Carrie A. Kauffman, Kyle N. Crabtree, Benjamin J. McCall

Department of Chemistry, University of Illinois

June 23rd, 2009

A Continuous Supersonic Expansion Discharge Nozzle For

Rotationally Cold Ions

MotivationMolecular

ions◦ Organic Reaction

Intermediates◦ Combustion◦ Atmospheric

Chemistry◦ Interstellar

Chemistry

Simulation of N2+ of the A 2∏u – X 2∑g

+

(4-0)+

For more on the progress of SCRIBES, stay for the next two talks.

Supersonic Source

Supersonic ExpansionBarrel Shock

High Pressure

Gas Small Orifice

•Adiabatic Process, dq = 0dU = dq –dw dU = -PV

•Tvib >> Trot > Ttrans , where Trot ~ 0.5-30 K

Low Pressure Region

Mach Disk

Compatible with SCRIBES

Leak tight

Robust

Modular

Maximize ion density

Design Considerations

Previous Reported Discharge Designs

First Generation - Corona

Engelking, P.C.; Corona Excited Supersonic Expansion. Rev. Sci. Instrum., 1986, 57, 2274-2277.

Advantages DisadvantagesContinuous Materials Chosen

No modular componentsCompatibility

Slit Design

Broks, B.; Brok, W.; Remy, J; van der Mullen, J.; Benidar, A.; Biennier, L. & Salama, F.; Modeling the Influence of Anode-Cathode Spacing in a Pulsed Discharge Nozzle. Spectrochim Acta B, 2005, 60, 1442-1449.

Advantages DisadvantagesMaterials Chosen Integration with SCRIBES

ClusteringPulsed

Nozzle Design

McCarthy, M. C., Chen, W.; Travers, M. J. & Thaddeus, P. Microwave Spectra of 11 Polyyne Carbon Chains. Astrophys. J. Suppl., 2000, 129, 611-623.

Advantages DisadvantagesCompatibility with SCRIBES

Pulsed

Modular Materials

Design

• 1-3 Atmosphere of backing pressure

•Orifice Size: 250 to 1000 micron with varying geometry

•Typical Chamber Pressure 100 mTorr

Source

•Nitrogen Gas

•Running Voltage: -200 to -500 V

•Running Current: 30 mA

•Operation Time: 100+ Hours

Characterization of the source

Ion Current

Optimization of Cooling Capabilities

SummaryDesign Continuous Supersonic Expansion

Nozzle Discharge

Modular

Self-Aligning

Robust

Acknowledgements

SCS Machine Shop

McCall Research Group

Ben McCall