Physics with Many Positrons

628 Pages·2010·10.1 MB·English

by  A. Dupasquier

SOCIETA` ITALIANA DI FISICA
RENDICONTI
DELLA
SCUOLA INTERNAZIONALE DI FISICA
“ENRICO FERMI”
CLXXIV Corso
a cura di A. Dupasquier e A. P. Mills jr.
Direttori del Corso
e di
R. S. Brusa
VARENNA SUL LAGO DI COMO
VILLA MONASTERO
7 – 17 Luglio 2009
Fisica con molti positroni
2010
SOCIETA` ITALIANA DI FISICA
BOLOGNA-ITALY
ITALIAN PHYSICAL SOCIETY
PROCEEDINGS
OF THE
INTERNATIONAL SCHOOL OF PHYSICS
“ENRICO FERMI”
Course CLXXIV
edited by A. Dupasquier and A. P. Mills jr.
Directors of the Course
and
R. S. Brusa
VARENNA ON LAKE COMO
VILLA MONASTERO
7 – 17 July 2009
Physics with Many Positrons
2010
AMSTERDAM, OXFORD, TOKIO, WASHINGTON DC
Copyright (cid:2)c 2010 by Societa` Italiana di Fisica
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INDICE
R. S. Brusa, A. Dupasquier and A. P. Mills jr. – Preface........... pag.XVII
Gruppo fotografico dei partecipanti al Corso .......................... XX
(cid:0)
D. B. Cassidy – Experiments with many-positron systems ............. 1
(cid:0)
1. Introduction.................................................... 1
(cid:0)
2. Positron accumulation............................................ 5
. (cid:0)
21. Positron beam ............................................. 7
. (cid:0)
22. Positron accumulator ....................................... 10
. (cid:0)
23. Positron plasma compression ................................. 13
(cid:0)
3. Productionand detection of intense positron pulses ................... 23
. (cid:0)
31. Single-shot positron annihilationlifetime spectroscopy ............ 23
. (cid:0)
32. Fast detectors.............................................. 27
. (cid:0)
32.1. Lead tungstate: PbWO4 .............................. 28
. (cid:0)
32.2. Lead fluoride: PbF2 .................................. 28
. (cid:0)
33. Spatiotemporalcompression.................................. 32
(cid:0)
4. Experiments with intense positron pulses............................ 33
. (cid:0)
41. Positroniumformation in porous materials...................... 35
. (cid:0)
41.1. Ps diffusion ......................................... 36
. (cid:0)
41.2. Ps cooling .......................................... 38
. (cid:0)
42. Laser spectroscopyof positronium............................. 40
. (cid:0)
43. Interactionsbetween positroniumatoms........................ 45
. (cid:0)
43.1. The effect of Ps-Ps quenching on lifetime spectra .......... 47
. (cid:0)
43.2. Spin exchange quenching .............................. 50
. (cid:0)
43.3. Molecular positroniumformation ....................... 55
. (cid:0)
44. Positroniumas a probe of transient phenomena ................. 59
(cid:0)
5. Concludingremarks and future work ............................... 64
(cid:0)
A. P. Mills jr. – Physics with many positrons........................ 77
(cid:0)
1. Physics with many positrons ...................................... 77
. (cid:0)
11. Introduction............................................... 77
. (cid:0)
11.1. Last of the polyelectrons .............................. 79
. (cid:0)
11.2. Observation of positroniummolecules.................... 81
. (cid:0)
11.3. Dreams of the gamma-ray laser......................... 81
. (cid:0)
11.4. Many-positronphysics ................................ 82
(cid:0)
VII
indice
VIII
.
12. Many-positronstates........................................ pag. 89
.
12.1. Introduction......................................... 89
. (cid:0)
12.2. Positron surface states ................................ 91
. (cid:0)
12.3. Many positrons in a solid.............................. 95
. (cid:0)
13. Ps-Ps Scattering and Ps2 molecule formation from Ps surface states 96
. (cid:0)
13.1. Ps2 formation interaction radius for dense positronium (Ps)
on an insulator surface ................................ 96
. (cid:0)
13.2. ScatteringstatesoftwoPsatomswithgiventotalspinangular
momentum.......................................... 100
. (cid:0)
13.3. ModelforthermalinactivationofPs2formationinporoussilica 104
. (cid:0)
13.4. Model for thermal dissociation of Ps2 in a cavity neglecting
wall interactions ..................................... 105
. (cid:0)
13.5. Thermal desorption of positroniumfrom an insulator surface 109
. (cid:0)
14. Neutral plasmas............................................ 112
. + − (cid:0)
14.1. Low density e -e plasmas ............................ 112
. (cid:0)
14.2. Long-term storage of low-density neutral electron-positron
plasmas ............................................ 116
. (cid:0)
14.3. Thermalizationof the positronsand electrons............. 119
. + − (cid:0)
14.4. High density e -e plasmas............................ 121
(cid:0)
2. PositroniumBose-Einstein condensation............................. 121
. (cid:0)
21. Introductorymaterial ....................................... 121
. (cid:0)
21.1. Identicalparticles .................................... 121
. (cid:0)
21.2. Consequences of particle identity ....................... 123
. (cid:0)
21.3. Stimulated emission .................................. 123
. (cid:0)
22. Formation of polarized positronium............................ 124
. (cid:0)
23. Laser cooling of positronium ................................. 124
. (cid:0)
23.1. Introduction......................................... 124
. (cid:0)
23.2. Pulsed laser cooling................................... 126
. (cid:0)
23.3. Sub-recoilcooling .................................... 128
. (cid:0)
24. BEC physics............................................... 129
. (cid:0)
24.1. Introduction......................................... 129
. (cid:0)
24.2. Importanceof positroniumBose-Einstein condensation ..... 130
. (cid:0)
24.3. Approach to thermal equilibrium in a Ps BEC ............ 131
. (cid:0)
24.4. Approach to phase coherence in a Ps BEC ............... 133
. (cid:0)
24.5. Effects of a fixed randompotential ...................... 133
. (cid:0)
25. BEC in alternate geometries ................................. 133
. (cid:0)
25.1. Introduction......................................... 133
. (cid:0)
25.2. Condensation........................................ 135
. (cid:0)
25.3. Spin exchange quenching .............................. 139
. (cid:0)
25.4. Special geometries.................................... 141
. (cid:0)
25.5. Superfluidity ........................................ 142
(cid:0)
3. Optical experiments on positronium ................................ 143
. (cid:0)
31. Motivation for measurements on antimatter..................... 143
. (cid:0)
32. Inducing triplet-to-singlet transitionsin positronium ............. 144
. (cid:0)
32.1. Ground-statehyperfine transitions ...................... 144
. (cid:0)
32.2. Triplet-singlet mixing via a pulsed magnetic field .......... 145
. (cid:0)
33. Laser requirements for experiments on positronium .............. 145
. (cid:0)
33.1. Laser excitation of Ps 1S-2P transitionsin vacuum ........ 145
3.3.2. Measurement of the 1So to 1Pe interval of Ps2 ............ (cid:0) 146
. (cid:0)
33.3. Laser cooling of a cloud of Ps atoms..................... 147
(cid:0)
indice
IX
.
33.4. Photographthe Ps molasses ........................... pag. 148
.
33.5. Measurement of the first-order Doppler-free cold Ps 1S-2S
linewidth ........................................... 149
. (cid:0)
33.6. First-orderDoppler-freetwo-photon(452nm)measurementof
the 1So to 1So∗ interval of Ps2 ......................... 149
. (cid:0)
33.7. Laser cooling of Ps atoms confined in a small cavity........ 149
. (cid:0)
33.8. Formationofalaser-cooledpositroniumBose-Einsteinconden-
sate (BEC) in a cavity ................................ 150
. (cid:0)
33.9. Optical observationsof cavity positronium ............... 151
. (cid:0)
33.10. Observation of the Bose-Einstein condensationof positronium 154
. (cid:0)
33.11. Demonstration of positroniumtunneling into vacuum ...... 155
. (cid:0)
33.12. Other experiments ................................... 156
. (cid:0)
34. Laser spectroscopyof di-positroniummolecules.................. 156
. (cid:0)
35. Experiments on positronic compounds ......................... 157
(cid:0)
4. Stimulated annihilationand the annihilationgamma-ray laser .......... 158
. (cid:0)
41. Introduction............................................... 158
. (cid:0)
41.1. Why would one wish to make a gamma-ray laser? ......... 159
. (cid:0)
41.2. Why is an annihilationlaser possible? ................... 160
. (cid:0)
41.3. Details of the Ps BEC ground state ..................... 161
. (cid:0)
42. Positron sources............................................ 163
. 79 (cid:0)
42.1. Isotope separation of Kr ............................. 163
. (cid:0)
42.2. Space charge limit to the focusing of a cylindricalcurrent... 166
. (cid:0)
42.3. Space charge limit to the focusing of a flat sheet of current.. 167
. (cid:0)
42.4. Anannihilationlaserrequiresaslow-positronlinefocusinzero
field................................................ 169
. (cid:0)
42.5. Heat dissipation...................................... 169
. (cid:0)
43. Thresholdsfor stimulated emission and lasing ................... 169
. (cid:0)
44. Fusion.................................................... 171
. (cid:0)
44.1. Deposition of gamma-ray energy in a DT plasma .......... 171
. (cid:0)
44.2. Fusion threshold ..................................... 172
. (cid:0)
45. Power generation........................................... 173
(cid:0)
AppendixA. Problems.............................................. 176
(cid:0)
M. Charlton and D. P. van der Werf – Antihydrogen physics ....... 189
(cid:0)
1. Introduction.................................................... 189
(cid:0)
2. Motivation for antihydrogenexperimentation ........................ 190
. (cid:0)
21. The CPT theorem.......................................... 190
. (cid:0)
22. Gravity ................................................... 191
(cid:0)
3. IntroductoryPenning trap and plasma physics ....................... 192
. (cid:0)
31. The Penning trap .......................................... 192
. (cid:0)
32. Plasma physics............................................. 194
(cid:0)
4. Antiparticletrapping and manipulationfor antihydrogen............... 197
. (cid:0)
41. Antiprotontrapping and cooling .............................. 197
. (cid:0)
42. Antiprotonstacking and manipulation ......................... 201
. (cid:0)
43. Positron trapping and manipulation ........................... 203
. (cid:0)
44. Positron accumulator—operationalissues....................... 206
(cid:0)
5. Antihydrogenformation .......................................... 208
(cid:0)
indice
X
.
51. Mechanisms ............................................... pag. 208
.
52. Positron-antiprotonmixinginanestedtrapandantihydrogenforma-
tion ...................................................... 209
. (cid:0)
53. Field ionization of antihydrogen............................... 213
. (cid:0)
54. Insights from simulations .................................... 214
(cid:0)
6. Antihydrogentrapping ........................................... 215
. (cid:0)
61. The magnetic minimum neutral trap—generalconsiderations ...... 215
. (cid:0)
62. Plasma stability in multipolar magnetic fields ................... 217
. (cid:0)
63. The ALPHA antihydrogentrap............................... 217
(cid:0)
7. Concludingremarks.............................................. 219
(cid:0)
E. Lodi Rizzini – Antihydrogen production in the ATHENA apparatus... 223
(cid:0)
1. Introduction.................................................... 223
(cid:0)
2. Experimental data............................................... 223
(cid:0)
3. Conclusions .................................................... 227
(cid:0)
J. Walz – Towards antihydrogen spectroscopy ........................ 229
(cid:0)
1. Introduction.................................................... 229
(cid:0)
2. Tests of the symmetry between matter and antimatter................. 231
(cid:0)
3. Laser-spectroscopyof the 1S–2S transition.......................... 232
. (cid:0)
31. Ultrahigh-resolutionlaserspectroscopyusingordinaryhydrogenatoms 233
. (cid:0)
32. Towards laser spectroscopyof antihydrogen..................... 234
(cid:0)
4. Microwave spectroscopyof the hyperfine splitting..................... 236
(cid:0)
5. Beyond antihydrogenspectroscopy ................................. 237
(cid:0)
6. Conclusions .................................................... 238
(cid:0)
R. S. Brusa and A. Dupasquier – Positronium emission and cooling.... 245
(cid:0)
Introduction ....................................................... 245
(cid:0)
1. Positroniumemission from solids................................... 246
. (cid:0)
11. Positroniumemission from metals............................. 247
. (cid:0)
11.1. Positroniumformed by backscattered positrons ........... 247
. (cid:0)
11.2. Positroniumformed by epithermal positrons .............. 249
. (cid:0)
11.3. Direct positroniumformation by thermal positrons ........ 250
. (cid:0)
11.4. Thermal emission of positronium ....................... 256
. (cid:0)
12. Positroniumemission from dielectrics .......................... 258
. (cid:0)
12.1. Small band gap dielectrics ............................. 259
. (cid:0)
12.2. Large band gap dielectrics ............................. 261
(cid:0)
2. Positroniumthermalizationand cooling ............................. 268
. (cid:0)
21. Ps emission at low temperature from modified metal surfaces ...... 268
. (cid:0)
22. Collisionalcooling of Ps (theory).............................. 270
. (cid:0)
23. Collisionalcooling of Ps (experiments) ......................... 276
. (cid:0)
23.1. Ps cooling in gases ................................... 276
. (cid:0)
23.2. Ps cooling in silica powders ............................ 281
(cid:0)