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Title: Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams

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 He{sub 2}{sup +} and He{sub 4}{sup +}, which are signatures of superfluid helium droplets. Without ionizing any helium atoms, multiphoton non-resonant laser ionization of CCl{sub 4} doped in superfluid helium droplets at 266 nm generates complex cluster ions of dopant fragments with helium atoms, including (He){sub n}C{sup +}, (He){sub n}Cl{sup +}, and (He){sub n}CCl{sup +}. 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 dopedmore » droplets.« less
Authors:
; ; ; ;  [1]
  1. Department of Chemistry, Oregon State University, Corvallis, Oregon 97331 (United States)
Publication Date:
OSTI Identifier:
22482750
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 86; Journal Issue: 8; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; BEAMS; CARBON TETRACHLORIDE; DOPED MATERIALS; DROPLETS; EFFICIENCY; ELECTRODES; ELECTRON DIFFRACTION; ELECTRON GUNS; FILAMENTS; HELIUM; ION PAIRS; LASERS; MASS SPECTROMETERS; MULTI-PHOTON PROCESSES; NOZZLES; PULSES; SUPERFLUIDITY; TIME-OF-FLIGHT METHOD; VALVES