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Electrical Engneering

For a high field user facility, the magnet development should provide different magnet systems to satisfy the experimental requirements. A number of magnets for different peak field and pulse duration are currently in operation at the WHMFC. The typical field waveforms are shown below. These can be divided into two groups: monolithic coil and dual-coil magnets. All the monolithic coil magnets are driven by capacitor bank modules except for the 40 T long pulse magnet which is driven by the lead-acid battery. The 50 T dual coil magnet for 100 ms flat-top field is driven by the pulse generator. Both the inner and outer coils of the 90 T dual coil system are energized by two independent capacitor bank modules.

Mechanically, all of our coils consist of layers of a continuous length of conductor supported by one or more layers of reinforcement. The design philosophy of all magnets includes the following principles:

·All the coils are internally reinforced with high strength, high modulus fiber composite.

·In the inner section of the winding, the thickness of reinforcement is optimized to nearly equalize hoop strain in all units.

·In the outer section, fiber composite layers of about 1.5 mm thickness are inserted between the conductor layers for electric insulation.

·The outer section is tightly confined by a stainless steel cylinder with 3 mm wall thickness, further reinforced by carbon fiber composite.

·The stress is calculated using anisotropic properties for the fiber composites with in-house developed package Pulsed Magnet Design Software (PMDS).

·At the end of the pulse, the highest temperature in the coil is kept below 400 K in order to prevent damage to the insulation.

·Fast cooling technology is used for 65 T user magnets. The cooling time is about 35 minutes and the average service life is 800~1000 pulses in the range of 60 to 65 T.

Field waveforms produced at the WHMFC. A) the 65 T user field with fast cooling design; B) the 50 T long pulse field with 100 ms flat-top produced by the pulse generator; C) the 35 T free running long pulse without ripples produced by the lead acid battery system; D) 25 T /200 ms flat-top with high stability produced by the lead acid battery system and the bypass circuit; E) the 50 T short pulse with 6 ms flat-top produced by the capacitor bank; F) 90.6 T record field produced by a dual coil magnet driven by the capacitor bank modules. The inserts on the top present the enlargement of pulse D and E at the peak field. 


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