In laser-plasma accelerators (LPA), due to extremely high accelerating gradients, electron bunches are accelerated to high energies in only a few millimeters to centimeters of acceleration length. To efficiently capture and transport the LPA-generated bunches in a compact transport line, beam line designs employing high-strength combined-function magnets based on high-temperature superconductor technology have been studied. Moreover, to overcome coil winding challenges in fabricating miniature HTS magnets, novel periodic magnets have been designed, which can collimate and guide the electron beams in a well-controlled short-length transport line. In this contribution, we present the beam dynamics calculations as well as the magnet designs for a 1.4 m transport line matching the LPA-generated electron beams to a transverse-gradient undulator.

Novel iron lamination with additional interlaminar insulation has been successfully developed for magnet cores of fast kicker magnets in particle accelerators. By minimizing the eddy current induced between core laminas, a pulse profile of the excited magnetic field has been significantly improved up to a few MHz range. The magnet core is formed by alternately stacking thin steel and insulation sheets to avoid electrical contact between the steel sheets on the cutting edge. A pair of test magnets with the new iron lamination was assembled to evaluate magnet performances focusing on applications to matched kickers in the accelerators. The magnetic field pulse profiles of the two magnets have successfully proved to match below 0.1% over the entire pulse duration, which is significantly better than those with conventional iron lamination. The developed fast kicker magnets are promising for the beam injection kickers in the coming next-generation light sources and future colliders, where suppression of the transient stored-beam oscillation during beam injection is crucial.

Coupled-bunch instability arising from impedances of higher-order modes (HOMs) in RF cavities is a problem to be suppressed in high-current, low-emittance electron storage rings. As a countermeasure against the problem, we have developed a compactly HOM-damped cavity resonating in the TM020-mode at a frequency of 509 MHz. The damping structure compromises circumferential and shallow slots in the cavity inner-wall and ferrites inside the slots. Since the slots are along the magnetic nodes of the TM020 mode, the ferrites absorb only RF powers of the HOMs. The cavity has a shunt impedance of 6.8 MΩ and generates an accelerating voltage of 825 kV at a 100 kW input. The cavity has a slot-type input coupler with a variable-length stub to match its coupling degree with change in beam loading during the operation. The prototype cavity demonstrated satisfactory performance in high-power operation up to 120 kW. Therefore, this innovative cavity is about to be utilized for beam acceleration in the new 3 GeV synchrotron radiation facility, NanoTerasu. We report on the performance of four fabricated cavities, problems and countermeasures experienced in their high-power tests.