Annual Report (MS-Word)

Progress of Three Large Tokamak Cooperation

January to December 1998
Executive Committee

I. Cooperative Activities

The Three Large Tokamak Collaboration has continued successfully in 1998, with active personnel and task assignment programs. The Implementing Agreement functioned efficiently to promote improved understanding of tokamak physics and enhanced tokamak plasma performance, which consequently has made significant contribution to ITER EDA.

1. Personnel Assignments, Workshops and Executive Committee meeting

The total number of personnel assignments in 1998 was fifty-seven (TFTR<-->JET (18), JET<-->JT-60 (15) and TFTR<-->JT-60 (24)), nine of which were long-term exchanges of one to eight months. The major activities are as follows: collaborations on MHD and confinement studies, including the physics of high energy particles in a plasma (25%); new diagnostics such as reflectometer, MSE and collective Thomson scattering (21%); current drive using negative ion based NBI and RF (12%); and work on remote experiments, plasma control, radiating discharges and first wall technology.
Two workshops were held: "Tritium experience in large tokamaks; Application to ITER" (60 participants) and "Heating and current drive for improved tokamak performance" (35 participants).
The Thirteenth Executive Committee (EC) meeting was held at JAERI in October 1998. The coordinated assignments in the year as well as the annual strategic work program were reviewed in this Meeting.

2. Collaborative activities and achievements

Six Task assignment Programs have been conducted intensively as follows.

(1) Negative-ion based neutral beams (N-NB) and related physics
Collaboration between TFTR and JT-60 was conducted successfully in this field. As for the N-NB technology, collaborative efforts for optimization of the beam optics and development of new technique termed "pre-arcing" resulted in an extension of pulse duration up to 1.9 s with 3.4 MW at 360 keV without breakdown.
Excitation of the n=2 toroidal Alfven eigenmode (TAE) during N-NB injection was analyzed using a theoretical code "NOVA-K", which was developed in PPPL. The code analysis showed that the observed mode characteristics could be understood as the effects of spatial variations of q profile. A new type of Alfven modes with bursty and strong frequency chirping was observed in the N-NB injection experiments on JT-60U, and analyses using the PPPL codes are in progress under this collaboration.
JET collaborations with JT-60 helped clarify the applicability of N-NB current drive to steady state high performance operation in JT-60U. JET collaborations with both TFTR and JT-60 have also concentrated on possible energetic particle effects in the 1997 D-T experiments on JET.

(2) Remote collaboration
Remote collaboration between TFTR and JT-60 was progressed further, with remote participation in experiments using the enhanced capabilities of the Data Link System and the Videoconference System. Joint data analyses with the aid of these systems were successful in MHD studies mentioned in (3).
PPPL and JET have also remote collaboration activities. During the last 18 months PPPL scientists have completed about 870 TRANSP runs of JET discharges, on the PPPL computers. The experimental data was transferred to PPPL via the INTERNET and the analyzed data was transferred back to JET and archived on the IBM mainframe system. This work has increased the number of TRANSP runs at JET by a factor of 6 and includes the record fusion performance pulses obtained during D-T operation in JET in 1997.
There has been significant collaboration between TFTR and JET on the construction, installation and commissioning of an MSE diagnostic for the measurement of the current profile on JET.

(3) High- studies and related modes of operation
MHD activities associated with large pressure gradient, which was observed in both tokamaks (JT-60 and TFTR), were identified as an ideal MHD n=1 instability. These achievements were reported in two joint papers at the IAEA Yokohama Conference and the APS New Orleans Meeting.
As for development of diagnostics for high beta plasmas, a core reflectometer diagnostic has been installed in JT-60. Its operation has been started successfully under collaboration between JT-60 and TFTR: The density fluctuation profiles and radial correlation length near the internal transport barriers (ITB) was investigated. Initial results were presented in the IAEA Yokohama Conference as a joint paper. This diagnostic was also effective in detecting TAE modes. TFTR and JET are also collaborating on reflectometry.

(4) Disruption studies
Collaboration between JET and JT-60 on halo current studies concluded that larger tokamaks may have a lower halo current and a low toroidal peaking factor. These results were reported in a paper for the IAEA Yokohama Conference and provided useful input to the design of ITER.

(5) Divertor Plate Technology
Fatigue tests on a JET vapotron will be performed on the JEBIS test set-up in JAERI. JET will make available thermal imaging software to JAERI.

(6) Impurity Content of Radiative Discharges
The multi-machine database of Zeff in radiative discharges will be rebuilt to include results from more closed divertor configurations (JET, JT-60U and possibly other Tokamaks) and to expand the range of seed impurities to higher Z including Argon and Krypton.

II. Planned activities in 1999

The next EC meeting will be held in June 1999 at PPPL. Two workshops and twenty-five personnel exchange assignments were authorized by the last Executive Committee. Titles of the workshops are "Advances towards Steady-state of Regimes with Internal Transport Barriers" and "Collaborative Exploitation of Fusion Facilities". The EC approved the start of a seventh Task Assignment Program "Scaling of access to ITB plasmas", which aims to characterize the mechanism of ITB formation and will soon be started.

III. Issues related to the collaboration

1. Maintaining the collaboration with the exploitation of the JET facilities

The representative of JET informed the Executive Committee that the JET Project will be completed at the end of 1999 and that the operation of the JET facilities is expected to continue under a new organizational structure presently under discussion in the EU. He expressed the view that the IEA Tripartite collaboration on Three Large Tokamak Facilities was very successful and important for the EU. He hoped that this collaboration could continue further under the new organizational structure. The other members of the Executive Committee shared his views. The Committee was unanimously favorable of continuing the Agreement with JET under its new structure.