Adiabatic Expansion of Electron Gas in a Magnetic Nozzle

Takahashi, Kazunori; Charles, Christine; Boswell, Rod; Andõ, Akira

doi:10.1103/physrevlett.120.045001

Cited by 44 publications

(36 citation statements)

References 28 publications

(32 reference statements)

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“…This study has great significance in that it is capable of explaining the formation of non-locally behaving Druyvesteyn-like distribution, which has been consistently observed in the research groups worldwide, as well as the locally behaving Maxwellian distribution found in other groups with the consideration of the non-locally behaving confined electrons. Especially, this study is significant to present a new perspective that various values of polytropic index observed in the laboratory MN of each research group [15,33,34,37] could be the result of the difference in bounce region of the isothermally behaving confined electrons determined by the strength and configuration of the magnetic field. From another point of view, our results indicate that it is possible to control the eepf within the magnetically expanding plasma generated by the ECR or helicon sources by changing the bounce region of confined electrons according to the magnetic field conditions.…”

Section: Discussionmentioning

confidence: 90%

“…Similar to previous study [34], the study showed a self-generating ambipolar potential with isothermally behaving electrons. However, by removing boundary potential, which mainly confines the electrons in the device, perfect adiabatic expansion occurred without the formation of ambipolar potential in a diffusion region [37]. Even though the explanations of above groups are successful to interpret their own experimental results, the correlation between the change in γ e and the nozzle characteristics that will support their claims on the fundamental understanding on the different value of γ e is still not given in laboratory experiments.…”

Section: Introductionmentioning

confidence: 99%

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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: Discussionmentioning

confidence: 90%

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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“…4 and 5(b), the energy fluxes estimated from Eqs. (9) and (10) are plotted by open and filled squares, respectively, in Fig. 6 for (a) I B = 0 A, (b) 5 A, (c) 10 A, and (d) 15 A cases.…”

Section: Resultsmentioning

confidence: 99%

“…Furthermore, the normalized power P w /P abs based on Eqs. (9) and (10) are also plotted by open and filled squares, respectively. Since these equations correspond to the upper and lower limits of the power estimation, the actual loss power and normalized power would be in the colored region in Fig.…”

Section: Resultsmentioning

confidence: 99%

Spatially- and vector-resolved momentum flux lost to a wall in a magnetic nozzle rf plasma thruster

Takahashi

Sugawara

Andõ

2020

Sci Rep

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Most of the artificial low-pressure plasmas contact with physical walls in laboratories; the plasma loss at the wall significantly affects the plasma device performance, e.g., an electric propulsion device. Near the surface of the wall, ions are spontaneously accelerated by a sheath and deliver their momentum and energy to the wall, while most of the electrons are reflected there. The momentum flux of the ions is a vector field, i.e., having both the radial and axial components even if the azimuthal components are neglected in a cylindrical system. Here the spatially-and vector-resolved measurement of the momentum flux near the cylindrical source wall of a magnetic nozzle radiofrequency (rf) plasma thruster configuration is successfully demonstrated by using a momentum vector measurement instrument. The results experimentally identify the spatial profile of a non-negligible axial momentum flux to the wall, while the radially accelerated ions seem to be responsible for the energy loss to the wall. The spatial profiles of the radial and axial momentum fluxes and the energy lost to the wall are significantly affected by the magnetic field strength. The results contribute to understand how and where the momentum and energy in the artificial plasma devices are lost, in addition to the presently tested thruster. The plasma momentum is one of the fundamental physical quantities associated with static and dynamic phenomena of plasmas in nature and laboratories. The energy flux being a scalar quantity can be given by the magnitude of the velocity, while the momentum flux is a vector quantity in general. It is crucial to understand and characterize the momentum transport, conversion, gain, and loss mechanisms for clarifying the structural formation of plasmas such as the astrophysical jets 1 , the particle acceleration in auroras at the Earth and Jupiter 2,3 , the coronal mass ejection from the Sun 4 , the interaction between the plasmas and the geomagnetic field 5 , and so on. In these naturally appearing plasmas, the processes involving the momentum and energy transfer occur due to the interaction with electromagnetic fields, collisions, turbulences, and so on, since they cannot see any physical boundaries in space except for the surface of planets. Terrestrial artificial plasmas ubiquitously contact to physical boundaries; forming a sheath maintaining charge balance in plasmas 6. Plasma-wall interactions involving the momentum transfer and loss also significantly affect the plasma behavior in the laboratories, e.g., in ref. 7,8 , in addition to the interactions occurring in the above-mentioned natural plasmas, e.g., interaction with the magnetic fields 9-11. The electric field perpendicular to the physical boundary is spontaneously formed in the sheath and accelerates the ions toward the boundary; resulting in the transfer of the momentum flux perpendicular to the surface. However, if they have velocity components parallel to the boundary surface, they can also deliver their momentum parallel to the boundary. Therefore,...

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“…in the present experiment. The whole structure of the plasma source can be biased by inserting the bipolar power supply (V bias ) between the discharge chamber and the plasma grid for the control of the plasma potential with respect to the PG, being similar to [20,21]. The positive ion beam can be extracted and accelerated from the plasma source by applying extraction and acceleration voltages V ext and V acc between the EG and PG and between the GG and EG, respectively, where V ext =1.5 kV and V acc =8 kV are chosen in the present experiment.…”

Section: Methodsmentioning

confidence: 99%

Spatiotemporal oscillation of an ion beam extracted from a potential-oscillating plasma source

et al. 2019

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A radiofrequency oscillation is successfully superimposed on a plasma potential of a filamented source plasma in an ion beam source while maintaining a constant plasma density, in order to investigate effects of oscillating source plasma potential on an extracted ion beam. The experiment is preliminarily performed with a positive argon ion beam source. A class-D amplifier operational over a wide range of a frequency from a few tens of kHz to several MHz is installed; leading the oscillation of the plasma potential in the plasma source for the frequency range being tested. The beam current profile downstream of the extraction grids shows an oscillation of the beam current at the peripheral region of the ion beam; implying that the oscillation of a beam halo is induced by the potential oscillation of the source plasma.

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Adiabatic Expansion of Electron Gas in a Magnetic Nozzle

Cited by 44 publications

References 28 publications

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Spatially- and vector-resolved momentum flux lost to a wall in a magnetic nozzle rf plasma thruster

Spatiotemporal oscillation of an ion beam extracted from a potential-oscillating plasma source

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