Third International Conference on Frontier Science Villa Mondragone – Monteporzio Catone Physics and Astrophysics in Space June 14, 2004 Mercedes Paniccia.

Third International Conference on Frontier Science Villa Mondragone – Monteporzio CatonePhysics and Astrophysics in Space June 14, 2004

Mercedes Paniccia University of Geneva - Switzerland

The AMS-02 TrackerThe AMS-02 Tracker



The AMS-02 detector is based on a large acceptance (~0.5 m² sr) and high sensitivity spectrometer, composed of a super-conducting magnet and a silicon tracking device (Tracker).

An Anti-Coincidence Counterplaced 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.



The superconducting magnet is cooled by evaporating liquid helium and has a reservoir for about three years of operation without refill.

Its dipolar field, normal to the aperture of the magnet, is based on a magic ring configuration of race track coils around a pair of Helmholtz coils.

With a field strength of 0.8 Tesla at the centre it extends the rigidity range for charged particles up to few TV.

Third International Conference on Frontier Science Villa Mondragone – Monteporzio CatonePhysics and Astrophysics in Space June 14, 2004 June 14, 2004

Mercedes Paniccia University of Geneva - SwitzerlandMercedes Paniccia University of Geneva - Switzerland

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.



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.

The AMS-01 Tracker has been the first application in space of the high precision silicon technology developed for position measurements in accelerator experiments. The high modularity, low voltage (<100 V), and gas-free operation of the device is well suited to operation in space. The 1998 shuttle test flight has proven both the successful adaptation of the technology to the space environment and the feasibility of large area detectors.



The n-type, high resistivity (> 6 kΩ) sensors are biased with the punch-through technique and p+ blocking strips, implanted on the n-side, are used to minimize the influence of surface charge on the position measurement obtained from the ohmic side.

The sensor design uses capacitive charge coupling with implantation (readout) strip pitches of 27.5 (110) µm for the p-side and 52 (208) µm for the n-side.

The finer pitch p-side strips measure the bending coordinate and the n-side strips measure the orthogonal coordinate, achieving a tracking resolution of 10 µm and of 30 µm respectively.

The measurement of specific energy loss, dE/dx proportional to Z², in the silicon allows independent nuclei identification in the Tracker.



AMS-02 silicon sensors characteristicsDimensions 7.2 cm × 4.1 cmThickness ~300 µmActive width p-side ~70.5 mmStrip pitch p-side 27.5 µmNum. of p-strips 2568Readout pitch p-side 110 µmNum. of p-side readout strips 640Active width n-side ~39.8 mmStrip pitch n-side 104 µmNum. of n-strips 384Readout pitch n-side 208 µmNum. of n-side readout strips 192



The silicon sensors will be arranged in 192 ladders.

The ladder is made of variable number of silicon sensors (from 7 to 15) with daisy chained strips

to increase the detection surface while using a limited readout. To connect the n-side strips a Upilex foil with copper strips is used to transmit the signal to the front-end electronics.



Two ladders ready to be installed:



The ladders will be installed in eight layers of ~1 m² each on five planes of an ultra-light support structure.



Installing ladders on plane:



The first layer assembled:



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).

Three out of eight layers have been fully equipped with ladders at University of Geneva.

The Tracker assembly is foreseen to be completed by 2005.

In the meantime an extensive series of tests have been performedto verify the performance of the AMS-02 silicon Tracker:results will be presented by next speaker P. Zuccon.

Third International Conference on Frontier Science Villa Mondragone – Monteporzio Catone Physics and Astrophysics in Space June 14, 2004 Mercedes Paniccia.

Documents

international conference

tracker slide

star tracker

tracker frontend electronics

superconducting magnet

strips measure

high modularity

high resistivity