Qualification Program of Lap Joints for ITER Coils

Ilyin, Y.; Simon, Fabrice; Hua, Qing; Baikalov, A.; Gung, C.; Turck, B.; Hamada, K.; Koczorowski, Sebastien; Dolgetta, N.; Cormany, C.; Gaxiola, E.; Vostner, A.; Lim, Byung Su; Libeyre, P.; Devred, A.; Mitchell, N.

doi:10.1109/tasc.2017.2778102

Cited by 16 publications

(6 citation statements)

References 20 publications

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“…However, the void fraction appeared to be larger in the portion of the conductors towards the box ends due to larger twist pitch, which could be responsible for the sensitivity of the joint resistance to the EM load. It should be noted, that after the trials with the PFJEU2 and PFJEU3 samples and consequent improvement of the technological process, the next qualification and production samples did not reveal any sensitivity to the EM load [22].…”

Section: Analysis and Validationmentioning

confidence: 91%

Modeling and validation of nonlinear voltage-current characteristics of ITER PF joint sample tested in the SULTAN facility

Huang

Bagni

Ilyin

et al. 2022

Supercond. Sci. Technol.

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The ITER Poloidal Field (PF) coils are wound into double pancakes with NbTi cable-in-conduit conductors, which are connected by joints in shaking hands lap-type configuration. The coils are operating in pulsed mode with a maximum operating current of 55 kA and peak magnetic field of 6.4 T, utilizing electromagnetic load on the conductors and joints. A series of PF qualification joint samples modified in praying hands configuration is measured in the SULTAN facility. For some samples, a nonlinear voltage-current (VI) characteristic is observed during the assessment of joint resistance. The growth of joint resistance versus the B×I product is larger than what is expected from the magneto-resistant copper contribution. Two non-homogeneous contact resistance models are developed and combined to quantitatively evaluate the reason for the nonlinear VI behavior in combination with the relevant power dissipation and current redistribution in the joint. The simulations reveal that, for the particular pre-qualification PFJEU2 sample with resistance variation up to 3.5 nΩ, the most probable reason for the nonlinear VI characteristic is a widely spread defective connection between copper sole and shim. The electromagnetic force involves a separation effect on the mechanically and electrically weakly connected parts, resulting into a varying resistance depending on transport current and background field. The hypothesis and models are validated by an experiment on a similar sample PFJEU3 and a post-mortem examination of the PFJEU2 sample.

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Section: Analysis and Validationmentioning

confidence: 91%

Modeling and validation of nonlinear voltage-current characteristics of ITER PF joint sample tested in the SULTAN facility

Huang

Bagni

Ilyin

et al. 2022

Supercond. Sci. Technol.

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“…An ITER toroidal coil (TFC) is electrically connected to the 68-kA main busbar of a feeder (terminal joint), as shown in Fig. 1 [1,2]. A large electrical contact resistance leads to severe consequences, such as magnet quenching and arc discharge.…”

Section: Introductionmentioning

confidence: 99%

Electric Potential Profile with Distributed Degradation in the Terminal Joint for ITER TF Coil System

HASEGAWA,

KAJITANI,

UNO

et al. 2024

Plasma and Fusion Research

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ITER toroidal field coils are electrically connected to 68-kA main busbars (terminal joints). We propose the measurement of the electric potential distribution in a terminal joint using electrical probes (e-probe method) to inspect the contact resistance in the joint. In this study, we experimented with a mockup of a terminal joint. The test current was 20 A, and the electric potential was measured using the e-probe method at room temperature and 77 K. Nine different degradation patterns were prepared by distributing polyimide films in the joint interface. Next, we performed finite element analysis to investigate the detailed relationship between the electric potential distribution and contact resistance at 300 K and 77 K. In the numerical analysis, the same degradation patterns and test current as in the experiment were assumed. The analysis results agree with the experimental results. Different degradation patterns exhibit different electric potential profiles with 10-µV-scale differences. The analysis results also indicate that the e-probe method works when the contact resistance in the degraded area is larger than 1.0 × 10 −5 Ωmm 2 at 77 K and 300 K. c

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“…The design of the PF joints is based on the twin-box layout [10][11][12][13][14][15][16][17][18] either in the 'shaking hands' or in the 'praying hands' configuration [19]. The two NbTi cables are connected by a saddle composed of two copper soles soldered together with a copper shim in between to relax the tolerances of the assembly [20]. The stainless-steel box presses the cable over the copper sole, thus reducing the void fraction of the cable from the nominal value of 34% to about 20%.…”

Section: Introductionmentioning

confidence: 99%

“…Inside the box, the Ni/Cr coating is removed from the strands at the cable terminations. The strands are soldered to the copper sole, thus reducing the overall electrical resistance of the joint [19,20].…”

Section: Introductionmentioning

confidence: 99%

“…During the qualification phase, the manufacturing techniques and procedures were demonstrated as mature enough to guarantee a reliable performance of the joints. The qualification phase was completed in 2017 and successfully passed by the manufacturers, thus allowing to start the production phase [20]. Three different suppliers have been involved in the manufacturing of the PF coils for the ITER tokamak, from the European Union, the Russian Federation and China.…”

Section: Introductionmentioning

confidence: 99%

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Performance review of the joints for the ITER poloidal field coils

Breschi

Cavallucci

Adeagbo

et al. 2023

Supercond. Sci. Technol.

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For large scale magnets wound with cable-in-conduit conductors, the safe operation of the joints is of paramount importance to guarantee adequate reliability and stability margin of the whole magnet. For this reason, during the R&D activities undertaken for the development of the ITER magnet system, several experimental campaigns were launched to study the AC and DC performance of the joint and limit the risk of thermal runaways at the joints during the tokamak operation. The joint electrical resistance must be limited below specified values to avoid excessive heating generated by the transport current. Moreover, in presence of time-varying fields, different type of losses arise at the joints, which can be associated to their superconducting and resistive parts. The relative importance of these losses depends on the joint manufacturing solution. The aim of this investigation is to analyse the performance at different working conditions of the joints for the connection of the conductors of the Poloidal Field (PF) coils of the ITER magnet system.This work presents, for the first time, a wide review of the test campaign performed from 2016 to 2021 on the PF joint samples during the three manufacturing phases, namely pre-qualification, qualification and production. The values of electrical resistances and losses under sinusoidal field variations are reported in the paper at different operating conditions, thus building a useful database to assess the joint performances during the machine operation. The data here collected show the impact of the manufacturing techniques on the joint performances and, furthermore, represent a useful tool for the validation of numerical and analytical models of joints.

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Qualification Program of Lap Joints for ITER Coils

Cited by 16 publications

References 20 publications

Modeling and validation of nonlinear voltage-current characteristics of ITER PF joint sample tested in the SULTAN facility

Modeling and validation of nonlinear voltage-current characteristics of ITER PF joint sample tested in the SULTAN facility

Electric Potential Profile with Distributed Degradation in the Terminal Joint for ITER TF Coil System

Performance review of the joints for the ITER poloidal field coils

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