Experiments with Supersonic Beams as a Source of Cold Atoms

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it does not need to be seeded into another carrier gas; a pure neon beam is used. To reduce the initial velocity, the nozzle is cooled to 77 K. A 50 psi backing pressure is used in these experiments. 4.4.2 18 Stage Coil Design As noted above, to significantly slow a beam of metastable neon from ≈ 500m/s fields of several Tesla per coil are desired. To produce these fields, a pulsed electro- magnetic coil is constructed which is modeled on the coil that drives the plunger in the Even-Lavie nozzle. The coil consists of 30 windings (6 layers of 5 turns) of .5 mm diameter Kapton insulated copper magnet wire. The wire is wound around a hollow Vespel cylinder with 50 μm wall thickness and 3 mm outer diameter. The coil is located between two Permendur discs (Permendur 49, ASTM-A-801 Type 1, from Carpenter Technology), one 3 mm thick, and the other 2.5mmthick, both10mmin diameter, and is surrounded by a 3 mm thick soft magnetic steel shell. Permendur is a high magnetic saturation material with a saturation value of 2.3 T, which confines the field lines and increases the peak field inside the coil. The reason that one disc is made thinner than the other is that the bottom of the soft steel shell is .5mm thick, and so there is 3mm of magnetic steel on each side of the coil. Additionally, a Kapton disc is inserted in between the coil and each Permendur disc, which helps to protect the insulation of the wire. The entire coil is held together using Epo-Tek H77 epoxy, which is a UHV compatible thermally conductive epoxy. A CAD image of the coil is shown in figure 4.9. The peak current in the coil is measured to be 400 A. Because the coil is surrounded by non-linear ferromagnetic materials, the field profile of the coil is very difficult to calculate analytically. As such, the field is instead calculated numerically using finite element analysis using the program COMSOL Multiphysics. This allows 77
Figure 4.9: A CAD overview of the slowing coils used in the proof-of-principle experiment. The coils are 3 mm bore coils of 5 × 6 windings, surrounded by Permendur discs and enclosed in a magnetic steel shell. the full non-linearity of the magnetic materials to be accounted for. Finite element analysis calculations of the field along the axis of the coil, and the radial field in the center of the coil are shown in figure 4.10. The peak field in the center of the coil is 3.6T. While great care was taken when winding the coils, during testing in vacuum two of the coils failed when the coil wire came into electrical contact with the permendur shell. These coils were numbers 17 and 19, and they were not used for the slowing. The Kapton insulation of the magnet wire was probably scratched during the winding process, and a test procedure was developed to prevent future coils from exhibiting this same behavior as described in section 4.5.1. 4.4.3 18 Stage Electronics and Coil Switching The coil wire is only .5 mm in diameter and carries 400 A, so the current must be pulsed or the wires would overheat and melt. A pulse length of 80μs is long enough 78
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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
Page 43 and 44: 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: nozzle front surface aluminum catho
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
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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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