Experiments with Supersonic Beams as a Source of Cold Atoms

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magnetic flux density (T) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 (a) -6 -4 -2 0 2 4 6 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 (b) -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 axial coordinate (mm) transverse coordinate (mm) Figure 4.10: Finite element calculations of the magnitude of the field in the proof-ofprinciple experiment coils are shown. The field calculated along the axis of the coil is shown in (a), while the transverse field magnitude at the center of the coil is shown in (b). that the atoms are still 3−4cm from the coil when the current is turned on, and they are still well outside of the extent of the field when the current reaches its maximum. Thus the atoms will see a steady state field whentheyenterthecoil,andthetime variation in the field experienced by the atoms is only due to their motion and the deliberate switch-off of the field. The current is produced by allowing a capacitor to discharge across the coil, with two solid state switches controlling the current. The switches used are an integrated gate bipolar transistor (IGBT), and a thyristor. The IGBT (Powerex CM400DY-12NF) is a fast switch, with well-defined switching characteristics, while the thyristor (Littelfuse S6040R) is slow, with relatively poorly defined switching pro- files. Using both switches allows the fast switching but much more expensive IGBT to be used to switch multiple coil channels, while the thyristor is used to isolate the channels from each other. A schematic of the switching circuit is shown in figure 4.11. The parts within the dashed box exist for each coil channel, while those outside the box are shared 79
258V 1MΩ 5V 1mF DC/DC Converter TTL TTL 5V 50Ω feedback controller 2Ω N Channels Figure 4.11: A schematic of the coil driver circuit used to drive the 18 stage coilgun coils. The coils are switched by two solid state switches, a thyristor and an IGBT. The elements inside the dashed box are unique to each coil, while those outside the box are shared by multiple coil channels. among multiple channels. There are 8 total IGBTs, so each IGBT is responsible for switching 2-3 coils. Each coil has a 1 mF capacitor, charged to 258 V by a set of five 50 V switching power supplies connected in series, which is capable of 2.1 A steady state. A 1 MΩ resistor is placed across the capacitor to allow it to discharge even if power is disconnected. This allows the circuits to be safely examined after some time, even if there is a fault that does not allow the capacitors to be discharged across the coils. The thyristor is controlled by the current flowing from the gate to the cathode, and requires 20 mA to close. Producing this current requires a positive voltage with respect to the cathode, and a DC/DC converter is used to create a 5 V bias between the gate and cathode. The bias is switched by an opto-coupler that protects the digital side of the circuit by physically disconnecting it from the high voltage side of the circuit. The thyristor requires ≈ 40 μs to effectively close after the current 80 .25Ω 2μF
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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
Page 45 and 46: successful. Any water that remains
Page 47 and 48: Skimmer 300 l/s Turbo Pump Even-Lav
Page 49 and 50: Figure 3.5: A CAD image of the dete
Page 51 and 52: from tubular aluminum welded togeth
Page 53 and 54: Figure 3.7: A CAD image of the roto
Page 55 and 56: Figure 3.10: A CAD image of large c
Page 57 and 58: Figure 3.11: This plot shows the am
Page 59 and 60: approximations are made in this cal
Page 61 and 62: 3.3.3 Detection An SRS [61] residua
Page 63 and 64: TTL pulse to the data acquisition c
Page 65 and 66: A comparison of the time-of-flight
Page 67 and 68: eceding crystal. Each curve is the
Page 69 and 70: calculated slow beam velocity is qu
Page 71 and 72: the RGA does have an effect on the
Page 73 and 74: Chapter 4 The Atomic and Molecular
Page 75 and 76: field. In the L − S coupling regi
Page 77 and 78: 3 P2 E Figure 4.2: This graph gives
Page 79 and 80: For intermediate fields, the full p
Page 81 and 82: 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
Page 89 and 90: the coil can instead be switched be
Page 91 and 92: the magnitude of the field some dis
Page 93 and 94: nozzle front surface aluminum catho
Page 95: Figure 4.9: A CAD overview of the s
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 and 146: Figure 5.8: Photograph of the trapp
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4.1.3. In an anti-Helmholtz trap, t
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Figure 5.11: Photograph of the hydr
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Photodiode Signal (V) Time (s) Figu
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Figure 5.13: Time of flight plot of
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500 l/s Turbo Pump Supersonic Nozzl
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Ionizer 500 l/s Turbo Pump Ion Opti
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guided the design of the apparatus.
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Z − Velocity (m/s) 100 60 30 0
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Atom Number 60 50 40 30 20 10 0.6 0
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scattered photon to extract informa
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where k1 · pi = − k2 · pi, wh
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the electron g-factor which causes
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Figure 5.24: A schematic of the tel
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prevent the determination of the is
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(a) (b) time Figure 5.25: A 1D illu
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experiment, where a being is capabl
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potential position 2 x 243 nm Lα |
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Appendix 164
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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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