Beam Loss in Initial Acceleration Process of KEK Booster

Beam intensity in KEK booster decreases within one milli second to about a half of the injected. This loss is explained by the mechanism of the increasing shift of the equilibrium orbits due to the rapid growing of the momentum spread accompanied with the increase of the accelerating RF voltage. The calculation of this loss was made numerically taking into account the beam distribution in the horizontal phase space resulting from the multi turn injection, momentum distribution of the injected beam and the distribution in the RF bucket. An important point in this calculation is that the number of the particles which takes relatively large momentum deviation in the bucket is not so small as expected, for example, from a Gaussian distribution but rather large because of the rotation of the particles in the bucket due to the synchrotron motion. Therefore many particles experience rather large shift of the equilibrium orbit, which results in much loss of the beam as is observed.