Carbon-Epoxy Composite Base Plates for the PHOBOS Spectrometer Arms J.Michalowski, M.Stodulski The H.Niewodniczanski Institute of Nuclear Physics, Krakow March 2000 PHOBOS Report 00-02

March, 2 Introduction Original base plates for the PHOBOS spectrometer arms were designed and fabricated from aluminum sandwich plates reinforced with aluminum rectangles situated, mostly, on their top surfaces along edges. There are also reinforcing rectangles from the bottom in the region where the magnet coils were cut off. Due to design constraints and requirements the base plates cannot be thicker than 5 mm and their sag should not exceed 300 microns. The base plates with silicon modules are placed in stable magnetic field of 2 T. Design assumption was that the magnetic filed would be ramped up and down in a controlled way to avoid eddy current effects.

March, 3 Aluminum outer base plate (sag measurement) Aluminum base plate (E = 70 GPa) with cooling frames prepared for sag measurements m ALplate = 3.2 kg, m total = 13.5 kg Comparison of measured and calculated sags for the aluminum base plate |sag max | = ~ 300 microns Lead pieces simulating weight of silicon modules, flex cables and water

March, 4 Aluminum base plates in magnetic field It has turned out that uncontrolled drop of the magnetic field can occur while the magnet crashed. Tests were performed to check the behavior of the fabricated base plates in case of the magnet crash. The plates were observed through theodolites allowing the measurement of the plate displacements. The magnet crash at full current (3600 A) caused a motion of the aluminum base plates about 1 mm in the horizontal and about 0.5 mm in the vertical direction. Silicon modules mounted on the base plates could be damaged in case of real magnet crash. Other materials considered as a replacement for aluminum were also tested. Most promising results were obtained for carbon-epoxy composite.

March, 5 Design and fabrication of the base plates from a carbon-epoxy composite The results of the magnet crash tests performed triggered the decision to construct new base plates from a carbon-epoxy composite. Two basic guidelines are applied to the new design: shape and dimensions of both, the old and new base plates, are the same, design of details should be modified in order to take advantage of new technology. Design and fabrication of the carbon-epoxy composite base plates is described on the following pages (6 -17).

March, 6 Sandwich plate design (5 mm thick) Outer skins of sandwich plate: material - high modulus carbon fiber (E = 395 GPa) tissue St886, epoxy resin skin thickness 0.5mm Core of sandwich plate: material - rohacel foam and G11 inserts core thickness 4 mm

March, 7 Sandwich plate core - 1 (4 mm thick ) G11 frame along plate edges and reinforcing ribs facilitating future machining 2 - Carbon-epoxy skin of sandwich plate

March, 8 Sandwich plate core - 2 (4 mm thick) rohacel foam 2 - G11 inserts along top rib 3 - G11 inserts along bottom rib 4 - G11 insert in mounting region of frames # 1,2,3, G11 inserts in mounting regions of frames # 5,6,7,8 6 - G11 insert in mounting region of cable posts 7 - G11 inserts in support point regions

March, 9 Sandwich plate core - 3 (4 mm thick) G11 inserts in the bottom rib regions 2 - G11 insert in mounting region of the cooling frames # 1,2,3,4 3 - G11 inserts in mounting region of the cable posts

March, 10 Sandwich plate core - 4 (4 mm thick) twelve G11 inserts to mount cooling frames # 5,6,7,8 2 - two G11 inserts for survey markers (at current location) 3 - two G11 inserts for additional survey markers (near supporting points)

March, 11 Carbon-epoxy composite sandwich plate Carbon-epoxy composite sandwich plate - already laminated; there is no reinforcing rib, yet

March, 12 Lamination of carbon fiber reinforcing ribs 1 - plywood mould prepared for lamination of unidirectional carbon fiber (T300, E = 230 GPa) reinforcing ribs 2 - groove for the top rib 3 - groove for the bottom rib 4 - aluminum pieces to press the ribs during lamination

March, 13 Gluing of the bottom rib and bushings bottom rib (not visible) already glued 2 - G11 bushings for mounting the cooling frames and aluminum ones for survey markers already glued 3 - plate edges machined to glue the top rib

March, 14 Carbon-epoxy composite base plate for the PHOBOS inner spectrometer arm in Krakow carbon-epoxy composite sandwich plate (E = 80 GPa) 2 - bottom rib (E = 115 GPa) 3 - G11 and aluminum bushings 4 - top rib (E = 115 GPa)

March, 15 General manager of the carbon-epoxy composite base plate project J.Michalowski with the carbon-epoxy composite base plate

March, 16 PHOBOS inner base plate at the Chemistry lab three points to support the spectrometer base plate in the magnet

March, 17 PHOBOS inner base plate at the Chemistry lab mounts for the hall probe

March, 18 Magnetic and mechanical features of the carbon-epoxy composite base plate The carbon-epoxy composite base plate for the PHOBOS inner arm was tested in the magnet crash conditions. Aluminum cooling frames and cable holders were mounted on the base plate. Two points on the base plate and one on a cooling frame were observed through theodolites. No motion observed during magnet crash! Sag of the new base plate was not measured. However, mechanical rigidity of the carbon-epoxy composite plate is roughly 40% bigger than that of the aluminum plate. Thus, its sag is expected to be smaller than that measured for the aluminum base plate. Flexural rigidity better than in case of aluminum plate!