FEL2011 - List of Authors (Chao, A.)

Paper	Title	Page
MOPB21	Seeded Radiation Sources with Sawtooth Waveforms	53
	D.F. Ratner Stanford University, Stanford, California, USA A. Chao SLAC, Menlo Park, California, USA
	Despite the recent success of SASE-based FELs, there is still considerable interest in driving coherent radiation sources with external seeding. Seeding schemes, such as HGHG and EEHG, can increase longitudinal coherence, decrease saturation lengths, and improve performance of tapering, polarization control and other FEL features. Typically, seeding schemes start with a simple sinusoidal modulation, which is manipulated to provide bunching at a high harmonic of the original wavelength. In this paper, we consider variations starting with a sawtooth modulation. The sawtooth creates a clean phase space structure, providing a maximal bunching factor without the need for an FEL interaction. While a pure sawtooth modulation is a theoretical construct, it is possible to approach the waveform by combining two or more of the composite wavelengths. We give examples of sawtooth seeding for HGHG, EEHG and other schemes including compressed seeding, steady state microbunching, and reversible seeding. Finally, we note that the sawtooth modulation may aid in suppression of the microbunching instability.

MOPB23	Reversible Seeding in Storage Rings	57
	D.F. Ratner Stanford University, Stanford, California, USA A. Chao SLAC, Menlo Park, California, USA
	We propose to generate steady-state microbunching in a storage ring by implementing a reversible seeding scheme. High gain harmonic generation (HGHG) and echo-enhanced harmonic generation (EEHG) are two promising methods for microbunching linac electron beams. Because both schemes increase the energy spread of the seeded beam, they cannot drive a coherent radiator turn-by-turn in a storage ring. However, reversing the seeding process following the radiator minimizes the impact on the electron beam and may allow coherent radiation at or near the storage ring repetition rate. In this paper we describe the general idea and outline a proof-of-principle experiment.

Paper

Title

Page

Seeded Radiation Sources with Sawtooth Waveforms

53

D.F. Ratner
Stanford University, Stanford, California, USA
A. Chao
SLAC, Menlo Park, California, USA

Despite the recent success of SASE-based FELs, there is still considerable interest in driving coherent radiation sources with external seeding. Seeding schemes, such as HGHG and EEHG, can increase longitudinal coherence, decrease saturation lengths, and improve performance of tapering, polarization control and other FEL features. Typically, seeding schemes start with a simple sinusoidal modulation, which is manipulated to provide bunching at a high harmonic of the original wavelength. In this paper, we consider variations starting with a sawtooth modulation. The sawtooth creates a clean phase space structure, providing a maximal bunching factor without the need for an FEL interaction. While a pure sawtooth modulation is a theoretical construct, it is possible to approach the waveform by combining two or more of the composite wavelengths. We give examples of sawtooth seeding for HGHG, EEHG and other schemes including compressed seeding, steady state microbunching, and reversible seeding. Finally, we note that the sawtooth modulation may aid in suppression of the microbunching instability.

MOPB23

Reversible Seeding in Storage Rings

57

D.F. Ratner
Stanford University, Stanford, California, USA
A. Chao
SLAC, Menlo Park, California, USA

We propose to generate steady-state microbunching in a storage ring by implementing a reversible seeding scheme. High gain harmonic generation (HGHG) and echo-enhanced harmonic generation (EEHG) are two promising methods for microbunching linac electron beams. Because both schemes increase the energy spread of the seeded beam, they cannot drive a coherent radiator turn-by-turn in a storage ring. However, reversing the seeding process following the radiator minimizes the impact on the electron beam and may allow coherent radiation at or near the storage ring repetition rate. In this paper we describe the general idea and outline a proof-of-principle experiment.