First Results in D-T from the Radiation Hardened Soft X-ray Cameras

Two soft X-ray cameras(KJ5) have been constructed for the D-T phase of JET operation. The active Si detector elements are placed within a substantial radiation shield made mainly from barytes concrete. The initial part of the DTE1 experimental programme has provided an opportunity to assess the operation of this diagnostic. The results show that the shield and detectors are working as expected and that the system will continue to work well when the highest power levels are reached. A comparison is made with the signals from an unshielded detector. INTRODUCTION A pair of radiation hardened soft X-ray cameras have been constructed), both to provide soft Xray signals from mhd events in D-T plasmas and also to provide signals for vertical stabilization of the plasma. The two cameras, located on the main horizontal ports at octants 4 and 8, each contain 17 detector assemblies embedded into a large barytes concrete shield with the detectors viewing the plasma through precision machined stainless steel collimators and 250μm Be windows which separate the machine and diagnostic vacua (Fig 1).The effects of the neutrons on the detectors have been previously been discussed). The detector vacuum is maintained at 10T. Each detector assembly has a stack of different elements (Fig 2) as follows: Fig. 1 The lines of sight are shown for the radiation hardened soft X-ray camera (KJ5) and the position of the unshielded vertical camera is also shown. –200 –150 –100 –50 0 50 100 150 200 100 200 300 400 500 Lines of sight of radiation shielded camera Position of vertical camera V12 S8/1 S8/2 V35 S8/10 S8/11 Major radius H ei gh t ( cm )