA/ ALPHA m Electron Cooling

35 Antiproton Catching & Cooling* a) Degrading Solenoid - B = 3 Tesla Antiprotons Degrader e - t = 0 s Cold electron cloud [cooled by Synchtrotron Radiation,! ~ 0.4s] b) Reflecting Potential 0.1% E<5kV 99.9% lost t = 200 ns c) Trapping Potential t = 500 ns c) Cooling Potential [through Coulomb interaction] t ~ 20 s ~ 10,000 antiprotons per AD pulse ATHENA/ALPHA Gabrielse, PRL 86

36 Antihydrogen Production (one scenario) Nested Penning traps antiprotons B p, e + plasmas trapped, cooled, RW-compresed Length (cm) ~ 10 8 positrons Launch ~ 10 4 antiprotons into mixing region Mixing time 190 sec Repeat cycle every 5 minutes ATHENA/ALPHA (pre-2007) ATRAP similar

37 Antihydrogen Formation Mechanisms + Radiative Three-body e + p " H + h! + e + + e + p! H + e + + Rate ~10 s Hz very fast Rate T p dep.* T p -0.6 T p -4.5 Final state tightly bound weakly bound, E b ~ kt p * equilibrium assumed - experiments are typically non-equilibrium

38 Detect Antihydrogen Atoms Annihilating on the Electrodes Cold e + Hot e + Images of antiproton decays ATHENA Amoretti, Nature (2002) Field-ionization detection too (ATRAP)

39 Antihydrogen Trapping minimum-b trap Ioffe-Pritchard geometry B quadrupole winding U = " v µ # v B mirror coils Well depth ~ 0.6 K Plasma lifetimes drastically reduced in the presence of quadrupolar field so use octopole* * ALPHA - Fajans, PRL 05 Andresen, PRL 07

40 Antihydrogen Production Many 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 In p cooling with e -, there can be extensive centrifugal separation p B e - Glinsky PF 91, Robicheaux PRA 04, Bass PP 09 Most processes are non-equilibrium Andresen PRL 08 Kuroda PRL 08 Gabrielse PRL 10

41 Search for Trapped Antihydrogen* + launch ~ 5 x 10 4 p into ~ 2 x 10 6 positrons (212 cycles) hold 130 ms then shut off min-b trap in 9 ms! six events are consistent with trapped antihydrogen however cannot yet rule out that the signal could be due to (hot) mirror-trapped p annihilation detector octupole * ALPHA collaboration Andresen, Phys. Lett. B, in press, Nov data Oct. - Nov mirror coils electrodes

42 Search for Trapped Antihydrogen* 50% 99% time (ms) Six events resolved in space and time p Simulate H and signals Data favor H interpretation simulated locations mirrortrapped p events z (cm) simulated locations H * ALPHA collaboration, Andresen, Phys. Lett. B, in press, Nov. 2010

43 Antihydrogen Production and Trapping Summary 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

44 Long-term goal: spectroscopic tests of symmetry hydrogen laser spectroscopy 1s-2s two-photon spectroscopy frequency measurements Doppler effect cancels need ~ 10 2 trapped H for a measurement Hansch, PRL 00

45 Many-Electron Many-Positron System

46 The Electron-Positron Phase Diagram n e + - e - liquid normal /supercond. n Mott ~ 3 x cm -3 T ~ 7 x 10 4 K Ps 2 gas Ps Ps Ps BEC BEC Ps gas e + - e - plasma 8 x 10 3 K (BEC Bose-Einstein condensate) Yabu, NIMB 04

47 Bose-Einstein Condensation (BEC) of Positronium Atoms (Ps) a quantum many-body e + e - system Small mass => 10 K, λ DeBroglie ~ 30 nm, n BEC ~ 3 x cm -3 Ps - Ps Interactions Long-lived Ps states (~ 140 ns) S = 1, m ±1 (Ps ) Low density quantum fluid Ps atom interferometer, γ-ray laser... Ps + Ps => Ps 2 + E b (.42 ev) => 2 Ps + E h (1meV) short lived states Ps + Ps => long lived - can form a BEC

48 Final Stages of the Quantum Ps Gas Experiment high voltage buncher accelerator target phosphor screen spin-aligned e + beam from accumulator pulsed magnet coil B = 2.3 T Implant e + in porous silica d ~ 10 nm PMT output (mv) Buncher on Buncher off time (ns) PMT output (mv) Use rotating wall to adjust areal density, n 2D D. Cassidy, A. Mills, U. California, Riverside

49 normalized delayed Q fraction, Q Buffer-gas Traps Preserve Positron Spin Polarization - critical for the BEC Ps experiment Ps 2 formation areal Beam density, areal density n ( 10 cm -2 ) 2D (10 10 cm -2 ) Delayed annihilation fraction, f d (150 t 50 ns) P m=1 (%) Q " f d / f d ( n 2D = 0) 28% aligned m = 1 Ps atoms At high densities, only S = 1, m = 1 remain Cassidy, PRL Na source => S = 1 spin- polarized Ps gas required for Ps BEC

50 Bose-Condensation of Positronium Produced Ps 2 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.

51 Electron-Positron Plasmas

52 Classical Electron-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 work on pair-ion plasmas (e.g.,c 60± )

53 Columbia Non-neutral Torus a stellarator for electron-positron plasmas Advantages Can confine e + & e - at arbitrary degrees of neutralization 1 m Status and plans 50 ms confinement achieved for electron plasmas Plan e + injection via (< 10 µs) electrostatic perturbations Need ~ e + use a multicell-trap T. Sunn Pedersen et al., PRL, 02; JPB 03 Other possible confinement schemes: Penning/Paul trap Magnetic mirror

54 Larger Collections of Antimatter

55 Goals High capacity Future of Trapping Antimatter Long-term storage Portable antimatter traps? Major technical issue Space charge becomes large (e.g., e + /cm ~ 10 kv)* breakdown, heating,... (Brillouin limit, n = B 2 /8πmc 2, not yet a problem) * cylindrical plasma

56 Positron Traping the Long View Multicell N > plasma space charge 100 kev trapped positrons Improved trap Solid neon moderator Computerized optimization Improve B-field Single cell N ~ V ~ 1kV ATHENA 10 kev 1 kev 100 ev 10 ev 1 ev 100 mev 10 mev Improve vacuum 1 mev Year mci 22 Na sources

57 Solution: Shield Parallel Cells with Copper Electrodes a multicell trap for positrons* e + in 1 m B 3 banks of 7 cells (21 cells, total), with 5 x e + each 1 kv confinement potentials & RW compression Move plasma across B with autoresonant Diocotron mode + Modular design so larger traps are possible * Surko, JRCP 03 Danielson, PP 06 + Fajans et al., 99-01

58 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)

59 Outstanding Challenges 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?

60 For references and links to other work see: positrons.ucsd.edu/ e + 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