The low-field diamagnetism of superconductors has often been used to design quasi-ideal magnetic circuits, especially for traveling wave maser (TWM) magnets. An analogical approach to the calculation of the efficiency of such nonideal cylindrical superconducting shields is presented. In most cases, the problem reduces to a 2-dimensional Laplace equation with given boundary conditions. The logarithmic complex potential \log (Bx - iBy) has been used to obtain the field homogeneity and disorientation. Partially penetrated shields may be replaced by perfect equivalent ones. The analog measurements on conducting paper permit quick iterations of the solution. Various field component measurements have been done on TWM magnets using bismuth thin film Hall probes and found to be in good agreement with the analog measurements.

Contribution to the use of superconducting shields for magnetic field shaping

Dans la premiere partie de cet article, les auteurs passent en revue les differents types d’aimants realises depuis 1962,en comparant leurs avantages relatifs selon le type du maser (a cavite, a onde progressive) et la valeur du champ necessaire. Ils indiquent aussi les methodes de calcul utilisables pour ces aimants et les particularites dues a l’emploi des supraconducteurs. La deuxieme partie est consacree a la description d’un aimant mis en fonctionnement a la station spatiale de Pleumeur-Bodou, utilisant des blindages supraconducteurs et a la verification, sur ce type d’aimant, de methodes de calcul de l’efficacite de tels blindages, dont l’utilisation pourra completer utilement celle des ferromagnetiques pour la mise en forme ou « l’ecranage » de champs magnetiques.

Calcul et réalisation d’aimants supraconducteurs pour masers

A superconducting magnet has been developed to supply the magnetic field necessary to operate a 4 Gc traveling wave ruby maser. The field required by the maser is about 3000 oersteds uniform throughout the volume of the ruby to one part in a thousand. The field is directed across a gap of about 0.8 inches whose cross section is 5 inches by 0.5 inches. A close approach to the ideal magnetic circuit has been achieved by placing superconducting shields adjacent to the pole pieces. Circulating currents are set up in the shields which prevent the existence of leakage and fringing flux. Since there is no loss mechanism in the shields, the currents persist and the air-gap field remains everywhere uniform. With the absence of leakage and fringing flux, the size and weight of the magnetic circuit is considerably reduced. Superconducting coils allow the use of a persistent current to generate the field. A heater element encased in a glass sleeve is used to initiate the persistent current. The switching procedure is simple and involves no moving parts in the cryostat.

http://ieeexplore.ieee.org/iel5/9928/31583/01473371.pdf

M.D. Bonfeld

Papers

Superconducting magnet for a traveling wave maser