Sextant a very fast beam spectrometer

Sextant is a new study of a beam spectrometer, it can be seen as a KABES upgrade (KAon Beam Spectrometer), a beam spectrometer on NA 4811 at CERN. The both are using a gaseous detector called Micromegas[1]. In this application this detector is used in a Time Projection Chamber (TPC) mode. Thus, we have a better efficiency, with the minimum amount of material in the way of the beam. Using the TPC technique, the Mesh of the detector is positioned outside the high intensity region covered by the beam. Performances of this detector are very good in high intensity hadrons beams (spatial resolution: 70 mum and time resolution 600 ps). The integration of the front end on the PCB of the detector provides a very low noise for the entire detector. Main characteristics of the preamplifier are 1 ns of rise time and a very low noise, lower than 600 muV rms. This concept has shown very good performances and robustness. The role of KABES is outlined, and the construction is described. The SEXTANT improvements are presented.