This product if admitting that β is not constant daramaticaly differs from considering here product B^4 R^3.hanelyp wrote:P fusion ∝ β^2 B^4 R^3 (5)
As in any device β is a function of many parameters and varies from 0 to 1.
And when β=0 Pfusion=0 too.
For your reference poloidal β in TOKAMAK is rather high while toroidal field is applied there for improving stability.
And here I see the groundless statements of people about absolute plasma stability in the device as though they have as confinement object not plasma but solid state.
I would believe to those people including for example Dr. Nebel if they would say that as result of theoretical and experimental investigations the certain stability area has been found. And in that area β value from 0.6 to 0.8 can be achieved. As this and this types of instabilities can be damped with the help of this and this ways. And they (instabilities) have acceptable scale. But such an unconditional statement that a beta is equally to 1 in all range of operating conditions is lightly and very unworthy. As turbulence and instabilities even if they have not catastrophic scale are in existence in any plasma device.
Once I wrote here such an analogy.
Let's imagine swimming pool filled to the edges with absolutely quiet water. This is a plasma device with a beta equally to 1.
As soon as there in this pool will appear waves, water will start to overflow and volume taken by water in a quiet condition excluding the water overflow will be less than pool’s volume. And will be dependent on intensity of waves. And only that will be a real β value.