Magnetic Field Control

Abstract

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.