Coil node voltage outputs for superconducting magnets
In a superconducting magnet assembly a plurality of superconducting coils, joined in series, are housed within a cryostat. A coil node between two electrically adjacent of the superconducting coils provides an input voltage. A coil node voltage output is provided comprising a series resistor connected between the coil node and a further node. A non-linear element is connected between the further node and a ground voltage, and an output connector is electrically connected to the further node and traverses a boundary of the cryostat.
1. A superconducting magnet assembly, comprising:
a plurality of superconducting coils, joined in series, and housed within a cryostat;
a coil node between two electrically adjacent of said superconducting coils providing an input voltage; and
a coil node voltage output comprising
a series resistor connected between the coil node and a further node,
a non-linear element connected between the further node and a ground voltage, and
an output connector electrically connected to the further node, and traversing a boundary of the cryostat.
2. A superconducting magnet assembly according to claim 1 , further comprising a second resistor of selectable resistance, electrically connected between the connector and a ground voltage, whose resistance is selectable from outside of the cryostat.
3. A superconducting magnet assembly according to claim 2 , wherein the second resistor is selected from among a range of discrete resistors.
4. A superconducting magnet assembly according to claim 2 , wherein the second resistor is selected among a bank of resistors by a switched circuit.
5. A superconducting magnet assembly according to claim 2 , wherein the second resistor is provided by a potentiometer arrangement, with a continuously-variable resistance.
6. A superconducting magnet assembly according to claim 2 , wherein the second resistor is external to the cryostat.
7. A superconducting magnet assembly according to claim 4 , wherein the bank of resistors are located within the cryostat, with field effect transistors provided to select among the resistors, with control voltages applied to gates of the field effect transistors from a controller outside the cryostat through electrical connectors traversing a boundary of the cryostat.
8. A superconducting magnet assembly according to claim 1 wherein the non-linear element is selected from among the following: a voltage dependent resistor, a zener diode, a diode network, and a transient voltage suppression diode.
9. A superconducting magnet assembly according to claim 1 , comprising at least three superconducting coils electrically connected in series, wherein each coil node between pairs of electrically adjacent coils provides a corresponding input voltage; and wherein each coil node is provided with a coil node voltage output comprising
a series resistor connected between the coil node and a further node,
a non-linear element connected between the further node and a ground voltage, and
an output connector electrically connected to the further node, and traversing a boundary of the cryostat.
10. A superconducting magnet assembly according to claim 9 , further comprising a second resistor of selectable resistance, electrically connected between the connector of the coil node voltage output and the ground voltage, whose resistance is selectable from outside of the cryostat.