The US ITER Domestic Agency is responsible for supplying seven Central Solenoid Modules (CSM) to the ITER organization. The modules are fabricated by General Atomics (GA). As part of the fabrication process, all CSMs undergo factory acceptance testing (FAT) prior to shipment to the IO. The FAT includes Paschen testing the CSMs up to 15 kV between 1e-3 and 100 mbar, and up to 30 kV at ambient conditions. During post-cooldown Paschen testing of CSM6, there was a fault on one of the terminal breakout locations which required a repair. This location of the fault consisted of complex geometry that required development of advanced insulation repair methods to return the module to Paschen-tight condition. Successful insulation repairs typically require sufficient compression to achieve a Paschen-tight seal of the applied insulation to the underlying surfaces. Typically for circumferential shapes, compression is achieved utilizing shrink tape or silicone tape wrapped around the perimeter. The complex geometry of CSM6 terminal required research into other compression methods including vacuum bagging, expanding foam, and externally pressurized bladders of complex shapes. Multiple test articles were created to replicate the shape of the fault area and repair methods were developed and Paschen tested to 30 kV, from 1e-3 to 1000 mbar. This paper will discuss the development of the qualified repair process for the complex geometry of the CSM6 terminal, and present to the magnet community the lessons learned from that development.

The ITER Central Solenoid (CS) is under fabrication by the US ITER organization and its subcontractors. All CS modules (CSM) were or will be tested at 40 kA in the Final Test facility at General Atomics. CSM 3 testing campaign took place in 2021, and a breakdown occurred that damaged the terminations of the module. To recover, new terminations needed to be designed, qualified and built to make the CSM3 fit for service. This effort had several challenges that were not addressed in the previous projects with large Nb3Sn magnets with cable-in-conduit conductors. This paper describes a design, fabrication and qualification of the terminations.

The ITER Central Solenoid (CS) is under fabrication by the US ITER organization and its subcontractors. US ITER will supply seven modules to ITER IO, six of which will be assembled in a stack that forms the ITER Central Solenoid. All CS modules (CSM) were or will be tested at 40 kA in the Final Test facility at General Atomics (GA). CSM 5, 6, and 7 were tested in 2023 and 2024. Some instrumentation was updated to obtain information on the suppression of the inductive noise in the CSMs at high dB/dt events, which will lead to improved quench detection and protection of the modules. All the standard tests performed on previous CSMs to validate the properties of the CSM have also been performed on CSMs 5-7 to confirm the consistency of the CSM properties for ITER CS. The Tcs margin demonstration was done for the first time at the GA Facility on CSM6. Test results and analysis are presented and discussed.

Central Solenoid (CS) components have an abundance of technical challenges ranging from material science to component interfacing. In manufacturing, a CS module is subjected to stringent high voltage insulation strength tests at multiple occasions. The engineering challenge is where a multitude of quench detection wires need to exit the bulk insulation and the materials boundary or compatibility become an issue. In assembly, each CS module terminals is jumped to its respective feeder line via an extension lead that is manufactured with interfacing constraints with the module terminal vector as well as the feeder terminal mating surface. Another critical aspect is the clearance available in assembly with other surrounding tokamak components. A summary of the issues found in manufacturing of large scale structural components is also given.

A low-AC loss Rare-earth barium copper oxide (REBCO) cable, based on the VIPER cable technology has been developed by commonwealth fusion systems for use in high-field, compact tokamaks. The new cable is composed of partitioned and transposed copper 'petals' shaped to fit together in a circular pattern with each petal containing a REBCO tape stack and insulated from each other to reduce AC losses. A stainless-steel jacket adds mechanical robustness-also serving as a vessel for solder impregnation-while a tube runs through the middle for cooling purposes. Additionally, fiber optic sensors are placed under the tape stacks for quench detection (QD). To qualify this design, a series of experiments were conducted as part of the SPARC tokamak central solenoid (CS) model coil program-to retire the risks associated with full-scale, fast-ramping, high-flux high temperature superconductors CS and poloidal field coils for tokamak fusion power plants and net-energy demonstrators. These risk-study and risk-reduction experiments include (1) AC loss measurement and model validation in the range of similar to 5 T s-1, (2) an IxB electromagnetic (EM) loading of over 850 kN m-1 at the cable level and up to 300 kN m-1 at the stack level, (3) a transverse compression resilience of over 350 MPa, (4) manufacturability at tokamak-relevant speeds and scales, (5) cable-to-cable joint performance, (6) fiber optic-based QD speed, accuracy, and feasibility, and (7) overall winding pack integration and magnet assembly. The result is a cable technology, now referred to as PIT VIPER, with AC losses that measure fifteen times lower (at similar to 5 T s-1) than its predecessor technology; a 2% or lower degradation of critical current (Ic) at high IxB EM loads; no detectable Ic degradation up to 600 MPa of transverse compression on the cable unit cell; end-to-end magnet manufacturing, consistently producing Ic values within 7% of the model prediction; cable-to-cable joint resistances at 20 K on the order of similar to 15 n Omega; and fast, functional QD capabilities that do not involve voltage taps.

General Atomics (GA) is under contract to UT-Battelle c/o Oak Ridge National Laboratory for the fabrication of ITER Central Solenoid Modules (CSM). GA will provide seven modules to ITER Organization (IO), six of which will be assembled in a stack that forms the ITER Central Solenoid. All CSMs are required to pass factory acceptance testing (FAT) at General Atomics’ Magnet Technology Center (MTC) test facility prior to shipment to IO. Currently, CSMs 1, 2, and 4 have completed FAT and have been delivered to IO. CSM5 has completed FAT and CSM3 will repeat FAT after resuming its test campaign. FATs on CSMs 6 and 7 are planned as the modules complete fabrication. The MTC test facility was designed and built to conduct CSM factory acceptance tests. The test facility consists of the test chamber, high vacuum system, 4.5 K recirculating supercritical helium refrigeration plant, 50 kA DC power supply, capacitor-pulsed DC circuit breakers, 1 GJ discharge resistor, high-temperature superconducting current feeders, data acquisition system, supervisory control and magnet quench protection system, and a multitude of supporting equipment. Where possible, the test facility utilizes similar equipment planned for use at IO for magnet operation. The test facility operational lessons learned as a result of CSM 1-4 FATs are presented and discussed in this paper.

The fourth CS Module (CSM#4) of the ITER Central Solenoid was tested in November/December 2022 at the premises of General Atomics, Poway, US. During the measurement campaign, the CSM#4 was submitted to dumps of the transport current from different initial values (from 0 to 40 kA) to 0 kA. The tests were performed both in virgin conditions and after 10 slow current cycles. This work analyses the experimental dumps of the CSM#4 to determine the losses in the CICC via the measurement of the energy deposited in the supercritical helium. The losses in the magnet are presented pointing out the impact of the slow current cycles. The latter also allow one measuring the hysteresis losses of the magnet. In the previous module tests, as well as in the tests of a single layer solenoid (referred to as CS Insert), it was very difficult to retrieve reliable values of the hysteresis losses in the CS conductor. However, the knowledge of hysteresis losses is crucial for a correct heat inventory of the magnet in operation. This study reports the results of their measurement, which represents a relevant added value of the CSM#4 tests. Finally, the experimental data are compared with the results of analytical models developed for the loss computation.

General Atomics (GA) is fabricating seven ITER Central Solenoid Modules (CSM) for the ITER Organization (IO). As part of the fabrication process, all CSMs undergo factory acceptance testing (FAT) prior to shipment to the IO. The FAT includes charging the modules to 40 kA and performing fast discharges (7.3 second decay time constant) to measure alternating current (AC) losses. These fast discharges generate high voltages at the electrical connections between the CSM and the test facility. Due to a fast discharge fault during the CSM 3 FAT, Paschenization methods of high voltage connections between the CSM and the test facility needed to be developed, qualified, and implemented. These connections included the coaxial and twinbox joints, all in-chamber instrumentation voltage tap wire splices, and voltage tap chamber feedthroughs. A test article was manufactured to replicate these connections and joints, and qualify the locally removable Paschenized insulation designs with a Paschen Test at 4.5 K. The 4.5 K Paschen test was comprised of 15 kV tests between 1E-03 and 1 mbar. This paper will present and discuss the Paschenization methods, lessons learned from research, and the CSM implementation in the test facility.

This paper describes critical assembly process qualifications, acceptance criteria, and worker training of ITER Central Solenoid Assembly. Coaxial joint assembly was qualified and trained to achieve resistance below 4.1 nOhm. The electrical insulation process was qualified to 30 kV and 15 kV under Paschen conditions. Shear pin drilling and installation within specified tolerance was achieved. Modules were lifted and positioned within 2 mm. The lessons learned, and subsequent work execution onsite within the IO facility assembly hall are also presented.

The primary Quench Detection System (QDS) of the Central Solenoid (CS) of the ITER magnet system must be able to distinguish the resistive component of the voltage, arising during quench, from the inductive one due to time-varying magnetic fluxes. This task is especially challenging for the six modules composing the CS (CSMs), with a coil self-inductance of the order of ∼ 1 H, subjected to current ramps up to ∼10 kA/s. Each CSM is equipped with stainless-steel tapes wrapped around the outer conduit of the conductor, referred to as Co-Wound Tapes (CWTs), linked to a magnetic flux approximating the one linked to the conductor itself. This work focuses on the definition of a model able to compute the voltages measured by the QDS with the high precision required. The analysis is based on a 2D axisymmetric FEM model of the entire CSM in a stand-alone configuration. A novel 3D approach based on an integral computation method allows one to account for the twisting of the conductor sub-cables of the last cabling stage (petals). The model is applied to quantify the impact of three main error sources contributing to the residual voltage signal measured by the QDS: the difference in self-field flux linked to the conductor and to the CWT, the inhomogeneity of the background field and the twisting of the petals.

The AC loss tests on the first ITER Central Solenoid Module (CSM) have been modelled and compared to the test results. The model has been implemented in the 4 C code, a thermal-hydraulic modelling tool which includes the CSM winding pack and the cryogenic circuit of the test facility. Two modes of operation of the circuit have been analyzed: the nominal and the “isolation” mode, i.e., when the cryogenic circuit valves are operated to isolate the coil during the current dumps. The computed mass flow rate, pressure and coil outlet temperature at different locations have been compared with the measurements, showing a very good agreement in both modes of operation of the circuit. The validated model helped in the interpretation of the experimental results, such as the backflow at the coil inlet -which cannot be measured- or the non-monotonic outlet temperature evolution following the current dump. Furthermore, the code was used to qualify the isochoric method for the quantification of the deposited energy due to AC losses, as it was the only method applicable in case of current dumps from high current.

The ITER Central Solenoid (CS) is under fabrication by the US ITER organization and its subcontractors. US ITER will supply seven modules to ITER IO (International Organization), six of which will be assembled in a stack that forms the ITER Central Solenoid. In the ITER operational scenario the CS modules (CSM) experience very high voltages, especially during plasma initiation and plasma disruption. Also, there are a significant induced voltages in the CSM due to magnetic coupling with the PF coils and plasma current. During initiating of plasma current, the voltage on the CSM reaches up to 11 kV. We need to suppress the inductive signal to a much lower level, 60 mV or lower. Thus, the noise rejection ratio (NRR) required for a reliable quench detection (QD) is extremely high, not demonstrated on any of the superconducting magnet systems built so far. This article describes the QD principles, expectations, and test results obtained in some CSMs during testing. Preliminary analyses and methods for improvements of the NRR in QD are presented and discussed.

The ITER Central Solenoid is under fabrication by the US ITER organization and its subcontractors. US ITER will supply seven modules to ITER IO, six of which will be assembled in a stack that forms the ITER Central Solenoid (CS). All CS modules were or will be tested at 40 kA in the Final Test facility at General Atomics, Poway, CA. Testing included high voltage, as well as Paschen testing in the vacuum and global leak tests before and after the cooldown to 4.5 K and EM cycling to 40 kA. In the paper we present the results of the CS Module 4 performance, after modifications to the test facility to improve reliability and instrumentation. We measured critical temperatures in several pancakes, AC losses before and after 10 cycles to 40 kA, joints resistance and hydraulic characteristics of the coils. We also measured displacements of the coil height and vertical strain of the CSM (central solenoid module) to verify structural mechanical characteristics of the coil along with cooldown shrinkage of the coil. We studied performance of the cowound quench detectors, confirmed their effectiveness in suppression of the inductive noise, but also developed a plan to improve sensitivity of the quench detection in ITER CS. This information is necessary for verification of the stack behavior of CS in ITER operation. The test results, preliminary analyses, comparisons to the other tested modules are presented and discussed.

The ITER Central Solenoid (CS) consists of a stack of six modules, each made of 40 pancakes wound with Nb3Sn Cable-In-Conduit Conductors (CICCs) cooled with supercritical helium (SHe). All six modules (plus one spare) are to be individually cold-tested at the General Atomics final test facility in San Diego (USA), in order to check their performance; the first CS Module (CSM1) was tested in early 2020.A test campaign on a CSM Mock-up (CSM MU) wound with 16 dummy pancakes, i.e., with nonsuperconducting (copper) strands, was already carried out in San Diego at the end of 2017, for the commissioning of the test facility. The analysis of the CSM MU experimental data is presented here.Each CSM is a full magnet with 554 turns; it did not have any thermal-hydraulic (TH) or electrical sensors inside the winding due to insulation reasons, so that, e.g., SHe pressure, temperature and mass flow rate, as well as the voltage, were only measured at the ends of selected pancakes.Therefore, it was essential to employ a thermal-hydraulic (TH) model in order to obtain information on the quantities of interest inside the coil, e.g. which was the voltage across the coil at the moment when the current sharing temperature (TCS) was reached for the first time somewhere in that double-pancake (DP) during a TCS test.The TH model of the CSM, developed and implemented in the validated 4C code, and eventually adopted for the test preparation and interpretation, includes some free parameters, i.e., the inter-pancake and inter-turn thermal coupling, whose uncertainty is mainly due to the complex, multi-layer structure of the turn and pancake insulation. The calibration of these parameters is required to correctly capture the TH behavior of the CSM. For this purpose, the results of the experimental campaign on the CSM MU have been used. The detailed topology of the CSM MU is described and implemented here in a dedicated 4C model. Both slow and fast transients are used for the calibration, e.g., quasi-steady state heating of the SHe, entering a single DP and heat slug tests, respectively. It is shown that the transverse heat transfer within the winding pack could be largely overestimated if the ideal heat conduction across a bulk insulation layer is considered. The calibrated model is then validated on the CSM1 test results.

The ITER Central Solenoid (CS) will be realized by assembling a stack of six modules. Each module is a solenoid consisting of 40 pancakes wound with a Nb 3 Sn Cable in Conduit Conductor (CICC). The tests of the second module (CSM#2) were performed at the General Atomics (GA) facility in Poway (US). During the test campaign, the CS Module is submitted to dumps of the transport current from different initial values (10, 15, 20, 25, 30, 35, 40 kA) to 0 kA, which allow measuring the AC losses in the coil. In this paper we present the results on AC losses during the dumps from different initial transport currents, as computed with two different methods. The first method is based on the observation that the dumps determine a very fast pressure rise of the supercritical helium embedded in the module, which undergoes an isochoric transformation. This approach is therefore based on the computation of the variation of internal energy of the helium during the pressure rise itself. The second method is based instead on a calorimetric procedure aimed at estimating the enthalpy variation of the supercritical helium due to the thermal power deposited during the current dumps. The main contribution to the losses during these dumps is due to the coupling losses. As for the hysteresis losses in the magnet, the results obtained through slow current cycle tests are also presented.

The ITER Central Solenoid is under fabrication by the U.S. ITER organization and its subcontractors. U.S. ITER will supply seven modules to ITER IO, six of which will be assembled in a stack that forms the ITER Central Solenoid. The first modules that were built by GA at their facility, went into high voltage testing, including Paschen testing in the vacuum, and then they were tested at 4.5 K and up to 40 kA to demonstrate compliance of the coil with the ITER requirements. In this article, we present the Test Plan and results of the central solenoid (CS) module's performance, especially at the full current. We measured critical temperatures in several pancakes, we measured ac losses, joint resistance, and hydraulic characteristics of the coils. We also measured displacements of the coil height and hoop strain of the CS module (CSM) to verify the structural mechanical characteristics of the coil along with the cooldown shrinkage of the coil. We studied the performance of the cowound quench detectors and confirmed their effectiveness in the suppression of inductive noise. This information is necessary for verification of the stack behavior of CS in ITER operation. The test results and preliminary analyses are presented, compared to expectations, and discussed.

The ITER Central Solenoid (CS) modules are under fabrication by the US ITER organization and its subcontractors. US ITER will supply seven modules to the ITER Organization (IO), six of which will be assembled in a stack that forms the ITER Central Solenoid, the last one being spare. The first module, namely CSM 1 was manufactured by General Atomics (GA) and went through Factory Acceptance Tests (FAT) including high voltage testing, Paschen testing and then cold test at 4.5 K and up to 40.0 kA in order to demonstrate compliance with coil performance requirements. The paper focuses on the results of the first CS Module thermal hydraulic characterization without current (and field). Pressure drops, transit time, and thermal coupling between pancakes are presented. Analysis results and tests are also compared.

The Central Solenoid (CS) is the core element of the ITER magnet system, contributed as in-kind procurement by the US Domestic Agency. Made up of six modular inter-exchangeable module coils, vertically stacked, forming a 15 m high and 4 m outer diameter solenoid, to be inserted inside the central tokamak core, after assembly of the 18 D-shaped Toroidal Field (TF) coils. Each module uses a Nb 3 Sn conductor internally cooled by circulation of supercritical helium at 4.5 K and supplied, for each module, with a 45 kA current by the way of two vertical leads exiting from the module outer radius. The available space between the CS and TF magnets being very limited, the US DA has developed a compact - so called Coax Joint (CJ) - devoted to connect the respective twelve module leads to the feeders located at top and bottom of the CS via dedicated busbar extensions. The CS coax joint assembly procedure as developed by US DA would make use of CS assembly onsite soldering process, to be executed under supervision of the ITER Organization (IO) in the tokamak assembly hall. In order to mitigate risks related to these soldering activities needed at assembly stage, IO has proposed an alternative assembly process based on indium wires compaction - so called Coax Compacted Joint (CCJ)- and initiated its prototype development and qualification in time. The hereby presented CCJ design solution is based on four copper quadrants, each including an embedded straight Rutherford-type superconductor cable-strip to transport the current. The current is transferred from the lead to the quadrants by the way of compacted indium wires. A steel jacket welded around the joint ensures the mechanical support as well as the needed leak tightness. The paper describes developments made by CEA under IO supervision from the conceptual design to the testing of joints in relevant cryogenic and operative conditions.

The ITER Central Solenoid (CS) is under fabrication by the US ITER organization and its subcontractors. US ITER will supply seven modules to ITER IO, six of which will be assembled in a stack that forms the ITER Central Solenoid, with one as a spare. The first module fabrication has been completed by General Atomics (GA) at their facility and has begun testing including high voltage testing, Paschen testing in the vacuum and then testing at 4.5 K and up to 40 kA in order to demonstrate compliance of the coil to ITER requirements. In the paper we present the Test Plan and results of the CS Module performance tests, especially at 40 kA current. AC losses, joint resistances and hydraulic characteristics of the coil are all measured. Displacements of the coil height and hoop strain of the CS Module are also measured to verify structural and mechanical characteristics of the coil along with cooldown shrinkage of the coil. This information is used for verification of the stack behavior of CS in ITER operation. The test results and preliminary analyses results are presented, compared to expectations, and discussed. All measured parameters suggest that the CS module will perform well in ITER machine.

The ITER Central Solenoid (CS) will be manufactured by assembling a stack of six modules, which are under fabrication by the US ITER organization and its subcontractors. The tests of the first CS Module have been performed at the premises of the General Atomics (GA) facility in Poway (US), in order to check compliance to the ITER requirements. Among other tests, the magnet was submitted to exponential dumps of the transport current from different initial values (10, 15, 20, 22.5, 25, 35, 40 kA) down to 0 kA. These tests are aimed at conducting DC breaker commissioning of the test facility and were used to measure the AC losses in the coil during electrodynamic transients. This paper presents the results of these measurements, along with a comparison with analytical computations of the losses in the magnet.