Image Sensor Technology for Beam Instrumentation

Beam monitoring using cameras has evolved from qualitative beam observation to precision measurement. After a description of the two main TV standards, various sensors including TV tubes (Vidicon), solid state sensors (Interline and Frame transfer CCDs, CMOS and CID X-Y matrices), and Fast Shutter/Intensifiers of the MCP type are reviewed. Comparative resolution measurements for the various sensors are given. The two types of sensor acquisition hardware, “frame grabbers” and “digital cameras,” am described Finally, special image processing requirements for beam instrumentation are reviewed, including radiation hardness, spectral sensitivity, fast acquisition, and enlarged dynamic range. INTRODUCTION Television cameras have been used since the early days of accelerators for beam observation. The main application was for a long time the observation of screens for beam steering purposes through transfer lines and for the first turn around circular machines. With the construction of lepton machines producing enough synchrotron radiation, and high intensity proton storage rings, the use of TV based monitors was extended to the measurement of beam dimensions for machine optimization and luminosity estimation. Instruments of this type were developed in several laboratories in the 1970s with tube TV cameras and included some form of digitization and numerical processing for beam size extraction. Despite the usefulness of these instruments, it took a certain number of years to have them accepted as precision instruments. The introduction of the CCD sensor, with its more than 100,000 cells having siliconengraved precision of a few microns, came to maturity in the early eighties, just in time for LEP. Camera-based beam monitors have now acquired a competitive position in beam instrumentation and are recognized as indispensable instruments in accelerators. The users now have maximum expectations from them. The recent improvements of CMOS sensors and the interest of industry and universities in machine vision have induced enormous progress in the field and there is now a wide variety of hardware and software available, some of which is directly useful for beam instrumentation.