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SC Conductor Testing Facility

2. SC Conductor testing facility

The superconductingconductor test facility is an important part of superconducting magnet systemin CRAFT. They are described as follows:

1.      Scientific Objective

There aretwo main scientific objectives of the superconducting conductor test facility:firstly, study the electro-magnetic behaviors of composite structuresuperconducting conductor under mult-field coupling condition; then, evaluatethe reliability of engineering technology and safe operation in fusion reactoroperation environment. Fig.1 shows the overviewof the test facility ini the hall and main machine design.

The mainfunction of this test facility is as follows:

(1) Testand evaluation of current sharing temperature (Tcs) for the conductors under complex operationcondition;

(2) Testand evaluation of critical current (Ic)for the conductors under complex operation condition;

(3) Testand evaluation of AC loss characteristics for the conductors under complexoperation condition;

(4) Testand evaluation of stability margin for the conductors under complex operationcondition;

1.      Main Technology Parameters

The mainparameters of this test facility are as follows:

(1) Maximum test magnetic field is 16.5 T in the center where thebackground magnet provides the 15 T;

(2) Test space is 160×100××550 mm;

(3) Field homogeneity at the test space is better than 98 %;

(4) Maximum test current is 100 kA;

2.      System Description

The systemis divided into two parts: main machine system and auxiliary system. The mainmachine system is divided into four parts again; namely, background DC magnet,100 kA superconducting transformer, AC magnet, bench system and cryostat.

3.1 Main Machine System

The spacesize occupied by the whole main machine system is 8.5(length)×6.5(width)×11m(height) and the total weight is about 175 ton. Fig.2 shows theexploded view of the main machine. The auxiliary system main includes the powersupply system (capability: 10 kA+15 kA), cryogenics system (capability: 1kW@3.8 K).

1) Background DC Magnet, provides the 15 TDC magnetic fields at the center for the conductor sample test. The wholemagnet consists of three coils, namely, high field magnet, medial field magnetand low field magnet. The inner and outer diameter is about 1660 and 2785 mm,the length is about 3300 mm. The total weight of the DC magnet is about 45 ton.The all magnets are made of Nb3Sn CICC conductor. The otherstructural components include pre-compression and braced structures. Themaximum current provided by power supply is about 15kA. Forced flow with Heliumis adopted for magnet cooling. Fig. 3 shows the overview of the DC magnet winding.

2) 100 kA superconducting transformer,provides the sample test current which the maximum value is 100 kA. Thesuperconducting transformer adopts the structure of coaxial superconductingcoil. The current of the primary coil is about 250 A and the maximum outputcurrent of the secondary coil is 100 kA. The coil is made of NbTisuperconductor and the maximum field in the winding is less than 4.3 T. Theouter diameter of the winding is about 380 mm and the length of the winding is280 mm. the joint resistance of the secondary loop is less than the 3 nΩ. Theprimary coil is cooled by indirect cooling, and the secondary coil is cooled byforced flow with Helium. Fig. 4 (a) shows the overview of the superconductingtransformer.

3) AC magnet provides the alternatingmagnetic field for AC loss and minimal quench energy test for conductor sample.The test aperture is 160×100×550 mm which is consistent with the test system.The amplitude of the AC magnet is about 0.4 T and the frequency is 0.02~10 Hz.The field homogeneity in the 500 mm length is better than 5%. The AC magnet iscooled directly by copper tube with flowing liquid helium. Fig. 4 (b) shows theoverview of the AC magnet.

4) Bench system provides the support forbackground DC magnet. The bench system is made of stainless steel. The spacesize is about 85×6.5×11m. The total weight is about 40 ton and the design ofcapacity is 200 tons.

5) Cryostat provides the necessary vacuumand low temperature environment for main machine system. The cryostat is mainlycomposed to Dewar and thermal shielding and some cooling pipe. The total staticthermal load is 150W@4.2K.

3.2 Auxiliary System

1) Cryogenics system provides necessarylow temperature Helium for cooling DC magnet, superconducting transformer, ACmagnet, structure parts, test sample and thermal shielding et al. The capacityof the cryogenics system is about 1 kw@3.8K. The maximum inlet pressure is about 6 bars andthe total mass flow is 150 g/s.

2) Power supply system provides necessarycurrent for exciting the DC magnet. The whole system consists of two sets ofpower supply, one is 10 kA@20 V and another is 15kA@20 V.

1.      Key Technologies

The mainkey technologies are as follows:

1) Thedevelopment of high field Nb3Sn conductor (16.5 T);

2) Theeffect of heat treatment on the properties of insulation materials ofsuperconducting coils and quench detection coils;

3) Reliabilityassembly of multi-parts and multi-interfaces for the test facility.