[en] Compact directional couplers-polarimeters were developed for the circular corrugated waveguide transmission lines of the joint IFP-ENEA Electron Cyclotron Resonance Heating experiment at 140 GHz, 2 MW on the Frascati Tokamak Upgrade in Frascati.A linear array of cutoff holes was drilled in the mirrors of the quasi-optical miter bends. The radiated pattern preserves the symmetry and polarization of the waveguide mode in the plane of the array. The direction of propagation is preserved too.Two pairs of standard gain horns with detectors are placed in the plane of the array along the propagation axes of incident and reflected radiation to detect both linear components. The whole assembly is enclosed in a shielded anechoic box of suitable geometry

[en] The measure of residual power of electron cyclotron (EC) waves propagating in FTU tokamak during ECRH experiments at 140 GHz is provided by three low-gain probes facing the tokamak walls. One probe is located in the same poloidal section of the EC launching system; the other two are toroidally displaced by 60 and 90 deg., respectively. A model for the estimate of the e.m. power coupled to the probes has been developed. Several discharges with two gyrotrons at 140 GHz, delivering 0.5 MW each for up to 0.5 s, and with different polarizations have been analyzed. Calculations of the power deposition and e.m. residual power are found to be in very good agreement with the experimental measurements

[en] A quasi-optical system has been designed to couple the power coming from a gyrotron with astigmatic gaussian beam output, into an oversized corrugated waveguide (HE11 mode). The fraction of the power injected in the transmission line can be controlled by means of a wire grid beam splitter. Polarization control is provided by two rotating corrugated mirrors of electrical depth λ/4 and λ/8 respectively

[en] The scrape-off layer (SOL) plasma of FTU is routinely studied by means of 5 fast reciprocating probes, located in the poloidal plane. Each of them bears 4 electrodes acting as 4 single Langmuir probes, and is able to span the entire SOL in less than 160 msec. The whole system (electrical + mechanical part) is remotely controlled via computer. The first aim of this diagnostics is to built a solid data base in order to study the scaling of the main quantities relevant for the SOL, with the core plasma parameters and to characterise possible poloidal asymmetries. (author) 6 refs., 4 figs

[en] FTU plasmas reached a peak electron temperature up to 11 keV with ECRH heating during the current ramp up phase. For these plasmas X-ray emission of highly ionized molybdenum, the dominant intrinsic impurity, are presented in section II, and VUV spectra of injected germanium are presented in section III. In section IV the conclusions are discussed

[en] The Electron Cyclotron Radio Frequency Heating (ECRH) system is mainly used to control the temperature profile of the plasma in a tokamak through sharp focusing of the RF power for bulk heating. Some experiments on tokamak devices have shown that Electron Cyclotron Current Drive (ECCD) can reduce the growth of rotating magnetic islands, thus controlling magnetohydrodynamic (MHD) resistive instabilities in steady-state operation. On Frascati Tokamak Upgrade (FTU), 1.6 MW 140 GHz Electron Cyclotron (EC) waves are injected using four gyrotrons, each emitting 0.4 MW for 0.5 s. A crucial point of the whole system is the fast control of the RF power output through a Digital Waveform Reference (DWR). This paper describes the new implementation of the DWR on FTU with a PXI-embedded controller and two PXI DAC boards by National Instruments. DWR control code integrates synthesized waveforms and graphic display, validity test on reference outputs, fully hardware-driven analog output, network process communication with ECRH plant PLC and the FTU Supervisor Control System. The validity test on the working parameters takes into account hardware constraints, system configuration and tetrode dissipation. The off-line calculations select the reference voltage using a wide choice of pulse shapes, while the real-time analog output is fully hardware-driven by the FTU central timing and trigger system. Because of the FIFO and DMA transfer data of the PXI DAC board, the 1 MHz update rate of the reference output has been successfully tested, largely matching the system requirements (up to 500 kHz). The high reliability shown by the present DWR gives us the chance to implement a 50 kHz closed-loop feedback system to control the growth of the plasma instabilities by EC waves

[en] The results of an ECRH experiment at 140 GHz, 0.5 MW, 15 ms, on the FTU tokamak are presented. The EC waves, generated by GYCOM, a gyrotron with Gaussian output, are transmitted to the plasma with an efficiency of approx. 93% by a hybrid system comprising both mirrors and corrugated waveguides. The waves, launched as an O-mode at the fundamental EC resonance from the low magnetic field side, are almost totally absorbed by the target plasma in a layer 4-8 cm wide, and cause an electron temperature increase of 0.8-2.5 keV. At electron densities above approx. 10²⁰ m^-3 the neutron production rate is also strongly enhanced (50-100%), the increase following the start of the ECRH pulse with a delay consistent with the e-i collision frequency. The ECRH power has been modulated to generate heat waves for confinement studies. (author). 2 refs, 5 figs

[en] For the electron cyclotron resonance heating (ECRH) system on the frascati tokamak upgrade (FTU), composed of four 0.5 MW gyrotrons pulsed for 0.5 s, two different calorimetric loads were designed to measure the mm-wave power at 140 GHz propagating either as a gaussian beam or as an HE₁₁ mode carried by an oversized corrugated waveguide. The first one, designed for low reflectivity and 1 MW power handling capability, is now routinely used for gyrotron testing, conditioning and optimization on the generator side of the transmission line at 500 kW, 0.5 s. The basic design of the load, with a substantial upgrading of the cooling system for adequate heat removal, has full CW operation capability. The other one, whose cylindrical shape allows positioning as a waveguide replacement, is occasionally used when tests on the transmitted power along the 40 m of waveguide are needed. The loads are described together with low power measurements of reflected radiation

[en] The Electron Cyclotron Emission (ECE) diagnostic on FTU tokamak is routinely performed with a Michelson interferometer with spectral range extending up to 1300 GHz. The diagnostic allowed accurate electron temperature measurements during the recent 140 Ghz Electron Cyclotron Resonance Heating (ECRH) experiments on FTU. Very accurate measurements have been performed on a wide range of electron temperatures and profile peaking. The ECE measurements have been compared with Thomson Scattering and with observations of X-ray spectra from highly stripped molybdenum ions. The suprathermal emission in these conditions has been studied

[en] In this paper the authors explore the possibility of using sections of overmoded smooth-wall circular waveguide instead of an overall corrugated waveguide transmission line to carry strong mm-wave power in ECRH experiments. To this end they carry out an exact analysis of the transitions from corrugated to smooth-wall waveguide and optimize the length and size of the smooth-wall waveguide to achieve minimum losses. The whole structure is described by a generalized scattering matrix whose elements are obtained using the exact quasi-TE and quasi-TM uncoupled modes in the lossy smooth-wall waveguide