An overview of the recent operations and the main results of cesium injection in the Source for the Production of Ions of Deuterium Extracted from Rf plasma (SPIDER) negative ion source are described in this contribution. In experiments without cesium injection, all SPIDER plants were tested to verify the basic expectations on the operational parameters (e.g., electron cooling effectiveness of magnetic filter field) and to determine its operational region. For beam properties, it was shown that the current density varies across the beam in the vertical direction. In preliminary cesium experiments, the expected increase of negative ion current and simultaneous decrease of co-extracted electrons were found, along with the influence of the control parameters (polarization of the plasma electrodes, magnetic filter field) on the SPIDER beam uniformity in the horizontal and vertical directions. It was shown that non-Gaussian tails can be identified in the angular distribution on the plane perpendicular to the beam propagation direction. Stray particles, nonhomogeneous beam and large divergence might result in unexpected heat and particle loads over ITER neutral beam injector (NBI) accelerator grids; it is the goal of SPIDER to assess and possibly to identify suitable methods for controlling these beam features. A major shutdown, planned for late 2021, to solve the issues identified during the operation and to carry out scheduled modifications, is outlined. Such improvements are expected to allow SPIDER to pursue the ITER requirements in terms of negative ion current, electron-to-ion ratio, and beam duration.

The RFX-mod2 Nuclear Fusion experiment is an upgrade of RFX-mod, shutdown in 2016. Among the other improvements in the machine structure and diagnostics, a larger number of electromagnetic probes (EMs) is foreseen to provide more information about plasma instabilities and to allow an improved real-time plasma control. An Analog to Digital Converter (ADC) architecture able to provide at the same time both transient recording and real-time streaming, as well as FPGA-based time integration of the inputs is foreseen in RFX-mod2. Transient recording provides full speed data acquisition (up to 1 MSample/s) by recording data in local memory and reading memory content after the plasma discharge. Real-time streaming of sub-sampled data is required for active control. The chosen technology is based on the XILINX Zynq architecture that provides in the same chip a multi-core ARM processor tightly coupled to a FPGA. Time critical functions are carried out by the FPGA, such as the management of the circular data buffer, low pass filtering for subsampling of the samples to be streamed and digital integration. Other functions are carried out by the processor, such as the management of the configuration setting, received via TCP/IP or HTTP, the data readout of acquired samples in transient recording buffers and network data streaming of data collected for active real-time plasma control.

Inductive measurement of magnetic fields is a diagnostic technique widely used in several scientific fields, such as magnetically confined fusion, plasma thrusters and particle accelerators, where real time control and detailed characterization of physics phenomena are required. The accuracy of the measured data strongly influences the machine controllability and the scientific results. In the framework of the assembly modifications of the RFX-mod experiment, a complete renew and improvement of the magnetic diagnostic system, from the probes moved inside the vacuum vessel to the integrator modules, has been carried out. In this paper, the whole system making up the magnetic diagnostics is described, following the acquisition chain from the probe to the streamed data and illustrating the requirements and conflicting limitations which affect the different components, in order to provide a comprehensive overview useful for an integrated design of any new systems. The characterization of a prototypical implementation of the whole acquisition chain is presented, focusing on the flexible ADC architecture adopted for providing a purely numerical signal integration, highlighting the advantages that this technology offers in terms of flexibility, compactness and cost effectiveness, along with the limitations found in existing implementation in terms of ADC noise characteristics and their possible solutions.

Source for the production of ions of deuterium extracted from a radio frequency plasma (SPIDER) is the full-scale prototype for the ITER heating neutral beam (HNB) source. Beam operation in SPIDER, with the eventual aim of achieving 100-keV, 46-A hydrogen negative ion beam for $1$ h, has mainly been performed in volume operation without cesium. Recently, with the introduction of cesium, SPIDER has moved to the surface operational regime, with a noted increase in beam current. Electrical and calorimetric measurements of the beam current have previously shown discrepancies between the two, possibly due to background gas interactions in the accelerator and upstream of the STRIKE calorimeter. Taking advantage of the reduced number of open apertures due to the plasma grid (PG) mask, a series of fluxgate current transducers have been installed in SPIDER to measure the current of individual beamlets. These beamlet current monitors (BCMs), positioned downstream of the grounded grid (GG) around individual grid apertures, have provided direct measurement of the current of up to five individual beamlets during the recent SPIDER campaigns with and without cesium. This contribution describes the installation of the BCM dc sensors, analysis of the dc signal, and initial characterization of the beamlet direct current component in volume and surface operational regimes.