Q: What is the pulsed structure of a linac beam?

A:

In the AccSys linac systems, the typical "time structure" of the output beam from the linac is shown in figure 1. The "macro-structure" of the output beam is determined by the pulsing of the rf power input to the linac and the injected charged particles. Typical values of the output beam pulse width and beam pulse repetition rate are indicated in figure 1. The minimum pulse width is determined by the risetime of the accelerating fields in the linac cavity. This risetime is about five microseconds for an RFQ linac operating at an radiofrequency of 425 MHz. Figure 1. Typical ion linac output beam time structure diagram In addition to the pulsed structure resulting from the pulsed input power and beam, the output beam during each "macropulse" also has a "microstructure" determined by the operating parameters of the linac. The frequency in the microstructure is determined by the operating frequency of the cavity and the pulse width is determined by the amount of each period that will stabily accelerate the beam through the linac. The typical microstructure of the output beam from an ion linac system is indicated on the right side of figure 1.