Timing Counter Report of Feb. 14 th, 2007 P.W. Cattaneo

4 problems related to the N2Bag-DC-EC matching: (1)-the upper corners are flexible and fall down to the COBRA center  right position must be assured by means of rigid supports. (2)-the DC fitting in the final position requires N2Bag radius of 300mm instead of 286mm at the top-end corners  reshape the N2Bag at the corners. (3)-the N2Bag Inner radius < DC radius: installation only after DC in final position (4)-Collar design not satisfactory: new solution under study N2bag 300mm 268mm COBRA BORE N2bag 300mm 268mm

N2Bag N2Bag He4 level: The final He4 level inside the bag at the PM positions is about 10 x ABL (Atmospheric Background Level), with 1 atm He4 outside. Gas washing: we reached 1x(ABL), by flushing 50l/m. Sniffer probe 1 atm He4 COBRA BORE N2Bag US Bag Us TC

TC TC US: not in final position because of a trivial error of rails support: 5mm higher than expected. The inner end of the scintillating bar are now at 242mm from the second COBRA step. TC DS mounted in symmetrical position. Now: improvement of TC supports for fine trimming (5mm) of position during insertion, mounting of laser calibration optics PMs of TC US Support of rails The support of rails blocks the TC 242mm TC US COBRA BORE

Connection to the Electronics The PM channels have be sent to the DRS, with the following scheme, which contains only 8 channels in the final configuration. Tuning-up 8 by 8 channels with “home made” electronics 8 Tempor ary Passive Split. 1 to 1 Dsc & Split Linear not conn. Timing to DRS Linear to DRS 8 Linear to Tuning-up elctronics

Run 2006 Tuning up in magnetic field required PM gain equalization with cosmics, many days of work for about 10% gain uniformity (found few PM not matched). Data taking for charge spectrum of each PM with Beam ON, with home-made electronics. Direct count rate (single PM, 2 PM coincidence, 2 bars coincidence, 3 bars coincidence)  PM anodic current evaluation and Bck contribution. Data taking with DRS.

PMT Life Life= time of stable gain operation = time needed to supply the total charge of 360 C at the anode Previous extimation with 2V av. signal and the only positron 50KHz  life = 833 d (2.2 y)  50% gain reduction: life  3y Single PM rate: V in the high mu- stop rate of 06-run What is the expected PM life? enhancing factor : 3 (beam), 2-3 ( average signal+bck) reducing factor: 10 (rate found/expected) …. Our estimation is not precise  needed a study of PM gain after 360 C

We are measuring the PM gain vs time in the “drift” region. If the gain drops down more quickly we need to introduce an amplification stage to match the required dynamic range life drift 10%/decade T(h) 100 uA

Fiber detector electronics We are ready to start the mounting of the fiber detector We have modified the position of APD electronics. We have fixed the cooling: 2 thermoelectric chillers (400w each). A test set-up with one chiller and one final APD support has been already tested in Genoa (125 W per support = 250 W per TC). Cooled Support APDs

Schedule 2007 March 31: N2Bag US+DS ready April 15 : N2Bag US mounted April 30 : End test of TC Us+DS at Frascati May 15 : Mounting of the TC US May 31 : Mounting of the N2Bag DS June 15 : Mounting of the TC DS