Towards Control of Steady State Plasma on Tore Supra

The Tore Supra tokamak is the largest superconducting magnetic fusion facility, has been devoted to long-duration high-performance discharge research. With a steady-state magnetic field and water cooled plasma facing components, discharges up to 6 minutes

Towards control of steady state plasma on Tore Supra

P. Moreau, O. Barana, S. Brémond, J. Bucalossi, E. Chatelier, E. Joffrin, D. Mazon, F. Saint-Laurent,

E. Witrant and Tore Supra Team

Abstract—Magnetic Fusion Research worldwide is now, with ITER, about to demonstrate the scientific feasibility of fusion energy production. Feedback control of fusion experiment gets more and more crucial both for performance, stability and machine protection. The Tore Supra tokamak is well suited to tackle these issues due to its unique capability to perform long duration discharges with many actuators/sensors available. The Tore Supra real time measurements and control system has been upgraded to address schemes dedicated to long pulse operation with simultaneous control of an increasing number of plasma parameters. A review of recent progress on several key control issues like measurement drift during long pulses, high efficient fuelling, plasma current profile tailoring, plasma facing component protection and self plasma protection is given.

I. INTRODUCTION

A

chieving long-duration high performance feedback

controlled discharges in a magnetic fusion device is one of the most important challenges to prepare the operation of fusion reactor [1], [2]. Hence, most of the major new projects on fusion energy, planned or under construction (W7-X, HT7-U JT60-SC, KSTAR, SST-1, and ITER) share this aim. Tore Supra (TS) tokamak is the largest superconducting magnetic fusion facility (torus dimensions: R = 2.40 m, a = 0.72 m, plasma current Ip ≤ 2 MA and magnetic field Bt ≤ 4.0 T). It has been devoted to long-duration high-performance discharge research. Recently, TS went through a major upgrade replacing all the in-vessel components by actively cooled components aiming at increasing its pulse duration ability. In 2002, discharges up to 6 minutes 24 seconds duration with injected / extracted energy up to 1 GJ have been performed. That offers a unique capability of addressing the plasma control issues in long pulse operation towards steady state plasma control. The plasma may be modelled as a resistive ionised fluid moving in a magnetic field. It reacts as a multi-time scale, non-linear distributed system with a large number of potential instabilities. Plasma parameters are often strongly coupled and available actuators are still in limited number. They consist in an external set of magnetic coils, pellet and gas injection, and heating systems. Plasma control has to be performed at several physics time-scale connected to different physical processes (Fig. 1): typically 10-100ms for plasma equilibrium, and plasma fuelling, a few seconds for plasma current diffusion, tens of seconds to minutes for plasma wall interaction. For intrinsically unstable and

complex system such as confined plasma, feedback control clearly has a crucial role for performance optimisation and machine protection.

Tore Supra domain

10-3

10-2

10-110+010+110+2

10+3

+4. . .

SecondPlasmaInstabilities

Control

diffusionCurrentThermalDisruptioncomponentsCoolingErosionParticles

confinementParticlesinteraction

WallFig. 1: Characteristic time scale on fusion devices.

This paper is an overview of basics and recent progress on TS real time measurements and control system. Section II describes the hardware. It depicts the network systems used for diagnostics (sensors), real time (RT) data computation, feedback controller and actuators. Section III discusses main key control issues: plasma equilibrium, plasma fuelling, plasma internal profiles, plasma facing components protection and pulse management. Section IV gives a conclusion pointing out the future needs.

II. HARDWARE

Most TS diagnostics use an acquisition unit equipped with two processors, each in charge of a specific function. The first one is dedicated to the communication with the real time server in order to synchronize the acquisition and the control with the timing unit of the discharge, transmit raw and processed data and store them. The second processor runs a single RT task dedicated to acquisition on input boards, raw data processing, using control loops of a few milliseconds from a specific algorithm. It is used to deliver the calculated control voltages to actuators or subsystems it manages. Intercommunication between processors is achieved by a Versatile Module Eurocard (VME) bus through shared memory.

Recently, PC units (INTEL Pentium® IV-2.8GHz) have been used for RT computation: high level feedback controller and plasma equilibrium reconstruction are now routinely available.

The TS data acquisition system must fulfill a broad variety of requirements. First, continuous data acquisition has been implemented, meaning that the supervision storage and timing tasks are continuously running at low sampling frequency. This allows continuous data recording of some diagnostics like calorimetric sensors, which is of major importance for plasma facing components heat load studies.

The Tore Supra tokamak is the largest superconducting magnetic fusion facility, has been devoted to long-duration high-performance discharge research. With a steady-state magnetic field and water cooled plasma facing components, discharges up to 6 minutes

In the opposite, some data acquisition units require a high data flow rate (100 kHz up to 1 GHz) when special plasma event occurs. During 1-2 seconds, several times per discharge, the data flow rate can reach 18 Mb/s per front-end unit. For these units, the row data are transferred via a private 100 Mb/s Etherne …… 此处隐藏：26729字，全部文档内容请下载后查看。喜欢就下载吧 ……