I know that a toroidal plasma current is an essential feature on tokamaks as it creates the poloidal magnetic field essential to avoid separation between negative and positive charges.

The current is created inducing a magnetic field with an increasing current applied to a central coil which in turn induces a current in the plasma.

My question is how to keep the current for long experiments (such as ITER project)? One can go from a minimum value on the central coil (even better maximum negative value) to a maximum value, but that is the limitation. What are the options there?


  • $\begingroup$ Hi Kyril. You are asking a question that researchers have been asking for 50+ years. I am not sure you will get many answers unless you greatly narrow it down. $\endgroup$ Jun 17 '21 at 12:50

This is indeed a big problem in modern tokamaks. It is known as current drive, as you need to have a plasma current in the toroidal direction and hence a poloidal field.

The current options, and what ITER will do, is a mix of:

  • Transformer: causing a $dI/dt$, it induces a current. Of course, the transformer at some point gets too expensive and physically impossible to operate since it cannot keep changing current ad infinitum.
  • Neutral beams: tangential injection in the torus, neutral beams also provide momentum to the plasma and current drive.
  • Electron cyclotron waves: to essentially still cause a tangential acceleration of the plasma.

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