Instrument Development: a High Density Source of Cold, Slow Molecules
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abstract
In this project, funded by the Chemical Measurements and Imaging Program of the Chemistry Division, Profs. Dudley Herschbach and Igor Lyuksyutov of Texas A&M University seek to develop an instrument capable of delivering beams of cold molecules with densities up to 1012 cm-3 at speeds as low as 5 m/s (the benchmark). The instrument is a pulsed, counter-rotating supersonic source (PCRS), with which any molecule available as a gas can be slowed (or speeded). Such densities at speeds so low are about four orders of magnitude larger than currently available by other means. Very slow beams of ~ 5 m/s are essential for many experiments that require trapping molecules. Anticipated beam densities, typically >1010 cm-3, are essemtial to enable the trapped molecules to be subsequently cooled down to the ultracold realm. Used in a different mode, for study of collisions, very low relative kinetic energies can be attained by pairing the PCRS with a codirectional stationary source and closely matching the beam velocities by adjusting the rotor speed. This merged-beam capability is widely applicable. It will open up the "matterwave" or "hyperquantum" realm of chemical reaction dynamics, where collisional deBroglie wavelengths much exceed the size of reactant molecules. The project also includes the development of an auxiliary instrument, applicable to molecules with magnetic moments. It is a single-stage magnetic decelerator (SSMD), designed to operate in combination with the PCRS. Computer simulations for a preliminary version of the SSMD demonstrate that a pulsed field only 7 cm long, with parabolic profile and strength 5 Tesla, can decelerate O2 from 50 m/s to 2 or 3 m/s. The combined PCRS + SSMD instrument will be compact, robust, simple to construct and operate. This project will provide tools that will significantly advance experimental research exploring and eventually using the novel properties of very slow molecules. Futuristic applications from information processing (quantum computers) to gravity detectors have been predicted to emerge from slow molecule technology. The adventurous character of the research fosters interest both among students and the wider public. Undergraduate students (supported either by REU funding or by TAMU) as well as graduate students will contribute significantly. The work involves design studies for apparatus, including many table-top components, and experimental protocols, thereby providing experience in computer simulations and other practical arts. Both PIs are evangelical about teaching and mentoring students and have undertaken efforts to improve K-12 science education and public understanding of science. Directly linked to this project are plans for a "Coolest Place in Texas" summer program for high school students and a pair of lecture series "The Ultracold World" and "Wizards of the NanoWorld" for the general public, including high school and middle school students.
