Okay, I am getting too old for this stuff, so let's start at the very beginning, a very good place to start.
Sol88's question if there are Electric currents in the solar wind?
That is an easy way to answer, in general space physics, and it is of course: YES.
The solar wind is a magnetoplasma and it would be absurd to think there are no currents in a magnetoplasma. HOWEVER, in Sol88's case we have to tread carefully, because of the background of this question, the EU claims that the Sun is electrically driven.
So, start at the beginning, what is a current? It is the flow of charged particles, which is defined as:
Name: Eq. 1.jpg Views: 51 Size: 1.1 KB
where subscript k stands for all species in the plasma (ions, electrons), n is the density, q the charge and v the velocity. So if, as measured, the solar wind is quasi-neutral and, as measured, all particles move at the same velocity, then it is easy to see that you get J = 0. The bulk flow of the solar wind does NOT constitute a current.
Next step is to look at the magnetic field that is flowing along with the solar wind. This comes from the Sun and at far distances the dipole component is of course dominant. The rotation of the Sun makes that the magnetic field is wound-up in a spiral form, often termed as the "bashfull ballerina.
The interplanetary magnetic field eiter points towards or away from the Sun, but as magnetic field lines are closed, they are loops. Just like in the Earth's magnetotail, the field goes in one direction at one side of the "equator! and in the other direction at the other side. As we all (maybe) know, oppositely directed magnetic fields create a current:
Name: Eq. 2.jpg Views: 52 Size: 986 Bytes
This creates the heliospheric current sheet:
http://www.internationalskeptics.com...d28c39dc4f.jpg
The current flows perpendicular to the magnetic field. Because of the spiral shape of the magnetic field, this perpendicular current has a radial component, see Israelevich et al. (2001). Their simulations estimate the total current to be I ~ 109 A. So this is, indeed, a global current flowing, because of the solar magnetic field and rotation. Note that there is no way that this current can power the Sun. But still, this is the only large scale flowing in what one could call a solar current circuit.
Then, of course there are other currents. The exploding promenences on the Sun, sending out coronal mass ejections, in the shape of flux tubes propagating fast through the slower solar wind (see e.g. Weiss et al. (2021). The rotation of the field inside has a current, and there are various other processes that can drive current sheets around the CME. Of course, with CMEs being only impulsive events, they cannot power the Sun.
The solar wind is turbulent, so the nice Parker spiral is only observed when you take a long-time average. This means that on small scales there will be all kinds of structures which can drive current sheets. I guess a good paper on the variety of current sheets is by Stefan Erkisson et al. (2022). We are getting here to smaller and smaller scales. Going to even smaller scales, there is a study by Khabarova et al. (2022) discussing the difference between electron and ion bulk velocity in small current sheets. But at this scale this has nothing more to do with powering the Sun, but still interesting what one can do with the excellent instruments of the MMS mission.
So, just a few words about the dos and donts of MHD. It was Hannes Alfvén's great idea that one could "simplify" plasma physics if one looks at large systems and long times (where large and long need to be defined). What are the characteristic scales in a plasma? That would be the gyro radius and the gyro period. Alfvén saw that if you look at scales much larger than the largest gyro radius and at times much longer than the gyro period, the individual motion of the particles does no longer matter and you arrive at a fluid in which the bulk motions are important only. So the kinetic equations are averaged over these scales and you end up with a hydrodynamic descriptino, and as there is also a magnetic field we can now work with MagnetoHydroDynamics (MHD).
Now, Alfvén complained about MHD during his Nobel prize lecture. The problem was that, with a new tool, everybody started using it willy-nilly, without checking whether the restrictions of MHD applied to the situation or not. So, in the beginning there was some junk published because of mis-application. Nowadays, plasma physics students get it hammered in that there are limitations to MDH.
But then, what to do when smaller scales get important? Well, in data analysis you have "all" the information (especially with MMS) and you just work with the data, then there is no discussion "is this MHD or not". You just see the relationships between N, B, E, v, etc. The picture is there.
But in numerical codes it becomes more difficult. I can make a grid for an MHD model, but if I zoom in then the motion of the ions becomes important. Then we get to hybrid codes, where the large scale is modeled by MHD, but in the areas (e.g. around a cometary nucleus) where the motion of the ions becomes important the kinetic equations are solved, which is done with Paricle In Cell (PIC) codes. And if you go even deeper at e.g. reconnection, you will have another scale for the electrons, where they have to be modeled kinetically.
Why not do it all the kinetic way? A simple answer: MONEY and TIME. Kinetic codes are very time expensive even on huge super computers.
Well, I guess this post is long enough, this old guy is signing off, So Long, Farewell, Auf Wiedersehen, Goodbye
Summarizing, we report important properties of CSs formed in the turbulent solar wind that are associated with electrons becoming the main current carriers.