Experimental activity of 2001
During 2001 the FTU experimental programme made full use of
the lower hybrid (LH) system which is now capable of delivering to the plasma
a power close to the maximum power allowed by the system (about 2.4MW). Up to
2.2MW have been injected with the level of 2.0 MW routinely achieved. In this
way, the LH system has been exploited in high-density scenarii, both for current
drive studies and for ITB formation. At densities around 1020m-3
collisional ion heating has indeed been observed.
Electron cyclotron (EC) resonance heating has been used both for transport studies and for synergy studies with combined injection of LH waves. Transport studies, also carried out using modulated EC heating, have focussed on the issue of profile stiffness on which FTU can investigate the specific role of collisionality. Also as a result of the Workshop on FTU programme (see below) experiments are planned for comparing the FTU results with the results of other devices such as ASDEX-U and Tore Supra.
Steady PEP Modes were extensively studied. Careful timing of the pellet sequence allowed to achieve a high degree of reproducibility for these high performance discharges. An interesting point is the further documentation on the respective role of sawteeth and impurity accumulation. A compromise seems achievable were sawteeth are sufficiently slow-down in order to achieve an improved confinement, but still sufficient not only to prevent impurity accumulation but also to produce an outward pinch reducing central radiation. Preliminary experiments have also been performed with Pellet + LH indicating that good RF coupling is possible at high field and density.
Finally, RI mode studies have been started in the last part of the 2001 campaign. This was made possible by the installation of the new boronization system which allows a significant decrease of impurity contamination and radiated fraction.
A workshop has been held in Frascati on November 22-23 to discuss the medium term FTU programme. The aim of the workshop was to increase the participation of the European laboratories to FTU. The workshop was organised in plenary session and parallel brainstorming sessions. Each brainstorming session has been organised by a chairman not belonging to the FTU group. The attendance to the workshop has been about thirty persons from laboratories other than ENEA Frascati and CNR Milan and forty persons from ENEA Frascati and CNR Milan. Most of the scientists came from European institutions, one from USA, one from Japan and two from Russia. The discussion was lively and focused on the programme elements on which FTU can provide unique results. Several proposals have emerged that are presently being considered for implementation.
On the diagnostic development, it should be noted the installation on NSTX of a new diagnostic for fast X-ray imaging using micro pattern gas detector based on GEM amplifier.
The ENEA participation to the C4 campaign in JET involved about 1 ppy and focussed on the activity of TF S2 and TF H. Plasma configuration with Internal Transport Barriers have been produced with a long duration (11s¼30tE¼tR, with tE the energy confinement time and tR the resistive diffusion time) thanks to the current profile control now possible with the LH system.