Momentum bandwidth of the KEK Accelerator Test Facility 2

Beam delivery and final focus systems for multi-TeV advanced linear colliders

“…An attempt has been underway for several years at ATF2 to demonstrate the ability to tune the FF with levels of chromaticity similar to CLIC (by reducing 𝛽 * 𝑦 ), which involves the addition of octupole magnets to the machine. It should be noted at the time of writing, that the achieved beam size in this configuration is still larger than that achieved for the ILC configuration [13] demonstrating the increased level of difficulty in tuning this presents.…”

“…Although the FF optics are designed to remove the chromatic beam size growth as described above, higher-order chromatic and chromo-geometric aberrations arise in the lattice from higher-order contributions from the multipolar magnets and from lattice imperfections. See [9] for a fuller account. This chromatic dependence can be depicted as the energy bandwidth of the BDS optics, calculated by measuring the rms vertical beam size as a function of beam energy offset (either directly or theoretically using tracking simulations).…”

“…The ATF2 test FF optics were designed with the same chromatic response function as ILC [7]. The energy bandwidth of these optics has been analytically calculated and directly measured [9], see figure 3. The simulated energy bandwidth includes treatments of known error sources and specifics of the beam size measurement.…”