Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève The Construction of AMS

Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève The Alpha Magnetic Spectrometer project aims at improving the current experimental status of cosmology and particle physics in space by providing a large area, high sensitivity spectrometer to be exposed to cosmic rays over a long observation period on the International Space Station.

Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève AMS is a particle physics experiment in space. The purpose is to perform accurate, large acceptance (~0.5 m ² sr), high statistics, long duration measurements of energetic (up to TeV) primary cosmic ray spectra in space. The AMS detector features sophisticated particle identification devices that will allow to discriminate the small amount of anti-protons up to high energies. It will also allow systematic observations of the gamma ray sky. The detector has been designed to survive to the strict conditions of space: the mechanical stress during the launch, the large temperature range, limited electrical power and limited weight.

Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève The Transition Radiation Detector measures the radiation emitted by charged particles upon changes in the index of refraction of the traversed medium. The detector is realized by a 20 mm thick fleece which is used as radiator. The TR photons are detected in straw tubes, filled with a Xe/C02 gas mixture. A total of 328 TRD modules, each containing 16 straw tubes, of lengths between 0.8 and 2 m are arranged in 20 layers each with 20 mm of 0.06 g/cm3 polypropylene/polyethylene 10 µ m fiber fleece. The lower and upper four layers are oriented parallel to the magnetic field while the middle 12 layers run perpendicular to provide 3D tracking. It will separate baryons from electrons up to energies of 300 GeV. It will also help in the tracking of charged particles, identification of photon conversion points and energy loss measurements.

Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève The Time of Flight system is composed of two crossed double sided planes of scintillators paddles positioned 1.3 m apart respectively above (upper TOF) and below the magnet (lower TOF). Each plane has a sensitive area of 1.2 m² and within one plane the paddles are overlapped by 0.5 cm. The TOF system provides the fast trigger for charged particles and converted photons, selection, at the trigger level, of particles within the main acceptance, measurement of the particles velocity, including the discrimination between upward and downward going particles, and a measurement of the absolute charge. A timing resolution of 120 ps is expected.

Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève A proximity focusing Ring Imaging Cherenkov counter placed on the lower part of the spectrometer, between the lower TOF and the Electromagnetic Calorimeter provides velocity and charge measurement. Light emitted in the combined Aerogel (n= ) and NaF (n=1.33) radiator on the top is detected as a circle of photons by an array of position sensitive photomultipliers on the bottom, occasionally after reflection off a conical mirror. The opening angle of the Cherenkov cone measures the velocity with a resolution of 0.2%. The number of photoelectrons measures the energy loss with a resolution of 8%. It identifies chemical elements up to Z=26 and up to the upper rigidity range of the spectrometer.

Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève The Electromagnetic Calorimeter is a fine grained lead-scintillating fiber sampling calorimeter, that allows precise 3D imaging of the longitudinal and lateral shower development, providing high electron/hadron discrimination and good energy resolution. It distinguishes hadrons from electromagnetic showers with a protons rejection of 0.01% up to several hundred GeV. The calorimeter is composed by superlayers, each 18.5 mm thick and made of 11 lead foils 1 mm thick interleaved with layers of 1 mm diameter scintillating fibers and glued together with epoxy. Fibers are read out on one end only by four anode photomultipliers.

The central subdetector is a large acceptance (~0.5 m ² sr) and high sensitivity spectrometer, composed of a superconducting magnet and a silicon tracking device (Tracker). An Anti-Coincidence Counter placed inside the inner bore of the magnet allows to reject particles entering the Tracker laterally, outside the main acceptance. A Star Tracker has been added to the AMS-02 set-up to ensure accurate knowledge about the instrument orientation, since the ISS attitude is rather variable. Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève

Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève The magnet system consists of superconducting coils, a superfluid helium vessel and a cryogenic system, all enclosed in a vacuum tank. The magnet operates at a temperature of 1.8 K, cooled by superfluid helium. It is launched at the operating temperature, with the vessel full of 2500 litres of superfluid helium, sufficient for three years of operation. The 14 superconducting coils, arranged in a magic ring configuration, generate a dipolar field perpendicular to the experiment axis. The magnetic flux density at the geometric centre of the system is 0.86 T.

Journée de réflexion du DPNC Cartigny – July 2, 2004 In order to remove the heat dissipation generated inside the magnet by the Tracker front-end electronics a dedicated Thermal Control System has been developed. It is based on a mechanically pumped two-phase loop with carbon dioxide as working fluid. Mercedes Paniccia Université de Genève

The silicon sensors are arranged in ladders, which will be installed in eight layers of ~1 m² each on five planes of an ultra-light support structure. The Tracker is built with close 2500 double sided silicon microstrip sensors, which allow to measure two coordinates with a single detector, reducing thus the material budget. Mercedes Paniccia Université de Genève Journée de réflexion du DPNC Cartigny – July 2, 2004

Mercedes Paniccia Université de Genève Journée de réflexion du DPNC Cartigny – July 2, 2004 The Tracker measures trajectories of charged particles with a tracking resolution of 10 µ m in the bending direction and of 30 µ m in the orthogonal direction, achieving a rigidity range up to few TV. The measurement of specific energy loss in the silicon allows independent nuclei identification. It can also measure the direction and the energy of photons converted in the material above its first layer..

Mercedes Paniccia Université de Genève Journée de réflexion du DPNC Cartigny – July 2, Three out of eight layers have been equipped with ladders at University of Geneva. The Tracker assembly is foreseen to be completed by In the meantime an extensive series of tests have been performed to verify the performance of the AMS-02 silicon Tracker. Until now 80% of ladders have been produced with the effort of several institutions involved in the AMS-02 Tracker collaboration (University of Geneva, INFN- Perugia, ETH-Zurich, University of Bucarest, University of Turku, Skobeltsyen INP, Southeast University and an industrial firm in Italy).

Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève Of particular interest will be next Test Beam (15 th September to 4 th October), which mainly aims at studying the Tracker performance in measuring converted photons. It will be held at the CERN PS experimental zone using the T7 beam (secondary beam of a 24 GeV/c proton beam) in collaboration with the ECAL group. The experimental program will also include the calibration and the study of the Tracker and ECAL response to electrons and positrons at different energies (from 3 to 15 GeV), the study of the “gamma stand-alone trigger” with the ECAL and of the e/p rejection with both detectors.

Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève C : Cherenkov counter to identify the amount of electrons in the beam S1, S2, S3: scintillation counters for trigger purposes R1: radiator to convert photons T1: silicon telescope to measures trajectories of particles entering the magnet B: minitracker (11 ladders simulating the AMS-02 Tracker) M: dipole magnet (field strength up to 1T) T2: silicon telescope to measure trajectories of particles exiting the magnet E: one AMS-02 ECAL superlayer

Journée de réflexion du DPNC Cartigny – July 2, 2004 Mercedes Paniccia Université de Genève There is still a long way to we are lucky that someone is taking care of the ISS up there! Image above: Spacewalkers Gennady Padalka (suite with red stripes) and Mike Fincke (suite with blue stripes) at the SO Truss worksite before successfully restoring power to a Control Moment Gyroscope. Credit: NASA TV.