Plasma performance is often expressed in terms of beta (β), defined as: [1]

i.e., the ratio of the plasma pressure to the magnetic pressure. Here, <p> is the mean plasma pressure, and B the mean total field strength. It is customary to introduce also the poloidal β (βp) and the toroidal β (βt), in which B is replaced by the poloidal and toroidal magnetic field component, respectively. One has:

Normalized beta

The normalized beta (or Troyon factor) is an operational parameter indicating how close the plasma is to reaching the Greenwald limit or destabilizing major MHD activity. Its definition is (for tokamaks): [2]

 

where B is in T, a in m, and Ip in MA. Typically, the maximum value of βN is 3.5, although higher values have been achieved.

References

  1. J.P. Freidberg, Plasma physics and fusion energy, Cambridge University Press (2007) ISBN 0521851076
  2. K. Miyamoto, Plasma Physics and Controlled Nuclear Fusion, Springer-Verlag (2005) ISBN 3540242171