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Velocity Augmentation of a Supersonic Source and
The Production of Slow, Cold, Molecular Beams
Presented by: Les Sheffield...
Committee Members Research Team
Fellow Students Department Staff
2
• Introduction
• Presentation
• Questions from the audience
• Questions from the committee
Defense Structure
http://xkcd.c...
4
Simple method of augmenting the lab frame velocity of molecular beams
Precision Spectroscopy
Long-range electric dipole−di...
6
Initial Conditions Relevant Parameters
Simple method of augmenting the lab frame velocity of molecular beams
7
Initial Conditions
Simple method of augmenting the lab frame velocity of molecular beams
Relevant Parameters
Pod
Supersonic vs Effusive Molecular Beams
Adiabatic Expansion
Orifice >> Mean Free Path
Converts thermal energy to kinetic en...
9
Initial Conditions Relevant Parameters Nozzle Beam
Pulsed Beam Skimmed Beam Stationary Source
Simple method of augmentin...
Simple method of augmenting the lab frame velocity of supersonic beams
Detector
Skimmer
Nozzle
AC Motor
(below)
Rotor
Gas ...
Gupta, M. (2000). A
mechanical means of
producing cold, slow
beams of molecules.
PhD, Harvard.
11
1st Generation Rotating ...
Experimental Layout
12
2014
Experimental Layout
13
20092014
Experimental Layout
14
20092014
Experimental Layout
15
Rotor (4)
Gas Feed System (6)
AC Motor
Eddy Current Sensor (2)
Foil Shield (3)
Skimmer (3)
Pulsed I...
Rotor 1 & 2
Improvements:
1. Length
• 𝑉𝑅 = 2𝜋𝑅 𝐹 −1
2. Nozzle
• Defines Spread
• Doesn’t Fall Off
3. Positioning Ring
16
Improvements:
1. Stem Conductance
• 𝐶 ∝ 𝑟 𝑛/ℓ
2. Limiting Frequency
• 𝐹 𝑚𝑎𝑥 ∝ 𝑚−1
17
Rotor 2 & 3
Eddy Current Sensor
18
E
Sampling Rate
100 kHz
19
To Gas
Supply
Manifold
Pulsed
Valve
Cooling Lines
Rotor
Section View
Cooling Block
T-Stage
QC Coupling
Clamping Ring
PE...
20
Valve Driver &
Timing Circuit
Fast Ionization Gauge
21
Typical Time-of-Flight Signal
22
23
Background Removal
Vrot = −141 m s Vrot = −282 m s Vrot = +282 m s Vrot = +24 m s
FIG Output contains 3 signals
1) Dete...
Time-of-Flight Properties
24
Experiment 1
25
𝜌
𝑐𝑚−3
∆𝑡
msec
FWHM
msec
𝑃 𝑇𝑜𝐹
𝑠𝑒𝑐
𝑐𝑚3
26
𝜌
𝑐𝑚−3
∆𝑡
msec
FWHM
msec
𝑃 𝑇𝑜𝐹
𝑠𝑒𝑐
𝑐𝑚3
Experiment 1
27
ρ FWHM
∆t PToF
• Beam Shape does NOT contain any reflected peaks, shoulders, or double peaks
• Time of flight spectrum reflects appropria...
29
30
Different Skimmers
1 mm 3 mm 5 mm
31
• Most peaks have shoulders or even
a double peak from skimmer edge
• Best signal to background ratio
occurs with the 3...
32
3 mm Skimmer with Foil Shield
33
3 mm Skimmer with Foil Shield
34
• Most peaks have shoulders or even
a double peak from skimmer edge
• Best signal to background ratio
occurs with the 3...
35
X ρ
𝑈𝑠𝑠
𝑋 = 𝑈𝑠𝑠 + 𝑉𝑟𝑜𝑡
What dictates the choice of gas type?
1) Pure Beams
2) Seeding
SupersonicFlowVelocity(m/s)
36
• Most peaks have shoulders or even
a double peak from skimmer edge
• Best signal to background ratio
occurs with the 3...
37
ρ ρ
ρ ∆𝑡
38
• Most peaks have shoulders or even
a double peak from skimmer edge
• Best signal to background ratio
occurs with the 3...
39
40
ρ ∆t
∆𝑡 ∆𝑡
41
• Most peaks have shoulders or even
a double peak from skimmer edge
• Best signal to background ratio
occurs with the 3...
42
3rd Generation Rotating Source
Primary Topic Ex/Th Year Author
Construction Ex 1999 Gupta and Herschbach
Construction E...
43
3rd Generation Rotating Source
Primary Difference Experimental Impact
Better performing Al alloys Higher limiting frequ...
44
Thank You
2009 2014
45
FIG Output
Photodiode Output
IGBT Input
46
ϕ2 ϕ1
ϕ4
Fast Ion
Gauge
Skimmer
Detector
Line-of-Sight ϕ3
ϕ = 0
Foil Shield
47
48
GasFeedSystem6
GasFeedSystem6
49
𝑋 = 𝑉𝑟𝑜𝑡 + 𝑈𝑠𝑠,𝑋𝑒
𝑉𝑟𝑜𝑡 = 0
Beam
Narrowing
𝑈𝑠𝑠,𝑋𝑒
𝑋
𝑋
𝑋
50
Methods of estimating Flow Velocity
51
𝑣1 =
2 𝐻 𝑜 − 𝐻1
𝑁𝐴 𝑚
𝑣1 =
2𝐶 𝑝 𝑇𝑜 − 𝑇1
𝑁𝐴 𝑚
𝑣1 =
𝛾
𝛾 − 1
2𝑅 𝑇𝑜 − 𝑇1
𝑁𝐴 𝑚
𝑣1 =
𝛾
𝛾 −...
Flow Velocity from Enthalpy 𝑣1 =
2 𝐻 𝑜 𝑃𝑜, 𝑇𝑜 − 𝐻1
𝑁𝐴 𝑚
52
• Ideal Gas Model matches at room temperature and low pressures
• SMALL DECREASE in velocity with increasing pressure
• LA...
Analytical Approach
• Precise measurement and control of:
• 𝑃𝑜 : Stagnation Pressure
• 𝑇𝑜 : Stagnation Temperature
• Compu...
Analytical Approach
Xenon
Tt = 161 K
Pt = 612 Torr
∆vHt = 12.657 kJ mol
∆vH = Hv − Hl
Hl = 12.5 kJ mol
55
Uses of Decelerated Molecular Beams
Molecules have enhanced sensitivity (compared with atoms) to VIOLATIONS OF FUNDAMENTAL...
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LSS - Defense - 12-1-2014

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LSS - Defense - 12-1-2014

  1. 1. Velocity Augmentation of a Supersonic Source and The Production of Slow, Cold, Molecular Beams Presented by: Les Sheffield 1
  2. 2. Committee Members Research Team Fellow Students Department Staff 2
  3. 3. • Introduction • Presentation • Questions from the audience • Questions from the committee Defense Structure http://xkcd.com/1403/ 3
  4. 4. 4
  5. 5. Simple method of augmenting the lab frame velocity of molecular beams Precision Spectroscopy Long-range electric dipole−dipole interaction Cold molecular chemistry Ultracold chemical reactions EM Deflection & Trapping 5
  6. 6. 6 Initial Conditions Relevant Parameters Simple method of augmenting the lab frame velocity of molecular beams
  7. 7. 7 Initial Conditions Simple method of augmenting the lab frame velocity of molecular beams Relevant Parameters Pod
  8. 8. Supersonic vs Effusive Molecular Beams Adiabatic Expansion Orifice >> Mean Free Path Converts thermal energy to kinetic energy Result: Dense, translationally & internally cold sample with high velocity 𝛼 = 2𝑘𝑇𝑜 𝑚 𝑢 = 2𝑘𝑇𝑜 𝑚 𝛾 𝛾 − 1 1 − 𝑇∥ 𝑇 8
  9. 9. 9 Initial Conditions Relevant Parameters Nozzle Beam Pulsed Beam Skimmed Beam Stationary Source Simple method of augmenting the lab frame velocity of molecular beams
  10. 10. Simple method of augmenting the lab frame velocity of supersonic beams Detector Skimmer Nozzle AC Motor (below) Rotor Gas Feed (above) 𝑋 = 𝑉𝑠𝑠 + 𝑉𝑟𝑜𝑡 10
  11. 11. Gupta, M. (2000). A mechanical means of producing cold, slow beams of molecules. PhD, Harvard. 11 1st Generation Rotating Source
  12. 12. Experimental Layout 12 2014
  13. 13. Experimental Layout 13 20092014
  14. 14. Experimental Layout 14 20092014
  15. 15. Experimental Layout 15 Rotor (4) Gas Feed System (6) AC Motor Eddy Current Sensor (2) Foil Shield (3) Skimmer (3) Pulsed Inlet Valve (2) Valve Control Electronics (2) Detector (2) Data Acquisition Card
  16. 16. Rotor 1 & 2 Improvements: 1. Length • 𝑉𝑅 = 2𝜋𝑅 𝐹 −1 2. Nozzle • Defines Spread • Doesn’t Fall Off 3. Positioning Ring 16
  17. 17. Improvements: 1. Stem Conductance • 𝐶 ∝ 𝑟 𝑛/ℓ 2. Limiting Frequency • 𝐹 𝑚𝑎𝑥 ∝ 𝑚−1 17 Rotor 2 & 3
  18. 18. Eddy Current Sensor 18 E Sampling Rate 100 kHz
  19. 19. 19 To Gas Supply Manifold Pulsed Valve Cooling Lines Rotor Section View Cooling Block T-Stage QC Coupling Clamping Ring PEEK Spacer Mounting Arm Rotor Stem Gas Feed System
  20. 20. 20 Valve Driver & Timing Circuit
  21. 21. Fast Ionization Gauge 21
  22. 22. Typical Time-of-Flight Signal 22
  23. 23. 23 Background Removal Vrot = −141 m s Vrot = −282 m s Vrot = +282 m s Vrot = +24 m s FIG Output contains 3 signals 1) Detection Chamber background 2) Effusive Beam from Main Chamber 3) Rotor Signal RAW Data Background Signal Corrected Signal
  24. 24. Time-of-Flight Properties 24
  25. 25. Experiment 1 25 𝜌 𝑐𝑚−3 ∆𝑡 msec FWHM msec 𝑃 𝑇𝑜𝐹 𝑠𝑒𝑐 𝑐𝑚3
  26. 26. 26 𝜌 𝑐𝑚−3 ∆𝑡 msec FWHM msec 𝑃 𝑇𝑜𝐹 𝑠𝑒𝑐 𝑐𝑚3 Experiment 1
  27. 27. 27 ρ FWHM ∆t PToF
  28. 28. • Beam Shape does NOT contain any reflected peaks, shoulders, or double peaks • Time of flight spectrum reflects appropriate shift due to rotor movement • Velocity spreading limits lowest velocities measured • Centrifugal enhancement of input pressure is observed • Skimmer interference observed at the highest beam densities • Beam narrowing restricts pulse width in speeded beams 28 Conclusions 1
  29. 29. 29
  30. 30. 30 Different Skimmers 1 mm 3 mm 5 mm
  31. 31. 31 • Most peaks have shoulders or even a double peak from skimmer edge • Best signal to background ratio occurs with the 3 mm skimmer
  32. 32. 32 3 mm Skimmer with Foil Shield
  33. 33. 33 3 mm Skimmer with Foil Shield
  34. 34. 34 • Most peaks have shoulders or even a double peak from skimmer edge • Best signal to background ratio occurs with the 3 mm skimmer • Shield can completely remove the beam scattered from the skimmer • Shield protects beam from scattering as the main chamber pressure rises
  35. 35. 35 X ρ 𝑈𝑠𝑠 𝑋 = 𝑈𝑠𝑠 + 𝑉𝑟𝑜𝑡 What dictates the choice of gas type? 1) Pure Beams 2) Seeding SupersonicFlowVelocity(m/s)
  36. 36. 36 • Most peaks have shoulders or even a double peak from skimmer edge • Best signal to background ratio occurs with the 3 mm skimmer • Shield can completely remove the beam scattered from the skimmer • Shield protects beam from scattering as the main chamber pressure rises • Centrifugal enhancement only effects high mass gas types • Other gasses perform in a similar manner to xenon
  37. 37. 37 ρ ρ ρ ∆𝑡
  38. 38. 38 • Most peaks have shoulders or even a double peak from skimmer edge • Best signal to background ratio occurs with the 3 mm skimmer • Shield can completely remove the beam scattered from the skimmer • Shield protects beam from scattering as the main chamber pressure rises • Centrifugal enhancement only effects high mass gasses • Other gasses perform in a similar manner to xenon • Location of density maximum is highly pressure dependent • Verifies the centrifugal enhancement effect
  39. 39. 39
  40. 40. 40 ρ ∆t ∆𝑡 ∆𝑡
  41. 41. 41 • Most peaks have shoulders or even a double peak from skimmer edge • Best signal to background ratio occurs with the 3 mm skimmer • Shield can completely remove the beam scattered from the skimmer • Shield protects beam from scattering as the main chamber pressure rises • Centrifugal enhancement only effects high mass gasses • Other gasses perform in a similar manner to xenon • Location of density maximum is highly pressure dependent • Verifies the centrifugal enhancement effect • Time of flight is affected by the shield position • Slow Frequencies effected much more by shield position
  42. 42. 42 3rd Generation Rotating Source Primary Topic Ex/Th Year Author Construction Ex 1999 Gupta and Herschbach Construction Ex 2000 Gupta and Herschbach EM Deflection Th 2006 Timko et al. Construction Ex 2010 Strebel et al. Scattering Ex 2012 Strebel et al. Merging Th 2012 Wei et al. Construction Ex 2012 Sheffield et al. Slowing Ex 2013 Spieler et al. Construction Ex 2015? (This work) 2030? 1st 2nd 3rd ?
  43. 43. 43 3rd Generation Rotating Source Primary Difference Experimental Impact Better performing Al alloys Higher limiting frequency Increase rotor length to 10” Ability to slow light atomic gasses Dynamic balancing of the rotor More stability at higher frequencies Secondary detection method Measure beam temperature Narrow edge skimmers Limits beam heating Improved cryopump geometry Faster pumping speeds
  44. 44. 44 Thank You 2009 2014
  45. 45. 45 FIG Output Photodiode Output IGBT Input
  46. 46. 46
  47. 47. ϕ2 ϕ1 ϕ4 Fast Ion Gauge Skimmer Detector Line-of-Sight ϕ3 ϕ = 0 Foil Shield 47
  48. 48. 48 GasFeedSystem6 GasFeedSystem6
  49. 49. 49 𝑋 = 𝑉𝑟𝑜𝑡 + 𝑈𝑠𝑠,𝑋𝑒 𝑉𝑟𝑜𝑡 = 0 Beam Narrowing 𝑈𝑠𝑠,𝑋𝑒 𝑋 𝑋 𝑋
  50. 50. 50
  51. 51. Methods of estimating Flow Velocity 51 𝑣1 = 2 𝐻 𝑜 − 𝐻1 𝑁𝐴 𝑚 𝑣1 = 2𝐶 𝑝 𝑇𝑜 − 𝑇1 𝑁𝐴 𝑚 𝑣1 = 𝛾 𝛾 − 1 2𝑅 𝑇𝑜 − 𝑇1 𝑁𝐴 𝑚 𝑣1 = 𝛾 𝛾 − 1 2𝑘𝑇𝑜 𝑚 Ideal Gas Model Specific Heat Poisson Coefficient Enthalpy 𝑣1 = 2 𝐻 𝑜 𝑃𝑜, 𝑇𝑜 − 𝐻1 𝑁𝐴 𝑚 𝑣1 = 2𝑇𝑜 𝑁𝐴 𝑚 𝐶 𝑝 𝑃𝑜, 𝑇𝑜 𝑣1 = 2𝑅𝑇𝑜 𝑁𝐴 𝑚 𝛾 𝑃𝑜, 𝑇𝑜 𝛾 𝑃𝑜, 𝑇𝑜 − 1 𝑣1 = 𝛾 𝛾 − 1 2𝑘𝑇𝑜 𝑚
  52. 52. Flow Velocity from Enthalpy 𝑣1 = 2 𝐻 𝑜 𝑃𝑜, 𝑇𝑜 − 𝐻1 𝑁𝐴 𝑚 52
  53. 53. • Ideal Gas Model matches at room temperature and low pressures • SMALL DECREASE in velocity with increasing pressure • LARGE INCREASE in velocity primarily due to condensation Estimates for vapor fraction: 𝜒 𝑣 𝑁𝐴 𝑚 2 𝑣1 2 = 𝐻 𝑜 − 1 − 𝜒 𝑣 𝐻1𝑙 − 𝜒 𝑣 𝐻1𝑣 Cluster formation and its impact on velocity 𝜒 𝑣 = 𝐻 𝑜 − 𝑁𝐴 𝑚 2 𝑣1 2 𝐻1𝑙 − 1 𝐻1𝑣 𝐻1𝑙 − 1 𝑁𝐴 𝑚 2 𝑣1 2 = 𝐻 𝑜 − 𝐻1 53
  54. 54. Analytical Approach • Precise measurement and control of: • 𝑃𝑜 : Stagnation Pressure • 𝑇𝑜 : Stagnation Temperature • Computation of thermodynamic quantities • 𝐻 𝑜 𝑃𝑜, 𝑇𝑜 : Stagnation Enthalpy • 𝑆 𝑜 𝑃𝑜, 𝑇𝑜 : Stagnation Entropy • Assumption of a reversible adiabatic expansion into vacuum, i.e. ∆𝑆 = 0 • Experimental determination of the mean terminal flow velocity, 𝑢 𝑋𝑒 • Calculation of terminal beam enthalpy, 𝐻1 = 𝐻 𝑜 − ∆𝐻 • Computation of vapor fraction to explain behavior of 𝑢 𝑋𝑒 54
  55. 55. Analytical Approach Xenon Tt = 161 K Pt = 612 Torr ∆vHt = 12.657 kJ mol ∆vH = Hv − Hl Hl = 12.5 kJ mol 55
  56. 56. Uses of Decelerated Molecular Beams Molecules have enhanced sensitivity (compared with atoms) to VIOLATIONS OF FUNDAMENTAL SYMMETRIES, such as the possible existence of the electron electric dipole moment, and parity-violating nuclear moments The internal degrees of freedom of polar molecules have been proposed as qubits for QUANTUM COMPUTERS and are ideal for storage of quantum information. The LONG-RANGE ELECTRIC DIPOLE−DIPOLE INTERACTION between polar molecules may give rise to novel quantum systems. PRECISION SPECTROSCOPY performed on vibrational or hyperfine states of cold molecules can probe the time variation of fundamental constants, such as the electron-to-proton mass ratio and the fine structure constant. Studies of COLD MOLECULAR CHEMISTRY in the laboratory play an important role in understanding gas-phase chemistry of interstellar clouds, which can be as cold as 10 K. ULTRACOLD CHEMICAL REACTIONS have been observed at a temperature of a few hundred nanokelvins, with reaction rates controllable by external electric fields. Molecular collisions in the few partial wave regime reveal the molecular interaction in great detail. 56

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