Mass Spectrometric Analysis of Colloid Thruster Ion Emission from Selected Propellants
Abstract
Retarding potential, time-of-flight (TOF), and quadrupole mass spectrometric methods are applied to study the charged species emitted from a colloid thruster operated in a cone-jet mode at high-specific-impulse operating conditions. Measurements are conducted for two propellants, a 28.4 wt% NaI/formamide electrolyte solution and the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]). When operated at a volume flow rate of 2-6 x 10(to the minus 14th power) m3/s and a positive polarity, the electrolyte solution yields an average specific charge, q/m, of ~11,000 C/kg with an ion/droplet current ratio of 9 to 1. Fully angularly integrated TOF measurements determine an average mass-to-charge ratio of 253 atomic mass units. The axial quadrupole mass spectrometric measurement identifies solvated sodium ions, Na+(HCONH2)n (n=1,...,10) with a distribution peaked at n=4. Stopping potential and retarding potential measurements suggest that most charged particles are produced with energies ~200 V below the capillary bias potentiaL The inability to operate this propellant in a pure ion emission mode makes the thruster inefficient when operated in the ion-evaporation, high-specific-impulse conditions. The ionic liquid, ([EMIM][BF4]), is operated in a pure ion emission mode for both positive and negative polarity, yielding mean specific charges exceeding 250,000 C/kg. X([EMIM][BF4])n (n=0,1,2) ions, where X=EMIM+ or BF-4, are identified. Contrary to the electrolyte solution, the energy analysis of the field-evaporated ions reveals that the ions are produced at the capillary potential with a narrower energy width of 50 V. For an acceleration voltage of 1500 V, a specific impulse of ~4000 s at an efficiency exceeding 90% is recorded.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 2005
- Accession Number
- ADA441264
Entities
People
- B. L. Austin
- Dale J. Levandier
- M. M. Sanchez Schatz
- P. T. Murray
- Paulo Lozano
- Rainer A. Dressler
- Yu-hui Chiu
Organizations
- Air Force Research Laboratory