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