Experiments with Supersonic Beams as a Source of Cold Atoms

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Figure 4.24: Photographs of the 64 stage coilgun coil driver board. At left, the entire board is shown (except for the IGBT which mounts to the three square pads). At right, a zoom-in view provides more detail. for multiple channels is also unchanged, though many of the individual components of the system are upgraded. The IGBTs are upgraded to a 1.2kV blocking voltage model (Powerex CM200DY-24A) and the thyristor is likewise upgraded to a 1 kV voltage model (Littlefuse SK055R). These changes allow the freewheel diode and resistor to be taken out of the circuit, which decreases the switching time of the coil. While the IGBT gate drive circuitry is unchanged, the method used to drive the thyristor gate is also modified. The DC/DC converter used to drive the gate was found to fail when subjected to the voltage spikes produced by the faster coil switching at higher current. Rather than replace the DC/DC converter with a different model, the solution implemented is simply to close the IGBT 20 μs before switching the thyristor. Closing the IGBT grounds the cathode of the thyristor, allowing a 5 V power supply, switched by an opto-coupler, to provide the necessary current to the gate. The change in the thyristor drive circuitry necessitates a change in the snubber capacitor circuitry across the IGBT. While the snubber capacitor is still needed in its initial role to absorb the continuing current from the coil after the IGBT is opened, in the original configuration, the snubber discharges very quickly when the IGBT is 95
closed. With the new thyristor gate drive system, this has the side effect of closing any thyristor attached to the IGBT, and subsequently all coils fire simultaneously, rather than individually. To rectify this, a resistor is added to the snubber capacitor, along with a diode network, such that the resistance is low when charging the capacitor and it can effectively absorb the current pulse from the coil, but the discharging resistance is raised to 4Ω, slowing the snubber capacitor discharge. This slower discharge profile of the snubber capacitor does not inadvertently close the thyristors, which enables their continued use as isolating switches between the individual coil channels. Similar to the circuitry used in the proof-of-principle experiment, there are still eight total IGBTs, and the digital timing pulses are sent by the same FPGA board. However, with 64 total coils, each IGBT now switches eight individual coil channels. The final alteration of the drive circuitry is the loss of the .25 Ω resistor in series with the coil. The resistor limited the current and with the new higher blocking voltage components is not needed in the improved circuit. This does mean that there is no convenient way to directly measure the current in the coil, as there is no resistor in series with the coil whose voltage drop can be measured. The total resistance of the circuit is measured to be ≈ 0.34Ω, leading to a calculated current of ≈ 750A, but this measurement is accurate to 10 % at best, limiting the accuracy of the estimations of the field strengths. While a pickup coil is used to measure the temporal profile of the magnetic field in the proof-of-principle experiment, this is not an good method for determining the overall field strength. The problem is that the pickup coil measures dB dt ,andso must be integrated to determine the absolute field. Small errors can accumulate and lead to a large uncertainty when determining the absolute field in the coil using this method. What is needed is a direct method of measuring the field, which would be accurate on the timescale of the pulse. 96
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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
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 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: 258V 1MΩ TTL 2.2mF 50Ω TTL 5V 5V
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
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
Page 159 and 160: guided the design of the apparatus.
Page 161 and 162: 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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