angularandenergydistributions of h inaniontrap · angularandenergydistributions ofh+ 3 inaniontrap...
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Angular and Energy Distributionsof H+
3 in an Ion Trap
Aalayah Spencer1,2
1Department of Physics and AstronomyMichigan State University
2Savin GroupColumbia University
REU Final Presentation, 2018
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Overview
1 Scientific Background
2 The Apparatus
3 My Work
4 Conclusions
5 Acknowledgments
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Cosmic Cycle of Gas
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What are Dense Molecular Clouds?
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What are Dense Molecular Clouds?
• n = 104 cm−3
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What are Dense Molecular Clouds?
• 10-20 K
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What are Dense Molecular Clouds?
• Ion-neutral reactiondriven chemistry
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What are Dense Molecular Clouds?
• Cosmic rays initiatethe chemistry in DMCsinstead of UV photons.
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H+3 formation
H2 + cosmic ray → H+2 + e− + cosmic ray’
H+2 + H2 → H+
3 + H
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H+3 Chemistry
H+3 is major driver in the chemistry of DMCsReacts as a proton donor
Participates in many ion-neutral reactionswhich tend to be barrierless and exoergic
Favored due to the low temperatures characteristicof DMCs
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H+3 Observations
H+3 has no dipole moment:No pure rotational spectrumNot excited at DMC temperatures
Observation of H2D+ and D2H
+ :Has dipole momentCan be excited at these low temperaturesEnables the H+
3 abundance to be inferredFormed from two possible reactions
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H+3 Deuteration
H+3 + HD → H2D
+ + H2:Rate coefficient calculations are beyond quantummechanical capabilitiesReaction rates known experimentally up to 15%uncertainty
H+3 + D → H2D
+ + HRate coefficient calculations are beyond quantummechanical capabilitiesClassical and semi-classical calculations differ byalmost an entire order of magnitudeNo experiments have been done
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Merged Fast-Beams Apparatus
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Merged Fast-Beams Apparatus
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Merged Fast-Beams Apparatus
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Merged Fast-Beams Apparatus
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Merged Fast-Beams Apparatus
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Merged Fast-Beams Apparatus
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Measuring the Cross Section
σ =
(S
TaTgη
)(e2vDvH+3
IDIH+3
)(1
Ω
)(1)
σ = absolute cross sectionS = Count ratee = elementary chargevD, vH+
3= D and H+
3 velocity
ID, IH+3= D and H+
3 currentΩ = Overlap factor
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Cross Section Measurement
• H+3 + D → H2D
+ + H
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Internal Energy Problem
• Beam production leads to unknown internal excitation of H+3
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Ion Source Issues
• Gives hot H+3
• Continuous source• Duty Cycle = 100%• S = 10 s−1
• Gives cold H+3
• Pulsed• Duty Cycle 10−4%• S = 10−3 s−1
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Solution for Higher Beam Current
• Simulate H+3 ion trajectories
• Determine trapping voltage for H+3 ions
• Determine angular distribution• Determine energy distribution
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Ion Trap Trajectory Simulations
• Modeling performed using SIMION, an ion opticssimulation program
Trap Characteristics:2D cylindrically symmetric potential array
Beam Characteristics:2500 particlesEnergy = 18.02 keVConical Distribution of 1 mradSimulations used either 5 mm or 10 mm diameter beamRequired a trapping voltage of 28.71 kV
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Angular Distribution Measurements
• Angular distributions from the center of the trap for a5mm beam after 50 cycles:
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Trapping Efficiency
• Measurements taken at the center of the trap after 5, 10,and 50 cycles:
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Angular Distribution Measurements
• Angular distributions from the center of the trap for a10mm beam after 50 cycles:
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Trapping Efficiency
• Measurements taken at the center of the trap after 5, 10,and 50 cycles:
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Center-of-Mass Collision Energy
• Measuring the angular distributions allows us thenmeasure the relative energy distributions of this reaction• For mono-energetic beams:
Er = µ
(En
Mn+Ei
Mi− 2
√EnEi
MnMicosθ
)(2)
µ = reduced massEn = Energy of neutrals (12 keV - D)Ei = Energy of ions (18.02 keV - H+
3 )Mn = Neutral Mass (1.88 GeV/c2 - D)Mi = Ion Mass (2.81 GeV/c2 - H+
3 )θ = Intersection angle
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Energy Distribution Measurements
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Conclusions
• The angular distributions over time were keptminimal
• We can keep the majority of the beam in adefined range.
• Enables us maximize the beam current from thepulsed gas jet while minimizing beam loss from thetrap
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Acknowledgments
MentorsDr. Kyle BowenDr. Pierre HillenbrandDr. Daniel Savin
Program CoordinatorsAmy GarwoodProfessor Georgia KaragiorgiProfessor John Parsons