SLAC - PUB - 7139 June 1996

In a final-focus system, space-charge forces can be significant even for very high beam energies. The reason is the inherent large chromaticity of such a system, which needs to be compensated to a high precision. The longitudinal space-charge force causes an energy variation along the bunch, which depends on beam size, beam-pipe radius, and bunch population. Since this energy variation is location-dependent, it may affect the chromatic correction and, thereby, increase the IP spot size. The space-charge force then gives rise to a limit on bunch intensity beyond which the resulting spot-size increase will degrade the final-focus performance. In this paper, the effect of longitudinal space charge is evaluated and intensity limits are derived for three existing or proposed final foci. Abstract In a final-focus system, space-charge forces can be significant even for very high beam energies. The reason is the inherent large chromaticity of such a system, which needs to be compensated to a high precision. The longitudinal space-charge force causes an energy variation along the bunch, which depends on beam size, beam-pipe radius , and bunch population. Since this energy variation is location-dependent, it may affect the chromatic correction and, thereby, increase the IP spot size. The space-charge force then gives rise to a limit on bunch intensity beyond which the resulting spot-size increase will degrade the final-focus performance. In this paper, the effect of longitudinal space charge is evaluated and intensity limits are derived for three existing or proposed final foci.