Role of the Cross Section Geometry in Rectangular ${\rm Nb}_{3}{\rm Sn}$ CICC Performances

We review progress in the design of high field superconducting cable-in-conduit conductors (CICCs) for fusion applications, with special attention to the results of recent key experiments, leading to the state-of-the-art CICC technology: the ITER Toroidal Field and Central Solenoid programs, the EFDA Dipole conductor development program, the NHFML Hybrid Magnet project, the EU-TF Alt conductor demonstration, and the CRPP React & Wind flat cable test. For these projects, the main CICC design driver was the mitigation of Nb 3 Sn conductor performance degradation with electro-magnetic loading cycles. This was achieved by proper choice of cable layout and of conductor geometry, depending on the specific operating conditions and project requirements. In all cases, the necessity to limit cable movements inside the conductor jacket was identified to be of crucial importance. The main aspects of CICC manufacture are also discussed here, at least for what is the experience gained by the authors in both CICC jacketing and cabling processes. Finally, the state of the art of high-temperature superconducting (HTS) cables is discussed: at present, this technology is still in its infancy, but it is highly likely that major technological improvements could eventually lead to a widespread use of HTS CICCs.

Section: The Eu-tfalt Conductor Demonstrationmentioning

confidence: 99%

Cable-in-conduit conductors: lessons from the recent past for future developments with low and high temperature superconductors

Muzzi

Marzi

Zenobio

et al. 2015

“…A stable T cs with EM cycles, is not only linked to the value of the twist pitches, but also to their reciprocal ratio, especially in the first stages [13]. Results as good as those of 'TF-A' leg, in terms of T cs stability versus # EM cycles and effective strain, have been obtained, among others, by the ENEA DEMO rectangular High field [19,34] and Low Field [32] conductors, by the EU-AltTF DEMO sample [33,35] and by the TFPRO2 OST-2 conductor [20,23], all cables designed with rectangular section, similar twist pitch cabling sequence (almost same ratio between pitches of the first stages) and low void fraction.…”

Section: Measurementsmentioning

confidence: 81%

“…The different behaviour of the two 'legs', in terms of both T cs and n-index, is here attributed to the different distribution of the load, as a result of the different cabling pitch sequence of the two samples, see for example [9,13,[32][33][34][35]. In particular, the difference between the initial current sharing temperature values measured for the two legs is consistent with what was reported in [13] about the T cs dependence on the cabling twist pitch of the first stage.…”

Section: Measurementsmentioning

confidence: 99%

“…In particular, the difference between the initial current sharing temperature values measured for the two legs is consistent with what was reported in [13] about the T cs dependence on the cabling twist pitch of the first stage. Concerning 'TF-A' conductor, the long twist pitch cabling sequence, together with the low void fraction and the rectangular cross-section, has been shown to lead to a favourable load distribution within the cable, corresponding to smaller ε eff [32][33][34][35], which has been found to be correlated to a narrow strain distribution in the cable crosssection [35], thus resulting in a stable T cs with cycling loading. A stable T cs with EM cycles, is not only linked to the value of the twist pitches, but also to their reciprocal ratio, especially in the first stages [13].…”

Section: Measurementsmentioning

confidence: 99%

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DTT toroidal field conductor samples test in Sultan: DC and AC characterization

Fiamozzi Zignani,

De Marzi,

Scarantino

et al. 2024

The superconducting magnet system of the Divertor Tokamak Test (DTT) facility, composed of 18 Toroidal Field (TF) coils, 6 Poloidal Field (PF) coils and a Central Solenoid (CS), has been designed and many procurements have been launched. Some manufacturing aspects and some conductor features require characterization under relevant close-to-operative conditions. To confirm the design choices in all details, cryogenic tests in qualified facilities have been foreseen. In this work, the results of the TF samples characterization at the SULTAN facility at the Swiss Plasma Centre (SPC, EPFL) are presented. The 3 weeks test campaign started on July the 8th, 2022. The DTT TF SULTAN sample was made of two Nb3Sn Cable-in-Conduit conductor “legs”, namely “TF-A” and “TF-B”, made with wires produced by Kiswire Advanced Technology (KAT), differing for the cabling twist pitch sequence only, and designed to work in DTT at 42.5 kA at 11.9 T peak field.The extensive characterization comprised 3000 Electro-Magnetic (EM) cycles and two Warm-Up-Cool-Down (WUCD) steps, and in detail it included: AC measurements on the virgin conductors, on cyclic loaded conductors and after WUCDs; DC tests at 10.85 T / 42.5 kA with intermediate electro-magnetic (EM) cycles at 10.85 T / 45 kA before and after WUCDs; DC tests using partial Lorentz force loads, and Minimum Quench Energy (MQE) tests at 9 T / 42.5 kA after cycles and WUCDs. The results of the DC measurements analysis verified the design, in terms of current sharing temperature (Tcs) and critical current (Ic), as both samples are over the minimum acceptance values. In particular, the “TF-A” sample, characterized by a so-called “long twist pitch” cabling sequence, showed higher performance without any degradation with loading and WUCD cycles, whereas sample “TF-B” presented an initial Tcs reduction that afterwards substantially remained unchanged. In terms of strain acting at the Nb3Sn filaments level, this result can be described by a lower effective strain in the “TF-A” sample. AC losses were measured with a calorimetric method as a function of frequency for each series of AC sinusoidal pulsing measurements, and the characteristic coupling time constants were determined.

“…The coils are wound from cablein-conduit conductors (CICCs). CICC, is characterized by wrapped superconducting cables inside a steel conduit, forming an integrated conductor structure, ensuring proper mechanical support and cooling [5][6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

High performance of an innovative cable-in-conduit conductor with CWS cable pattern

Guo,

Liu,

Dai

et al. 2024

Cable-in-conduit conductors, known as CICCs, were developed for constructing superconducting coils in tokamak fusion reactors. To achieve large currents in high magnetic field, CICCs were utilized with a short-twist-pitch (STP) cable pattern to prevent irreversible performance degradation, but also inducing higher AC losses. Institute Of Plasma Physics Chinese Academy Of Sciences (ASIPP) designed and manufactured three innovative CICCs, all featuring CWS (copper wire with a short-twist-pitch wound around superconducting strands with a long-twist-pitch) structure to increase both the current density and structure stiffness of CICC cable. These CICCs had the same new CWS cable pattern but the Nb3Sn superconducting strands were from different suppliers. All samples were subsequently tested under electromagnetic cycling tests in SULTAN. For similar electromagnetic performance degradation, the Lorentz load threshold of the CWS cable pattern exhibited to be higher than that of STP cable pattern. Moreover, the AC losses of CWS were 15% lower than that of STP cable pattern for low frequencies of the applied alternating magnetic field. Both results indicated that the CWS cable pattern has a higher margin of engineering safety and lower AC losses than STP cable pattern under the target operating conditions. This provides new insights in finding solutions for optimizing the CICCs’ cable pattern and preventing its electromagnetic performance degradation.