Magnetic Field Control
An assembly for generating a superconducting magnetic field with high stability comprises a main power supply unit arranged to provide a main current to generate a superconducting magnetic field, a magnetic field measurement device for measuring the generated magnetic field, and an auxiliary power supply unit arranged to output an auxiliary current based on the measured magnetic field.
1 . An assembly for generating a superconducting magnetic field comprising a main power supply unit arranged to provide a main current to generate a superconducting magnetic field, a magnetic field measurement device for measuring the generated magnetic field, and an auxiliary power supply unit arranged to output an auxiliary current based on the measured magnetic field.
2 . An assembly according to claim 1 wherein the main power supply unit is connected in parallel with the auxiliary power supply unit.
3 . An assembly according to claim 1 wherein the magnetic field measurement device produces an error signal based on the measured magnetic field value and a predetermined magnetic field value.
4 . An assembly according to claim 3 wherein the error signal is proportional to the difference between the measured magnetic field value and the predetermined magnetic field value.
5 . An assembly according to claim 1 wherein the field measurement device comprises a nuclear magnetic resonance probe and a detection circuit.
6 . An assembly according to claim 1 wherein the field measurement device comprises a pick up coil which produces an error signal, dependent upon the rate of change of the magnetic field, indicating the difference between the measured magnetic field and a predetermined magnetic field value.
7 . An assembly according to claim 1 wherein the field measurement device is a Hall effect sensor, GMR sensor, or SQUID sensor.
8 . An assembly according to claim 1 wherein the error signal is conditioned by a PID function before it is input to the auxiliary power supply unit.
9 . An assembly according to claim 1 wherein the auxiliary power supply unit has a maximum output current of about +/−0.01 to about 1% of the output current of the main current unit.
10 .- 11 . (canceled)
12 . An assembly according to claim 1 wherein the auxiliary power supply unit has a stability of better than 25 PPM (parts per million) per hour of its maximum output current.
13 .- 14 . (canceled)
15 . An assembly according to claim 1 wherein the superconducting magnetic circuit comprises a high temperature superconductor coil.
16 . (canceled)
17 . An assembly according to claim 1 wherein the assembly further comprises a DC current transducer to control the main power supply unit.
18 . A method for generating a superconducting magnetic field comprising the following steps:
providing a mains current to a superconducting magnetic circuit to generate a magnetic field,
measuring the generated magnetic field,
providing an auxiliary current to the superconducting magnetic circuit based on the measured magnetic field value.
19 . A method according to claim 18 wherein the main power supply unit is connected in parallel with the auxiliary power supply unit.
20 . A method according to claim 19 including measuring the generated magnetic field and producing an error signal based on the measured magnetic field value and a predetermined magnetic field value.
21 . A method according to claim 19 including measuring the generated magnetic field and producing an error signal based on the measured magnetic field value and a predetermined magnetic field value proportional to the difference between the measured magnetic field value and the predetermined magnetic field value.
22 .- 24 . (canceled)
25 . A method according to claim 19 including conditioning the error signal is by a PID function before providing an auxiliary current to the superconducting magnetic circuit based.
26 .- 31 . (canceled)
32 . A method according to claim 19 wherein the superconducting magnetic circuit comprises a high temperature superconductor coil.
33 . (canceled)
34 . A method according to claim 18 including controlling the main power supply unit via a DC current transducer.
35 . A method for stabilising a superconducting magnetic field comprising measuring a generated magnetic field value, comparing the measured magnetic field value with a predetermined magnetic field value and calculating an error signal, supplying the error signal to an auxiliary power supply unit to produce a stabilising current, feeding the stabilising current to the superconducting magnetic field generating circuit to thereby stabilise the generated magnetic field.