## Mcf And Icf Fusion A Comparison

The plasma responsible for thrust in rockets based on mirror MCF is controlled by B fields, as mentioned in Section 8.9. At a B of the order of a few tesla, gyration radius may be of the order 1 cm, and overall plasma cross-section ("bottle" cross-sectional area) is determined by the mass flow-rate to obtain a certain thrust. In sizing an MCF fusion chamber the next question is, what is the length of the mirror "bottle". An accurate estimate involves much calculating and assuming, but a quick answer for estimating purposes only may be obtained by noticing that the length, L, of the bottle, or of the torus radius in the case of a tokamak, is, once more, ruled by the need to contain plasma for a time sufficiently long for fusion to start and self-sustain.

A simple kinematic criterion can therefore be derived to estimate L (for a much more detailed analysis of this problem see Appendix B). This criterion states that the average distance traveled by the average ion while fusing must be contained within the magnetic bottle size L (it must be shorter than L). Ion distance traveled is proportional to ion velocity, that scales with \/E, or \ff from Boltzmann, times the residence time in the bottle, t. To account for the shape of the ion trajectory (not rectilinear!) and that depends on the shape of the magnetic bottle, L is weighted with the ratio ^max > 1 between peak and mean B field inside the bottle. In essence, if t is the residence time of the fusing plasma, and if

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