Timeline for Particle acceleration at magnetized shocks by convective electric fields?
Current License: CC BY-SA 3.0
17 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jul 8, 2017 at 20:26 | vote | accept | honeste_vivere | ||
| Jul 8, 2017 at 20:25 | answer | added | honeste_vivere | timeline score: 0 | |
| Sep 22, 2014 at 16:51 | comment | added | Kyle Kanos | @honeste: Often in, shock acceleration, the ambient thermal velocity is smaller than the shock velocity so that you can approximate the velocity of the particle as small & simply use $\mathbf V_{sw}$ instead of $\mathbf V_{rel}$. | |
| Sep 22, 2014 at 16:00 | comment | added | honeste_vivere | @KyleKanos I think you point out the primary issue I have with the picture I outlined in my question. Namely, the idea of a frame-dependent electric field doing work on a particle bothers me. However, I should have realized (since I already know this) that energy is not a Lorentz invariant. Though I still think the electric field observed by the particle will be dependent upon the particle's velocity relative to the background field, not just $\mathbf{V}_{sw}$. I am now thinking that my comment regarding the bar magnet was wrong as well. | |
| Sep 22, 2014 at 14:03 | comment | added | Kyle Kanos | As long as the particle is moving at a different speed than the field, it will know the electric field is there. That's basically E&M theory of a charged particle moving in a stationary magnetic field (and probably an okay way of looking at this). Remember that it's the electric field that accelerates particles while the magnetic field changes the direction of the particle. | |
| Sep 22, 2014 at 13:40 | comment | added | honeste_vivere | @KyleKanos what if we had a uniform field and then we insert a charged particle? Would it know the field is moving as well? If so, how? I think I can follow the plasma part, as this would be the source moving. However, if the source is not local, it confuses me how a charged particle could know whether a homogeneous field was moving or not. | |
| Sep 21, 2014 at 15:57 | comment | added | Kyle Kanos | The electric & magnetic field is the field of the plasma, so a particle moving at velocity $v$ that suddenly reflects, $v\to-v$, sees the new electric field that is opposite in direction (effectively). Any charged particle in a magnetic field sees an electric field, the fact that $B$ is homogeneous shouldn't change this. | |
| Sep 21, 2014 at 14:51 | comment | added | honeste_vivere | P.S. The answer to my last question is no if the bar magnet has no imperfections and produces an ideal dipole magnetic field. Sources move, not the magnetic fields (which propagate at the speed of light)... So in the case I originally stated, even if it's like the field is moving upstream, its homogeneity makes it impossible for an observer to know this since nothing changes. So how would a particle know to drift in addition to gyration? | |
| Sep 21, 2014 at 14:48 | comment | added | honeste_vivere | @CuriousOne, my problem is largely about the idea of a magnetic field moving. The problem is specific to collisionless shocks, so yes it does relate to Fermi's original magnetic mirror idea. The issue I have is that if the upstream field is everywhere homogeneous, how can there be $\mathbf{E}$ = -$\mathbf{V}_{sw} \times \mathbf{B}_{o}$? This may seem like I am missing a trivial point, but if you were sitting at some radial distance away from a bar magnetic (at the center of the bar) in vacuum, could you tell it was rotating? [BTW, yes, I got your joke] | |
| Sep 21, 2014 at 2:31 | comment | added | CuriousOne | @KyleKanos: I can not see how the OPs problem with the scenario is related to Fermi acceleration, it seems more fundamental than that. That's not the same thing as not seeing the physics of the mechanism myself. Let's leave it at that, you are free to explain the lab frame joke to the OP, if you think the he didn't get it. | |
| Sep 21, 2014 at 2:23 | comment | added | Kyle Kanos | @CuriousOne: If you don't see how this is related to Fermi acceleration, than all I can say is you need to do some more reading on it. Magnetized shocks + collisions/reflections + particle acceleration should scream "Fermi acceleration" to everyone. | |
| Sep 21, 2014 at 2:21 | comment | added | CuriousOne | @KyleKanos: I don't see a question particularly related to Fermi acceleration here. The OP seems to have doubts about how to calculate the proper field components seen by particles. The setup for the moving magnetic field is IMHO identical to a moving magnet scenario. Why not simplify the physics before we get into the question of which frame this has to be analyzed in (which should lead to the conclusion that the physics is the same in all rest frames). | |
| Sep 21, 2014 at 2:17 | comment | added | Kyle Kanos | @honeste: Have you read Kirk's work on particle acceleration? He's got an excellent Saas-Fee lecture on it, plus some other papers with Duffy. There's also some work by Luke O'C Drury that is probably a good start. | |
| Sep 21, 2014 at 2:08 | comment | added | Kyle Kanos | @CuriousOne: This question is asking some of the basics about Fermi acceleration (often improperly called diffusive shock acceleration, which is really a subset of Fermi acceleration). Perhaps you could tone down your sarcasm? | |
| Sep 21, 2014 at 2:04 | comment | added | CuriousOne | Somehow this sounds like a Rube Goldberg version of the question why a moving magnet induces a current in a wire. Maybe you could draw a picture for clarification? What, by the way is a "lab frame"? Is that like the picture frame that somebody hung in one of my labs with a drawing of three arrows and a warning that this label is not to be removed by threat of the laws of nature? | |
| Sep 20, 2014 at 22:40 | history | edited | honeste_vivere | CC BY-SA 3.0 |
switched from using asterisks to \mathbf{} to represent boldface characters as vectors
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| Sep 20, 2014 at 22:32 | history | asked | honeste_vivere | CC BY-SA 3.0 |