[Fusion] Basic concept behind the Stellarator

[Meaning]

Hey

I am starting a course on plasma physics, I don't understand the principle of Stellarators.

If there is no plasma current, how is the mhd equilibrium achieved (J \times B = grad P)?

I apologize if the answer is obvious, but I starting with this

 

[artis]

@Meaning Well the answer is by no means obvious.

Well as far as I know they achieve the MHD equilibrium with the geometry of the field. That is why the stellarator looks like a weird twisted and warped ring. This is the reason why you need toroidal and poloidal(plasma induced current) and vertical balancing fields in a symmetrical torus like a tokamak, otherwise the plasma tends to expands outward , form islands of charge and eventually hit the walls.

 

[raining Pete]

topic and I am a bit confused.Hey there,

Don't worry, it's completely normal to feel confused when starting a new topic. I'll try my best to explain the principle of Stellarators and how mhd equilibrium is achieved without plasma current.

Stellarators are a type of fusion reactor that uses magnetic fields to confine and control plasma. The magnetic field in a Stellarator is created by a complex system of magnets that produce a twisting and turning effect on the plasma. This twisting and turning creates a helical path for the plasma to follow, which helps to confine it.

Now, onto the mhd equilibrium. MHD stands for magnetohydrodynamics, which is the study of the interaction between magnetic fields and electrically conducting fluids like plasma. In a Stellarator, the magnetic field is used to control the plasma and keep it in a stable state. This means that the plasma particles are not moving in a random manner, but rather in a controlled and stable way.

To achieve this equilibrium, the magnetic field must be carefully designed to balance the forces acting on the plasma. This includes the magnetic force (J x B) and the pressure gradient force (grad P). The pressure gradient force is the force that pushes the plasma particles in a certain direction, while the magnetic force acts perpendicular to this direction. By carefully adjusting the magnetic field, the two forces can be balanced, resulting in a stable mhd equilibrium.

So to answer your question, the mhd equilibrium is achieved in a Stellarator through the careful design of the magnetic field, which balances the pressure gradient force and the magnetic force. This equilibrium is necessary for the plasma to be stable and for the fusion reaction to occur.

I hope this helps clarify things for you. If you have any other questions, feel free to ask. Good luck with your course on plasma physics!