BEGIN:VCALENDAR
VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-2584
DTSTART:20120201T180000Z
DURATION:PT1H0M0S
DTSTAMP:20260420T062201Z
LAST-MODIFIED:20120125T150348Z
LOCATION:2241 Chamberlin
SUMMARY:Ambipolar ion acceleration from plasma expansion through a mag
 netic nozzle and near-term spacecraft propulsion applications\, Plasma
  Physics (Physics/ECE/NE 922) Seminar\, Dr. Benjamin Longmier\, Univer
 sity of Houston
DESCRIPTION:The helicon plasma stage in the Variable Specific Impulse 
 Magnetoplasma Rocket (VASIMR) engine was used to characterize an axial
  plasma potential profile within an expanding magnetic nozzle region o
 f the laboratory based device. The ion acceleration mechanism is ident
 ified as an ambipolar electric field produced by an electron pressure 
 gradient\, resulting in a local axial ion speed of Mach 4 downstream o
 f the magnetic nozzle. A 20 eV argon ion kinetic energy was measured i
 n the helicon source\, which had a peak magnetic field strength of 0.1
 7 T. The helicon plasma source was operated with 25 mg s−1 argon pro
 pellant and 30kW of RF power. The maximum measured values of plasma de
 nsity and electron temperature within the exhaust plume were 1e20 m−
 3 and 9 eV\, respectively. The measured plasma density is nearly an or
 der of magnitude larger than previously reported steady-state helicon 
 plasma sources. The exhaust plume also exhibits a 95% to 100% ionizati
 on fraction. The thickness of the potential structure was found to be 
 1e4 to 1e5 Debye lengths depending on the local electron temperature i
 n the magnetic nozzle\, many orders of magnitude larger than previousl
 y reported laboratory double layer structures. The background plasma d
 ensity and neutral argon pressure were 1e15 m−3 and 2e−5 Torr\, re
 spectively\, in a 150m^3 vacuum chamber during operation of the helico
 n plasma source. The agreement between the measured plasma potential a
 nd plasma potential that was calculated from an ambipolar ion accelera
 tion analysis over the bulk of the axial distance where the potential 
 drop was located is a strong confirmation of the ambipolar acceleratio
 n process. Future propulsion applications using ambipolar ion accelera
 tion will be discussed.
URL:https://www.physics.wisc.edu/events/?id=2584
END:VEVENT
END:VCALENDAR