Coordinate Detector: prototype design

1. Coordinate Detector: prototype design • The Coordinate Detector (CDET): • Three independent vertical planes with 15 cm plastic shield in front, all planes as close as possible • One detector plane consists of four sections each covering 96x116 cm2 • The active element of each section is a stack of 0.5x3 cm2 scintillator bars, split in half, viewing the target • WLS fibers run through holes in the bars and transmit light to H8711-10 16-channel PMT • The prototype reported here, will represent mechanically one section of the CDET: • Instead of using 5 mm thick scintillators we will use plastic bars cut from 3/16” acrylic sheet; no holes in the bars • The fibers will run from the end of the bars to the cookies • No light sealing

2. CDET prototype design • Prototype with the cover removed • Front plate: ¼” aluminum • Six vertical stacks (each 32 bars), split in half • Each stack is strapped to the front plate at different positions to make transition between the sections • The straps run through holes in the front plate • 1/2” smooth polyester straps, 0.5 mm thick, with seals • niches in the stacks for straps

3. Connection between detector sections • End of the front plate of one section inserted into the other section • Cover on the back attached to the two cross-bars • Light tightness using black tape and sealant between sections (front and back plates), on the cover edges and in the openings for the straps • End plugs on the top and bottom sections (not in the present design) • Scintillators removed from the left half to see the openings for the straps • Fibers not shown • All dimensions in mm

4. Fibers to PMT connections • Cross-bar (1/2” Al) attached to front plate • Cookies with 16 holes in which fibers are glued • PMT holders with PMTsglued to them

5. Cookie and PMT holder attachment • PMT is glued in a plastic PMT holder • PMT holder is firmly attached with four screws to the cross bar while the PMT goes through a hole sticking outside of the cross-bar by 1.5 mm • The WLS (not shown) are glued in the cookie inside 16 holes • The cookie is attached to the front plate with four screws with springs (not shown) • Two dowel pins in the cross bar center the positions of the PMT holder and the cookie (along red line)

6. Cookie and PMT holder attachment • PMT holder is firmly attached with four screws to the cross bar while the PMT goes through a hole sticking outside of the cross-bar by 1.5 mm • The cookie is attached to the front plate with four screws with springs (not shown) • Two dowel pins in the cross bar center the positions of the PMT holder and the cookie

7. Outlook • Prototype of one section of the CDET designed to test mechanically the concept: • The rigidity of the whole construction (trying to minimize distance between planes using only ¼” front plate) • The cross-bar: at some places it has 1.5 mm wall • The technique of gluing PMT to the PMT holder and the fibers to the cookie • The attachment of the cookies (with fibers already glued) to the cross-bar • Stacking the bars at the right angles and strapping them to the front plate • Tolerances: gluing the PMT to the PMT holder, centering the PMT to the fibers • To design tools helping all of the above operations • The technical documentation is close to completion, expect it in few weeks