Design and verification status of COMPASS-U vacuum vessel and stabilization loop

Highlights

• COMPASS-U vacuum vessel (VV) design concept and its mechanical verification against the electromagnetic forces.

• Design concept of passive stabilizing plates (PSP), PSP support and VV support.

• Mechanical verification for 14 different load combinations of plasma transient events.

Abstract

The COMPASS-U is a new tokamak in the design phase at Institute of Plasma Physics, Prague, Czech Republic. It is a medium-sized tokamak with high magnetic field (B_t = 5 T) and high temperature vessel (< 500 °C). Hence, large electromagnetic forces are expected on the Passive Stabilizing Plates (PSP) and Vacuum Vessel (VV) during plasma disruption events. A non-selfconsistent approach is selected for the electromagnetic calculations using ANSYS Maxwell software to determine the highest probable forces on passive structures and to design a robust vacuum vessel.

This paper outlines the latest status on the design activities of the vacuum vessel concept and its mechanical verification against the electromagnetic forces. The vessel design concept is developed considering the spatial constraints, fabrication simplicity, minimum cost and the design is verified for minimum deformation and stresses in the vessel. It also includes the design evolution of PSP, PSP support and VV support. The mechanical analyses are carried out for load combinations of plasma transient events.

Introduction

The COMPASS-U is a new medium-sized (R = 0.894 m, a = 0.27 m) tokamak with high magnetic field (B_t = 5 T) and high temperature (< 500 °C) operation. It is designed to address key challenges related to plasma exhaust, liquid metal divertor, enhanced confinement modes and edge plasma physics important for the next-step devices [1]. Fig. 1 shows the geometrical arrangements of the major components of the tokamak. The Poloidal Field (PF) coils and Central Solenoids (CS) are placed surrounding the Vacuum Vessel (VV) and inside the demountable Toroidal Field (TF) coils. The vacuum vessel is supported on the external support structure [2].

The COMPASS-U is designed to operate with 2 MA plasma current and 5 T toroidal magnetic field, hence strong eddy currents can be induced in the VV and surrounding passive structures during a plasma disruption event. Interaction of the induced current with the magnetic field generates large electromagnetic forces on the systems. The COMPASS-U VV design is mainly based on the electromagnetic forces produced during plasma disruption events and several FE simulations are carried out for different load combinations to ensure its structural integrity.

A number of design changes take place during progress of the VV design from the conceptual design study [3]. The wall thickness of the VV shell is reduced, corner ribs are replaced by forged ring and equatorial port height is reduced to 500 mm to keep clearance between port and PF4 during thermal movement. The design of the Passive Stabilizinging Plate, PSP support and PSP bridge are also added in the vessel. The VV support design is optimized through a series of FE simulations.