Shielding effect by the thin iron tube

Abstract

The reset of the self-correction current is performed by heating up a part of the self-correction coil and dumping the self-correction current to zero and then cool down again to make the superconducting state under the high multipole components free condition. If we perform the reset procedure of self-correction coil with higher multi-components not in free condition then these higher multi-components will be trapped by self-correction coils. From this point of view we must notice that after excitation of the main coil, even in the zero current in the mail coil, there exists a residual magnetic field due to the persistent current in the main coil superconducting wires. To get the higher multi-components free space in the coil, we insert a thin iron tube inside the main coil, outside the self-correction coil. At very low magnetic field, even if we use a thin soft iron tube, we will be able to get enough shielding effect. On the other hand, at very high magnetic field, the iron tube will saturate completely and its permeability ..mu.. decreases from about 4000 ..mu../sub 0/ to lower than 2 ..mu../sub 0/. This means the iron shielding tube becomes completely transparent against the magnetic flux atmore » high field. We discuss here the shielding effect of a thin iron tube in very low field and very high field, by a simple analytical calculation and saturation effects of a thin iron tube in medium magnetic field by the numerical calculation using the computer code POISSON.« less