Annual Report (MS-Word)

1. Cooperation Activities

2. Status of the Three Large Tokamaks

JET

Beryllium was adopted as the plasma facing material (300 angstrom thickness). High plasma purity ( Zeff < 1.5, n_D/ n_e > 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 <n_e> R / B_T = 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 ( n_D / n_e = 0.9 ) and high ion temperatures ( T_i > 25 keV ). The fusion product n_D T_i reached 7~9x10²⁰ m^-3 s keV with T_i = 22 keV and = 1.1 sec. The observed Q_DD of 2.5x10^-3 corresponds to an equivalent Q_DT= 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.

JT-60

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 I_p = 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 n_e(0) > 3.0x10²⁰ m^-3, n_e(0) / <n_e> ~3-5 was obtained. The achieved fusion product n_e(0) T_i(0) is 1.2x10²⁰ m^-3 s keV. The plasma pressure gradient within the q=1 surface reaches ballooning limit. High-T_i ( ~ 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.

TFTR

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 ( T_i ~ 30 keV, T_e ~ 9 keV, n_e ~ 0.9x10²⁰ m^-3, Q_DT ~ 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, <n_e> ~ 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

4. Phasing of the Executive Committee Meeting with FPCC Meeting

5. Contribution to the ITER Physics R & D