Enhancement of axial momentum lost to the radial wall by the upstream magnetic field in a helicon source

Takahashi, Kazunori; Andõ, Akira

doi:10.1088/1361-6587/aa626f

Cited by 20 publications

(15 citation statements)

References 33 publications

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“…Particularly, in the case of electrodeless thruster, MNs are proposed as next-generation electric propulsion system due to its advantages in terms of lifetime and economic efficiency of the device without erosion of generation and acceleration electrode [12][13][14][15][16]. Accordingly, there has been a significant interest in the MN to elucidate the physics of plasmas expanding in divergent magnetic fields for electric propulsion systems and laboratory plasmas [17][18][19][20][21][22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Kim

Ryu

et al. 2018

New J. Phys.

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Thermodynamics of a magnetically expanding plasma (magnetic nozzle (MN)) has been investigated considering the existence of confined electrons bouncing back and forth inside a potential well formed by a combination of external magnetic field and self-generating ambipolar electrostatic potential. The properties of confined electrons are distinguished from that of the adiabatically expanding electrons with γ e ≈5/3 by the separate measurement of each species using a double-sided planar Langmuir probe. Relationship between the electron pressure versus electron density averaged over electron energy probability functions (eepfs) clearly reveals that the confined electrons in MN have a nearly isothermal characteristic. Existence of isothermally behaving confined electrons together with adiabatically expanding electrons separates the MN system into two regions with different thermodynamic properties; one is a nearly adiabatic region located near the nozzle throat and the other is nearly isothermal region located far from the nozzle. A transition of electron thermodynamic property along a distance from the nozzle throat can be explained with conservation of magnetic moment of electrons bounced back by ambipolar electrostatic potential. Coexistence of the nearly adiabatic electrons with Maxwellian eepf and the nearly isothermal electrons with high energydepleted eepf makes the overall eepf shape low energy-populated eepf, indicating a need for careful analysis on the measured eepfs near the nozzle throat. In spite of significant contribution of confined electrons to eepf and overall electron thermodynamics, it is found that the confined electrons behaving isothermally do not contribute to the generation of ambipolar electrostatic potential which is important for ion acceleration in MN. The present study suggests that ion acceleration should not be directly inferred from the value of polytropic exponent γ e because thermodynamic property of a MN is influenced by isothermally behaving confined electrons as well as adiabatically expanding electrons.

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Section: Introductionmentioning

confidence: 99%

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Kim

Ryu

et al. 2018

New J. Phys.

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“…When the neutral gas is introduced from the upstream side of the source, the neutral density is depleted near the thruster exit due to the high ionization rate and the plasma density is lowered there as predicted in an analytical model 48 and observed in the experiment 49 . In such a density profile having the axial density peak in the upstream side, a non-negligible axial momentum flux is transferred to the radial wall, corresponding to the loss of the thrust to the wall 50 , 51 . One of the experiments has shown that the thrust loss can be inhibited by injecting the gas near the thruster exit and that the thrust can be increased by introducing the gas near the thruster exit 52 , in addition to the inhibition of the loss by the magnetic field 53 .…”

mentioning

confidence: 99%

Magnetic nozzle radiofrequency plasma thruster approaching twenty percent thruster efficiency

Takahashi

2021

Sci Rep

Self Cite

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Development of a magnetic nozzle radiofrequency (rf) plasma thruster has been one of challenging topics in space electric propulsion technologies. The thruster typically consists of an rf plasma source and a magnetic nozzle, where the plasma produced inside the source is transported along the magnetic field and expands in the magnetic nozzle. An imparted thrust is significantly affected by the rf power coupling for the plasma production, the plasma transport, the plasma loss to the wall, and the plasma acceleration process in the magnetic nozzle. The rf power transfer efficiency and the imparted thrust are assessed for two types of rf antennas exciting azimuthal mode number of $$m=+1$$ m = + 1 and $$m=0$$ m = 0 , where propellant argon gas is introduced from the upstream of the thruster source tube. The rf power transfer efficiency and the density measured at the radial center for the $$m=+1$$ m = + 1 mode antenna are higher than those for the $$m=0$$ m = 0 mode antenna, while a larger thrust is obtained for the $$m=0$$ m = 0 mode antenna. Two-dimensional plume characterization suggests that the lowered performance for the $$m=+1$$ m = + 1 mode case is due to the plasma production at the radial center, where contribution on a thrust exerted to the magnetic nozzle is weak due to the absence of the radial magnetic field. Subsequently, the configuration is modified so as to introduce the propellant gas near the thruster exit for the $$m=0$$ m = 0 mode configuration and the thruster efficiency approaching twenty percent is successfully obtained, being highest to date in the kW-class magnetic nozzle rf plasma thrusters.

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“…Most of fundamental studies involving HP sources have been employing argon as working gas because of the main interest in plasma processing applications. Likewise, more recent studies focused on space propulsion have equally employed argon propellant [25][26][27] . However, it is expected that the use of krypton or xenon in electric propulsion systems would enhance thrust, thrust density and thrust efficiency due to higher ion mass and larger ionization cross section.…”

Section: Introductionmentioning

confidence: 99%

Direct experimental comparison of krypton and xenon discharge properties in the magnetic nozzle of a helicon plasma source

Vinci

Mazouffre

2021

Physics of Plasmas

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Enhancement of axial momentum lost to the radial wall by the upstream magnetic field in a helicon source

Cited by 20 publications

References 33 publications

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Magnetic nozzle radiofrequency plasma thruster approaching twenty percent thruster efficiency

Direct experimental comparison of krypton and xenon discharge properties in the magnetic nozzle of a helicon plasma source

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