AC Losses in the First ITER CS Module Tests: Experimental Results and Comparison to Analytical Models

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

Bank Upgrade for Sspx at Llnl

A new 5kV, 1.5MJ modular capacitor bank has been designed for the Sustained Spheromak Physics Experiment (SSPX) at LLNL. The new bank consists of thirty 4mF capacitors that are independently controlled by light-triggered thyristors. By closing all switches simultaneously, the bank will provide a mega-ampere discharge. The new bank will also allow additional capabilities to SSPX, including higher peak gun current, longer current pulses, and multi-pulse plasma buildup. Experiment results for a single stage prototype will be presented, deliver a single large current spike, or, switches can be triggered in sequence to deliver a longer lower current pulse. Multiple pulses can be created by triggering sections of the modular bank in intervals

Normal-zone detection in tokamak superconducting magnets with Co- wound voltage sensors

This paper discusses advantages and disadvantages of different locations of co-wound voltage sensors for quench detection in tokamak magnets with a cable-in-conduit conductor. The voltage sensor locations are analyzed and estimates of the anticipated noise vs. dB/dt are derived for transverse, parallel, and self fields. The LLNL Noise Rejection Experiment, also described here, is designed to verify theoretical expectations on a copper cable exposed to these fields that will simulate the tokamak field environment

Detection of the normal zone with cowound sensors in cable-in conduit conductors

Tokamaks in the future will use superconducting cable-in-conduit- conductors (CICC) in all poloidal field (PF) and toroidal field (TF) magnets. Conventional quench detection, the measurement of small resistive normal zone voltages ({lt}1 V) in the magnets will be complicated by the presence of large inductive voltages ({gt}4 kV). In the quench detection design for TPX, we have considered several different locations for internal co-wound voltage sensors in the cable cross-section as the primary mechanism to cancel this inductive noise. The Noise Rejection Experiment (NRE) at LLNL has been designed to evaluate which internal locations will produce the best inductive- noise cancellation, and provide us with experimental data for comparison with previously developed theory. The details of the experiments and resulting data are presented and analyzed

Co-wound voltage sensor R&D for TPX magnets

The Tokamak Physics Experiment (TPX) will be the first tokamak to use superconducting cable-in-conduit-conductors (CICC) in all Poloidal Field (PF) & Toroidal Field (TF) magnets. Conventional quench detection, the measurement of small resistive normal-zone voltages (4 kV). In the quench detection design for TPX, we have considered several different locations for internal co-wound voltage sensors in the cable cross-section as the primary mechanism to cancel this inductive noise. The Noise Rejection Experiment (NRE) at LLNL and the Noise Injection Experiment (NIE) at MIT have been designed to evaluate which internal locations will produce the best inductive-noise cancellation, and provide us with experimental data to calibrate analysis codes. The details of the experiments and resulting data are presented

TPX superconducting cable-in-conduit 1995 design and development progress

A unique feature of the magnet system for the Tokamak Physics Experiment (TPX) is that all the magnets are superconducting. With the exception of the outer poloidal coils, the magnet system uses Nb{sub 3}Sn cable-in-conduit conductor; the outer poloidal coils use Nb-Ti cable-in-conduit conductor. We describe the current TPX conductor design and present a progress report on the conductor development. Our strand development contracts have resulted in demonstrating that at least two vendors can produce Nb{sub 3}Sn strand which meets the TPX specification. Subcable testing gives confidence that the TPX conductor will satisfy the magnet operational requirements. Fabrication of full-size conductors is underway and tests on these will give verification that the TPX conductor meets the operational requirements. Our industrial cabling and sheathing contract to produce demonstration conductor using copper strands is exploring a production technique that differs from the conventional tube mill approach

Modeling the ITER CS AC Losses Based on the CS Insert Analysis

The cable-in-conduit conductor that will be used for the manufacturing of the ITER central solenoid (CS) modules has undergone a long series of qualification tests: the latest was performed in 2015 at QST, Naka, Japan, on the central solenoid insert (CSI) coil. In this work, the AC losses dataset collected during the CSI test campaign is interpreted using a lumped-parameter model for the coupling and hysteresis losses. The model is first benchmarked against the results of the THELMA code and then, after the implementation in the 4C thermal-hydraulic code, successfully validated against experimental data from tests performed on the CSI.With the validatedACloss model, the predictive analysis of the performance of the ITER CS is then carried out using again the 4C code, both in nominal conditions and with a reduced coolant mass flow rate in the most loaded pancake; it is shown that the minimum temperature margin required by the design is always satisfied, for both virgin (1 K) and cycled (1.5 K) conductor

Analysis of the ITER central solenoid insert (CSI) coil stability tests

At the end of the test campaign of the ITER Central Solenoid Insert (CSI) coil in 2015, after 16,000 electromagnetic (EM) cycles, some tests were devoted to the study of the conductor stability, through the measurement of the Minimum Quench Energy (MQE). The tests were performed by means of an inductive heater (IH), located in the high-field region of the CSI and wrapped around the conductor. The calorimetric calibration of the IH is presented here, aimed at assessing the energy deposited in the conductor for different values of the IH electrical operating conditions. The MQE of the conductor of the ITER CS module 3L can be estimated as ~200 J ± 20%, deposited on the whole conductor on a length of ~10 cm (the IH length) in ~40 ms, at current and magnetic field conditions relevant for the ITER CS operation. The repartition of the energy deposited in the conductor under the IH is computed to be ~10% in the cable and 90% in the jacket by means of a 3D Finite Elements EM model. It is shown how this repartition implies that the bundle (cable + helium) heat capacity is fully available for stability on the time scale of the tested disturbances. This repartition is used in input to the thermal-hydraulic analysis performed with the 4C code, to assess the capability of the model to accurately reproduce the stability threshold of the conductor. The MQE computed by the code for this disturbance is in good agreement with the measured value, with an underestimation within 15% of the experimental value