To show that this is so, we assume an average density to again give PO = 55.8 MW m-3 of raw power, independent of magnetic field for moderate variations of B. This is justified by the fact that the central density is limited by beam focusing accuracy and dominates the average density. The coil-generated magnetic wall feels only a modest effect of beam diamagnetism. The radius of the Exyder disc is as opposed to 2>p for the migma. There the relationship was fixed by diamagnetic effect; here it is set by focusing requirements. As before,/>=0.56/B and we take the volume of the disc to be The estimation of the magnet mass is somewhat more involved than before. The geometry is as shown in Fig. 7. The Exyder disc is centered in the z=0 plane. Using units where the Exyder radius P=l, we locate current filaments at (r, ^) = (1.28, 0.4) and (r, z) = (0.72, 0.4). If the current through the inner coil is /, we find that the current through the outer coil must be —1.37/ in order that Bz(0, 0) = zero. Next, we calculate the field at the periphery of the Exyder disc, B.(l, 0) and find [12] If we now invoke the same current density limits as before, we find for the dimensions of the square coils: inner coil = 22 cm square; outer coil = 26 cm square. The number of coil pairs required is N+ 1, where N is the number of Exyder discs needed to supply the power.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==