ASDEX Upgrade

LetterLetter No. 1/March 2002

Foreword

For a very good reason the Max Planck Institute for Physics (IPP) is actively encouraging the more intensive use of its experiment ASDEX Upgrade by the other European fusion research centres (or „Associations“). The chances for ITER have improved dramatically in the last eighteen months: the Canadian site offer, French and Spanish proposals to provide a European site, the start of negotiations on the legal entity and the re-awakening of American interest. Our attention now turns necessarily to the European fusion programme which must be ration- alised and restructured in preparation for ITER con- struction. Resources, in particular funding, in the Associations will become scarcer.

A plausible scenario can be envisaged in which only very few fusion experiments remain in the Associations but there are exploited on a fully European basis.ASDEX Upgrade with its ITER-relevant geometry as well as its state-of-the- art plasma heating and diagnostics can play an important role. A necessary pre-requisite, however, is that other Associations are formally involved in the decision-making processes, in particular on the scientific programme and its execution.This epitomises the philosophy of the European fusion programme.We recall a conclusion from its last ma- jor external evaluation („Airaghi Panel“): „The fusion programme is probably the best example of European Added Value. The good co-ordination and co-operation between the Community and national research pro- grammes has enabled far greater achievements to be made than would be possible at a national level.“

In future, IPP will be informing the whole ASDEX Upgrade community about recent developments and latest results with the help of a regular Newsletter. A. M. Bradshaw ASDEX UPGRADE on the way to a European Fusion Facility

Task Force Leaders. By definition, Members of the ASDEX Upgrade Programme Committee every Association involved in the K. Behringer (Dept. E4, IPP) T. Klinger (Dept. E5, IPP Greifswald) ADEX Upgrade Programme has the H. Bindslev (Risø, DK) Vice-Chair E. Lazzaro (CNR Milano, I) right to nominate a member. In addi- H. Bolt (Dept. Mat. Research, IPP) M. Manso (IST Lisbon, P) P.Mc Carthy (DCU Cork, IRL) R. Salomaa (TEKES, FIN) tion, the IPP Department Heads in- C. Challis (UKAEA Culham, UK) U. Samm (TEC, B/D/NL) volved in the ASDEX Upgrade A. Fasoli (CRPP Lausanne, CH) R. Wilhelm (Dept. Technology, IPP) programme as well as the ASDEX O. Gruber (Project Head, IPP) Chair H. P.Winter (ÖAW,AUT) Upgrade Project Leader and a repre- S. Günter (Dept. TOK, IPP) H. Zohm (Dept. E2, IPP) sentative of the IPP pro- M. Kaufmann (Dept. E1, IPP) gramme are part of the AUG-PC. At present, it comprises 9 members from The ASDEX Upgrade programme has This was recently started by opening the Associations and 8 from IPP (see always had strong international links, the ASDEX Upgrade Programme box left).The first meeting took place especially within the EURATOM Committee (AUG-PC) to the Asso- in Garching on January 31st, 2002. Associations. However, with the in- ciations. This body defines the Task The experimental programme for the creasing number of experiments pro- Forces responsible for the different 2002 campaign was discussed and posed by collaborators, also a formal elements of the ASDEX Upgrade pro- finally approved. structure was needed in which the gramme and nominates the Task Force Associations could take responsibility Leaders. It also approves the experi- Furthermore,the bodies that work out for the ASDEX Upgrade programme. mental programme proposed by the the programme proposals, namely the yearly ‘Programme Seminar’,the ‘Task Force Meetings’ as well as the weekly Experimental proposals ‘Operations Meeting’ are now open for external participants. In parallel, an initiative has been started to ease submitted to remote participation in these meet- proposes TF ings. Finally, the ASDEX Upgrade programme to Intranet and the means for data ac- ASDEX Upgrade Task Forces (TFs) Ringberg seminar Program Commitee cess are constantly being improved. approves and discussion With this structure, a clear route from prioritises within AUG AUG exp. prog. community an experimental proposal to the final detailed discussion of TF programme in discharge exists (see figure). We aim at a compromise between the in- creased international participation and the flexibility that has so far been TF meetings* typical for the ASDEX Upgrade pro- gramme. We expect significant added enqueues discharge value and exciting new results. requests for

ASDEX Upgrade Collaborations

The ASDEX Upgrade programme enjoys Operation meeting* fruitful collaborations with many other re- search institutes, both nationally and inter- nationally. Amongst these are 8 German decides when proposal universities, laboratories from all EURA- is carried out in TOM Associations,as well as a number of in- stitutions world-wide,including the big fusion experiments in Japan and the US,various re- ASDEX Upgrade search institutes in Russia and also the toka- experimental session* mak programmes of China,India and Korea. Highlights from recent ASDEX Upgrade experiments

Progress towards an Integrated Advanced Scenario At ASDEX Upgrade, significant progress was made in 2001 towards achieving steady state H-mode discharges The ASDEX Upgrade with improved confinement and weak magnetic shear. Recent experiments have concentrated on simulta- Scientific Programme neously increasing confinement, density and normalised β beta ( N) by using pressure and current profile control. The ASDEX Upgrade Scientific Programme gives priori- In highly shaped, nearly double null plasma configura- ty to experiments which could influence detailed aspects β tions, H-mode discharges with high N (>3.5) and good of ITER’s operational scenarios: plasma shaping, mitiga- ≤ confinement (H98-P 1.3) have been obtained. Values of tion and physics of ELMs, operation near boundaries, fur- β the figure of merit NH98=8.0 are observed for 20 ener- ther characterisation of the edge/ plasma, effect ≈ gy confinement times at q95 3.6-4. In these reactor rel- and control of neoclassical tearing modes, optimisation of evant conditions the total non-inductively driven advanced tokamak scenarios and assessment of current exceeds 50% of the plasma current. Line aver- as a potential first wall material. It includes joint experi- aged densities of up to 9·1019 m-3 (80-90%) of the ments with other to obtain important scaling in-

Greenwald density nGW are achieved by the combina- formation in several areas. Especially comparisons with tion of NBI and gas fuelling,while maintaining the good the JET tokamak are routinely done and facilitated by the confinement. At the highest densities a transition from strong involvement of ASDEX Upgrade scientists in Type I to Type II ELMs is observed, providing a strong EFDA-JET campaigns. reduction of the peak heat load on the divertor which becomes steady in the range of 6 MW/m2, despite the The hardware improvements of the 2000/2001 shutdown high input power used (10 MW). will also come to further exploitation.These changes com- prise an optimised divertor geometry with enhanced flexi- bility for shaping, a re-direction of one neutral beam box to improve current drive efficiency, a further replacement of carbon by tungsten in the main chamber and a substan- tial increase of the pulse length to values beyond the cur- rent diffusion time. The latter improvement will allow to investigate the stationarity of scenarios and makes in this respect ASDEX Upgrade unique among all ITER-shaped tokamaks. Experiments on ASDEX Upgrade in 2002 will be performed throughout the year and are interrupted on- ly by a shutdown of 12 weeks starting in August.This break will mainly be used to improve the mechanical stability of the upper divertor and to increase the area of tungsten coated tiles leading to a further reduction of carbon in the machine.

The scientific programme is organised in the form of Task Forces,with their Leaders being the main actors in the pro- cess of preparation and execution.Currently four Task Forces (TFs) exist. Their programme approved by the AUG-PC will be introduced in the following in more detail. TASK FORCES

TASK A The exploration of an operational and – Edge, Divertor and Wall Physics space with high confinement and high TASK D – Physics of Advanced Task Force Leader: R. Neu density with tolerable ELMs (Type Tokamak Scenarios In a stepwise II) is a major goal. The influence of Task Force Leader: A. Peeters manner ASDEX ICRH on small ELMs and the com- Improved H- Upgrade will in- parison with the EDA mode of mode discharges crease the tung- Alcator C-Mod is investigated. at low density sten covered with peaked pro- area in the ma- The physics of the L/H threshold will files and zero chine and docu- be investigated by varying plasma magnetic shear:

ment the effect rotation, the ratio of Ti/Te and 2002 activities of each step on plasma operation by the charge and mass of the ions will focus on advanced diagnostic methods and (operation in H and He). physics of density peaking, operation by dedicated pulses. Experimental time will be devoted to at q95=3, ion temperature modulation improve radiation cooled scenarios experiments and strategies to control Characterisation of ELM properties on ASDEX Upgrade. the impurity content by RF heating. and the ELM impact on the upper β and lower divertor, especially in the The investigations on temperature High N H-mode discharges at high favourable operation close to double profile stiffness with ECRH will be density with low magnetic shear and a null is a major goal. extended to the ion channel. substantial fraction of non-inductive- Pellet injection will be used for par- ly driven current: Further optimisa- The relation between parameters of ticle fuelling and triggering ELMs in tion of this scenario, especially the Scrape-Off Layer and the con- discharges with otherwise low ELM improved NTM stability and extend- finement of the core plasma will be frequency. ed duration are the goals for the com- further analysed with improved ing campaign. (see highlight). measurements.The origin of the scat- The relation between particle and ter in edge and divertor data which energy transport will be investigated. Formation of Internal Transport exceeds in general the error bars of Disruption mitigation by fast gas Barriers (ITBs) in discharges with re- the measurements will be investigated. puffs will be performed. versed q-profiles: Future studies will NTM stabilisation methods using aim to combine electron and ion bar- Activities to improve the model for ECCD will be optimised. NTM-onset rier formation, to explore ITB access carbon impurity production and experiments will be compared with conditions, to perform comparisons transport to the central plasma are on JET. with JET and to prolong reversed the way. shear phases with off-axis current TASK C drive. TASK B – – Advanced Pedestal and Core Physics in Tokamak Full non inductive current drive sce- Conventional Scenarios Scenario narios at low plasma current (400 Task Force Leader: J. Stober Development kA): The MSE diagnostic system will Due to the tem- Task Force be upgraded to access the efficiency perature profile Leader: A. Sips of the neutral beam current drive. stiffness no separ- ation of pedestal and core plasma ASDEX Upgrade Letter investigations is published by done. Therefore Max-Planck-Institut für Plasmaphysik almost all scien- Association Euratom-IPP Contact Prof. Dr. tific issues of conventional, inductive- Boltzmannstraße 2 Phone +49/89/3299 1925 D-85748 Garching Fax +49/89/3299 1313 ly driven scenarios are addressed in www.ipp.mpg.de [email protected] the frame of a single Task Force.