ITER CTA NEWSLETTER
No. 1, AUGUST-SEPTEMBER 2001

INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, AUSTRIAISSN 1024-5642

ITER CO-ORDINATED TECHNICAL ACTIVITIESAs agreed upon between the ITER Engineering Design Activities (EDA) Parties at their Meeting in Tokyo in
December 2000, “Co-ordinated Technical Activities” (CTA) means technical activities which are deemednecessary to maintain the integrity of the international project, so as to prepare for ITER JointImplementation.
Such activities will build on the results of the ITER EDA and be conducted considering specific conditions ofthe site(s) offered. They will result in technical documents in support of negotiations towards the ITER Joint
Implementation, to enable the project to move smoothly towards construction.
Participants in the CTA are the Parties who had been involved in the ITER Engineering Design Activities(EDA), as well as the governments of other countries that have presented to the Parties a specificconstruction site offer. The invitation to join this latest phase of ITER was made by the IAEA Director General
Dr. ElBaradei earlier this year. Canada, the European Union, Japan, and the Russian Federation have all
accepted this invitation and confirmed their participation. At this time, only Canada has offered a site to HostITER. Other interested countries which possess relevant specific capabilities and which can contributesignificantly to ITER Joint Implementation may also join under terms to be unanimously approved by theParticipants.
The Participants will conduct the CTA in a co-ordinated manner, under the auspices of the International
Atomic Energy Agency (IAEA) till the end of 2002. The scope of the activities includes:• Design adaptation to the specific site(s) conditions,• Safety analysis and licensing preparation that are based on specific site offer(s),• Evaluation of cost and construction schedules,• Preparation of procurement documents, and• Other technical issues raised by the Negotiators collectively, whilst assuring the coherence of the ITER
project including design control.
The organizational structure for the CTA consists of the Project Board, the International Team and theParticipants’ Teams.
The Project Board has executive functions to the CTA and is co-ordinating the Participants’ contributions tothe activities, facilitating liaison within the organizational structure. The Board consists of the Leader of theInternational Team and the Leader of each Participant Team. The Chair of the Board is AcademicianE. Velikhov. The results of the activities will be reported by the Chair to the Negotiators. In addition, theBoard will respond to issues raised by the Negotiators collectively. The Board will be assisted by theInternational Team dedicated to the co-ordination of the technical activities, with particular emphasis on
assuring the coherence of the ITER project.
Each CTA Participant will contribute staff to the International Team which, collectively, should have thecapability of assisting the Project Board in the oversight of the CTA. The Team will use the work sites
Garching (near Munich) and Naka (north of Tokyo).

Each Participant will establish its own Team in order to undertake activities described above as entrusted to
it by the Project Board. The Team of a Participant offering a specific construction site will play a leading rolein developing details of the design adaptation and in licensing preparations for its specific site.
The IAEA has played an important role in starting the CTA. As confirmed by Dr. ElBaradei, IAEA DirectorGeneral, the Agency is in agreement with the CTA Terms of Reference and will provide the auspices for theCTA as well as services of the same nature as during the ITER EDA. These services essentially include thefollowing:• Providing meeting space for CTA Meetings held in Vienna together with the required support;• Publishing and distributing the CTA documents and reports;• Editing, printing and distributing the CTA Newsletter.
To support these services, the IAEA is maintaining the adequately staffed and equipped ITER Office at its
Headquarters at the Vienna International Center.

MEETING OF THE ITER CTA PROJECT BOARD
A preparatory meeting of the Co-ordinated Technical Activities (CTA) Project Board took place in Vienna on
16 July 2001. The Board Members of Canada, EU, Japan, RF and of the CTA International Teamparticipated in the Meeting, which was chaired by Acad. E. Velikhov.
The major item on the Meeting Agenda was the discussion of the scope of the CTA. In this discussion thefollowing comments were expressed:• One of the prime objectives during the CTA is to develop technical specifications
for procurement of critical items (magnets, vacuum vessel, and buildings). It wasnoted that the discussions with potential suppliers should confirm manufacturing
processes in details in order to explore possible schedule reduction strategies.
• Safety analysis and licensing preparation should proceed on all proposed sites
up to the preferred site designation, to ensure the overall implementation
schedule is minimized and to resolve major technical issues needed for licensing.
• Several R&D issues remain to be further developed during the CTA. Special
attention should be given by the Participants to two areas: Diagnostics; Heatingand Current Drive Systems.
• Arrangements for continuation of the ITER Physics Expert Groups activities
should be provided. To this end a new framework, called International Tokamak
Physics Activity, is being planned. The Board encouraged the Participants’Representatives in the Co-ordinating committee of this activity to support thepreparation for urgent Topical Group Meetings.
The Board agreed that the Design Authority will be invested in the International Team and that proposals forsite specific design changes should be agreed upon by the International Team Leader before being studied
in detail.
The Meeting agreed on some arrangements which will remain from the EDA, namely the ITER EDA Council
Office in Moscow as Office of the PB Chair, and the ITER Office located at the IAEA in Vienna as agreed bythe IAEA. The Board recommended that effective August 2001 the ITER Newsletter will be published in thesame way as the ITER EDA Newsletter had been done.
It has been agreed that, as a rule, the Project Board will meet every two to three months for one or two days
before the Negotiators’ meetings, at the same place. In line with this decision, the next meeting will be held
in November in Toronto, Canada. For that meeting the International Team would prepare a preliminary Work
Plan for the CTA and all Participants’ Teams would provide their organization charts.

2MEETING OF THE EXPERT GROUP ON MHD, DISRUPTIONS AND PLASMACONTROLby Dr. M. Shimada, ITER Naka Joint Work Site
The Expert Group Meeting on MHD, Disruption and Plasma Control was held on 25–26 June 2001 inFunchal, Madeira, Portugal. The meeting followed the 28th EPS Conference on Plasma Physics andControlled Fusion.
The main objectives of the meeting were:- stabilization of ß limiting MHD modes in conventional and advanced tokamak scenarios(NTMs, RWMs);- tolerable ELMs with good confinement alternate to type I ELMs;- disruptions at q≈3; prediction, avoidance and mitigation of disruptions; related time scales;- control issues in conventional and advanced scenarios including current drive/profile control.
A review of high priority research issues for burning plasma experiments was done at the end of the meeting.
A brief summary of the discussions at the meeting is given below.
Neoclassical Tearing Modes (NTMs)
NTMs limit plasma performance in conventional and advanced scenarios with peaked to flat current density profiles.
A high confinement regime at high values of β has been found on ASDEX Upgrade (βN ≥ 2.3) and JET (β N ≥ 2.1) in spiteof existence of a (3,2) NTM. The reason for confinement improvement is frequent amplitude drops due to non-linear
coupling to an ideal (m+1, n+1) mode. High confinement regime with βN ≥ 2 can be also expected for ITER.
One of the typical characteristics of NTMs is the hysteresis observed between the β value at which the mode is triggered(βonset) and the β value at which the mode is stabilised or below which the mode is unconditionally stable (βcrit > βonset).
Both values scale with rho*ion gyration radius/plasma radius, and depend only weakly on collisionality. The value ofβonset depends on the perturbation (size of island) triggering the NTM. Recent JET experiments have shown a direct
relation between the sawtooth period and βonset. Ion cyclotron current drive was used both to stabilise or destabilise
sawteeth, leading to longer sawtooth period and hence lower βonset in the first case, and vice versa. Ion cyclotron orelectron cyclotron current drives could also be used on ITER to destabilise sawteeth. The value of βcrit depends only on
plasma parameters, and can be established by a slow power ramp-down in presence of an excited NTM until the modevanishes. This study of βcrit has been started at ASDEX Upgrade and JET. Comparisons with other machines would bevery helpful for predicting βcrit for ITER.
Experiments for NTM stabilisation by external non-resonant helical fields have been carried out on JET and DIII-D,
supporting the hypothesis that NTMs with different helicity can not exist simultaneously in ITER. The applied helicalfields, however, lead to a strong drop in plasma rotation, and often to a reduced plasma pressure. This role of poloidal
and toroidal plasma rotation through the polarization term on the NTM was further investigated on JT-60U.
Very similar instability behaviour is observed for m=2,n=1 NTMs in joint experiments on JET and DIII-D. Similarity
experiments using closely matched non-dimensional plasma parameters (plasma shape, aspect ratio, q, ρ*, collisionality)
show similar β onset values. First results from spherical tokamak MAST contribute to the database both for 3/2 and 2/1NTMS.
Resistive Wall Modes
The feedback stabilization of the n=1 resistive wall mode (RWM) at DIII-D prolongs the duration of a state with β ≈ 2βnowall for many wall times (more than 50). Thereby the role of direct stabilization of the RWM and the effect of a quasi-ideal

wall by sustained toroidal rotation via reduced error fields was a matter of debate. A negative effect of ELMs, whose
amplitudes and periods increase with RWM feedback, was observed, as the control coils (“C-Coils”) respond on each
ELM despite the quite different frequencies involved deteriorating the RWM stabilization.
Edge Localized Modes
Type II ELMy H-mode operation in ASDEX Upgrade was achieved at high plasma triangularity (δ = 0.4) close to a double
null configuration. It allows to reduce and to smooth the power flux to the target plates significantly as compared to type I
ELMs, even at Greenwald density and without reducing the confinement compared with ITER-H98P scaling. The
operational regime for pure type II ELMy H-modes has been extended downwards q = 3.5.

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Disruptions
Improved experimental characterisation of disruptions, namely quench time scales and halo current amplitudes andtoroidal distribution should contribute to the establishment of adequate margins for structural integrity of ITER FEAT inextreme cases (e.g. in 17 MA scenario).
Previous JET data (presented in the ITER Physics Basis) on current quench rates during disruption is confirmed byanalysis of more recent pulses. Neither the minimum current quench rate, nor the halo current fraction, seems to show
any obvious change for q95 < 3. The JT-60 disruption data were also re-examined. The minimum current quench time
seems to be independent of both the current density and the safety factor. The minimum current quench time in amachine with a metal wall was not significantly different from that with a graphite wall.
The product of toroidal peaking factor (TPF) and Ih/Ipo is decreasing with the size of machine and with the actual
normalised plasma current during the current quench Ip/Ipo. Here Ip and Ih are the actual plasma and maximum halocurrents, Ipo is the plasma current before the current quench. For JET and JT-60U the product Ih/Ip × TPF ≤ 0.4 isreduced compared with smaller devices Ih/Ip × TPF ≤ 0.6. Influence of smaller elongations and closeness to the neutral
point (verified in JT-60, AcatorC-MOD, ASDEX Upgrade, not seen in TCV) in this comparison has still to be established.
The experimental observations from several tokamaks suggest that the n = 1 halo current asymmetry, producing theTPF, originates on the q = 1 surface. This is probably the manifestation of a common MHD phenomenon during thedisruption. A clear m = 1 n = 1 perturbation of the halo current is seen in many ASDEX Upgrade disruptions; which isclearly correlated with qcyl dropping below 2 and with an MHD event. The local degree of asymmetry of the halo current
can be relatively large (ftp = 3.5). There is clear indication that avoiding peaking of the current profile after thermal
quench and reducing the region inside of the q = 1 surface, suppresses the (1,1) asymmetry.
Analysis of the DIII-D disruption database for 1998, 1999 and 2000, in current flat top only, shows an average disruptivityof 13% and is not distinctly increasing when qedge approaches 3. This does not include "forced" disruptions, power supply
failures, control errors etc. Comparable rates were reported from other devices during the last years.
Runaway discharges have been produced in JET by inducing disruptions in low elongation plasmas by argon injection.
These data show similar lower limits in qedge and Bt for runaway production as observed on JT-60U. This runaway
production can be avoided by quenching the discharge by massive helium puffs.
Plasma control and current drive
Inductive 15 MA and steady-state 9 MA ITER scenarios were studied with DINA code. The code simulates feedback andfeedforward plasma current, position and shape control provided by the PF system simultaneous with solution of the 1D
plasma transport equations. The study demonstrated the capability of ITER PF system to support these scenarios. For
the problem of AC-loss minimisation in ITER a model was developed and validated at CRPPL including effects from thecontroller design. There are still open points which have to be adressed in the next meetings, as location of thebreakdown region compared with the region having minimum stray field or plasma disturbances in scenarios with weaknegative shear.
Large ELMs can significantly perturb the vertical position observer and lead to bad control of plasma position. The
vertical position observer is usually a weighted sum of the magnetic field on pick-up coils around the plasma. It has beenshown on TCV and JET that slight modifications of the coefficients can avoid or strongly limit the perturbations due tolarge ELMs, while maintaining an accurate measure of the plasma position, thus avoiding changes in the control
algorithm.

The next expert group meeting will be under the auspices of International Tokamak Physics Activities. It wasproposed to be held in combination with the IEA Large Tokamak Agreement Workshop W49 (Real Time
Control of ITB Discharges Approaching Steady State) and the US-Japan MHD workshop FP2-1 at JAERI,Naka, Japan, in February or March 2002. The organizers of the present meeting were complimented for theirarrangements. We are especially indebted to Mrs. Maria Fernanda Pinto of IST Lisboa, Portugal, for her
excellent assistance.

4Participants in the meeting
List of participants
M. Shimada
Y. Gribov

ITER, Naka
ITER, Naka

Takahisa Ozeki

JAERID. Campbell
K. Lackner
S. Guenter
O. Gruber
T. Hender
J.B. Lister

EFDA Garching
EFDA Garching
IPP Garching
IPP Garching
UKEA Culham
ECFPL LausanneO. Sauter
G. Pautasso

ECFPL Lausanne
IPP Garching

N. IvanovV. Lukash
S. Mirnov
V. Pustovitov

Kurchatov Moscow
Kurchatov Moscow
TRINITY
Kurchatov Moscow

R. LaHaye
J. Manickam
J. Snipes

GA San Diego
PPPL Princeton
MIT Boston

5Items to be considered for inclusion in the ITER CTA Newsletter should be submitted to B. Kuvshinnikov, ITER Office, IAEA,
Wagramer Strasse 5, P.O. Box 100, A-1400 Vienna, Austria, or Facsimile: +43 1 2633832, or e-mail: c.basaldella@iaea.org(phone +43 1 260026392).
Printed by the IAEA in Austria
December 2001
01-04682

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