A reviewer raised that the burner's central field and 17 T throat implied a modest mirror ratio and a large confinement penalty. Checked directly, the penalty is 1.21x, not the 3.3x the simple heuristic suggested — and the two concerns do not compound.
The relevant mirror ratio is not throat field over central field; at beta 0.55 the pressure dilation raises the effective ratio to 5.89, nearly 50% above the vacuum value. And Pastukhov confinement enters through a logarithmic function of that ratio, so sweeping the throat field from 12 to 30 T moves confinement time only from 1.99 s to 2.42 s. The penalty is 1.21x.
Working the concern all the way through — rather than waving it off or conceding it — is the method. Confinement in this device is set by the plug density ratio through an exponential, which is exactly why the mirror ratio does not dominate and the penalties do not stack.
| Feared penalty | 3.3x (heuristic) |
| Actual penalty | 1.21x (computed) |
| Effective mirror ratio R_mc | 5.89 (beta-dilated) |
| Confinement sweep | 1.99-2.42 s over 12-30 T |
| Dominant parameter | plug density ratio (exponential) |