HTS Magnet Ramping to Reduce Screening Currents

A method of energizing or de-energizing a high temperature superconducting, HTS, coil, from an initial transport current to a final transport current, the HTS coil comprising a plurality of turns of HTS material, the method comprising:

• supplying a transport current to the HTS coil, the transport current starting at the initial transport current and varying over time to the final transport current;
• monitoring a non-inductive component of the start to end voltage across the HTS coil;
• applying cooling to the HTS coil to maintain the temperature of the HTS material at or below the zero field critical temperature of the HTS material;
• controlling one or both of:
• the rate of change of transport current;
• or
• the net cooling power applied to the coil, where the net cooling power comprises the applied cooling and any applied heating of the coil;
• such that the non-inductive component of the start-to-end voltage across the HTS coil remains above a threshold at least until the transport current is equal to the final transport current.

A method of energizing or de-energizing a high temperature superconducting, HTS, coil, from an initial transport current to a final transport current, the HTS coil comprising a plurality of turns of HTS material, the method comprising:

• supplying a transport current to the HTS coil, the transport current starting at the initial transport current and varying over time to the final transport current;
• monitoring temperature of the HTS coil;
• applying cooling to the HTS coil to maintain the temperature of the HTS material at or below the zero field critical temperature of the HTS material;
• controlling one or both of:
• the rate of change of transport current;
• or
• the net cooling power applied to the coil, where the net cooling power comprises the applied cooling and any applied heating of the coil;
• such that the rate of change of temperature over time of the HTS coil does not exceed a predetermined threshold dependent upon the controlled rate of change of transport current and/or net cooling power.

A high temperature superconducting, HTS, magnet system, the HTS magnet system comprising:

• an HTS coil comprising a plurality of turns of HTS material;
• a power supply configured to supply a transport current to the HTS coil;
• a cooling system configured to apply cooling to the HTS coil to maintain the temperature of the HTS material at or below the zero field critical temperature of the HTS material;
• a voltage monitoring system configured to monitor the start-to-end voltage of the HTS coil;
• a controller configured to control ramping of the magnet by:
• causing the power supply to provide a transport current which starts at an initial transport current and varies over time to a final transport current;
• and
• determining the non-inductive component of the monitored start-to-end voltage of the HTS coil;
• controlling one or both of:
• the rate of change of transport current;
• the net cooling power applied to the coil, where the net cooling power comprises the cooling applied by the cooling system and any applied heating of the coil;
• such that the non-inductive component of the start-to-end voltage of the HTS coil remains above a threshold at least until the transport current is equal to the final transport current.

A high temperature superconducting, HTS, magnet system, the HTS magnet system comprising:

• an HTS coil comprising a plurality of turns of HTS material;
• a power supply configured to supply a transport current to the HTS coil;
• a cooling system configured to apply cooling to the HTS coil to maintain the temperature of the HTS material at or below the zero field critical temperature of the HTS material;
• a controller configured to control ramping of the magnet by:
• causing the power supply to provide a transport current which starts at an initial transport current and varies over time to a final transport current;
• controlling one or both of:
• the rate of change of transport current;
• or
• the net cooling power applied to the coil, where the net cooling power comprises the applied cooling and any applied heating of the coil;
• such that the rate of change of temperature over time of the HTS coil does not exceed a predetermined threshold dependent upon the controlled rate of change of transport current and/or net cooling power.