Experiments with Supersonic Beams as a Source of Cold Atoms

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Position in Trapping Coils Position in Trapping Coils Position in Trapping Coils Figure 5.9: Magnetic field values on the axis of the trapping coils measured by Faraday rotation. The dashed lines indicate the center of the two trapping coils. The field measurements are taken 2.5 mm apart. The plot on the left shows the field for a single coil, while the plot in the center and on the right show the fields with the coils running in Helmholtz and anti-Helmholtz configurations respectively. In all three configurations, the current in the coils is 450 A. are held in position on the chamber by Delrin clamps, which also hold the final three slowing coils of the coilgun. Once wound and clamped in position, the coils are epoxied (Epo-Tek 353nd) and wrapped with epoxy impregnated nylon cloth. This ensures that the coils do not shift or move under the exerted magnetic forces. The center of the trapping volume is located 2.99 cm from the center of the last coilgun coil, and the coils are 2.7 cm apart, measured center-to-center. A photo of the trap coils on the chamber is shown in figure 5.8. The magnetic field values on the axis of the trapping coils, measured by Fara- day rotation, is shown in figure 5.9. When 450A is run through a single coil, the peak field on axis is 1.05 T. The measured field at the center of a coil is higher when the coils are run in Helmholtz configuration, with a measured peak field of 1.11 T. When the coils are run in anti-Helmholtz configuration, the field value on axis is lower, 0.85 T. In anti-Helmholtz configureation, the field is at a minimum at the center of the trap, creating a 100 mK deep trapping potential. The oscillation period for a hydrogen atom in this potential is approximately 1 ms. Atoms in the trap need to adiabatically follow the field, as discussed in section 129
4.1.3. In an anti-Helmholtz trap, the trapping field vanishes at the center of the trap. This means that the Larmor frequency also goes to zero and thus the atoms cannot follow changes in the field direction. The radius from the trap center where atoms of a particular velocity cannot follow the field and undergo spin flips is derived in [104]. For the trapping fields described above, the calculated radius of spin flits is ≈ 3 μm for 100 m/s hydrogen atoms. Most of the atoms in the trap are slower than 100 m/s, and the radius for spin flips will be even smaller for slower atoms. Such a small radius, even for the fastest atoms, means that spin flips are not expected to be a significant source of trap loss. 5.2.2.3 Trapping Electronics and Switching Due to the requirements of the experiment, each trapping coil must be able to have current flow in either direction. In addition, the polarity of the current in one coil must be independent of the polarity or state of the other coil. Each coil needs to be able to be switched on or off independent of the state of the other coil as well. Fast switching times are required, because the loading of the trap depends on using the front coil as the final coilgun coil and on switching this coil back on quickly to confine the atoms in the trap. It is desireable to have the coils operating in series, rather than in parallel to ensure that both coils operate at the same current, locating the trap center in the middle of the trapping volume. It also means that any current noise will appear in both coils, rather than just one. This avoids heating of the atoms due to an induced motion of the trap center. A schematic of the circuit constructed to fulfill these requirements is shown in figure 5.10 and a photograph of the circuit is presented in figure 5.11. Each coil is switched using an H-bridge configuration of discrete metal-oxide-semiconductor field-effect transistors (MOSFET). Each MOSFET shown in the figure represents a 130
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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
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The same effect is also responsible
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(a) (b) (c) Time Figure 4.5: A pict
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which the particles enter). The oth
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the coil can instead be switched be
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the magnitude of the field some dis
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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 and 134: Chapter 5 Towards Trapping and Cool
Page 135 and 136: Energy meV 0.05 0.00 0.05 0.0 0.2 0
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: Figure 5.8: Photograph of the trapp
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
Page 159 and 160: guided the design of the apparatus.
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
Page 179 and 180: potential position 2 x 243 nm Lα |
Page 181 and 182: Appendix 164
Page 183 and 184: y x V i Figure A.1: The geometry us
Page 185 and 186: Bibliography [1] H.J.MetcalfandP.va
Page 187 and 188: [17] Brian C. Sawyer, Benjamin L. L
Page 189 and 190: [34] R. Campargue. Progress in over
Page 191 and 192: [51] O. Carnal, M. Sigel, T. Sleato
Page 193 and 194: [70] Edvardas Narevicius, Adam Libs
Page 195 and 196: [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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