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Questions tagged [plasma-physics]

Theory, lab and space experiments, and calculations related the physics of plasmas, i.e., matter constituted by ionized atoms.

199 questions with no upvoted or accepted answers
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Who invented the term “Coulomb logarithm”?

Who is the author of the term "Coulomb logarithm"? In fact, Coulomb logarithm was computed by Langmuir in his paper of 1928 where the term "plasma" was introduced into physics, but the term "Coulomb ...
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89 views

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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2answers
549 views

The behavior of an ionized gas in an electric field

Say, I have a gas and then I ionize it (provide enough energy for the electrons to escape the nucleus' potential).And there exists, a SLIGHTLY positively charged surface beside the gas. Now, will the ...
5
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1answer
173 views

How to classifies the distinct “plasma” phases of matter?

How to classifies the distinct "plasma" phases of matter? and What theory classifies the distinct "plasma" phases of matter? According to Wikipedia: Plasma (from Greek πλάσμα, "anything ...
5
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1answer
173 views

Special conditions at layer F2 ionosphere

I saw this graph about the electrons density in different altitudes and difference between night and day, the difference between the 2 electron densities (day and night) decreases till 300 Km (F2 ...
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293 views

Magnetic flux ropes - are they stable for topological reasons like fluxon/Abrikosov vortex?

In images of sun's corona there are clear bright lines - nearly 1D stable structures interpreted as magnetic flux ropes, often suggested to have a topological nature e.g. (source): They have some ...
4
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382 views

Don't we know how the magnetic field of the Sun is created?

This is how Wikipedia explains stellar magnetic fields: Stellar magnetic fields, according to solar dynamo theory, are caused within the convective zone of the star. The convective circulation of ...
4
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2answers
129 views

How does the Earth's magnetic field protect it from the solar wind?

Several sources (see linked questions at the end) say that earth's magnetic field shields us from the solar wind. The general consensus is that without earth's magnetic field, the atmosphere would be ...
3
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53 views

Debye screening in $\mathbb{R^d}$

Consider the Poisson-Boltzmann equation $$ \nabla^2 V(r) = -\frac{1}{\epsilon_0}en\left(1 - e^{e V(r)/k_BT}\right) $$ which models the electrostatic potential in a spherically symmetric ideal gas of ...
3
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1answer
127 views

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 ...
3
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1answer
138 views

Is a dipole fusion reactor feasible?

It is well known that the earth's dipole-like magnetic field is able to confine charged particles to paths that spiral along the field lines. That's why we have auroras and the Van Allen radiation ...
3
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1answer
154 views

Does a homemade evacuated tube produce X rays?

Recently, I've bought a tiny USB powered spark gap bipolar Tesla coil (rated at 15 mA and (35-50)kV). I am a pretty interested in spectroscopy, so I played around with the tesla coil and a couple of ...
3
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252 views

Ion charge exchange mean free path

I am using the following equation to calculate the mean free path between a deuteron ion and background gas: $$\lambda_{d-gas} = \frac{kT_{gas}}{p_{gas} \, \sigma_{10}}$$ Where $\sigma_{10}$ is the ...
3
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301 views

Simulation of plasma in tokamak

I am reading some papers on numerical algorithms for simulation of plasma in the context of nuclear fusion in a tokamak. I am getting a little lost as there is a huge number of references, and it is ...
3
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0answers
95 views

Estimating temperature with Boltzmann relation with split emission lines

I'm trying to estimate the temperature of a plasma through the use of hydrogen lines, $H_{\alpha}$ and $H_{\beta}$ using the Boltzmann relation: $$ \frac{ n_{2} }{ n_{1} } = \frac{ g_{2} }{ g_{1} }e^...
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554 views

What is the effective electron mass in a plasma?

Is there a way to calculate the effective electron mass in plasmas? Effective electron mass is usually defined as varying from the vacuum electron mass in solid state physics. However, momentum ...
3
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1answer
252 views

How much of the Solar convection zone is completely ionized?

I was reading about the energy transportation in stars here, and I found this: "The outer portion of solar mass stars is cool enough that hydrogen is neutral and thus opaque to ultraviolet photons, so ...
3
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50 views

Why are low m,n modes more dominant?

Consider an axially symmetric, toroidal, magnetized plasma with some safety factor (q) profile. A flux surface has q=m/n where m is the number of toroidal transits and n is the number of poloidal ...
3
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110 views

Why do rings form on microwaved CD/DVDs?

Here's a microwaved CD. As you can see, the disc has been destroyed, but there are very clear circular rings bridged with lines. Why are rings formed when microwaving discs?
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40 views

Why do the high curvature bends in CFLs have their phosphor coating erode?

I have this pretty old compact fluorescent (CFL) bulb from several years ago still going strong. There was a period where the bulb sat unused when I moved away from home and put the lamp in storage. I'...
3
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1answer
196 views

Spectrum of discharge of air

Where do the various colors in electrical discharge of air with a high voltage originate from? Are these transitions in ionized nitrogen gas or unionized gas? Are chemical reactions involved? I assume ...
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0answers
17 views

Simplified laser wakefield accelerator model

so I am working on a summer essay and trying to work my way through the following online material I found; https://www.cockcroft.ac.uk/wp-content/uploads/2018/04/LWFA_comp.pdf. However, there are ...
2
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1answer
82 views

What Debye length should be used in plasma?

In short Which expression should be used: (1) or (2)? At length Definition of the Debye length $r_D$ is following: $$r_D=\left( \sum_{j}\frac{4\pi q_j^2 n_j}{kT_j} \right)^{-\frac{1}{2}}$$ It is ...
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51 views

Are / Why are the H II regions positively charged?

One of the questions in our recent astrophysics course homework was to find the general opacity $\kappa$ of H II regions. We know that the H II regions are almost entirely ionized hydrogen and I ...
2
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35 views

What are the prerequisites for a free electron and an atom/ion to recombine?

I'm mostly interested about recombination not in plasma (e.g., recombination of beta particles with atoms that they pass by), although the rules are probably the same. Say, there's a free electron ...
2
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51 views

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 ...
2
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1answer
50 views

Are microwave-generating devices (gyrotrons) in the ITER system phased to heat plasma?

Provided electricity from grid is converted and supplies 24 gyrotrons, which generate electromagnetic waves, which in turn, will transfer their energy to the electrons of the ITER plasma to heat it up....
2
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1answer
86 views

What is an active region in sun's photosphere? Why sometimes there is an active region but no sunspots?

What is the theory behind an active region? If we check data in solar monitors, there are some cases where there is no sunspot but there is still an active region. Why is that the case?
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42 views

What is the optimum altitude for tapping atmospheric charge?

The atmosphere appears to have a large potential difference (voltage) in relation to ground. The obvious example is the thunder where this voltage becomes large enough to break the insulator - air. Of ...
2
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0answers
89 views

In a plasma, can the ion temperature become larger than the electron temperature?

Let's assume a hydrogen gas, initially at low temperature The density is low enough so that heating of this gas by inverse bremsstrahlung can be neglected. Now if a high-intensity radiation source ...
2
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1answer
201 views

Joule heating for a fluid

Say you have a conductive liquid with a changing magnetic field going right through it, causing an electric current. How exactly does the electric current travel and how could you calculate the ...
2
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0answers
137 views

Will it be easier to separate a low or high density plasma into negative electrons and positive ions

I know separating plasmas into positive ions and negative particles requires energy. Now, I was wondering whether it would be easy to separate a low or high density plasma. The first thing I thought ...
2
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277 views

Deriving coupled equations of motion using optical master equation for atom-plasmon system

I am learning the interaction between surface plasmons (which are bosons that act much like photons) and atoms. I came across the following scenario describing the interaction between a two level ...
2
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115 views

What are the pragmatic solutions to point charge self-force/self-energy in relativistic simulations?

(I'm considering classical relativistic mechanics and classical electrodynamics throughout this post.) Usually, you calculate the motion of charges due to an external electromagnetic field, or you ...
2
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0answers
1k views

Limitations of the ideal gas law: When does it fail?

Motivation I ask this question precisely because I am looking for a fundamental, quantitative explanation of the limitations of the ideal gas law and when it should not be used. Note, I have found ...
2
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0answers
212 views

Does the motion of a free electron in a plane wave electromagnetic field have analytical solutions?

Does the motion $[x(t), y(t), z(t)]$ of a free electron in plane wave electromagnetic field have analytical solution (oscillating E and B fields)? The Lorentz force is : \begin{align}m_e\begin{...
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0answers
106 views

Ionospheric electron density measurements

I've been working on measuring total electron column density (TEC) with multi frequency GPS data. In theory, signal delay caused by TEC differences should affect the code and carrier nearly evenly in ...
2
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0answers
56 views

Schwinger metals?

Consider an electromagnetic field that does reach values above the Schwinger limit inside a region of space $R$, on each oscillation. Once the field exceeds the Schwinger intensity, the field causes ...
2
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0answers
113 views

Pair correlation function of the QHE “plasma”

I am trying to teach myself the theory of quantum Hall effect, and realized that I can not reproduce a basic textbook result. Let me closely follow Girvin's Les Houches lectures (http://arxiv.org/abs/...
2
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1answer
115 views

Induction equation in a rotating frame

In his book, Tom Cravens refers to the induction equation (perfectly conducting limit) in a rotating frame, the Sun. See link below: https://books.google.com/books?id=xw50iZep-McC&pg=PA222&...
2
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0answers
113 views

Geometry of magnetic field lines in plasmas/MHD

So I'm trying to gain an intuitive grasp of plasmas and magnetohydrodynamics. There's a couple of questions I have. What does it means magnetic field lines are frozen into "plasmas"? Is it that ...
2
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1answer
358 views

Polarization of a transverse wave travelling in ionosphere with polarization direction perpendicular to earths magnetic field

Assume a transverse electromagnetic wave entering ionosphere such that its electric field is perpendicular to Earth's magnetic field. Now, I read that as it will enter plasma, the wave will tend to be ...
2
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0answers
106 views

After quantization of electron vibrations, do we need electrons anyway?

The title question is not ment in a general context, but one in which goes to the plasmon theory. In that case, how is are the statistics (boson vs. fermions) of plasmons determined? And is there an ...
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34 views

Why do tokamaks have so few toroidal field magnets?

From the ITER webpage itself, the tokamak has only eighteen toroidal field magnets. If the magnetic field is directly and linearly dependant on the number of coils around the torus, then why did the ...
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0answers
37 views

Plasma Maintenance

What are energy efficient ways that can be used to keep a plasma in its fully ionized mode while minimizing losses due to recombination? Let’s say I have 1 mole of some material, and I need 15eV to ...
1
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1answer
31 views

Why does the ion and electron currents saturate in Langmuir probes?

From the I-V characteristics of the Langmuir probes used in Plasma diagnostics, we can calculate the plasma density, temperature, etc from the ion and electron saturation currents. But why does the ...
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11 views

Does anyone knows where can I find the phase diagram of oxygen free copper (OFC or OFHC)?

I am having problems with a niobium deposition I made on a substrate. I increased the temperature to 500 degrees celsius and in theory the film should have a better quality. However this wasn't the ...
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0answers
32 views

Discrepancy when using Saha equation?

I was trying to calculate the level of ionization using Saha eq. for hydrogen gas at 1 atm pressure at 10 000 K and upwards. I used an Excel spreadsheet and the values I get don't match with other ...
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0answers
21 views

Question about spatial uniformity of particle density in plasmas (from Bellan)

Early in Bellan he asks us to consider a finite-temperature plasma and assume that the ion and electron densities are initially equal and spatially uniform. He approaches the problem of calculating ...
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2answers
26 views

Problem while constructing langmuir probe

I am working on DC glow discharges and want to construct a langmuir probe. Circuit I am using is as shown in the picture Also, I am applying ~1KV across cathode and anode. Problem I am facing is that ...