Experiments with Supersonic Beams as a Source of Cold Atoms

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and possible future improvements to the coilgun, are described. 5.1 Hydrogen Motivation and Structure As the simplest atom, and the atom best understood by theorists, hydrogen serves as an important test system for fundamental physics. Precision measurements of the atomic structure of hydrogen, such as the determination of the Lamb-shift [87], provide stringent tests of theory. The frequency of the 1S − 2S transition is one of the most precise atomic measurements to date [88–91], and is important in the determination of fundamental constants, such as the Rydberg constant. Measurements on muonic hydrogen have contributed to the determination of the size of the proton [92], and studies of the isotopic shift of deuterium have helped to determine the size and structure of the deuteron [93, 94]. Finally, work with anti-hydrogen [95–97] promises to shed light on important fundamental symmetries. Due to the importance of hydrogen, considerable effort has been spent on trapping and cooling of hydrogen over the years. Hydrogen has been magnetically trapped at high phase space density [98] and has been evaporatively cooled to quan- tum degeneracy in a cryogenic apparatus [99, 100]. Unlike many other atoms, the internal structure of hydrogen is amenable to laser cooling, but the 121 nm wave- length needed to excite the cycling transition is difficult to produce with sufficient power for laser cooling. Nevertheless, hydrogen has been laser cooled, though at very low cooling rates [101]. A pulsed Sisyphus cooling scheme has been proposed [102], as has a scheme using ultrafast pulses [103]. The difficulties that present themselves in all of the above experiments and proposals, along with the canonical importance of hydrogen, motivate the search for a method of trapping and cooling of hydrogen isotopes in a room temperature apparatus. As a gas, hydrogen is simple to seed into a supersonic beam, and the cooling 117
Energy meV 0.05 0.00 0.05 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Magnetic Field T Figure 5.1: The hyperfine structure of the ground state of hydrogen. The transition between the low field and high field regimes takes place around .01 T, and at the fields used in the experiment described below the structure can be approximated as two states, with magnetic moments of ± 1 Bohr magneton. provided by the expansion is sufficient to trap a significant portion of the beam. Furthermore, the magnetic properties of atomic hydrogen are ideal for use in the coilgun. Hydrogen is the lightest of the atoms with a mass of 1 amu, and in the high field limit, has a magnetic moment of ± 1 Bohr magneton. The hyperfine structure of the ground state of hydrogen as a function of magnetic field is shown in figure 5.1. Because the transition between the high field and low field limits takes place around 0.01 T, the behavior of hydrogen in the fields of the coilgun and trap is nearly always that of the high field limit. The large magnetic moment to mass ratio (the highest for ground state atoms), makes hydrogen ideal for use in the coilgun. The importance of precision measurements on hydrogen isotopes, coupled with the excellent compatibility of hydrogen with the coilgun method, motivates the work described here. It should also be noted that the coilgun method has been pursued independently and in parallel to the one described here [21, 22], and been used to confine hydrogen and deuterium for a few milliseconds [23, 24]. 118
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Copyright by Adam Alexander Libson
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General Methods of Controlling Atom
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Acknowledgments First and foremost,
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to problems, and I frequently went
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General Methods of Controlling Atom
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Table of Contents Acknowledgments v
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Chapter 5. Towards Trapping and Coo
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List of Figures 2.1 Comparison of e
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5.12 Faraday Rotation Signal During
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producing a cold sample. Alternativ
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place inside a dilution refrigerato
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atoms or molecules are slowed using
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2.1 Thermodynamics of Ideal Gases F
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Since there will be no heat exchang
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Using equation 2.17 to modify equat
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Normalized Effusive Beam Flux Norma
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general method for producing cold a
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The gas throughput of the nozzle ca
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Chapter 3 Slowing Supersonic Beams
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3.1 Using Helium for Atom Optics Ex
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Figure 3.1: Calculated elastic scat
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that they can be prepared ex-situ a
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successful. Any water that remains
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Skimmer 300 l/s Turbo Pump Even-Lav
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Figure 3.5: A CAD image of the dete
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from tubular aluminum welded togeth
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Figure 3.7: A CAD image of the roto
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Figure 3.10: A CAD image of large c
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Figure 3.11: This plot shows the am
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approximations are made in this cal
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3.3.3 Detection An SRS [61] residua
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TTL pulse to the data acquisition c
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A comparison of the time-of-flight
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eceding crystal. Each curve is the
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calculated slow beam velocity is qu
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the RGA does have an effect on the
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Chapter 4 The Atomic and Molecular
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field. In the L − S coupling regi
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3 P2 E Figure 4.2: This graph gives
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For intermediate fields, the full p
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Figure 4.4: This figure illustrates
Page 83 and 84: The same effect is also responsible
Page 85 and 86: (a) (b) (c) Time Figure 4.5: A pict
Page 87 and 88: which the particles enter). The oth
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Page 91 and 92: the magnitude of the field some dis
Page 93 and 94: nozzle front surface aluminum catho
Page 95 and 96: Figure 4.9: A CAD overview of the s
Page 97 and 98: 258V 1MΩ 5V 1mF DC/DC Converter TT
Page 99 and 100: Figure 4.12: An oscilloscope trace
Page 101 and 102: (a) (b) Figure 4.14: A CAD image of
Page 103 and 104: -HV PS 4 M MCP Anode 10 M 1 M Trans
Page 105 and 106: Signal [V] 2.5 2.0 1.5 1.0 0.5 refe
Page 107 and 108: Figure 4.20: An exploded view of th
Page 109 and 110: (a) (b) (c) (e) Figure 4.21: A pict
Page 111 and 112: 258V 1MΩ TTL 2.2mF 50Ω TTL 5V 5V
Page 113 and 114: closed. With the new thyristor gate
Page 115 and 116: HeNe M2 M1 BB /2 L BB PC coil PC PD
Page 117 and 118: Table 4.1: Peak magnetic fields mea
Page 119 and 120: Figure 4.28: A cut-away CAD image o
Page 121 and 122: ameters. The coilgun chamber consis
Page 123 and 124: Table 4.2: Final velocities (vf), s
Page 125 and 126: MCP Signal [arb. units] 2.0 1.5 (1)
Page 127 and 128: viability for molecules essential.
Page 129 and 130: 8 Ω LN2 Liquid Nitrogen Dewar Nozz
Page 131 and 132: Figure 4.33: Molecular oxygen slowi
Page 133: Chapter 5 Towards Trapping and Cool
Page 137 and 138: 10 mm 2.0 T 1.8 1.6 1.4 1.2 1.0 0.8
Page 139 and 140: 250V 1MΩ 3x 2.2mF TTL 5V feedback
Page 141 and 142: Magnetic Field (T) 1.9 1.7 1.5 1.3
Page 143 and 144: 5.2.2.1 Principle of Operation of t
Page 145 and 146: Figure 5.8: Photograph of the trapp
Page 147 and 148: 4.1.3. In an anti-Helmholtz trap, t
Page 149 and 150: Figure 5.11: Photograph of the hydr
Page 151 and 152: Photodiode Signal (V) Time (s) Figu
Page 153 and 154: Figure 5.13: Time of flight plot of
Page 155 and 156: 500 l/s Turbo Pump Supersonic Nozzl
Page 157 and 158: Ionizer 500 l/s Turbo Pump Ion Opti
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Page 161 and 162: Z − Velocity (m/s) 100 60 30 0
Page 163 and 164: Atom Number 60 50 40 30 20 10 0.6 0
Page 165 and 166: scattered photon to extract informa
Page 167 and 168: where k1 · pi = − k2 · pi, wh
Page 169 and 170: the electron g-factor which causes
Page 171 and 172: Figure 5.24: A schematic of the tel
Page 173 and 174: prevent the determination of the is
Page 175 and 176: (a) (b) time Figure 5.25: A 1D illu
Page 177 and 178: experiment, where a being is capabl
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Page 181 and 182: Appendix 164
Page 183 and 184: y x V i Figure A.1: The geometry us
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Bibliography [1] H.J.MetcalfandP.va
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[17] Brian C. Sawyer, Benjamin L. L
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[34] R. Campargue. Progress in over
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[51] O. Carnal, M. Sigel, T. Sleato
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[70] Edvardas Narevicius, Adam Libs
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[87] Willis E. Lamb and Robert C. R
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[96] G.Gabrielse,N.S.Bowden,P.Oxley
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[110] N. Kolachevsky, J. Alnis, S.
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[125] Andreas Osterwalder, Samuel A
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[142] C. Cohen-Tannoudji, B. Diu, a
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[161] Paulo F. Bedaque, Aurel Bulga
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Experiments with Supersonic Beams as a Source of Cold Atoms

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