Annual Report (MS-Word)

Presented at the 19th FPCC meeting on 24th Jan. 1990

Three Large Tokamak Cooperation

(January to December 1989)

1. Cooperation Activities

The fourth Executive Committee meeting took place at JT-60 site on January 19 and 20 in 1989. Workshop and personnel assignment in 1988 were reviewed and the plans of activity in 1989 and 1990 were discussed and decided.
Two workshops were held in 1989, one at JT-60 on Negative Ions in August, and the other at TFTR on Plasma Transport Measurement and Analysis in November. There were eight personnel exchanges which were started in 1989 for the periods of longer than two weeks. Seven review tours were made, in which eleven staffs participated.

2. Status of the Three Large Tokamaks

The status and major results of three large tokamaks are summarized below.


Beryllium was adopted as the plasma facing material (300 angstrom thickness). High plasma purity ( Zeff < 1.5, nD/ ne > 0.8 ) in high power ( > 30MW ) limiter discharges was achieved and oxygen impurity is essentially eliminated from the plasma. Be becomes the dominant impurity ( ~3% ). Low radiative cooling rate of Be and reduced impurity level has doubled the density limit to <ne> R / BT = 16x1019 m-2T-1. This limit is principally a fuelling limit and not a disruption limit. Strong getter and pumping action of Be has permitted H-mode plasma with low dilution ( nD / ne = 0.9 ) and high ion temperatures ( Ti > 25 keV ). The fusion product nD Ti reached 7~9x1020 m-3 s keV with Ti = 22 keV and = 1.1 sec. The observed QDD of 2.5x10-3 corresponds to an equivalent QDT= 0.8. H-mode plasmas have been created with ICRH alone for periods more than one second, whose characteristics are similar to the NBI only H-modes.


Using a multi-junction LH launcher, the maximum current drive efficiency of 3.4x1019 m-2AW-1 was achieved with up to 3.0x1019 m-2 and Ip = 1~1.75 MA. The H-mode was achieved in limiter plasmas with LH current drive phase. The threshold LH heating power is 1.2 MW and the duration time is 3.3 sec. Improved energy confinement has been obtained by injection of hydrogen pellet with 3mm, 4mm size and 2.3 km/s velocity. When the pellet penetrated inside or close to the q=1 magnetic surface, energy confinement time is enhanced by 30 % comparing with the gas fuelled discharges. Peaked density profile with ne(0) > 3.0x1020 m-3, ne(0) / <ne> ~3-5 was obtained. The achieved fusion product ne(0) Ti(0) is 1.2x1020 m-3 s keV. The plasma pressure gradient within the q=1 surface reaches ballooning limit. High-Ti ( ~ 12 keV ) and high- ( ~3 ) discharges similar to the supershot in TFTR were obtained in low plasma current with perpendicular NB injection. In these shots, the neoclassical theory predict the bootstrap current reaching 80 % of the total plasma current, which is supported by the measured loop voltage.


The TFTR program was redirected in early 1989 to respond to the Hunter Transport Initiative. Transport coefficients both in ohmic and beam heated plasmas have been extensively studied by steady-state power balance calculations or by the measurements of density fluctuations. The results show the drift wave-like characteristics of transport in TFTR. The performance of supershots ( Ti ~ 30 keV, Te ~ 9 keV, ne ~ 0.9x1020 m-3, QDT ~ 0.5 ) has been limited by the large influx of carbon (blooms). The walls of TFTR was boronized in late 1989. This is expected to provide improved supershot and high density and large energy confinement time plasma performance. A peaked density profile H-mode regime was discovered, which has / L ~ 2.3, <ne> ~ 2.2 and lasts for 1.5 sec during NB heating phase, with circular cross-section limiter plasma. This phenomena cannot be explained by the presented H-mode models which require a separatrix or X-point. Initial experiments on ICRF heating have shown improved confinement, 40 % above the L-mode. The DT experiments are scheduled to begin in mid-1993.

3. Desire for Extension of the Implementing Agreement

The Implementing Agreement is in force for the initial period of five years; January 15, 1986 to January 14, 1991.
It is necessary to continue the cooperation under the Implementing Agreement, by taking into account of important developments regarding DT burning and non-inductive current drive in high density plasmas, and detailed investigation on confinement of reactor-grade plasmas, which are programmed in the next period of five years.

4. Phasing of the Executive Committee Meeting with FPCC Meeting

In due consideration of effective implementation of the Agreement along the guideline of the FPCC, the Executive Committee meeting is held generally in February or March, being phased with the FPCC meeting scheduled in every January. The report reviewing the progress of cooperation activities during the past year will be submitted to the FPCC annually just before the FPCC meeting.

5. Contribution to the ITER Physics R & D

The Executive Committee discussed coordinated contribution to the ITER-related physics R & D tasks, and agreed that the large tokamaks will make best efforts to plan their research programs and to carry out them to meet the requirements from the physics design of ITER. Along this line, each party has contributed to the ITER Conceptual Design Activity by conducting more than 10 R&D tasks out of 23 required from the ITER Design Team ( see attached list ).


PH1: Power and helium exhaust conditions. x x x
PH2: Helium radial distribution in high-temperature tokamak discharges. x x x
PH3: Viability of a radiative edge.
x x
PH4: Sweeping of the divertor target load.
PH5: Characterization of low-Z materials for plasma-facing components. x x x
PH6: Characterization of high-Z materials for plasma-facing components.
PH7: Characterization of disruptions. x x x
PH8: Disruption control.
PH9: RF plasma formation and preheating.
x x
PH10: RF current initiation.
PH11: Scaling of volt-second consumption during inductive current rampup in large tokamaks. x x x
PH12: Alpha-particle losses induced by the toroidal magnetic field ripple.

PH13: Compatibility of plasma diagnostics with ITER conditions.
x x
PH14: Steady-state operation in enhanced confinement regimes (H-mode and "enhanced" L-mode). x x x
PH15: Comparison of theoretical transport models with experimental data. x x x
PH16: Control of MHD activity. x x x
PH17: Density limit. x x x
PH19: Alpha-particle simulation experiments. x
PH21: Ion cyclotron current drive. x x
PH22: Impact of Alfven wave instability on neutral beam current drive.