Radiation hardness, excess noise factor and short-term gain instability of vacuum phototriodes for the operation in pseudorapidity range 15 < eta < 30 at CMS ECAL

The operation of super radiation hard prototypes of vacuum fine-mesh phototriodes (VPT) proposed for application in CMS Endcap ECAL at the pseudorapidity of eta greater than or equivalent 2.6 has been investigated in radiation fields up to 50 kGy and neutron fluence of 7 multiplied by 10**1**5neutroncm**-**2. It is shown that anode response and the excess noise factor of VPT are independent of given above radiation dose and neutron fluence. The results of VPT gain variation measurements under rapid changes of counting rate are presented for the operation in the pseudorapidity range 1.5 less than approximately equals eta less than approximately equals 3.0.