Method for use with superconducting devices
In many cases after degaussing the field distribution in a magnetic material there may be regions within the magnetic material that have ordered domains that contribute a remnant field. There is the need to reduce or eliminate non-uniform fields within a volume of interest left after degaussing a magnetic shield. Degaussing coils surrounding a metal shield can be used to favorably order magnetic domains within the material to counteract the remnant fields left behind following imperfect degaussing. The remnant field value can be measured and a small current may be applied through the degaussing coils. After removing the current, the field can be measured again and a higher current may be applied again through the coils. Repeated applications of currents and field measurement will progressively order domains in the direction of the applied field, resulting in a reduction of the net field and lower field gradient across the volume of interest.
1. A method, comprising:
causing a degaussing field to be applied to a first shield that provides a magnetic shielding to an environment;
determining an initial measurement of a magnetic field in at least one location in the magnetically shielded environment by a control circuit, the initial measurement representative of the magnetic field in the at least one location in the magnetically shielded environment following application of the degaussing field to the first shield;
after determining the initial measurement of the magnetic field in the at least one location in the magnetically shielded environment, iteratively from i=1 until at least one exit condition is reached,
causing a direct current of an i th amperage to pass through at least one electrically conductive coil located about the first shield during an i th period of time, where the i th amperage is greater than a previous amperage, if any;
after the direct current of the i th amperage passes through the at least one electrically conductive coil during the i th period of time, determining an i th measurement of the magnetic field in the at least one location in the magnetically shielded environment, the i th measurement representative of the magnetic field in the at least one location in the magnetically shielded environment following application of the direct current of the i th amperage and before application of the direct current of an i th +1 amperage, if any; and
determining whether the magnetic field in the at least one location in the magnetically shielded environment has reached a minimum, wherein the at least one exit condition corresponds to the determination that the magnetic field in the at least one location in the magnetically shielded environment has reached the minimum.
2. The method of claim 1 wherein determining whether the magnetic field in the at least one location in the magnetically shielded environment has reached the minimum includes determining whether a most current one of the measurements of the magnetic field in the at least one location in the magnetically shielded environment is larger than a previous one of the measurements of the magnetic field in the at least one location in the magnetically shielded environment.
3. The method of claim 1 wherein causing the direct current to pass through the at least one electrically conductive coil includes controlling operation of a current source.
4. The apparatus of method 1 wherein causing the direct current to pass through the at least one electrically conductive coil includes controlling a switch to electrically couple a current source to the at least one electrically conductive coil.
5. The method of claim 1 wherein causing theft degaussing field to be applied to the first shield that provides magnetic shielding to an environment includes causing the degaussing field to be applied to the first shield via the at least one electrically conductive coil.
6. The method of claim 1 , further comprising:
during each iteration, determining whether a maximum number of iterations has been reached, wherein the at least one exit condition corresponds to the determination that the maximum number of iterations has been reached.