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Along 2017 ALBA magnetic measurements facility has measured LIPAc HEBT quadrupoles and dipole designed by CIEMAT and built by ELYTT company. ALBA magnetic measurements laboratory has been improved through an upgrade program of its measurement benches to complete their measurements. One of the main aims of the upgrade has been to standardize both the hardware and software and therefore ensure an easy maintenance. Especially relevant has been the upgrade of the flipping coil bench, in which the DC motors and the obsolete controller have been replaced by step-motors and ICEPAP controller. Also, software has been migrated to Tango package. Hardware and software of Hall probe bench has been upgraded as well, using the last DeltaTau motion controller. Tango has been upgraded too, using Devian 8 as operative system. Next step will be the upgrade of the rotating coil hardware and software using also step-motor and ICEPAP controller. In parallel, new shafts have been build and tested, with specific designs to improve the sensitivity and minimize the noise to signal ratio. In this contribution we detail the upgrades and the results of performance tests., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

ELM-like activity has been recently observed in TJ-II, in plasmas with stored energy above 1 kJ. The plasma is observed to develop bursts of magnetic activity (seen in Mirnov coil signals) which are followed by a large and distinct spike in the Hα signal. An increase in electrostatic and magnetic fluctuations at the plasma edge and a cold pulse towards the plasma centre are also characteristics of these events. In addition, the electron temperature profile locally flattens at the plasma radius where the temperature is in the range 100-200 eV. This flattening can be explained in terms of enhanced electron heat conductivity. Between ELM-like events the electromagnetic turbulence at the edge decreases and the Te profiles recover their former shapes. This activity is probably triggered by a resonant m = 2, n = 3 mode.

We show that the modulational instability growth rate of zonal flows is determined directly from the quasilinear wave kinetic equation. We also demonstrate the relation between zonal-flow growth and the cross bispectrum of the high-frequency drift-wave-driven Reynolds stress and the low-frequency plasma potential by explicit calculation. Experimental measurements of the spatiotemporal evolution of the spectrum integrated bicoherence at the L → H transition near the edge shear layer indicate a modification in the nonlinear phase coupling, which might be linked to the generation of sheared E × B flows © 2000 The American Physical Society.

In this article we present experimental results obtained with a heterodyne/amplitude modulated (AM) reflectometer at W7-AS and simulations [two-dimensional (2D) (WKB)] of reflection on a rotating cutoff layer corrugated by turbulence for the W7-AS conditions. When the turbulence has a large amplitude and a small size relative to the illuminated spot, the calculations show the existence of a phase runaway and reproduce the typical behavior of the measured phase and amplitude signals. It is not possible to deduce the plasma rotation from the phase runaway value at “close to normal” incidence, as this value depends on the turbulence characteristics. When the illuminated cutoff surface is smooth, no runaway occurs, amplitude and phase signals are coherent and in certain poloidal wavelength ranges (∼1 to 2 cm for W7-AS conditions) their relative phase is π/2, conditions that have been observed experimentally during H mode. The phase runaway can affect the ne(r) measurements. However, the comparison between the...

Amplitude modulation (AM) reflectometry is a technique for density profile measurements in magnetic fusion plasmas based on the measurement of the phase delay of the modulation in the amplitude of a microwave beam launched and reflected at the plasma. Results from AM experiments in the PBX-M tokamak and the W7-AS stellarator are presented. A general analysis of the capabilities of the technique is performed, particularly centered in the effects of spatial turbulence. Simulations of the effects of two-dimensional turbulence have been performed for medium size (W7-AS) and large devices (LHD stellarator, ITER), showing the capability of the AM technique to operate in turbulent plasmas. Finally, possible solutions to the problem of parasitic reflections in AM systems are presented as development options.

In April 1994 first ECRH plasmas (28 GHz, 2nd harmonic) have been produced in the TJ-I U torsatron (R=0.6m, [a]=0.1m, B(0)=0.52 T, E(0)=0.21). In November 1994 a second experimental campaign using a 37.5 GHz gyrotron (B(o)=0.69 T) has started. The main parameters of the device, the basic characteristics of the heating system and some results concerning magnetic surface mapping and first plasma discharges, are reported. 4 refs., 4 figs.

Experimental evidence of the nonlinear nature of the broadband edge fluctuations has been obtained in edge turbulence in the Advanced Toroidal Facility torsatron. Whereas little nonlinear wave interaction is found in the scrape-off layer region, three-wave coupling is enhanced in the plasma edge region (r

A microwave reflectometer has been used in the TJ‐I tomakak (R=0.30 m, a=0.10 m, IpIp< 50 kA, Bt < 1.5 T) to monitor density fluctuations in the plasma bulk. Experiments were made in the range 33–50 GHz, x mode. The system uses a single antenna for launching and receiving the microwave beam. Since broadband operation usually requires homodyne detection, different techniques were used to overcome the limitations due to this detection scheme. Radial profiles of the density turbulence were taken and the behavior of the spectra analyzed. A slow frequency sweeping has been performed to provide a method to normalize the signals reflected from different radial positions. In addition this technique can be used to obtain information on the absolute value of the phase oscillation amplitude. Spectra of the edge density fluctuations obtained by reflectometry and by Langmuir probes are compared. By the use of two reflectometers in the same antenna, radial correlation experiments can be performed. Some discussions on t...

One of the limiting factors in reflectometers when trying to measure the density profile in fusion plasmas is the existence of a fraction of experiments where the measurement becomes impossible: very noisy signals leading to nonsense density profiles. Those so called “bad shots” are usually linked with strongly turbulent plasmas and the remaining problem is to be able to assess “a priori” if the data coming from a given experiment will correspond to a normal profile or if they will be meaningless.

The first experimental campaign of the TJ-II stellarator has been conducted using electron cyclotron resonance heating (f = 53.2 GHz, P-ECRH approximate to 250 kW) with a pulse length of Delta t approximate to (80-200) ms. The flexibility of the device has been used to study five different configurations varying plasma volume and rotational transform. In this paper, the main results of this campaign are presented and, in particular, the influence of plasma-wall interaction phenomena on TJ-II confinement is briefly discussed.

Recent experiments in the Advanced Toroidal Facility (ATF) torsatron [Plasma Physics and Controlled Nuclear Fusion Research 1990 (IAEA, Vienna, in press)] have emphasized the role of magnetic configuration control in transport studies. Long‐pulse plasma operation up to 20 sec has been achieved with electron cyclotron heating (ECH). With neutral beam injection (NBI) power of ≥1 MW, global energy confinement times of 30 msec have been obtained with line‐average densities up to 1.3×1020 m−3. The energy confinement and the operational space in ATF are roughly the same as those in tokamaks of similar size and field. The empirical scaling observed is similar to gyro‐reduced Bohm scaling with favorable dependences on density and field offsetting an unfavorable power dependence. The toroidal current measured during ECH is identified as the bootstrap current. The observed currents agree well with predictions of neoclassical theory in magnitude and in parametric dependence. Variations of the magnetic configuration ...

ECR (electron cyclotron resonance) heated plasmas have been studied in the low magnetic shear TJ-II stellarator (R = 1.5 m, a < 0.22 m, B = 1 T, f = 53.2 GHz, P-ECRH = 300 kW, power density = 1-25 W cm(-3)). Recent experiments have explored the flexibility of the TJ-II across a wide range of plasma volumes with different rotational transforms and rational surface densities. In this paper, the main results of this campaign are presented and, in particular, the influence of iota and rational surfaces on plasma profiles is discussed.