The High Acceptance Di Electron Spectrometer is a detector system for lepton pair spectroscopy built at GSI (Darmstadt, Germany). The physics program includes the study of electron-positron pair emission in relativistic heavy ion collisions, di-lepton production in elementary reactions and experiments aimint at hadron structure studies.

A variety of instruments are working in this spectrometer:
- a superconducting toroidal field magnet;
- a trigger consisting of granular pre-shower detectors at forward angles and two scintillator walls (TOF and TOFINO);
- a Ring Imaging Cherenkov Counter (RICH);
- four stations of Multiwire Drift Chambers (MDC) for tracking (2 before the magnet and 2 after).

The of IPN Orsay took in charge the study and fabrication of 4 of the Multiwire Drift Chambers of the 4^th station (MDC4). They are covering 3.5 m² per sector, and are the largest stage of the tracking system. The design was made by CAD and elements manufactured by subcontractors.

A chamber module is composed of 6 anodes and 7 cathode layers. The anodes are composed of 30 micron diameter gold plated tungsten readout wires separated by 100-µm diameter gold plated aluminium wire (field wires). The cell drift length is 7 mm. The cathodes are composed of gold plated aluminium wires with a pich of 4 mm.

The high voltage of –2 400 V is applied on the cathode and field wires whereas the anode wires are at 0 V for the signal readout.

Two mylar windows close the chamber which is filled with Helium Isobutane gas mixture. The wires are glued and soldered on printed circuits which are themselves glued on 5-mm thick epoxy frames.

For the assembly, the frames are piling up together between metallic frames which sustain the tension of wires. This tension gives a load close to 8 000 N.
The construction of one chamber necessitates 25 000 meters of wires, 350 printed circuits, 25 000 points of gluing and soldering. A special large winding machine (at the Saclay CEA site) tenses all the wires on transfer frames. For the anode layer, the 2 different types of wires are successively winded on the same support to reduce time transfer.

All operations are performed in the clean rooms.

The precision of the distance between wires is 50 microns. The layer positions are measured with the tridimensionnal measuring machine. All mechanical tensions of wires are controlled afterwards to prevent instabilities arising from electrostatic forces.

A full-scall prototype comprising of one anode and two cathode planes was made in 2000. It permitted the validation of the fabrication process in the industry and the assembly.
The effect of breakdown on wire breaking was investigated. Finally, the anode wire diameter was increased from 20 to 30 microns.

The chamber design includes electromagnetic compatibility rules to reduce the noise level despite the chamber large dimensions. All electronics (ASICs developped by GSI) and cables are mounted on the sides of the chamber. The developped a tool for the test and diagnostic of the cables and connectors. Some weeks are necessary to test the 1 300 channels and validate the reliability of the whole system under gas and high voltage. During the tests, the ASICs are controlled and read with a PC through a PCI board developped by GSI. The adapted the C program written by GSI for a faster test analysis (including the ROOT macros).

The chambers are shipped to GSI by truck. They are protected by a damping system.

Four chambers were delivered in between 2001 and 2003. In order to complete the system and reach the ultimate resolution over the full angular detector acceptance, the HADES collaboration asked the to construct the last two chambers with a funding provided by the collaboration. These two chambers were delivered in 2005 and early 2006 and are now integrated in the HADES frame.