High temperature electrons exhausted from rf plasma sources along a magnetic nozzle

Takahashi, Kazunori; Akahoshi, Hikaru; Charles, Christine; Boswell, Roderick; Andõ, Akira

doi:10.1063/1.4990110

Cited by 68 publications

(71 citation statements)

References 29 publications

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“…The EEPF obtained at (z, r) = (10 cm, 3 cm) corresponding to Circle 3 shows the broadening EEPF indicating the high electron temperature, compared to the other cases. The high temperature electrons generated near the source wall and transported to the diffusion chamber have been observed in the magnetically expanding plasmas in previous experiments, 23 while the high temperature electrons is detected only inside the source tube in the present experiment. Detailed axial measurements are performed at r = 0 cm and 2.5 cm, while the radial measurements are performed at z = 10 cm and 0 cm.…”

Section: Resultssupporting

confidence: 61%

“…These are probably due to a heating of electrons by the rf electromagnetic fields demonstrated previously in experiment 23 and due to an effect of a short trapping length along the magnetic field lines intersecting the source wall as presented in previous numerical study. 35 The steady-state electron density is typically determined by the balance …”

Section: -5supporting

confidence: 51%

“…Previous fundamental studies on magnetically expanding rf plasmas, which are typically used for plasma processing devices and the electric propulsion device called a helicon thruster, have shown a presence of high temperature electrons near the plasma-vacuum boundary downstream of the source, [20][21][22][23] where the energetic electrons are produced near the rf antenna and transported to the downstream side along the magnetic field lines. According to the previous studies, the thrust components corresponding to the pressure inside the source and the Lorentz force in the magnetic nozzle originates from the electron pressure.…”

Section: Introductionmentioning

confidence: 99%

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Filtering peripheral high temperature electrons in a cylindrical rf-driven plasmas by an axisymmetric radial magnetic field

2018

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High temperature electrons generated near a radial wall of a cylindrical source tube in a radiofrequency (rf) inductively-coupled plasma is filtered by an axisymmetric radial magnetic field formed near the source exit by locating annular permanent magnets, where the axial magnetic field strength in the radially central region is fairly uniform inside the source tube and is close to zero near the source exit. The source is operated at 3 mTorr in argon and the rf antenna is powered by a 13.56 MHz and 400 W rf generator. Measurement of electron energy probability functions shows the presence of the peripheral high temperature electrons inside the source, while the temperature of the peripheral electrons downstream of the source is observed to be reduced.

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Section: Resultssupporting

confidence: 61%

Section: -5supporting

confidence: 51%

Section: Introductionmentioning

confidence: 99%

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Filtering peripheral high temperature electrons in a cylindrical rf-driven plasmas by an axisymmetric radial magnetic field

2018

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“…4 are the first experimental identification of both the radial and axial momentum fluxes lost to the wall and identify where the plasma momentum components are lost. The momentum transport and loss in the source are expected to be related with various physical processes arising from the magnetic field and geometric configurations 35 , the plasma-neutral interaction 12,36,37 , the non-Maxwellian energy distributions of ions and electrons [38][39][40] , and the plasma structural formations [41][42][43][44] . Hence more detailed investigation on the momentum transport physics still remains further challenge.…”

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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“…These devices typically consist of a rf plasma source surrounded by a set of solenoids and contiguously attached to a larger radius expansion chamber. Much of the previous work conducted in these devices has focused on characterizing the axial DL [9][10][11][12][13] and subsequent ion beam [14][15][16] as well as a region of high density plasma located off-axis in the expansion chamber known as the high-density conics [17][18][19][20][21][22]. The conics are ionized locally by hot electron populations, which stream along the most radial magnetic field lines to escape the source region, and result in a hollow radial plasma density profile in the expansion region.…”

Section: Introductionmentioning

confidence: 99%

Characterization and Control of an Ion-Acoustic Plasma Instability Downstream of a Diverging Magnetic Nozzle

et al. 2020

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The study and control of resonant instabilities in magnetized plasmas is of fundamental interest over a wide range of applications from industrially relevant plasmas to plasma sources for spacecraft propulsion. In this work electrostatic probes were employed to measure a 4-20 kHz instability in the ion saturation current downstream of an electric double layer (DL) in an expanding helicon plasma source. The amplitude and frequency of the instability were found to vary in inverse proportion to the operating argon gas pressure (0.2-0.6 mTorr) and in direct proportion to the applied rf power (100-600 W) and applied solenoid current (3-8 A). A spatially resolved characterization of the maximum instability amplitude determined two radial maxima, corresponding to the locations of most positive radial ion density gradient. Control and inhibition of the instability were achieved through the application of a kHz voltage amplitude modulation to the 13.56 MHz radio-frequency (rf) power supplied to the helicon antenna. Through the application of voltage amplitude modulations in the frequency range 2-12 kHz the instability was reduced by up to 65%, exhibiting a greater reduction at higher applied modulation frequencies. This effect is described through a variation in the radial ion density gradient via asymmetrically attenuated ion acoustic density perturbations induced by the applied voltage modulation. The application of voltage amplitude modulations has been demonstrated as a potential control mechanism for density gradient driven instabilities in magnetized plasmas.

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High temperature electrons exhausted from rf plasma sources along a magnetic nozzle

Cited by 68 publications

References 29 publications

Filtering peripheral high temperature electrons in a cylindrical rf-driven plasmas by an axisymmetric radial magnetic field

Filtering peripheral high temperature electrons in a cylindrical rf-driven plasmas by an axisymmetric radial magnetic field

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

Characterization and Control of an Ion-Acoustic Plasma Instability Downstream of a Diverging Magnetic Nozzle

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