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Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams 公开 Deposited

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https://ir.library.oregonstate.edu/concern/articles/td96k436j

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  • We present two facile time-of-flight (TOF) methods of detecting superfluid helium droplets and droplets with neutral dopants. Without an electron gun and with only a heated filament and pulsed electrodes, the electron impact ionization TOF mass spectrometer can resolve ionized helium clusters such as He₂ ⁺ and He₄ ⁺, which are signatures of superfluid helium droplets. Without ionizing any helium atoms, multiphoton non-resonant laser ionization of CCl₄ doped in superfluid helium droplets at 266 nm generates complex cluster ions of dopant fragments with helium atoms, including (He)[subscript]nC⁺, (He)[subscript]nCl⁺, and (He)[subscript]nCCl⁺. Using both methods, we have characterized our cryogenic pulsed valve—the Even-Lavie valve. We have observed a primary pulse with larger helium droplets traveling at a slower speed and a rebound pulse with smaller droplets at a faster speed. In addition, the pickup efficiency of dopant is higher for the primary pulse when the nozzle temperature is higher than 13 K, and the total time duration of the doped droplet pulse is only on the order of 20 μs. These results stress the importance of fast and easy characterization of the droplet beam for sensitive measurements such as electron diffraction of doped droplets.
  • Article Copyright 2015 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments and may be found at http://scitation.aip.org/content/aip/journal/rsi
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  • He, Y., Zhang, J., Li, Y., Freund, W. M., & Kong, W. (2015). Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams. Review of Scientific Instruments, 86(8), 084102. doi:10.1063/1.4928107
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  • 86
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  • 8
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  • This work is supported by the National Institute of General Medical Sciences (Nos. 1RC1GM092054-01 and 1R01GM101392-01A1) from the National Institutes of Health. Additional support from the Oregon Nanoscience and Microtechnologies Institute and the Environmental Health Science Center at Oregon State University funded by the National Institute of Environmental Health Sciences (No. ES000210) is also deeply appreciated.
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