Structural Simulation of the Central Solenoid for the Burning Plasma Experiment (bpx)

The structural design and analysis of the BPX Central Solenoid is presented. The largescale structural behavior of the solenoid is simulated with a two-dimensional (2-D) axisymmetric ANSYS' finite element model. The computer model is used to determine the time-dependent stress history in the coils and tie rods, and to perform various structural performance studies. Some of these studies are included here such as tie-rod preload optimization, relative movement at low-friction surfaces, alternate material and transient cool down effects. The results of these simulations are presented and discussed. A fatigue analysis of the conductor stresses is presented based on the BPX design criteria2 and preliminary material property data. The relationships between the 2-D solenoid model and more detailed 3-D models of sub-components are also discussed. Introduction The function of the BPX poloidal field (PF) coil system is to produce the flux swing required to induce the current in the plasma and the field characteristics necessary to shape and control the plasma position. The PF coil system consists of ring coils, internal control coils and a five-coil central solenoid. At about 120 metric tons, the central solenoid represents the heart of the PF coil system. Of all the PF coils, the central solenoid presents the most challenging engineering problems. In essence, it must withstand large electromagnetic (EM) forces, high stresses and significant thermal transients for thousands of cycles. In addition, cost and size requirements demand an aggressive coil design. Design and analysis are closely coupled in the development of the central solenoid. And an important part of the analysis requires an accurate estimation of the solenoid's forces, stresses and displacements. Finite element analysis (FEA) has brought speed and flexibility to the engineering process, and provided a means of exploring and evaluating the details and characteristics of the structure. This paper presents a review of the 2-D axisymmetric model and analyses as they apply to designing the BPX central solenoid. The purpose of the model is to capture the global structural behavior of the solenoid, and to evaluate the effects of variations in structural components, materials, low friction surfaces, and thermal transients. The general purpose ANSYS computer code is used to perform these analyses. The 2-D Axisymmetric Model The central solenoid is predominantly axisymmetric in form. The beryllium copper (BeCu) conductor is waterjet cut from plate stock forming a circular current path three-quarters of the way around the coil. A "transition region" spirals out from one "conductor turn" to the next over the remaining 900 segment, thus defining the most significant variation from axis symmetry. Other major structural components such as covers, coil-to-coil shims and terminal support plates are also predominantly axisymmetric except for subtle machining details. Even the effects of the ten 140 mm (5%") diameter tie rods can be approximated by an equivalent ring of similar tensile area. Figure 1 shows a plot of the FE model.