Questions tagged [plasma-physics]
Theory, lab and space experiments, and calculations related the physics of plasmas, i.e., matter constituted by ionized atoms.
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Is there a limit on the magnetic field in a Hall generator?
In a Hall generator, charge accumulation on electrodes occurs because there is a generated current, $\bf{J}$, in a magnetic field, $\bf{B}$. This results in charge separation due to a Hall current ...
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1answer
19 views
What is the solar wind speed as function of distance from the Sun?
Someone must have calculated at least a "zero-order approximation" of the behavior of solar wind speed, density, and pressure as a function of distance from the Sun, but the heck if I can find it. ...
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4answers
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What determines the colour of the light emissions in a Tokamak?
We see images of Tokamak plasma with all sorts of colours from red to purple. Why do we see any light at all, since the plasma should be so hot to have dissociated all its electrons? It is all from ...
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Do radio beams self-focus in the interstellar medium?
Summary: In a plasma, electromagnetic waves create a ponderomotive force that pushes electrons and ions out of the way. Thus, in an intense laser beam, electrons tends to move away from the areas ...
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1answer
19 views
Linearization of MHD equations for a cold plasma and low frequencies
I'm trying to convert the next equations for a cold plasma (consider $P=0$ the pressure), for low frequencies and ignoring dissipative effects:
$$\rho \left(\left(\frac{\partial \vec{v} }{\partial t}\...
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16 views
Would it be possible to build a wakefield particle accelerator in space
I have read that plasma wake accelerators use metal plasma (lithium)
to transfer the energy from a laser pulse to a group of charged particles travelling behind the laser pulse and giving about 10 GeV/...
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1answer
26 views
Physical significance of growth rate in plasma
Let us say that we have a dispersion relation curve and associated instability curve as shown below for a magnetised plasma, which have been formulated through kinetic theory. The frequencies and ...
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2answers
66 views
Extreme high voltage path of least resistance changes?
In this video, there is an extremely high voltage being sent through a blank breadboard. The arcs go through different, seemingly random new paths. What causes this? How could you determine what the ...
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1answer
16 views
How can there be an electric field normal to the surface in a surface plasmon in a metal
Ashcroft and Mermin's Solid State Physics, chapter one, has an exercise about surface plasmons. They give the electric field normal to the surface of the metal as $E_z=Be^{iqx}e^{-Kz}$ How can this be?...
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1answer
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Plasma and helicon wave frequencies in iron according to Drude model
The first chapter of Ashcroft and Mermin's Solid State Physics discusses electromagnetic waves in metals. One of the exercises requires calculation of the plasma and helicon frequenies using the Drude ...
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2answers
34 views
How does the energy of a solar flare propagate?
Does it radiate outward, spherically, or is it more directed? Is there some opening angle? Is it more complex than this?
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Is exercise 4, part b of chapter one of Ashcroft and Mermin wrong?
This is from Solid State Physics. It is about helicon waves in a metal.
When I take the curl of the given electric field it does not equal zero even though the magnetic field is static. Is this an ...
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Converting Discharge Voltage to Temperature? Hall Effect Thruster Calculation
Trying to follow a Hall Effect Thruster design process given in this video:
Hall Effect Thruster Design Video
In 25:59, there's a calculation in which the presenter takes discharge voltage and ...
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0answers
20 views
What is the electrical resistivity of air during breakdown?
There is a well-documented theory for breakdown voltage vs pressure in the form of Paschen's law.
But what is the trend of the electrical resistivity of air as a function of the electric field ...
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1answer
43 views
Energy Equation of an ideal gas in expanding space-time
Short question:
If the energy equation of an ideal plasma is written as follows:
$\begin{equation}
\frac{\mathrm{d}p}{\mathrm{d}t}=-\Gamma p\nabla\cdot v-\left(\Gamma-1\right)\left( \nabla\cdot q-\...
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2answers
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Can some one tell me what can detect the accurate gas electric conductivity? [duplicate]
Can someone tell me how and what kind of gas could conduct electricity and what instrument could detect it?
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Why does E-field decay in direction perpendicular to surface plasmons?
Ref: Surface Plasmons on Smooth and Rough Surfaces and on Gratings
(by Heinz Raether), page 4
The setup described here is essentially depicted above.
The field is described by $E=E_0^{\pm}exp[+i(...
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1answer
61 views
Significance of the ion Hall parameter
For an ionized Helium gas, for example, MHD Hall generators rely on the mobility ratios between electrons and ions to function and produce a Hall current. As far as I can tell, intuitively, increasing ...
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1answer
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How to derive Walen's equation? [closed]
This is perhaps a simple math problem, therefore no books ever given detail calculation. Could someone help to give a proof?
We have continuity eqution as
$\frac{\partial\rho}{\partial t} = -\rho\...
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3answers
113 views
Is it possible to have a liquid plasma?
Plasmas are generally thought of an ionized gases, which are conductive and can respond to electric and magnetic fields. However, I was just wondering if it is possible (in theory or in practice) to ...
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0answers
29 views
Examples of perturbative force-free electrodynamics on top of vacuum solutions?
Imagine I have a solution $A_{(0)\mu }$ for the four-vector potential of vacuum electrodynamics. That is, the solution fulfills source-free Maxwell equations $F^{\mu\nu}_{(0)\;\;;\nu} = 0$ with $F_{(0)...
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2answers
62 views
How is fusion reactor fuel initially accelerated?
If, in a nuclear fusion tokamak reactor, you start with neutral fuels, how do you accelerate the atoms fast enough to start the reactor?
Or do all of the particles have to ionized to begin with?
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Angular momentum with magnetic field
I was computing the Lagrangian of an electron in the presence of a constant and uniaxial magnetic field. Indeed it comes out that,
$$ p_r = m \dot{r} $$
$$ p_\theta = m r(\dot{\theta}-\omega_c/2)$$
...
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1answer
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If a mix of elements in a plasma are frozen rapidly, does the crystalline structure of the frozen material reflect the plasma phase?
If you have a mix of elements in a plasma, with ions flying around freely, and you freeze it, would you see reflections of that plasma phase in the crystalline structure of the frozen material? Plasma ...
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1answer
26 views
Ideal MHD stability with a Fourier analyzed perturbation
I'm learning through the basics of ideal MHD instabilities and the textbook (Friedberg, Plasma Physics and Fusion Energy, 12.4-12.6) writes the linearized momentum equation in terms of the ...
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When can we say $x$ and $p$ are “independent variable”, in order to find the Vlasov equation?
I have a question about "independent variable" in physics, and especially variable in Lagrangian or Density Function. I read several questions about it in this forum and although I have the feeling I ...
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54 views
Van de Graaff generator with glass of water on top
I watched a video of Van de Graaff generator with a plastic bottle on top and lightning type sparks being produced in the bottle and was wondering if the same thing would occur if a person used a ...
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1answer
30 views
Electron distribution in Low Earth Orbit
I have been searching online for some kind of pdf function that describes the charged electron distribution in Low Earth Orbit in regards to their energies. Any ideas on whether something like that ...
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1answer
50 views
Application of Darboux's theorem to magnetic field line flows
In this famous paper by Cary and Littlejohn on noncanonical Hamiltonian mechanics and its application to magnetic field line flow, they claim that as a result of Darboux's theorem, it is always ...
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1answer
67 views
What is a quasi-axisymmetric stellarator?
I know that a tokamak is a donut shape fusion confinement device with an axisymmetric magnetic field configuration. The stellarator is similar but its field configuration is non-axisymmetric.
I've ...
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0answers
20 views
Measure or estimate temperature of plasma?
How would one measure or estimate the temperature of the plasma in the film below? It's a still from a YouTube film. Let's say the gas is hydrogen or deuterium, instead of Argon. How would one know ...
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1answer
46 views
RF-sputtering: where comes the target self-bias voltage from?
While learning for an exam, I stumbled over the following Question:
According to Material Science of thin Films by Milton Ohring,
"RF sputtering essentially works
because the target self-biases ...
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1answer
30 views
Quantifying electrical energy stored in a plasma
The energy stored in the electric field in a medium is given by $U = \frac{1}{2} \epsilon E^2$, where $\epsilon$ is the permittivity in the medium and $E$ is the electric field. When considering a ...
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2answers
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Colors of the Aurora
I've seen several web pages that attempt to explain the colours of the aurora but they seem to gloss over or leave out certain details, so I'm still confused. For example, this page explains it in ...
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0answers
35 views
Books about quantum effects in plasmas?
Does anybody have any tips on books or web-pages about quantum effects in plasmas?
I found section (pp. 17-19) of Introduction to Plasma Physics: With Space and Laboratory Applications by D. A. ...
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1answer
50 views
Difference between speed of sound into a star
I try to understand the following graphics with x-axis being the radius of a typical star :
I would like to knwo if $\delta c/c$ represents the relative error between theorical and experimental ...
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0answers
18 views
Looking for the paper plasma equilibrium in a magnetic field by V. D. Shafranov (1966)
Does anyone know where I can find the classical paper:
V. D. Shafranov, “Plasma Equilibrium in a Magnetic Field,” Reviews of Plasma Physics, Vol. 2, 1966, p. 103.
I can't seem to find it online ...
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What is the Relative Radiation Absorbtion per unit Mass of the various states of matter?
I am trying to find information on the relative merits of using a gas, liquid, solid or even a plasma as a radiation shield.
Examples
Ice, water and water vapour.
Iron, molten Iron, Iron ...
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1answer
31 views
How do poloidal and toroidal field lines become single helical lines?
In a tokamak, there are toroidal and poloidal fields created by separate sources. The resultant picture typically visualized are helical field lines in the tokamak. I am simply wondering: is this a ...
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Does the stretch twist fold dynamo reconnect at any point?
At the end of the folding of the magnetic field lines, it appears as though two loops are stacked above one another to increase the total magnetic flux. But are these two loops themselves connected at ...
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1answer
37 views
In what cases should plasmas be considered compressible?
I was listening to a lecture where it was mentioned incompressibility was assumed during derivation of an electrostatic instability, but incompressibility was not assumed for an electromagnetic ...
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1answer
34 views
Using superconducting coils as a transformer
In experiments such as tokamaks, typically an ohmic transformer (primary) is used to produce current in the plasma (secondary) by swinging from to the most positive to negative magnetic field. Ideally ...
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0answers
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Is magnetic reconnection possible in vacuum?
Magnetic reconnection occurs due to flux-breaking behaviour (e.g. finite resistivity) in a medium. But can reconnection be observed in a vacuum (where there may be virtual particles)? Has this been ...
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0answers
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Can inductance be dependent on direction in plasmas?
Inductance is given by the ratio of magnetic flux to the current. For a given plasma at a particular density and temperature (which itself could be a tensor), one may define $$L = {\Phi(i) \over i},$$
...
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1answer
47 views
How to handle electron-electron or proton-proton repulsion in Cosmology?
In Scott Dodleson's book, he considers that baryons are all tightly coupled. I know this can be proved by calculating the interaction time scales and comparing with Hubble's Expansion time scale.
...
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0answers
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What is the voltage requirement for glow discharge of a hollow cathode?
I'm trying to build a remote plasma source for a dusty plasma experiment. The key thing this needs to do is operate at 1 millitorr Argon gas. To keep it simple, I'm just putting a glass tube on the ...
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1answer
91 views
Plane waves in plasmas
Waves in plasmas can be classified as electromagnetic or electrostatic according to whether or not there is an oscillating magnetic field. A corresponding wiki article states:
Applying Faraday's ...
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1answer
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Are both ions and electrons assumed to be moving in plasma currents?
In a tokamak plasma, for example, an ohmic transformer is used to inductively drive current. In this scenario, is it simply assumed that the electrons are mobile and driving all the current in a ...
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What determines direction of plasma current in tokamaks?
Plasma current is used to ohmically heat fusion plasmas and provide stabilization of grad-B drift in tokamaks as the resulting poloidal motion of the charged particles results in the particles ...
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0answers
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Speed of sound in non-conformal strongly coupled plasma?
For a conformal system in (d+1)-dimensions, the speed of sound is given by $ v_{s} = 1/\sqrt{d}$ (for ex : $\mathcal{N}=4$ SYM in four dimensions). Is it possible to have a non-conformal strongly ...
