TY - JOUR
T1 - On collisionless ion and electron populations in the magnetic nozzle experiment (MNX)
AU - Cohen, Samuel A.
AU - Sun, Xuan
AU - Ferraro, Nathaniel M.
AU - Scime, Earl E.
AU - Miah, Mahmood
AU - Stange, Sy
AU - Siefert, Nicholas S.
AU - Boivin, Robert F.
N1 - Funding Information:
Manuscript received July 28, 2005; revised October 3, 2005. This work was supported in part by the U.S. Department of Energy under Contract DE-AC02-76-CHO-3073. The West Virginia University portion of this work was supported by the U.S. Department of Energy EPSCoR Laboratory Partnership Program under Grant ER45849. S. A. Cohen, N. M. Ferraro, and M. Miah are with the Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 USA (e-mail: scohen@pppl. gov). X. Sun and E. E. Scime are with the Physics Department, West Virginia University, Morgantown, WV 26506 USA. S. Stange is with the University Research Program in Robotics, University of Michigan, Ann Arbor, MI 48109 USA. N. S. Siefert is with the Air Force Research Laboratory, Wright-Patterson Air Force Base, Wright-Patterson Air Force Base, OH 45433-5543 USA. R. F. Boivin is with the Physics Department, Auburn University, Auburn, AL 36849-5311 USA. Digital Object Identifier 10.1109/TPS.2006.875846
PY - 2006
Y1 - 2006
N2 - The Magnetic Nozzle Experiment (MNX) is a linear magnetized helicon-heated plasma device, with applications to advanced spacecraft-propulsion methods and solar-corona physics. This paper reviews ion and electron energy distributions measured in MNX with laser-induced fluorescence (LIF) and probes, respectively. Ions, cold and highly collisional in the main MNX region, are accelerated along a uniform magnetic field to sonic then supersonic speeds as they exit the main region through either mechanical or magnetic apertures. A sharp decrease in density downstream of the aperture(s) helps effect a transition from collisional to collisionless plasma. The electrons in the downstream region have an average energy somewhat higher than that in the main region. From LIF ion-velocity measurements, we find upstream of the aperture a presheath of strength Δφps = mrTe, where mrTe is the electron temperature in the main region, and length ∼3 cm, comparable to the ion-neutral mean-free-path; immediately downstream of the aperture is an electrostatic double layer of strength ΔφDL = 3-10 mrTe and length 0.3-0.6 cm, 30-600λD. The existence of a small, ca. 0.1%, superthermal electron population with average energy ∼10mrTe is inferred from considerations of spectroscopic line ratios, floating potentials, and Langmuir probe data. The superthermal electrons are suggested to be the source for the large ΔφDL.
AB - The Magnetic Nozzle Experiment (MNX) is a linear magnetized helicon-heated plasma device, with applications to advanced spacecraft-propulsion methods and solar-corona physics. This paper reviews ion and electron energy distributions measured in MNX with laser-induced fluorescence (LIF) and probes, respectively. Ions, cold and highly collisional in the main MNX region, are accelerated along a uniform magnetic field to sonic then supersonic speeds as they exit the main region through either mechanical or magnetic apertures. A sharp decrease in density downstream of the aperture(s) helps effect a transition from collisional to collisionless plasma. The electrons in the downstream region have an average energy somewhat higher than that in the main region. From LIF ion-velocity measurements, we find upstream of the aperture a presheath of strength Δφps = mrTe, where mrTe is the electron temperature in the main region, and length ∼3 cm, comparable to the ion-neutral mean-free-path; immediately downstream of the aperture is an electrostatic double layer of strength ΔφDL = 3-10 mrTe and length 0.3-0.6 cm, 30-600λD. The existence of a small, ca. 0.1%, superthermal electron population with average energy ∼10mrTe is inferred from considerations of spectroscopic line ratios, floating potentials, and Langmuir probe data. The superthermal electrons are suggested to be the source for the large ΔφDL.
KW - Double layer
KW - Helicon
KW - Laser-induced-fluorescence (LIF)
KW - Magnetic nozzle
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U2 - 10.1109/TPS.2006.875846
DO - 10.1109/TPS.2006.875846
M3 - Article
AN - SCOPUS:38849180353
SN - 0093-3813
VL - 34
SP - 792
EP - 803
JO - IEEE Transactions on Plasma Science
JF - IEEE Transactions on Plasma Science
IS - 3 PART 2
ER -