Fusion Programme - ENEA - Fusione

1. Magnetic Confinement2007 Progress ReportNew capabilities of beam shaping (zooming: a change of beam waist in the plasma shot-by-shot) wereproposed for the first time and implemented.Additional space is available in the launcher for insertion of a narrow remote-steering antenna, which canbe used as an alternative launcher/receiver line (e.g., for collective Thomson scattering [CTS]). Theexperiments proposed for the new launcher include i) real-time control of MHD instability (tearing modesand sawtooth triggering); ii) heating of over-dense plasma (via ordinary/extraordinary Bernstein waveconversion); iii) proof-of-principle of thermal CTS.The electron distribution function in thermonuclear plasmas behaves differently to aOblique ECE Maxwellian in particular circumstances (e.g., in the presence of strong additional heating).diagnostic To study the deviations a polychromator and a heterodyne radiomemeter, both capable ofreceiving signals from an oblique line of sight, have been installed on FTU. Both instruments,together with the Michelson interferometer (which has only a perpendicular line of sight), willprovide measurements in different regions of the energy space, so it might be possible to infer informationabout the non-thermal component of the electron distribution.The 12-channel polychromator antenna was modified in order to steer the line of view from perpendicularto -18° continuously (with respect to the perpendicular view). The heterodyne radiometer (characterised byhigh spectral and time resolutions) has been installed on an ECRH corrugated waveguide (88.9 mm diam.).The receiving antenna is a mirror that can be steered in four different toroidal angles (0°, ±10°, ±20°, ±30°).Two interchangeable front-ends allow measurements that cover the frequency range between247 – 325 GHz (2 nd harmonic for the typical FTU magnetic field). Both front-ends use a double-frequencyconversion unit in order to give two intermediate-frequency outputs between 2 – 22 GHz each, furtherseparated by a diplexer into 16 parts, depending on the frequency input. Finally the signals are processedby a programmable CAEN preamplifier and acquired at a frequency of up to 2 kHz.Some preliminary measurements were made during both ECRH and LH auxiliary heating, using thepolychromator only. The oblique and the perpendicular spectra are compared in figures 1.5 and 1.6 forECRH and LH respectively. The spectra from the Michelson interferometer and polychromator (see fig. 1.5)were used to recalibrate the polychromator channels across the Michelson. A very high temperature wasobtained because ECRH with central resonance was applied during the current ramp-up, when density isvery low (2-3×10 19 m -3 ) and sawtooth activity has not yetstarted. The polychromator line of sight formed an angleof -18° with respect to the perpendicular to the magneticfield. In figure 1.6 the spectra were obtained for LH(1.2 MW) during the current flat-top, with a density ofabout 9×10 19 m -3 . To interpret the spectra, a numericalcode is being developed to compute the ECE arbitrarydistribution function and direction.Fig. 1.5 - ECE spectra from Michelson interferometer (solidline) and polychomator (dots) during ECRH (blue, t=0.104 s)and Ohmic (red, t=0.4 s) phaseTemperature (keV)1086420ECE spectra at 90° and 72° (#29209)ll harmt=0.104 s(ECRH)t=0.4 s (OH)GPC (72°)llI harmMich (90°)200 250 300 350 400 450Frequency (GHz)15