Forced-flow gas cooled current leads for SCQ magnets in BEPCⅡ

Current leads are used to connect the superconducting magnets in cryogenic temperature to the power station in room temperature. It is the main source of heat leak into the eryostat of magnets on static operation. This paper presents the optimized methods of the leads for BEPC Ⅱ , and the effects of different cross section ar- ea on the heat leak, temperature profile as well as the voltage drop of the leads. The multi-tube structure is adopted and improved for the leads. The results of numerical simulation using CFD software package Fluent6. 0 for the muhi-tube-structure leads are presented, which can be used to improve the design of the leads.

R&D on Resistive Heat Exchangers for HTS High Rated Current Leads

The HTS current leads of superconducting magnets for large scale fusion devices and high energy particle colliders can reduce the power consumption for cooling by 2/3 compared with conventional leads. The resistive sections of high-rated current leads are usually made of a heat exchanger cooled by gas flow. The supply of the cooling mass flow incurs more than 90% of the cooling cost for the HTS leads. The mass flow rate requirement depends not only on the length and material of the resistive heat exchanger, but also on the heat transfer coefficient and HEX surface, the joint resistance at the cold end of a sheet-stack HEX with a larger specific presented in the paper. The test results of efficiency can be achieved. and its cooling approach. The design and operation surface and a much smaller hydraulic diameter are an HTS lead optimized for 8 kA show that a 98.4%

Experimental Investigation and Modelling for the Optimisation of Conduction Cooled HTS Hybrid Current Leads for SMES

It′s important that HTS tapes have lower thermal conductivity and higher transversal resistivity in order to reduce the heat leaks conducted along the tapes and AC losses in the high temperature superconducting system conduction cooled by GM coolers. This paper presents an experimental investigation into the effects of pure Ag and AgAu alloys sheath materials on the properties of Bi(2223) multifilamentary tapes and the optimisation of conduction cooled hybrid current leads made from copper and Bi(2223)/Ag or Bi(2223)/AgAu tapes. The thermal conductivity of the tapes were measured by cryogenic steady heat flux method and the resistance was measured by using standard DC four probe method at low temperature. The results showed that the reduction of thermal conductivity by the addition of Au into the sheath material of Bi(2223) tapes was 65 0 0, 75 0 0 and 85 0 0 lower than that of pure Ag sheathed Bi(2223) tapes and the increase of resistivity was 4.9 , 10 and 19.4 times higher than that of pure Ag for the addition of 2.2 0 0, 5.7 0 0 and 10.7 0 0Au(atom ratio) respectively. And the study also attempts to optimise thermodynamically the conduction cooled hybrid current lead by using a developed model, which took the irreversibility of commercial GM coolers, the contact resistance and thermal conductance into account. Predictions from the model showed that AgAu alloys were suitable candidate materials to replace Ag as sheath material of Bi(2223) tapes applied in HTS current leads. In addition, Bi(2223)/AgAu was a suitable material to be applied as the HTS section of hybrid current leads in conduction cooled superconducting electric systems.

Current leads for superconducting magnets of ADS injector Ⅰ

In an ADS injector i, there are five superconducting magnets in each cryomodule. Each superconducting magnet contains a solenoid magnet, a horizontal dipole corrector （HDC）, and a vertical dipole corrector （VDC）. Six current leads will tm required to power the electrical circuits, from room temperature to the 2.1 K liquid helium bath： two leads carry 100 A current for the solenoid magnet while the other four carry 12 A for the HDC and the VDC. This paper presents the principle of current lead optimization, which includes the cooling methods, the choice of material and structure, and the issues for current lead integration.

Photon-Assisted Heat Generation by Electric Current in a Quantum Dot Attached to Ferromagnetic Leads

Heat generated by electric current in a quantum dot device contacting a phonon bath is studied using the non- equilibrium Green function technique. Spin-polarized current is generated owing to the Zeeman splitting of the dot level. The current＇s strength and the spin polarization are further manipulated by changing the frequency of an applied photon field and the ferromagnetism on the leads. We find that the associated heat by this spin- polarized current emerges even if the bias voltage is smaller than the phonon energy quanta and obvious negative differential of the heat generation develops when the photon frequency exceeds that of the phonon. It is also found that both the strength and the resonant peaks＇ position of the heat generation can be tuned by changing the value and the arrangement configurations of the magnetic moments of the two leads, and then provides an effective method to generate large spin-polarized current with weak heat. Such a result may be useful in designing low energy consumption spintronic devices.

Experimental Study on Paschen Tests of ITER Current Lead Insulation

An experimental Paschen test setup has been established to analyze the quality of ITER current lead （CL） insulation and extend the research on Paschen＇s law under various conditions. Insulation problems can destroy a machine if a Paschen discharge is triggered by an insulation defect that is caused by faulty manufacturing, electromagnetic force, and thermal stress load with a certain degree of vacuum helium or pipe leakage. The results show that the CL insulation mock-up worked well under normal temperature and pressure. Besides, the mock-up also worked well in helium conditions and at 80 K temperature at different pressures. One area of CL insulation was severely destroyed when the 80 K test was conducted after 5 thermal cycles, resulting in Paschen discharge phenomenon. The breakdown voltage is maintained at a relatively low level under different pressure conditions; the change of breakdown voltage was mainly due to the change of pressure, and such change was in line with the Paschen law.

The superconducting magnet for ADS injection-I

Purpose As the world energetic demand is increasing day by day,the development of nuclear energy is of great necessity.However,the development is followed by a lot of tough questions like the management and storage of the nuclear waste.ADS,which is short for the accelerator-driven sub-critical system,may be a good choice because it can provide an efficient transmutations of nuclear waste.Many countries have carried out some research in related areas like the USA,Japan and China.The superconducting magnet system The cryomodule I(CM1)for China’s ADS Injection-I had been designed,fabricated and online tested.The CM1 is mainly composed of superconducting spoke cavities,beam positionmonitors,cryogenic system and superconducting magnets.The superconducting magnet system,which includes the magnet and current leads,is aimed at focusing and correcting the proton beams.Conclusion Seven superconducting magnets and current leads for CM1 are successfully designed and manufactured.Structural strength meets design specifications,the field meets the design demands,and the online test shows that the magnets can work in a rather stable state.In this paper,the detailed design and installation of the superconducting magnets are presented.