1. GainEnergy resolution DIRECTION DES SCIENCES DE LA MATIERE LABORATOIRE DE RECHERCHE SUR LES LOIS FONDAMENTALES DE L’UNIVERS CENTRE DE SACLAY Contact : Stéphan AUNE CEA/DSM/DAPNIA/SEDI (saune@cea.fr) MICROMEGAS BULK DAPNIA Saclay Micromegas in a bulk Gaz (ex: Ar + 5% isobutane) Drift (HV 2) Pad readout Ionizing particle Mesh (HV 1) e-e- Conversion gap: 1 mm to m Amplification gap ~ 100  m E ~ 50 kV/cm E ~ 1kV/cm Strips or pads  In a Micromegas detector (micromesh gaseous detector) the mesh (microgrid) is held parallel to the readout plane at a distance about 100 microns, at a potential of several 100 V. This creates the electric field responsible for gas amplification.  The planarity and the parallelism of the mesh influence the gain homogeneity of the device. Downward excursions of the gap would limit the gas gain by breakdown.  In a standard Micromegas, the gap was obtained by an array of pillars on the PCB and the mesh had to be stretched on a frame.  The pillars are made out of photoimageable solder mask (Photoresist) available in films of different thicknesses (38 to 100 microns).  The bulk concept is to use two Photoresist films to permanently hold the mesh between two arrays of pillars. The whole detector (pad array and mesh) is in one piece, a bulk. development Le pain La tartine The sandwich The pizza Le bulk !!! UV Bare PCB with strips or pads PCB with a photoresist layer A part of the photoresist is insolated (exposed to UVs) PCB with a mesh between two photoresist layers The bulk is ready for cabling. The mesh is 100  m from the PCB. Lamination High temperature deposition (100°C) and under pressure of the photoresist film to glue it to the PCB. Cut the edges, remove the protection film of the photoresist. Deposition of the mesh stretched on a frame. Lamination of a second layer of photoresist on the mesh. PCB in Wrapped PCB out The laminator Development Dissolution of the non insolated photoresist using a Sodium carbonate jet at 40°C. Deep rinsing with de-ionised water. Oven and UV hardening of the bulk. Development Bulk before development Insolation PCB with mask Positionning of the mask defining the pattern to polymerise by UVs (pillars, edges,...). Insolation of the photoresist. ( = 350 to 450 nm). Hardening in the oven UV insolator Insolation Lamination 2 Lamination 1 Manufacturing process 4 3 2 1 Advantages of the bulk  Robustness and simplicity of operation  Suppression of the dead area  possibility of segmenting the mesh  Further possibilities Multi-stage Micromegas Micromegas mosaïc Segmented mesh  Upgrade of the process Laser insolation Use of de fine meshes Resistive liquid photoresist Please touch  Stainless steel woven mesh (19 microns, 500 LPI) Principe Micromegas Mesurements with a Fe55 source Detector gain as a function of the mesh voltage 120 x 140 mm bulk Mesh prisonned between 2 pillars Results CEA Saclay / DAPNIA S. Aune, G. Charpak, P. Colas, R. De Oliveira, A. Giganon, I. Giomataris, Ph. Rebourgeard (Saclay and CERN) Laser cut mesh (70  wide) Application: T2K test at CERN