Superconducting switch operation
A method of operating a superconducting switch system to protect against quenching in a superconducting magnet circuit is provided. The system comprises a magnet circuit, a main superconducting switch and an auxiliary superconducting switch connected in parallel thereto by low resistance connecting parts. In an initial magnet energisation procedure, after establishing superconducting flow in the circuit, the main and auxiliary switches are closed to cause current to persist in the circuit without further power input. If the main switch quenches, the current will transfer to the auxiliary switch through the resistive connecting parts. Upon restoring the main switch to the superconducting state, the voltage drop through the resistive connecting parts will drive the current back through the main switch. A preconditioning procedure is carried out as part of the magnet energisation procedure to ensure that opening the main switch will establish superconducting current through the auxiliary switch.
1. A method of operating a superconducting switch for a persistent mode superconducting magnet system so as to condition the system against quenching of a superconducting magnetic circuit of the system, the method comprising:
connecting a main superconducting switch to the magnetic circuit by two connecting parts, the main superconducting switch providing a resistance of a first resistance value between the connecting parts;
connecting an auxiliary superconducting switch to the magnetic circuit by the connecting parts, the auxiliary superconducting switch providing a resistance of a second resistance value greater than the first resistance value between the connecting parts;
energising the magnetic circuit by means of a power supply connected to the connecting parts;
closing the main superconducting switch and the auxiliary superconducting switch so as to cause superconducting current flow through the main superconducting switch within the magnetic circuit and so as to cause the superconducting current flow to persist within the magnet circuit when the power supply is disconnected;
carrying out a preconditioning step by opening the main superconducting switch and determining whether the superconducting current flow persists within the magnet circuit by flowing through the auxiliary superconducting switch;
closing the main superconducting switch so as to cause the superconducting current flow to revert to flowing through the main superconducting switch as a result of the second resistance value being greater than the first resistance value; and
where the determination in the preconditioning step indicates failure of the superconducting current flow to transfer from the main superconducting switch to the auxiliary superconducting switch, repeating the preconditioning step as many times as is necessary to condition the system against quenching.
2. The method as claimed in claim 1 , wherein a plurality of auxiliary superconducting switches are connected to the magnetic circuit in parallel between the connecting parts, each of the auxiliary superconducting switches providing a resistance of the second resistance value between the connecting parts when in a superconducting mode so that, when the main superconducting switch is in the open state, the superconducting current flows in parallel through the auxiliary superconducting switches, in order to decrease the risk of the magnet running down in the event of high current operation.
3. The method as claimed in claim 1 , wherein a plurality of main superconducting switches are connected to the magnetic circuit in parallel between the connecting parts, each of the main superconducting switches providing a resistance of the first resistance value between the connecting parts when in a superconducting mode so that the superconducting current flows in parallel through the main superconducting switches when in the closed state.
4. The method as claimed in claim 1 , wherein an inductor is connected in series with the or each main superconducting switch between the connecting parts, in order to slow down the current rate of change when the superconducting current flow changes to the or each auxiliary superconducting switch.
5. The method as claimed in claim 1 , wherein the or each main superconducting switch is an inductive wound superconducting switch.
6. The method as claimed in claim 1 , wherein an inductor is connected in series with the or each auxiliary superconducting switch between the connecting parts, in order to slow down the current rate of change when the superconducting current flow changes to the or each auxiliary superconducting switch and prevent the or each auxiliary superconducting switch from opening.
7. The method as claimed in claim 1 , wherein the or each auxiliary superconducting switch is an inductive wound superconducting switch.
8. The method as claimed in claim 1 , wherein the or each main superconducting switch is a single-strand or multi-strand wound.
9. The method as claimed in claim 1 , wherein the or each auxiliary superconducting switch is a single-strand or multi-strand wound.
10. The method as claimed in claim 1 , wherein the or each main superconducting switch is combined with an associated auxiliary superconducting switch in a single multi-strand wound switch component having one strand portion serving as the main superconducting switch and another strand portion serving as the auxiliary superconducting switch.
11. The method as claimed in claim 1 , wherein the or each auxiliary superconducting switch is connected between the connecting parts by connecting means providing the resistance of the second resistance value.
12. The method as claimed in claim 11 , wherein the connecting means comprise solder connections.
13. The method as claimed in claim 1 , wherein one or more main superconducting switches are connected in series between the connecting parts, and a plurality of auxiliary superconducting switches are connected in series between the connecting parts.