Experiments with Supersonic Beams as a Source of Cold Atoms

More documents

Recommendations

Info

5.2.3 Beam Creation and Detection Creating and detecting a supersonic beam of hydrogen is more challenging than for the neon and oxygen slowed in previous generations of the coilgun. Creating metastable neon requires a discharge, and the efficiency of metastable creation is likely around 10 −4 −10 −5 . However, detecting of the metastable atoms is possible with near unit efficiency using an MCP. Molecular oxygen is simple to seed into a beam and no state preparation is required. Detecting oxygen is more difficult however, and in the experiments described in chapter 4, oxygen is detected by an RGA, which has a similar efficiency to the discharge. Hydrogen is particularly difficult to work with because it requires a state preparation (cracking molecular hydrogen into atomic hydrogen) similar to metastable neon, and hydrogen must also be excited or ionized in order to detect it. In this experiment, atomic hydrogen is created using the same discharge apparatus that is used to create metastable neon, described in section 4.4.1. Molecular hydrogen is mixed into a neon carrier at a ratio of 1:4, and the nozzle is run with a backing pressure of 50 psi. The near resonance between the neon metastable energy and the cracking energy of hydrogen plus the excitation energy of one hydrogen atom increases the efficiency of cracking with a discharge in the presence of neon [105]. Detection is accomplished by a custom designed jumbo ionizer and quadrupole mass spectrometer (Ardara Technologies). Hydrogen is ionized by electron bombard- ment and guided by ion optics into the quadrupole, which provides mass filtering. The electron energy can be tuned to optimize the ionization process. Unfortunatly, the detected atomic hydrogen ions are produced via two channels, and only one of these is desired. The first, and desired channel, is that atomic hydrogen produced by the discharge at the nozzle is ionized and detected. In the second channel, molecular hydrogen in the beam is cracked and ionized in the ionizer, creating a hydrogen ion 135
Figure 5.13: Time of flight plot of the ratio of D(×100) to D2 with and without the discharge firing. The noise on either side of this signal is meaningless as the signals go to 0 and the increased noise is a result of dividing by nearly 0. The greater ratio of D to D2 with the discharge indicates that the discharge is working properly and producing atomic hydrogen, but that it is covered by the background signal due to molecular hydrogen. which is then detected. This second channel is an undesired background which causes a significant problem. The background signal due to the cracking of hydrogen molecules in the ionizer causes atomic hydrogen to be observed even without firing the discharge. In fact, the observed atomic hydrogen signal actually decreases when the discharge is fired, since the beam is heated by the discharge and less of it arrives at the detector. It is thus difficult to determine the quality of the beam and discharge. However, one method of examining the beam did produce interesting results, and this was to look at the ratio of atomic deuterium to molecular deuterium, with and without the discharge (deuterium is chosen for its heavier mass, ensuring more atoms stay on the centerline of the beam). Doing this allows the effect of the discharge to be seen more clearly and shows that atomic deuterium is being produced by the discharge, but that the 136
Page 1 and 2:
Copyright by Adam Alexander Libson
Page 3 and 4:
General Methods of Controlling Atom
Page 5 and 6:
Acknowledgments First and foremost,
Page 7 and 8:
to problems, and I frequently went
Page 9 and 10:
General Methods of Controlling Atom
Page 11 and 12:
Table of Contents Acknowledgments v
Page 13 and 14:
Chapter 5. Towards Trapping and Coo
Page 15 and 16:
List of Figures 2.1 Comparison of e
Page 17 and 18:
5.12 Faraday Rotation Signal During
Page 19 and 20:
producing a cold sample. Alternativ
Page 21 and 22:
place inside a dilution refrigerato
Page 23 and 24:
atoms or molecules are slowed using
Page 25 and 26:
2.1 Thermodynamics of Ideal Gases F
Page 27 and 28:
Since there will be no heat exchang
Page 29 and 30:
Using equation 2.17 to modify equat
Page 31 and 32:
Normalized Effusive Beam Flux Norma
Page 33 and 34:
general method for producing cold a
Page 35 and 36:
The gas throughput of the nozzle ca
Page 37 and 38:
Chapter 3 Slowing Supersonic Beams
Page 39 and 40:
3.1 Using Helium for Atom Optics Ex
Page 41 and 42:
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 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 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: Photodiode Signal (V) Time (s) Figu
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
Page 197 and 198: [96] G.Gabrielse,N.S.Bowden,P.Oxley
Page 199 and 200: [110] N. Kolachevsky, J. Alnis, S.
Page 201 and 202: [125] Andreas Osterwalder, Samuel A
Page 203 and 204:
[142] C. Cohen-Tannoudji, B. Diu, a
Page 205 and 206:
[161] Paulo F. Bedaque, Aurel Bulga
show all

Experiments with Supersonic Beams as a Source of Cold Atoms

Create successful ePaper yourself

Delete template?

Save as template?