Electron temperature profiles and local energy tran sport in RFX-mod

Aiming at a more resolved and accurate measurement of the Te profile, the Thomson scattering (TS) diagnostic has recently undergone a n extensive upgrade, and it has been routinely operational since the beginning of 2005 w hen the modified RFX experiment (RFXmod) restarted its operation. RFX-mod (r=0.459m, R=2m) has a passive conductive shell thinner than the old RFX (3mm thick instead of 65mm), but this is compensated by a set of 4 (poloidally distributed) x 48 (toroidally) saddle c oils with independent power supplies, that allow to actively control the magneto-hydro-dynamic (MHD) modes, like cancelling the local Br (Virtual Shell, VS [1]). This paper presents a desc ription of the new TS diagnostic, illustrates the T e profiles measured during the first experimental ca mpaigns of RFX-mod, showing how VS mode allows to achieve higher Te, suggesting an improvement in the thermal transport properties of electrons [2]. 2. The main Thomson scattering diagnostic on RFX-mod Only the geometry and the mechanical structure of t he old TS system have been retained [3]. The most significant modification is the replacemen t of the grating spectrometers by a set of 4-filter polychromators with avalanche photodiodes (APDs), which improves the sensitivity by a factor of about 50 using the same ruby laser a s input source. More resolved profiles with 84 points and 10 mm resolution (‐0.96 to 0.84 r/a) are now being measured with 28 polychromators employing optical delay lines. As th e APDs are compatible with Neodymium lasers, the ruby laser has been replaced by a Nd:YL F laser that can produce a burst of 10 pulses at 50Hz during a plasma discharge of 300 ms. Finally the data acquisition system is not any more gating-based, but the full time trace is r ecorded by means of waveform digitizers. Moreover, the relative calibration of spectral chan nels has been performed with a Supercontinuuum pulsed white Light Source (SLS) [4] and ne profiles have been measured using the absolute calibration of the system with R otational Raman Scattering in Nitrogen.