HTS Coil Ramping Control for Screening Current Reduction
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Solution Overview
Problem
Superconducting magnets using high temperature superconducting (HTS) materials face challenges with screening currents during ramp-up, which cause local stress and degrade the critical current of the tapes, leading to potential damage and reduced performance.
Innovation Solution
A method of controlling the transport current and net cooling power in HTS coils to maintain the ratio of transport current to critical current above a threshold, keeping the coil near saturation during ramping, thereby reducing the formation of screening currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the transport current is ramped up quickly to achieve high productivity, then the ramping time is reduced, but screening currents form and cause local stress that degrades the critical current and may damage the coil
Solution Approach 1:
The patent applies dynamic control of the ramping rate, adjusting it in real-time based on the coil's thermal and electrical state. The ramping rate is not fixed but varies during the energization process to maintain the I/Ic ratio within safe limits, preventing screening current formation while achieving efficient charging.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the transport current I and critical current Ic to calculate their ratio I/Ic. This feedback information is used to adjust the ramping rate dynamically, ensuring the ratio remains above the threshold and preventing damage from screening currents.
2Reliability
If the transport current is kept low to avoid forming screening currents, then the coil is protected from damage, but the time to reach the required operating current increases significantly
Solution Approach 1:
The ramping rate is made dynamic rather than static. It starts conservatively when the coil is cold and I/Ic is low, then increases as the coil warms up and I/Ic increases. This dynamic adjustment minimizes the total ramping time while始终保持保护条件.
Solution Approach 2:
The patent changes the operating parameters during the ramping process. The ramping rate is adjusted as a function of the I/Ic ratio, which itself changes with temperature and current. This parameter adaptation allows optimal balancing of speed and safety throughout the charging process.
3Reliability
If additional cooling is applied to maintain low temperature and increase critical current, then the I/Ic ratio increases and screening currents are reduced, but the system complexity and cooling power requirements increase
Solution Approach 1:
The cooling system operates autonomously based on predefined control logic. It automatically adjusts the cooling power as a function of the I/Ic ratio without requiring complex real-time optimization algorithms or human intervention, simplifying the control system while maintaining effectiveness.
Solution Approach 2:
The cooling power is adjusted as a variable parameter during the ramping process. By changing the cooling power in response to the I/Ic ratio, the system maintains an optimal safety margin without requiring maximum cooling capacity throughout, reducing the overall cooling system requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively limits the stresses on the HTS coil during ramp-up, reducing the risk of damage and maintaining high field homogeneity and stability, which is crucial for applications like NMR and MRI.
Implementation Method 1
All low temperature superconductors have a self-field critical temperature (the temperature above which the material cannot be superconducting even in zero external magnetic field) below about 30K
Implementation Method 2
Cooling is applied to the HTS coil
Implementation Method 3
A transport current is supplied to the HTS coil, the transport current starting at an initial transport current and varying over time to the final transport current
Data Source
AI summary
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 comprises a plurality of turns of HTS material. A transport current is supplied to the HTS coil, the transport current starting at the initial transport current and varying over time to the final transport current. Cooling is applied to the HTS coil. An operating condition of the HTS coil is monitored, wherein the operating condition is indicative of a ratio I/Ic of the transport current, I, to a critical current, Ic, of the HTS material in at least a part of the HTS coil. One or both of the transport current applied to the coil and a net cooling applied to the coil are controlled in a feedback loop responsive to the operating condition, in order to maintain the operating condition in a desired range during energisation or de-energisation, such that the indicated ratio I/Ic is maintained above a threshold ratio (e.g. 0.7).