The ANTARES collaboration is building a deep sea neutrino telescope in the Mediterranean Sea. This detector will cover a sensitive area of typically 0.1 km2 and will be equipped with about 1000 optical modules. Each of these optical modules consists of a large area photomultiplier and its associated electronics housed in a pressure resistant glass sphere. The design of the ANTARES optical module, which is a key element of the detector, has been finalized following extensive R&D studies and is reviewed here in detail.

We built and commissioned a new type of Compton polarimeter to measure the electron beam polarization at the Thomas Jefferson National Accelerator Facility (Virginia, USA). The heart of this polarimeter is a high-finesse monolithic Fabry–Pérot cavity. Its purpose is to amplify a primary 300 mW laser beam in order to improve the signal to noise ratio of the polarimeter. It is the first time that a high-finesse Fabry–Pérot cavity is enclosed in the vacuum of a particle accelerator to monitor the beam polarization by Compton polarimetry. The measured finesse and amplification gain of the cavity are F=26000 and G=7300. The electron beam crosses this high-power photon source at an angle of 23 mrad in the middle of the cavity where the photon beam power density is estimated to be 0.85MW/cm2. We have used this facility during the HAPPEX experiment (April–July 1999) and we give a preliminary measurement of Compton scattering asymmetry.

A new spectrometer is being built for the COMPASS particle physics experiment at CERN. Saclay is in charge of the construction and the operation of two types of gaseous detectors: Micromegas microstrip detectors and Drift chambers [1], [2]. The operation of the detectors requires the slow control of high voltages and currents, and of the thresholds for the Front-End. This control system has been implemented using the Experimental Physics and Industrial Control System (EPICS) Software tool kit. For the high voltages, the system CAEN SY127 was chosen and has been controlled since March 2000. For the thresholds of the Micromegas chambers, a specific VME hardware and a JAVA graphical interface were developed to configure and monitor the thresholds.

The ANTARES collaboration has performed a series of {\em in situ} measurements to study the background light for a planned undersea neutrino telescope. Such background can be caused by $^{40}$K decays or by biological activity. We report on measurements at two sites in the Mediterranean Sea at depths of 2400~m and 2700~m, respectively. Three photomultiplier tubes were used to measure single counting rates and coincidence rates for pairs of tubes at various distances. The background rate is seen to consist of three components: a constant rate due to $^{40}$K decays, a continuum rate that varies on a time scale of several hours simultaneously over distances up to at least 40~m, and random bursts a few seconds long that are only correlated in time over distances of the order of a meter. A trigger requiring coincidences between nearby photomultiplier tubes should reduce the trigger rate for a neutrino telescope to a manageable level with only a small loss in efficiency.

The ANTARES Collaboration proposes to construct a large area water Cherenkov detector in the deep Mediterranean Sea, optimised for the detection of muons from high-energy astrophysical neutrinos. This paper presents the scientific motivation for building such a device, along with a review of the technical issues involved in its design and construction. The observation of high energy neutrinos will open a new window on the universe. The primary aim is to study particle acceleration mechanisms in energetic astrophysical objects such as AGN's and GRB's, which may also shed light on the origin of ultra-high-energy cosmic rays. At lower energies, non-baryonic dark matter may be detected through the neutrinos produced when gravitationally captured WIMPs annihilate in the cores of the Earth and the Sun. Neutrino oscillations can be measured by studying distortions in the energy spectrum of upward-going atmospheric nu's. The characteristics of the proposed site are an important consideration in detector design. Water properties and detector environment parameters were measured. These tests have shown that the proposed site provides a good-quality environment for the detector, and have also demonstrated the feasibility of the deployment technique. The present proposal concerns the construction and deployment of a detector with surface area 0.1 km^2. The conceptual design for such a detector is discussed, and the physics performance evaluated. An overview of costs and schedules is presented. It is concluded that a 0.1 km^2 detector is technically feasible at realistic cost, and offers an exciting and varied physics and astrophysics programme. Such a detector will also provide practical experience which will be invaluable in the design and operation of future detectors on the astrophysically desirable 1 km^2 scale.

A new kind of Compton polarimeter using a resonant Fabry–Pérot cavity as a power buildup for the photon beam is proposed. A prototype of such a cavity is described, along with the results obtained in terms of source to be used in a Compton scattering polarimeter.

In this paper, we present the principle and the studies for a new type of Compton polarimeter based on the use of power buildup Fabry-Perot cavity to get a 3% measurement of the Jefferson Lab electron polarization within minutes.