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Jet Joint Undertaking : Progress Report 1994 JOINT EUROPEAN TORUS ttlW JET JOINT UNDERTAKING PROGRESS REPORT 1994 EUR 16474-EN-C EUR-JET-PR12 JET JOINT UNDERTAKING PROGRESS REPORT 1994 APRIL 1995 This document is intended for information only and should not be used as a technical reference. EUR 16474 EN (EUR-JET-PR12) April 1995. Editorial work on this report was carried out by B.E.Keen. The preparation for publication was undertaken by JET Publications Group, JET Joint Undertaking, Abingdon, UK. © Copyright ECSC/EEC/EURATOM, Luxembourg 1995 Enquiries about copyright and reproduction should be addressed to: The Publications Officer, JET Joint Undertaking, Abingdon, Oxon. 0X14 3EA, UK. Legal Notice Neither the commission of the European Communities nor any person acting on behalf of the Commission is responsible for the the use which might be made of the following information. Catalogue number : CD-NB-16474-EN-C for the Report EUR 16474-EN-C Printed in England Contents Introduction, Background and Summary 1 Technical Achievements during 1994 11 - Torus Systems 11 - Power Supplies and Magnet Systems 15 - Neutral Beam Heating Systems 31 - RF Heating Systems 42 - Operations Systems 57 - Remote Handling Systems 61 - Waste and Beryllium Handling 65 - Vacuum Systems 67 - Control and Data Acquisition System (CODAS) 69 - Data Management 74 - Diagnostic Systems 76 - Summary of Machine Operations 100 - Summary of Technical Achievements 103 St-it-iil¡fit- Achievements during 1994 107 - High Performance 108 - Di vertor Assessment and Di vertor Physics 115 - Tokamak Concept Improvements 141 - Transport and Fluctuations 154 - MHD and Beta Limits 164 - Physics Issues relating to Next Step Devices 166 - Data Analysis and Modelling 168 - Summary of Scientific Progress and Perspective 183 Developments and Future Plans 187 - Pellet Injection 189 - Advanced Divertor Development 192 - Tritium Handling 193 - Technical Preparation for D-T Experiments 197 - Future Plans 202 Appendices 205 I JET Task Agreements 1994 205 II List of Articles, Reports and Conference Papers published in 1994 208 FOREWORD Foreword This is the twelvth JET Progress Report, which provides a new Lower Hybrid launcher (designed to couple 1OMW). an overview summary and puts into context scientific and Other new installations included a system for plasma technical advances made on JET during 1994. This Re­ current and shape control, a Fast Radial Field Amplifier port presents a more detailed account of JET's progress for vertical position control, eight Saddle Coils inside the than that contained in the JET Annual Report. It is aimed vacuum vessel for disruption control and the study of not only at specialists and experts engaged in nuclear Toroidal Alfvén Eigenmodes and an extensive array of fusion and plasma physics, but also at a more general new diagnostics, especially for divertor measurements. scientific community. To meet these aims, the Report The shutdown was successfully completed with contains a brief summary of the background of the Project, pumpdown of the torus in January 1994. The first plasma and describes the basic objectives of JET and the princi­ in the new pumped divertor configuration was produced pal design aspects of the machine. In addition, the Project in February and by mid­March successful 2MA diverted Team structure is included, as it is within this structure plasmas had been established. that activities and responsibilities for machine operation The general objectives of the experimental programme are carried out and the scientific programme is executed. with the Mark I divertor were to assess the performance JET entered 1994 nearing the end of the longest and of the pumped divertor configuration, using the horizon­ most extensive modification since the initial assembly of tal target tiles and, within their limitations, the vertical the device. Two faulty toroidal magnetic field coils had side tiles. The relatively open geometry of the Mark I been replaced and the new pumped divertor configuration divertor accepts a wide range of plasma equilibria, and (Mark I) had been installed. The interior of the torus had divertor physics studies, high performance operation and been completely rebuilt to include four new divertor coils, advanced tokamak concept studies are possible for this an inertially­cooled divertor target structure and a cryo­ configuration within the designed maximum plasma cur­ genic vacuum pump. The heating and current drive sys­ rent capability of 6MA. tems had been modified and included an upgraded neutral 1994 has seen significant progress in optimising peak beam system to inject 7.8MW of power at 140keV and fusion performance and extending operation to the reactor 13.6MW at 80keV, new Ion Cyclotron Resonance Fre­ relevant steady­state ELMy Η­mode, which has now been quency heating antennae (designed to couple 20MW) and obtained undera variety of conditions: plasma currents up FOREWORD to 4MA, power levels up to 26MW, in the high ßp regime, The saddle coils have been used for initial experi­ in discharges with negative central magnetic shear, and at ments on TAEs and the disruption feedback stabilisation high ßN.The high β regime has also been extended to system is in the final stages of commissioning. Only steady­state and to the reactor relevant domain. the lower saddle coils are now available, since the The high power handling capability of the Mark I upper saddle coils were disabled in September 1994 divertor target has been demonstrated and the severe after being damaged. impurity influxes (carbon "blooms"), which previously The 1994/95 campaign (scheduled to end in June terminated high performance plasmas, have been elimi­ 1995) has still to address: high power combined heating; nated. The cryopump reduces recycling, eliminates the further exploration of the detached divertor regime and effects of wall saturation (observed in previous long pulse its compatibility with ELMy Η­mode operation; helium operation), allows effective particle control, and gener­ pumping and transport using argon frost on the cryopump; ally allows higher plasma performance. work on current profile control; toroidal magnetic field The best steady­state results (achieved in ELMy H­ ripple studies; use of the saddle coils for disruption modes at 4MA/3.4T with more than 18MW of additional feedback control; and extension of X­point operation heating) show a stored energy of =8MJ and a fusion triple towards 6MA. In March 1995, the CFC divertor target 2O 3 product (nDT.tE) of 2.6x 10 m keVs being maintained for tiles will be exchanged for beryllium target tiles and a more than four energy confinement times. The best tran­ comparison will then be made between CFC and beryl­ sient results (achieved at the end of the ELM­free phase lium tiles for a few specific plasma configurations. One of hot­ion Η­modes) were comparable to the best of past RF antenna, modified to incorporate a bumper limiter, campaigns even though plasmas are now = 15% smaller in will also be tested. volume. The highest stored energy was 11.3MJ and the The next major milestone will be to demonstrate com­ 20 3 fusion triple product (nQT.tE greater than 8x 10 nr keVs) patibility between the high confinement reactor­relevant and neutron rate (4xl016s') were within 10% of the best ELMy Η­mode regime and detached divertor operation. obtained with deuterium in 1991/92. However, this may require the more closed Mark II The two neutral beam injectors have routinely in­ divertor structure. This will be installed in 1995 and jected up to 19MW and 140MJ has been injected tested in 1996 with particular emphasis on the effect of during a 20s ELMy H­mode. 13MW of ICRF power has geometry on gas target/radiative divertor plasmas, which also been coupled, but this is limited by a combination form the physics basis for the divertor concept favoured of unsatisfactory control electronics, unequal coupling by the ITER Joint Central Team. of the straps of the antennae array and low power During the second half of 1996, a limited period of D­T transfer to the plasma under some phase conditions. operation (DTE­1, producing up to 2 χ IO20neutrons) will New control electronics systems are currently being demonstrate long pulse fusion power production (fusion installed and will be tested with plasmas in February amplification factor, Q>1 with more than 10 MW of 1995. Further antenna modifications are scheduled for fusion power for a few energy replacement times) and the beryllium tile exchange shutdown and the Mark II will make important contributions to D­T physics (in­ divertor shutdown planned to start in March and June cluding Η­mode threshold, ELM and confinement behav­ 1995, respectively. Combined NB and ICRF powers of iour, and some D­T specific radio frequency heating 26MW have been injected and 3MA has been driven studies) which JET alone can provide in an ITER­rele vant non­inductively with 6MW of LH power. divertor configuration. DTE­1 would allow the original FOREWORD four areas of JET work to be completed and would period would validate high power, high performance provide timely input to the ITER EDA. It would also physics in a divertor configuration specifically for ITER. address the important technology issues of reactor rel­ The subsequent programme would then progress to evant tritium processing and remote handling. In particu­ divertor/plasma optimisation studies before a more exten­ lar, it would demonstrate the ability of the Active Gas sive period of D-T operation (DTE-2) in 1999. In DTE-2, Handling System to process tritium while supporting a D-T plasmas would be studied with substantial reacting tokamak plasma. alpha-particle heating, capitalising on the performance A proposal for the extension of the JET Programme to improvements achieved in the preceding experimental the end of 1999, which is supported by the JET Council, campaigns. DTE-2 experiments could produce up to is currently being sent to the Council of Ministers for 5 χ 1021 neutrons, but every effort would be made to approval.
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