scholarly journals Ion Distribution Functions in the Vicinity of Comet Giacobini-Zinner

2013 ◽  
pp. 275-278
Author(s):  
T.E. Cravens
Keyword(s):  
Distribution Functions ◽  
Ion Distribution

The hot hELicon eXperiment (HELIX) and the large experiment on instabilities and anisotropy (LEIA)

2014 ◽  
Vol 81 (1) ◽  
Author(s):  
E. E. Scime ◽  
P. A. Keiter ◽  
M. M. Balkey ◽  
J. L. Kline ◽  
X. Sun ◽  
...  
Keyword(s):  
Double Layer ◽  
Noble Gas ◽  
Velocity Distribution Function ◽  
Plasma Source ◽  
Distribution Functions ◽  
Double Layers ◽  
Driving Frequency ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Ion Distribution

The West Virginia University Hot hELIcon eXperiment (HELIX) provides variable density and ion temperature plasmas, with controllable levels of thermal anisotropy, for space relevant laboratory experiments in the Large Experiment on Instabilities and Anisotropy (LEIA) as well as fundamental studies of helicon source physics in HELIX. Through auxiliary ion heating, the ion temperature anisotropy (T⊥/T∥) is variable from 1 to 20 for parallel plasma beta (β = 8πnkTi∥/B2) values that span the range of 0.0001 to 0.01 in LEIA. The ion velocity distribution function is measured throughout the discharge volume in steady-state and pulsed plasmas with laser induced fluorescence (LIF). The wavelengths of very short wavelength electrostatic fluctuations are measured with a coherent microwave scattering system. Operating at low neutral pressures triggers spontaneous formation of a current-free electric double layer. Ion acceleration through the double layer is detected through LIF. LIF-based velocity space tomography of the accelerated beam provides a two-dimensional mapping of the bulk and beam ion distribution functions. The driving frequency for the m = 1 helical antenna is continuously variable from 8.5 to 16 MHz and frequency dependent variations of the RF coupling to the plasma allow the spontaneously appearing double layers to be turned on and off without modifying the plasma collisionality or magnetic field geometry. Single and multi-species plasmas are created with argon, helium, nitrogen, krypton, and xenon. The noble gas plasmas have steep neutral density gradients, with ionization levels reaching 100% in the core of the plasma source. The large plasma density in the source enables the study of Aflvén waves in the HELIX device.

scholarly journals Dependence on ion temperature of shallow-angle magnetic presheaths with adiabatic electrons

2019 ◽  
Vol 85 (6) ◽  
Author(s):  
Alessandro Geraldini ◽  
F. I. Parra ◽  
F. Militello
Keyword(s):  
Magnetic Field ◽  
Fluid Model ◽  
Boltzmann Distribution ◽  
Distribution Functions ◽  
Magnetized Plasma ◽  
Electron Mass ◽  
Ion Temperature ◽  
Ion Distribution ◽  
Ionic Charge ◽  
The Magnetic Field

The magnetic presheath is a boundary layer occurring when magnetized plasma is in contact with a wall and the angle $\unicode[STIX]{x1D6FC}$ between the wall and the magnetic field $\boldsymbol{B}$ is oblique. Here, we consider the fusion-relevant case of a shallow-angle, $\unicode[STIX]{x1D6FC}\ll 1$ , electron-repelling sheath, with the electron density given by a Boltzmann distribution, valid for $\unicode[STIX]{x1D6FC}/\sqrt{\unicode[STIX]{x1D70F}+1}\gg \sqrt{m_{\text{e}}/m_{\text{i}}}$ , where $m_{\text{e}}$ is the electron mass, $m_{\text{i}}$ is the ion mass, $\unicode[STIX]{x1D70F}=T_{\text{i}}/ZT_{\text{e}}$ , $T_{\text{e}}$ is the electron temperature, $T_{\text{i}}$ is the ion temperature and $Z$ is the ionic charge state. The thickness of the magnetic presheath is of the order of a few ion sound Larmor radii $\unicode[STIX]{x1D70C}_{\text{s}}=\sqrt{m_{\text{i}}(ZT_{\text{e}}+T_{\text{i}})}/ZeB$ , where e is the proton charge and $B=|\boldsymbol{B}|$ is the magnitude of the magnetic field. We study the dependence on $\unicode[STIX]{x1D70F}$ of the electrostatic potential and ion distribution function in the magnetic presheath by using a set of prescribed ion distribution functions at the magnetic presheath entrance, parameterized by $\unicode[STIX]{x1D70F}$ . The kinetic model is shown to be asymptotically equivalent to Chodura’s fluid model at small ion temperature, $\unicode[STIX]{x1D70F}\ll 1$ , for $|\text{ln}\,\unicode[STIX]{x1D6FC}|>3|\text{ln}\,\unicode[STIX]{x1D70F}|\gg 1$ . In this limit, despite the fact that fluid equations give a reasonable approximation to the potential, ion gyro-orbits acquire a spatial extent that occupies a large portion of the magnetic presheath. At large ion temperature, $\unicode[STIX]{x1D70F}\gg 1$ , relevant because $T_{\text{i}}$ is measured to be a few times larger than $T_{\text{e}}$ near divertor targets of fusion devices, ions reach the Debye sheath entrance (and subsequently the wall) at a shallow angle whose size is given by $\sqrt{\unicode[STIX]{x1D6FC}}$ or $1/\sqrt{\unicode[STIX]{x1D70F}}$ , depending on which is largest.

scholarly journals Retarded Field Energy Analyzer as a tool to Study the Ion Velocity Distribution Functions on Radio Frequency Argon Plasma in Expanding Magnetic Field at Low Pressures

2016 ◽  
Vol 3 (1) ◽  
pp. 82
Author(s):  
L.N. Mishra
Keyword(s):  
Magnetic Field ◽  
Velocity Distribution ◽  
Argon Plasma ◽  
Distribution Functions ◽  
Field Energy ◽  
Geometrical Shape ◽  
Ion Distribution ◽  
Plasma Flows ◽  
Temperature Plasma ◽  
Plasma Device

<p>Plasma expanding in the space along the magnetic filed is well known phenomenon. This plasma device was constructed to investigate the space plasma in laboratory in connection with plasma flows, electron distribution, ion distribution, instability and turbulence. For this purpose, the low-temperature plasma is produced by means of a 13.56 MHz Helicon plasma source at 300-1000 W rf power. The plasma is expanding from the 13.5 cm diameter source into a 150 cm long chamber of 60 cm diameter. Ion energy and its velocity distribution produced by a current-free double layer at the expansion region have been studied by means of retarding field energy analyzers. Furthermore, the effects due to the geometrical shape of the expanding magnetic field in plasma flows have also been investigated.</p><p>Journal of Nepal Physical Society Vol.3(1) 2015: 82-88</p>

scholarly journals A Statistical investigation of the invariant latitude dependence of unstable magnetospheric ion populations in relation to high m ULF wave generation

2006 ◽  
Vol 24 (11) ◽  
pp. 3027-3040 ◽  
Author(s):  
M. E. Wilson ◽  
T. K. Yeoman ◽  
L. J. Baddeley ◽  
B. J. Kellet
Keyword(s):  
Free Energy ◽  
Proton Energy ◽  
Statistical Investigation ◽  
Distribution Functions ◽  
Small Scale ◽  
Free Energies ◽  
Ion Distribution ◽  
Resonant Wave ◽  
Morning Sector ◽  
Field Lines

Abstract. A statistical study is presented of the unstable proton populations, which contain the free energy required to drive small-scale poloidal mode ULF waves in the magnetosphere, observed at invariant latitudes of 60° to 80°. The data are all in the form of Ion Distribution Functions (IDFs) amassed over ~6 years using the CAMMICE (MICS) instrument on the Polar spacecraft, and cover proton energies of 1 keV to 328 keV. The free energy contained in the unstable, positive gradient regions of the IDFs is available to drive resonant wave growth. The results show that positive gradient regions in IDFs on magnetic field lines corresponding to the lower invariant latitudes in the range under study occur predominantly in the afternoon sector at proton energies of 5 keV to 20 keV. In the morning and dawn sectors positive gradient regions are seen with a typical proton energy range of 5 keV to 45 keV. While the proton energy peaks in the afternoon sector at around ~7 keV the morning sector has two peaks occurring at ~10 keV and ~20–30 keV. The technique of Baddeley et al. (2004), employed to quantify the free energy in each IDF, found that as invariant latitude increased the free energy contained in the positive gradient regions fell. Positive gradient regions in the afternoon sector decrease in number with invariant latitude at a faster rate than those in the morning sector. The majority of positive gradient regions had free energy values of >1010 J with many at the lowest invariant latitudes having free energies of in excess of 1011 J. Positive gradient regions at proton energies of >100 keV are rarely observed, and have free energies of typically <10

scholarly journals On the coupling between unstable magnetospheric particle populations and resonant high <i>m</i> ULF wave signatures in the ionosphere

2005 ◽  
Vol 23 (2) ◽  
pp. 567-577 ◽  
Author(s):  
L. J. Baddeley ◽  
T. K. Yeoman ◽  
D. M. Wright ◽  
K. J. Trattner ◽  
B. J. Kellet
Keyword(s):  
Wave Energy ◽  
Low Frequency ◽  
Distribution Functions ◽  
Wave Number ◽  
Particle Interactions ◽  
Ion Distribution ◽  
M Wave ◽  
Ulf Wave ◽  
Energy Dissipated ◽  
Giant Pulsations

Abstract. Many theories state that Ultra Low Frequency (ULF) waves with a high azimuthal wave number (m) have their energy source in wave-particle interactions, yet this assumption has been rarely tested numerically and thus many questions still remain as to the waves' exact generation mechanism. For the first time, this paper investigates the cause and effect relationship between the driving magnetospheric particle populations and the ULF wave signatures as observed in the conjugate ionosphere by quantitatively examining the energy exchange that occurs. Firstly, a Monte Carlo method is used to demonstrate statistically that the particle populations observed during conjugate ionospheric high m wave events have more free energy available than populations extracted at random. Secondly, this paper quantifies the energy transferred on a case study basis, for two classes of high m waves, by examining magnetospheric Ion Distribution Functions, (IDFs) and directly comparing these with the calculated wave energy dissipated into the conjugate ionosphere. Estimates of the wave energy at the source and the sink are in excellent agreement, with both being of the order of 1010J for a typical high m wave. Ten times more energy (1011J) is transferred from the magnetospheric particle population and dissipated in the ionosphere when considering a subset of high m waves known as giant pulsations (Pgs). Previous work has demonstrated that 1010J is frequently available from non - Maxwellian IDFs at L=6, whereas 1011J is not. The combination of these studies thus provides an explanation for both the rarity of Pgs and the ubiquity of other high m waves in this region.

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