Superconducting magnet system is the most important part of the superconducting tokamak host , which is mainly used to initiation, control and confine plasma to ensure the occurrence and continuation of fusion device

    Large thermal and electromagnetic disturbances during the operation of a superconducting magnet can cause the normal region of the magnet to expand uncontrollably, resulting in unrecoverable quench.

    Once the superconducting magnets system is damaged or performance degradation occurs, it is irreversible and extremely difficult to repair, which directly leads to the device cannot operate and causes huge economic losses.

    As one of the most important and precious key components of the fusion reactor, it is very crucial to ensure long-term safe operation of the superconducting magnet system. For this purpose, it is very important to establish an effective quench detection and magnet protection system, such that magnet energy could be released safely without damage to superconducting magnets when quenching occurs.  
    This system is the most important issue to guarantee the long-term steady-state operation of superconducting fusion device, which is performed through the analysis of magnets’characteristics, quenching transition process and other physical properties via theoretical calculation and experimental studies to account for the influence of electromagnetic noise and other external interference sources on detection system.

     The complex magnet system of EAST consists of arrange of separate coils, including the 6 Central Solenoid, , 8 Poloidal Field coils , 16 Toroidal Field coils and 13 HTS current leads connecting superconducting magnets and external power supply.

    The EAST quench detection system is divided into four parts: TF quench detection, PF quench detection, quench detection in the feeders and signal processing units as shown in Fig.1.

    The primary quench detection in EAST is based on voltage detection, which is the most rapid detection. The very magnetically disturbed environment during the plasma scenario makes the voltage detection particularly difficult, inducing large inductive components in the coils and voltage compensations have to be designed to discriminate the resistive voltage associated with the quench.

Technical requirements

    The magnet quench detection system must be able to distinguish between superconductor quench and the electromagnetic perturbations caused by a plasma disruption with a reliability of >99% for the CS and PF coils for disruptions and VDEs and >99.9% for the TF coils for major disruptions and VDEs.

    The TF quench detection system will be able to distinguish between a fast discharge of the CS and PF coils and a TF superconductor quench with a reliability >99.99%.

    A fast discharge of the TF system will require a fast discharge of all coils (TF, CS, and PF ).

    Fast discharge of a CS or PF coil will require an associated fast discharge only of the CS and PF system.

Fig.1    the  EAST quench detection system