Instrumentation of the very forward region of a linear collider detector

The very forward region of a linear collider detector is a particularly challenging area for instrumentation. For the TESLA project a luminometer (LAT) at small polar angles is foreseen to perform a high precision (O(10/sup -4/)) luminosity measurement, requiring the control of the systematics on the corresponding level. Monte Carlo simulations to optimize the shape and the structure of the calorimeter are presented. A second calorimeter (LCAL) is positioned just adjacent to the beampipe. Into this device a large amount of bremsstrahlung remnants, several ten TeV per bunch crossing, is scattered, resulting in a radiation dose of about 10 MGy per year. The distribution of the bremsstrahlung has to be measured in order to assist in the tuning of the beams at the final focus. Furthermore, single hard electrons have to be measured, or at least vetoed. The latter is important, since events with high energetic electrons near the beampipe are a serious background in many search channels with missing energy and momentum. Monte Carlo simulations for a heavy crystal calorimeter and a diamond/tungsten sandwich structures are presented and compared. First results on sensor tests are given.