Accelerator Test Facility

A Dissertation Presented by Adnan Doyuran to The Graduate School in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Physics State University of New York at Stony Brook December, 2000

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State University of New York at Stony Brook

The Graduate School Adnan Doyuran We, the dissertation committee for the above candidate for the Doctor of Philosophy degree, hereby recommend acceptance of this dissertation.

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Professor Ilan Ben-Zvi, Dissertation Advisor, Department of Physics ______________________________________________

Professor Chris Jacobsen, Chairperson, Department of Physics

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Professor Laszlo Mihaly, Department of Physics, Experimental Solid State

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Professor Jacobus Verbaarschot, Department of Physics

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Professor Stephen Peggs, Department of Physics

This Dissertation is accepted by the Graduate School

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Abstract of the Dissertation

The High-Gain Harmonic-Generation Free-Electron Laser Experiment

by Adnan Doyuran Doctor of Philosophy in Physics State University of New York at Stony Brook 2000

The High Gain Harmonic Generation Experiment has been performed at the Accelerator Test Facility and the measured results are presented. The 41.3 MeV electron beam is seeded by 10.6 mm 0.7 MW power CO2 laser beam. The FEL interaction takes place in a periodic magnetic array (wiggler) comprising three elements: Modulator, dispersive section and radiator. The energy of the electrons is modulated by a seed laser in the modulator, which is tuned to 10.6 mm wavelength. The energy modulation is converted into a density modulation in the dispersive magnet to produce microbunching. The radiator is tuned to one of the higher harmonics of the seed laser beam, which is 5.3 mm in this case. In the radiator section, the microbunched electron beam starts radiating coherently and the radiation is amplified exponentially until it reaches saturation.

When the seed laser is turned off, the radiator may still produce radiation, based on the Self Amplified Spontaneous Emission (SASE) process. The energy, spectrum and the gain of the SASE FEL were measured.

HGHG radiation is produced with the seed laser turned on. The HGHG output has been characterized. Properties such as the energy, the spectrum and the pulse length were measured and compared with the SASE case. The HGHG spectrum was measured to be of the order of magnitude narrower than the SASE case and longitudinal coherence was demonstrated. The results were found to be in agreement with simulations. Special purpose diagnostics were developed for carrying out some of these measurements.

The preliminary harmonic content of the HGHG was measured. The second (2.65 mm) and the third (1.77 mm) harmonics of the fundamental (5.3 mm) were observed. The rapid amplification of the higher harmonic reveals that a saturation (or near saturation) condition has been achieved. The measured ratio of the harmonics to the fundamental was found to be consistent with the simulations

Finally the HGHG output was steered using the electron beam steering. This measurement may have importance when we want to cascade the HGHG process to the X-Ray regime, which requires more than one HGHG sections.

to my family: my mother Sabiha Doyuran, my father Metin Doyuran, my wife Saadet, my brother Arif, my sisters Ayfer and Aysenur

Table of Contents

ACKNOWLEDGMENT………………………………………………….……..….…xviii ………………………………………………………...……..….………………..xix

Chapter 1 Introduction………………………………………………...……..…….…1

Chapter 2 FEL THEORY…………………………………………..…3

2.3 Planar Wiggler

2.4 Eqn. of Motion in High Gain Regime

2.5 The Fluid model

2.6 The High Gain FEL1-D Theory

2.7 The Initial Value Problem in 1-D Theory

2.8 3D FEL Theory and Optical Guiding

2.9 The FEL Equations with Betatron Oscillation