Beam Diagnostics and Applications

Particle beams in accelerators are detected through the electromagnetic elds they create. Position and intensity monitors are based on the near eld which stays attached to the charges. A large variety of measurements can be carried out with these devices. The closed orbit is obtained by reading out the position averaged over many turns. Change in the orbit resulting from a controlled de ection reveals the lattice functions. With a fast position monitor the betatron frequency can be measured. Its dependence on energy deviation, current, and quadrupole strength gives information on chromaticity, impedance, and local beta function. Turn-by-turn reading in all monitors allows one to check the optics and to measure the beta function and phase advance around the machine. Diagnostics based on the far eld is done with synchrotron radiation. It is used to form an image of the beam cross section and to get its dimensions. Due to the small natural opening angle of the radiation, di raction e ects are important and limit the resolution. The angular spread of the particles in the beam can be measured by a direct observation of the emitted radiation. ELECTROMAGNETIC FIELDS USED FOR BEAM