angularandenergydistributions of h inaniontrap · angularandenergydistributions ofh+ 3 inaniontrap...
TRANSCRIPT
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
Overview
1 Scientific Background
2 The Apparatus
3 My Work
4 Conclusions
5 Acknowledgments
Cosmic Cycle of Gas
What are Dense Molecular Clouds?
What are Dense Molecular Clouds?
• n = 104 cm−3
What are Dense Molecular Clouds?
• 10-20 K
What are Dense Molecular Clouds?
• Ion-neutral reactiondriven chemistry
What are Dense Molecular Clouds?
• Cosmic rays initiatethe chemistry in DMCsinstead of UV photons.
H+3 formation
H2 + cosmic ray → H+2 + e− + cosmic ray’
H+2 + H2 → H+
3 + H
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
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
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
Merged Fast-Beams Apparatus
Merged Fast-Beams Apparatus
Merged Fast-Beams Apparatus
Merged Fast-Beams Apparatus
Merged Fast-Beams Apparatus
Merged Fast-Beams Apparatus
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
Cross Section Measurement
• H+3 + D → H2D
+ + H
Internal Energy Problem
• Beam production leads to unknown internal excitation of H+3
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
Solution for Higher Beam Current
• Simulate H+3 ion trajectories
• Determine trapping voltage for H+3 ions
• Determine angular distribution• Determine energy distribution
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
Angular Distribution Measurements
• Angular distributions from the center of the trap for a5mm beam after 50 cycles:
Trapping Efficiency
• Measurements taken at the center of the trap after 5, 10,and 50 cycles:
Angular Distribution Measurements
• Angular distributions from the center of the trap for a10mm beam after 50 cycles:
Trapping Efficiency
• Measurements taken at the center of the trap after 5, 10,and 50 cycles:
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
Energy Distribution Measurements
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
Acknowledgments
MentorsDr. Kyle BowenDr. Pierre HillenbrandDr. Daniel Savin
Program CoordinatorsAmy GarwoodProfessor Georgia KaragiorgiProfessor John Parsons