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Description
A 700 MeV-class S-band RF linac platform is designed as a dedicated testbed for validating angular dispersion–driven fully coherent radiation (ADM) and its modulation–demodulation scheme. The machine consists of an ∼10 m RF photoinjector, a laser-heater section, a movable chicane section and an 76 m S-band main linac, enabling multiple beam working points on a common lattice. In the baseline round-beam working point (baseline linac design), the photoinjector delivers a near-round bunch at its exit with a charge of Q =0.25 nC and an energy of ∼110 MeV, which is accelerated in the main linac to ∼730 MeV. On the same beamline, a flat-beam working point (flat beam design) is obtained by introducing an axial magnetic field near the gun and operating a small subset of injector quadrupoles as skew quadrupoles to remove canonical angular momentum (CAM), yielding at the injector exit a flat beam with a transverse emittance ratio of ∼10 (representative normalized emittances εx ≈0.26 mm·mrad and εy≈2.9mm·mrad) and a peak current of ∼38A, i.e., storage-ring–like ultralow vertical emittance already at low energy. These two complementary working points demonstrate that, with only local adjustments of a few injector magnets, a single 700 MeV S-band linac can switch between a robust baseline round beam and a flat beam better adapted to ADM-oriented coherent-radiation experiments. In this work, the detailed physics design is described and the recent commissioning result is reported.
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