In order to define the specification on trajectory jitter at the linac end, it is necessary to understand what impact this jitter will have on the transfer line and booster injection. From this specification comes the maximum tolerable kick from the long range transverse wakefields in the linac and what trajectory jitter can be tolerated from the electron source and from the DR.
Participants: S. Bettoni, A. Latina, A. Grudiev, Y. Dutheil, A. Chance, S. Yue, P. Craievich, (W. Bartmann)
Andrea presented estimates of jitter amplification for multi and single bunch. In the simulations, an initial trajectory jitter (from the electron source) of 10%, for example of the beam size and tansverse momentum (launching angle into the linac), is assumed. More details about the approach taken in the simulations can be found in the slides. Furthermore, in order to define the specifications on the effect of transverse wakes, it is arbitrarily assumed that the amplification of jitter along the linac must be at most 10%. The jitter amplification through the linac has no significant effect on the emittance, which remains conserved even at large jitter amplification.
The purpose of the meeting is to define what jitter is tolerable in the transfer line and for injection into the booster.The discussion focuses on the transverse jitter, and other discussions will need to take place concerning energy and timing jitters.
Yann explains that for Z-mode the emittance is at least partially conserved from injection to extraction due to the long damping time at injection and limited time we can stay at flat-top. Therefore, the trajectory jitter specification for injection into the booster is (0.1-0.15)*sigma (beam size) if we want to avoid the injection oscillation dampers in the booster and accept emittance increase due to filamentation. This results in a not feasible specification for jitter amplification in the linac.
As a conclusion, we decided to assume as a specification for the trajectory jitter at the injector end of 1*sigma. This target specification is compatible with the present results for the inejctor but requires further consideration on the use of dampers in the booster, Antoine and Yann will look at this.
The vacuum chamber diameter of the transfer line is approximately 40-50 mm and this should not be a problem with transverse wakes in the transfer line. However, this will have to be checked.
Actions
- Antoine and Yann to consider the specifications/requirements injection oscillation dampers
- Everyone : Quantify the effect of wakefield in the transfer line between the linac and the booster
