Status of the PWO crystal production from Russia for CMS-ECAL

Since September 1998, the CMS electromagnetic calorimeter has entered into its construction phase. Before starting the mass production of the PWO crystals for its calorimeter, CMS-ECAL decided to set up a pre-production phase in order to define and optimise the process parameters for the mass production of the 80000 PbWO₄ scintillating crystals needed for the CMS electromagnetic calorimeter. From September 1998 to December 2000, the Bogoroditsk Techno-Chemical Plant (BTCP) in Russia has produced 6000 PbWO₄ (PWO) pre-production crystals. The most important results of the pre-production phase were a continuous increase of the yield and a production rate up to 1000 crystals per month, together with a significant improvement and homogenisation of the crystal quality. Taking into account the experience from the pre-production period, by the end of 2000 the BTCP has started the mass production of PWO crystals for CMS ECAL. In parallel to this production, a new development has been set up in order to increase the PWO production yield. As a result, following a large R&D effort, the ingot size could be increased so that it is now possible to extract 2 crystals rather than 1 out of one ingot. In this paper, an overview on the characteristics of the pre-production crystals will be presented as well as the results obtained on the new crystals, showing the same excellent quality and homogeneity as the pre-production crystals.