FEL2011 - List of Keywords (damping)

Paper	Title	Other Keywords	Page
MOPB21	Seeded Radiation Sources with Sawtooth Waveforms	bunching, FEL, laser, radiation	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.

WEPB16	Study for Evaluation of Undulator Magnetic Field Using Vibrating Wire Method	undulator, electron, resonance, radiation	413
	Y. Tanaka Tohoku University, School of Science, Sendai, Japan H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, X. Li, T. Muto, K. Nanbu Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
	A test accelerator for a terahertz source project (t-ACTS) has been progressed at the Electron Light Science Centre, Tohoku University, in which a generation of intense coherent terahertz radiation from the very short electron bunch will be demonstrated. A narrow-band coherent terahertz radiation using an undulator has been considered to be implemented. We have constructed a planer undulator that is basically a Halbach type composed of permanent magnet blocks. The period length of the undulator and the number of periods are 100 mm and 25, respectively. The vibrating wire method is studied to measure the periodic magnetic field of the undulator. A thin copper-beryllium wire is placed on beam axis in the undulator, and an AC current flow is applied in the wire. By measuring amplitudes and phases of standing waves excited on the wire by the Lorentz force between AC current and magnetic field, we can reconstruct the magnetic field distribution along the wire. We discuss relations between reproducibility of the undulator field and the mode harmonics number used for the reconstruction. The results of preliminary measurement using the vibrating wire will be shown in this conference.

Paper

Title

Other Keywords

Page

MOPB21

Seeded Radiation Sources with Sawtooth Waveforms

bunching, FEL, laser, radiation

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.

WEPB16

Study for Evaluation of Undulator Magnetic Field Using Vibrating Wire Method

undulator, electron, resonance, radiation

413

Y. Tanaka
Tohoku University, School of Science, Sendai, Japan
H. Hama, F. Hinode, S. Kashiwagi, M. Kawai, X. Li, T. Muto, K. Nanbu
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan

A test accelerator for a terahertz source project (t-ACTS) has been progressed at the Electron Light Science Centre, Tohoku University, in which a generation of intense coherent terahertz radiation from the very short electron bunch will be demonstrated. A narrow-band coherent terahertz radiation using an undulator has been considered to be implemented. We have constructed a planer undulator that is basically a Halbach type composed of permanent magnet blocks. The period length of the undulator and the number of periods are 100 mm and 25, respectively. The vibrating wire method is studied to measure the periodic magnetic field of the undulator. A thin copper-beryllium wire is placed on beam axis in the undulator, and an AC current flow is applied in the wire. By measuring amplitudes and phases of standing waves excited on the wire by the Lorentz force between AC current and magnetic field, we can reconstruct the magnetic field distribution along the wire. We discuss relations between reproducibility of the undulator field and the mode harmonics number used for the reconstruction. The results of preliminary measurement using the vibrating wire will be shown in this conference.