Plasmas and Trap-Based Beams as Drivers for New Science with Antimatter - Cliff Surko* - Surko Group: UC San Diego
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Plasmas and Trap-Based Beams as Drivers for New Science with Antimatter Cliff Surko* University of California San Diego * Supported by the U. S. NSF, DoE and the UCSD Foundation GEC October 9, 2020
Well, a better title for this audience is: Gaseous Electronics with Antimatter Cliff Surko* University of California San Diego * Supported by the U. S. NSF, DoE and the UCSD Foundation GEC October 9, 2020
The Mirror World of Antimatter positron « electron antiproton « proton New Particles: Positron e- + e+ => gamma rays 2g* (S = 0) or 3g (S = 1) (2g decay: eg = mec2 = 511 keV) Antiproton p + p => shower of pions (e.g., p+, p-) New Atoms: Antihydrogen (pe+) : EB = 13.6 eV (stable) Positronium atom (e+e-): EB = 6.8 eV ts=0 = 0.12 ns; ts=1 = 140 ns GEC October 9, 2020
Tailoring and Delivery of Trapped Antimatter Antiparticles are scarce in our world of matter Confine antiparticles as a single-component plasma in an electromagnetic trap Accumulate, tailor the plasma, then tailor the delivery for specific applications GEC October 9, 2020
Outline Tools for antimatter studies Trapped antimatter Efficient trapping Cooling Radial compression (for density control) Beams and delivery Narrow energy spreads Time bunching Merging plasmas High quality Ps beams New science Positron binding to matter Precision measurements on Ps and H ! Ps BEC and e+- e- (“pair”) plasma GEC October 9, 2020
Sources of e+and p Positrons (energies ~ keV - MeV) Radioisotopes (18F, 58Co, 22Na) (portable, or reactor-based) Electron accelerators (e.g., LINACs) (e ≥ 2mec2 = 1 MeV) Antiprotons (energies ~ GeV) Particle accelerators (CERN, Fermilab) (fast protons: ep ≥ 6 mpc2 ~ 5.6 GeV) Use materials (degraders or moderators) to slow antiparticles to eV energies GEC October 9, 2020
History of Trapped Antimatter – the March Goes On Antiprotons, Penning trap, Gabrielse, 1986 Positron plasma, Penning-Malmberg trap, 1989 Merge antiprotons & positrons for antihydrogen ATHENA, ATRAP, 2002 Trap antihydrogen, ALPHA, 2010 High-quality positronium atom beams Riverside, London, and Tokyo (~2018 - 2020) GEC October 9, 2020
e+ p Positronium physics Ps2, Ps beams antihydrogen Antimatter positron-matter Exploiting binding the Plasma Connection Pulsar crab nebula positron-Auger e+- e- (pair) plasmas g-ray line trap-based beam Munich high-flux GEC October 9, 2020 Ps-atom BEC positron source
GEC October 9, 2020 Trapping antiparticles
GEC October 9, 2020 A Near-Perfect “Antimatter Bottle” the Penning-Malmberg Trap fE B B V V E × plasma rotates: single-component John Malmberg f E = cne /B plasma (1927 – 1992) V(z) z Canonical angular momentum No torques Þ is constant. No expansion! GEC October 9, 2020 (Malmberg & deGrassie ‘75; O’Neil ‘80)
GEC October 9, 2020 Buffer-Gas Positron Trap (down-home gaseous positronics!) 1.7 m CF4 ¨ Trap using electronic excitation of N2 ¨ Positrons cool to 300K on CF4 in ~ 0.1s 30% trapping efficiency using Ne moderator Surko PRL ‘88; Murphy, PR ‘92
GEC October 9, 2020 Shuttle to UHV for Long Term Storage UHV high-field trap Plasma cools by annihilation cyclotron radiation negligible Γ = 0.26 B ! "# c ≈ 0.2 s Confinement times of days possible Surko, Greaves, Charlton Hyperfine Int. 1997 50cm
GEC October 9, 2020 Antiparticle Cooling Critical for Most Applications Collisional cooling on molecules 50 K Cyclotron radiation for positrons and electrons 10 K Laser cooling (sympathetic on Be+, for positrons) 5 K Evaporation (positrons or antiprotons) 10 K ____________________________________________ Latest result: Cyclotron cooling in a resonant cavity increases cooling rate by x 100!* T = 10 K (B = 0.15 tesla) *Hunter & Fajans estimates of temperatures achieved to date Phys. Pl. (2018)
GEC October 9, 2020 Increase Density by Radial Compression with Rotating Electric Fields “The Rotating Wall Technique” Vconf Vconf B . E segmented electrode V = VRW cos[(2pfRW) t + f] Apply a torque using a rotating electric field => (Huang, Anderegg, Hollmann, radial compression for f RW > f E Greaves, Danielson, 1997 - 2007)
GEC October 9, 2020 Positron Plasma Parameters Trivelpiece-Gould modes* Magnetic field 10-2 – 5 tesla Number 104 - 109 mz mz mz Density 105 - 1010 cm-3 Space charge 10-3 – 103 eV Temperature 10-3 – 1 eV Plasma length 1 – 30 cm frequency Plasma radius 0.5 – 10 mm Dubin PF ’93, Tinkle PP‘94 Debye length 10-2 – 1 cm Confinement time 102 – 106 s Diagnostics: modes to measure N, n, T, & aspect ratio evaporate to measure temperature 2D CCD images Surko AIP ‘99, Weber PP ‘08
GEC October 9, 2020 Delivery Trap-based Positron and Ps Beams
Cold Positron Beam Cryogenic Buffer-Gas Trap at 50 K Trap, cool and release: 6.9 meV, FWHM CO cooling gas Tunable from ~ 20 meV to tens of volts Natisin, et al., APL (2016) GEC October 9, 2020
Trap-based Beams – Bunch in Time “harmonic bunching” using a parabolic potential positrons Cassidy, RSI 2006 GEC October 9, 2020
Trap-based Beams – Bunch in Time “harmonic bunching” using a parabolic potential positrons PMT output (mV) 00 PMT output (mV) 0 -40 -2 Buncher on 0 Buncher off -4 -80 - 120 -6 -120 -8 -20 -10 0 10 20 30 40 50 time (ns) time focus 15 ns pulse -> 1 ns pulse Cassidy, RSI 2006 GEC October 9, 2020
Manipulating Ps Atoms and Novel Ps Beams exploiting pulsed lasers Trap efficiently Cool Compress radially Bunch in time => then laser excitation GEC October 9, 2020
GEC October 9, 2020 High-Rydberg-state Positronium Tailored positron pulses, cooled, compressed in space and time Positron pulse in S = 1 positronium atoms Large principle quantum number n => weak positron-electron overlap, so long lifetime
Short e+ Pulses Enable Laser Manipulation High-Rydberg Ps Beams Positron pulses, cooled, compressed in space and time. Match to lasers Stark states Create Ps in an electric field => E-field manipulation 3 control both the positron beam implantation energy and L. theJONES et field electric al. in the excitation region independently. PHYSICAL REVIEW A 90, 012503 (2014) The former controls the kineticUV energy & IRof the emitted low Ps substates, whichfield Ps [47]. The latter allows the Stark state degeneracy in zero electric field to be lifted andlasers thus specific parts of will remain in the original Stark manifold seekers the Stark manifold to be addressed by tuning the laser for 10 ! n ! 30. For Ps with n " 30, some n,m,l mixing wavelength [24]. Specifically, in this way we may predom- will occur for the fastest atoms in the highest magnetic field EStark /h (THz) inantly photoexcite Stark states with either positive or regions [19]. We note that use of an electrostatic positron beam Positrons negative energy shifts, despite e + the limited laser resolution and magnetic shielding would eliminate the motional Stark and Doppler broadening e↵ects. in To allow the incident positron beam to reach the target effects. Detection of annihilation γ ’s is achieved via two 3 × 3- all electrode voltages (exceptPs* those applied to T and E1) in. cylindrical NaI(Tl) detectors, coupled to photomultiplier were initially set to zero, and were then switched on af- tubes (PMTs). Detector A (see Fig. 1 for labeling) is attached ter the beam had passed through using fast high-voltage to a Hamamatsu R2238 PMT, while B is coupled to an EMI switches (with 10-90% voltage rise times of ⇡ 25 ns). The 9821A. The high detectors are situated outside of the vacuum mean Ps flight time to the first electrode was ⇡ 60 ns, field and the mean time to reach the end of the guide was chamber on opposing sides of the annihilation plate, with seekers on the order of 2 µs. The -ray signals observed by de- each covering a solid angle dω/2π ≈ 15%. This arrangement tectors D2-5 were generated primarily by Ps atoms that allows for coincident detection of the two 511-keV γ ’s were either field ionized, or that collided with the vacuum emitted following Ps collisions with the plate. The detection chamber walls after leaving the guide; the latter process of coincident pulses, as well as alternating measurements is indicated in Fig. 1 (a) (see also Sec. IV). GEC October 9, 2020 performed with dipole giant and without the lasers, provide unambiguous moments FIG. 2. Energy level structure of the n = 13 Stark states in evidence Ps with |m| = of 1. long-lived Ps atoms. The energy shift of each state, labeled with III. THEORETICAL BACKGROUND the index k (see text for details), is displayed over the range of
Rydberg Ps Atom Stark Focusing Mirror Focus low-field seekers L ~ 6.0 m ePs ~ 0.25 eV reflecting surface - High electric field + - repels the low-field + seekers Jones, PRL (2017) GEC October 9, 2020
GEC October 9, 2020 Higher-energy Ps Beams Positron pulses, cooled, compressed in space and time - match to laser Review of Scientific Instruments ARTICLE scitation.org/journal/rsi Accelerate and laser-strip ! In order to eliminate any charged particles generated in the Ps production chamber, such as secondary electrons from the converter, a pair of permanent magnets (⇠0.3 T on the sur- face) is mounted on the outside of the entrance of the detector Na-coated W film chamber. Therefore, the background in our detection system can be mainly attributed to the gamma rays of the positrons annihilating in the converter. Two lead shields (5 cm thick each) with a 10 mm center hole are also housed in the vac- uum chambers to further reduce the annihilation gamma-ray " → ! background. ! + ℎ → Ps III. PERFORMANCE OF THE Ps BEAM SYSTEM We carried out production tests of the Ps beam employ- ing this system. Figure 6 shows the TOF spectra of the MCP signals, accumulated over 720 s each, with a Ps accelera- tion voltage of W = 5.0 kV. When the pulsed positron beam was incident onto the converter, a small peak was observed around 2 ns. The TOF of this peak corresponds to that of the positron annihilation gamma-rays originating from the con- verter. Here, the time zero of the spectra was defined as the beam energy 0.3 – 3 keV incidence time of positrons onto the converter. A delayed peak was clearly observed only with the laser and positron beams. ∘ The TOF of this latter peak is in good agreement with that divergence 0.3 calculated for Ps atoms formed p by the photodetachment of the accelerated Ps ions, t = L/ 2|e|W/3me + tPs = 18.0 ns, showing clear evidence for the Ps beam production. Here, tPs = 0.7 ns is the TOF of the Ps ions from the converter FIG. 7. Time-of-flight spectra of the MCP signals for various acceleration volt- to the photodetachment point as estimated by tracking sim- ages of the Ps ions, W. The kinetic energy of the Ps atoms, K Ps , formed by the ulations. The detection rate of the Ps atoms was 23 cps for photodetachment, was calculated as 2W/3 and is also given for each spectrum. W = 5.0 kV. The signal to background ratio was ⇠300, which is One goal: Ps diffraction from material surfaces high enough to perform various experiments with this beam. Note that the introduction of the IR laser beam into the chamber did not contribute to the background. Figure 7 exhibits the measured TOF spectra for various Ps acceleration voltages W from 0.3 kV to 5.0 kV. Here, was set perpendicular (90 ) to the acceleration direction of Michishio, Nakagima, et al., RSI (2019) the Ps ions (the effect of the polarization angle is discussed below). The TOF of the peak of the Ps beam in each spectrum is shifted according to the respective acceleration voltage. The
GEC October 9, 2020 New Science Sketches by A. P. Mills, Jr. with Antimatter
Atomic Physics Positrons Bind to Atoms and Molecules vibrational Feshbach resonances (a) e+ (b) C-H V(r) wCH e stretch annihilation mode rate eb wCH eb (c) e = wCH - eb Using cold positron beam, measured binding energies for > 85 molecules GEC October 9, 2020 Gilbert PRL, 2002; Gribakin RMP, 2010
GEC October 9, 2020 Positron Binding to Molecules pp - - N N +C + Acetonitrile (C2H3N) C p p + - predicted: eb = 135 meV Complementary theory by measured: eb = 180 meV Swann, Gribakin Dermot Green Tachikawa, PCCP 2011 (Belfast) Want to understand e+ - e- correlation & virtual positronium effects
sufficient to broaden the linewidths to the observed values. TheAtomic transverse Physics velocity distribution of the excited state Ps along the xPrecision direction was determined Measurement by the 100 GHz of the Fine Structure excitation laser Positronium bandwidth,23Sbroadening 3 the line by less than 1 -> 2 P0 Transition Positron pulses, cooled, compressed in space and time PHYSICAL REVIEW LETTERS 125, 073002 (2020) B (a) (b) define the analysis time windows used SiO2 h µ-wave antenna induced changes to Ps decay rates were VT guide the parameter Sγ ¼ ½f d ðoffÞ − f d ðonÞ'=f d ð D2 D1 and (off) refer to the microwave radiation. Ps Spectra of the 23S1 → 23P0 transition w 12.95 mm measuring Sγ as a function of the micro F UV laser y The data were corrected according to x dependence of the electric field intensity UV laser D3 D4 power in a waveguide, as described by Ha SiO2 x z although for the waveguide used here this 6 mm 6.48 mm effect. Lorentzian functions, using ins weighting, were used to fit the data and obt FIG. 1. (a) Schematic of the positronium formation and frequencies. Although more complicated li excitation region and WR-51 waveguide and (b) the positions used [35], for symmetric Gurung, PRL (2020) line shapes an GEC October 9, 2020 of the four LYSO detectors D1-4. The spatial profile of the UV metric function (including Lorentzian profi excitation laser light is indicated by the (blue) rectangle in (a). F same center frequencies [36].
blevel sufficient to broaden the linewidths to the observed values. s not The transverse velocity distribution of the excited state Ps etime along 9, GEC October the2020 x direction was determined by the 100 GHz excitation laser bandwidth, broadening the line by less than 23P0 with a Positronium 23S1 -> 23P0 Transition -anni- ; self- atural τrad ≈ 4.5 s disagreement may indi- with theory at the ng the ma6 level. mean which ma7 in progress lation e-shot PHYSICAL REVIEW LETTERS 125, 073002 (2020) lation ortho- placed A discrepancy! tic errors as described FIG. in the text. 2. Example line shape and Lorentzian fit for the ν0 transition measured in a magnetic field of 32 G using detector 1(b). theory? (kHz) line at Δν ¼ 0 corresponds to the calculated Shiftvertical D2. The antity transition frequency, including the Zeeman shift. The inset shows detec- experiment? $ 215 the microwave (solid arrow) and optical (dashed arrows) tran- 00Þ ns new sitions physics? by which 23S1 atoms reach the 13S1 ground state. s (< 1 V=cm)
Atomic Physics continued Stable, Neutral Antimatter Antihydrogen Test CPT Theorem and Gravity ! 1S – 2S inteval Compare H and H GEC October 9, 2020
GEC October 9, 2020 Antihydrogen Production Nested Penning traps -125 ,̅ e+ plasmas antiprotons -100 trapped, cooled, -75 RW-compressed B -50 0 2 4 6 8 10 12 Length (cm) Trap positrons Launch antiprotons into mixing region Mix – make lots of antihydrogen! + + + Formed by three-body collisions: p + e + e = H + e ATHENA/ALPHA (2002-2007) ATRAP similar
! Production (gaseous leptonics) New Protocol for H • Use Rotating Wall to set n • Use evaporative cooling to set the plasma potential • -> sets N, n and rp Use for e- and e+ plasma reproducibility Number of trappable ! increased tenfold! H Ahmadi, PRL (2018) GEC October 9, 2020
GEC October 9, 2020 2-Photon Spectroscopy 1S – 2S Transition in H! LETTER RESEARCH measured using SDREVC a 1.2 Trappable states Disappearance, rs(D) Non-trappable states Appearance, rl(D) Simulation, 1 W |2Sd > 1.0 |2Sc > 0.8 fd–d > Relative (Laser) Normalized signal |2Sb 0.6 |2Sa > precision 0.4 2 x 10-12! 0.2 |1Sd > 0 > |1Sc –0.2 f c–b b 1.2 |1S > (Microwave) 110 1.15 W b FWHM (kHz at 243 nm) 1W 100 0.9 W |1S > Refineda spectroscopy, 1.0 90 80 Near term goal ~ 3 x 10-15 & gravity tests in progress 0.8 70 l normalized to 1 W 0.2 0.4 0.6 0.8 1.0 1.2 60 by several groups Magnetic field (T) 0.6 50 0.7 1.0 Ahmadi, Nature (2018) 1.3 ydrogenic energy levels. Calculated energies (E; for hydrogen) Laser power (W) perfine sublevels of the 1 S (bottom) and 2 S (top) states are ainst magnetic field strength. The centroid energy difference 0.4 15
GEC October 9, 2020 Many-Electron Many-Positron System Sketches by A. P. Mills, Jr.
GEC October 9, 2020 Many Body Physics with Antimatter electron-positron phase diagram n e+ - e- liquid normal /supercond… nMott~ 3 x 1022 cm-3 density T ~ 7 x 104 K PsBEC Ps BEC Ps BEC e+ - e- Ps gas plasma Ps2 gas temperature 8 x 103 K (BEC º Bose-Einstein condensate) Yabu, NIMB ‘04
GEC October 9, 2020 hn Spectroscopy of Ps2 Ps2 Al(1,1,1) Doppler shifts Optical spectrum of the Ps2 molecule Ps2: 1s – 2p (e+e-e+e–) First many-electron many-positron state Cassidy, PRL 2012
remoderated Route to a Ps BEC beam 108 e+ from accumulator 5 keV -> Ni remoderator 5 keV -> porous silica Ps Ps Ps 1.5 µ 1.5 µm 5 x 105 hat brim Ps 1 x 105 top of the hat Ps Ps Ps Ps e+ goal n ~ 1019 cm-3 Tc = 70 K 4µ many challenges e.g., sample heating Mills, Proc. ICPA (AIP 2019) GEC October 9, 2020
GEC October 9, 2020 Classical Electron-Positron (“Pair”) Plasmas Novel nonlinear phenomena for T+= T- and n+ = n- • Remarkably good confinement • Heavily damped acoustic mode • Faraday rotation absent • Very strong nonlinear growth and damping processes* * Tsytovich & Wharton, Comm. on Pl. Phys. (1978) Relativistic e- - e+ plasmas • Astrophysical relevance Electron beam – positron plasma experiment Greaves, PRL (1995); Gilbert, PP (2001)
GEC October 9, 2020 e- - e+ (“Pair”) Plasma– the APEX Collaboration Levitated Superconducting Magnetic Dipole 8.2GHz Lifting magnet microwave 100G 50G Positron test 2930G 875G Electron gun experiments with 5000G plasma 5000G 2.45GHz permanent magnet microwave Stenson, PRL 2018 Horn-Stanja, PRL 2018 Levitating Yoshida, PP (2013) magnet Coil catcher Coil lift 0 0.5 1 1.5 r (m) Reviews: Advantages Stoneking, JPP (in press) Pedersen, NJP (2012) 300 s confinement Can confine e+ & e-
GEC October 9, 2020 A Positron Trap on the NEPOMUC Beam in Munich (~ 5 x 108 e+/s) Immediate goal: giant pulses for e+ - e- plasmas (the APEX collaboration) Will need a “multicell trap” for large N* ____________________________________________ Goals for other NEPOMUC experiments: Positron-Auger spectroscopy using bunched e+ Single-shot PALS (buncher for ≤ 300 ps timing) RW and centerline-extraction for positron microscope * Hurst, Phys. Plasmas (2019)
GEC October 9, 2020 Antimatter in the Laboratory Gaseous Positronics is the Driver Much Progress and Many Opportunities ! Materials and atomic physics ! Tests of fundamental physics ! Antimatter plasmas & BEC Ps
GEC October 9, 2020 Future of Antimatter Plasma Technology Tools Improved plasma compression Colder antimatter plasmas Antihydrogen Improved p, -positron mixing Antihydrogen beams Positron and Ps Physics Larger numbers of positrons Higher quality Ps beams Portable antimatter traps
GEC October 9, 2020 Thanks to many for material and advice: David Cassidy, Mike Charlton, Joel Fajans, Gleb Gribakin, Christoph Hugenschmidt, Adric Jones, Allen Mills, Yasayuki Nagashima, Andrew Swann. and present and former collaborators: L Barnes, S. Buckman, J. Danielson, A. Deller, D. Dubin, S. Gilbert, S. Ghosh, R. Greaves, G. Gribakin, C. Hugenschmidt, N. Hurst, E. Jerzewski, M. Leventhal, J. Marler, T. Murphy, M. Natisin, T. O’Neil, A. Passner, T. Pedersen, E. Stenson, M. Stoneking, J. Sullivan, M. Tinkle, T. Weber, J. Young, the APEX Collaboration. Thanks too for support from AT&T Bell Labs, ONR, NSF, DOE, DTRA, and the UCSD Foundation.
GEC October 9, 2020 e+ Review Articles: Plasma and Trap-Based Techniques for Science with Positrons J. R. Danielson, et al., Rev. Mod. Phys. 87, 247 (2015). Experimental Progress in Positronium Laser Physics D. B. Cassidy, Euro. Phys. J. D. 72, 53 (2018) Plasma and Trap-Based Techniques for Science with Antimatter J. Fajans and C. M. Surko, Phys. Plasmas 27, 030601 (2020) positrons.ucsd.edu
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