THOA07 　ビームダイナミ／レーザー　 8月1日 アプローズ 10:50-11:10

Emittance control by a ponderomotive laser lens

○Vitaliy Goryashko (SPring-8, RIKEN), Johan Ribbing, Giovanni Perosa (Uppsala University), Kazuaki Togawa (SPring-8, RIKEN)

Emittance of an electron beam is the key parameter that determines the degree of transverse coherence and the efficiency of a SASE X-ray Free-Electron-Laser (XFEL). The emittance preservation of a high-brightness beam during acceleration, compression and transportation from the cathode to the undulator in an XFEL is a challenging task. The beam emittance tends to degrade, for example, due to nonlinear space-charge forces and chromatic effects during compression. Here, we propose a method that allows to control and suppress linear and nonlinear emittance growth using a time-profiled laser field. The laser field works as a time-dependent lens based on a ponderomotive force effect – the effect used in a plasma acceleration method, in which a laser pulse is focused into a plasma. In contrast, we study the case of an electron beam propagating in a transversely and longitudinally profiled laser beam, which works as a lens. Advanced linear emittance compensation can be implemented applying such a laser lens. The SACLA XFEL injector is used as a theoretical case study to demonstrate capabilities of the proposed ponderomotive laser lens. A plan for experimental studies is also discussed.