Overview of recent TJ-II stellarator results

The main results obtained in the TJ-II stellarator in the last two years are reported. The most important topics investigated have been modelling and validation of impurity transport, validation of gyrokinetic simulations, turbulence characterisation, effect of magnetic configuration on transport, fuelling with pellet injection, fast particles and liquid metal plasma facing components. As regards impurity transport research, a number of working lines exploring several recently discovered effects have been developed: the effect of tangential drifts on stellarator neoclassical transport, the impurity flux driven by electric fields tangent to magnetic surfaces and attempts of experimental validation with Doppler reflectometry of the variation of the radial electric field on the flux surface. Concerning gyrokinetic simulations, two validation activities have been performed, the comparison with measurements of zonal flow relaxation in pellet-induced fast transients and the comparison with experimental poloidal variation of fluctuations amplitude. The impact of radial electric fields on turbulence spreading in the edge and scrape-off layer has been also experimentally characterized using a 2D Langmuir probe array. Another remarkable piece of work has been the investigation of the radial propagation of small temperature perturbations using transfer entropy. Research on the physics and modelling of plasma core fuelling with pellet and tracer-encapsulated solid-pellet injection has produced also relevant results. Neutral beam injection driven Alfvénic activity and its possible control by electron cyclotron current drive has been examined as well in TJ-II. Finally, recent results on alternative plasma facing components based on liquid metals are also presentedThis work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 under Grant Agreement No. 633053. It has been partially funded by the Ministerio de Ciencia, Inovación y Universidades of Spain under projects ENE2013-48109-P, ENE2015-70142-P and FIS2017-88892-P. It has also received funds from the Spanish Government via mobility grant PRX17/00425. The authors thankfully acknowledge the computer resources at MareNostrum and the technical support provided by the Barcelona S.C. It has been supported as well by The Science and Technology Center in Ukraine (STCU), Project P-507F

CMS physics technical design report : Addendum on high density QCD with heavy ions

Peer reviewe

Conceptual design of a low-temperature radiation-hard tracker detector

Silicon sensors have about ten times improved radiation hardness around 130 K temperature, compared with the state-of-art sensors close to room temperature. This is based on the Lazarus effect studied by the RD39 Collaboration of CERN. Other benefits of low temperatures will also be discussed. We shall describe the conceptual design of low-mass detector modules cooled using two-phase flow of argon in miniature cooling pipes integrated in the module structure between the sensors and the readout hybrid circuit. The main engineering features of the cooling system and mechanical support structures are discussed, as well as the benefits arising from the operation of the tracker under cryogenic vacuum. 4 Refs

Cryogenic detector modules and edgeless silicon sensors

We are studying the operation of silicon microstrip detector with readout electronics in the temperature range from 90 to 130 K. The sensor can be operated in the current-injection mode which significantly improves its radiation hardness. A first module prototype has been built, with APV25 readout chips and an embedded microtube, providing efficient low-mass cooling of the whole module with a two-phase flow of N2 or Ar. First pedestal and pulse shape temperature dependencies are presented for this module. We have also built an edgeless test module with two pairs of laser cut sensors, with both angular and parallel cuts with respect to the strips (at pitch). We are studying the efficiency of the microstrip sensors very close () to the physical border of the cut silicon crystal and present here some electrical characteristics

First test of cold edgeless silicon microstrip detectors

Silicon microstrip detectors will provide the forward tracking in the TOTEM experiment at the LHC. To allow efficient tracking closest to the beam ( approximately equals 1 mm) these detectors should be sensitive up to their physical edge (i.e. edgeless). Edgeless (without guard rings) microstrip planar detectors can be operated at cryogenic temperatures (about 130 degree K) where leakage currents due to the active edge are drastically reduced. A silicon microstrip prototype, cut perpendicular to the strips, has been tested with a pion beam at CERN to study its efficiency close to the edge by using reference tracks from a simple silicon telescope. Results indicate that the detector measures tracks with good efficiency up to the physical edge of the silicon