| Paper |
Title |
Page |
| MOPPH068 |
Controlling Wiggler Harmonic Radiation to Reduce Damage to FEL Cavity Mirrors
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135 |
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- S. Huang, G. Swift, Y. K. Wu
FEL/Duke University, Durham, North Carolina
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Wigglers emit both fundamental and harmonic radiation. For oscillator FELs, UV-VUV harmonic radiation can cause serious damage to the downstream mirror of the FEL cavity. Compared to a planar wiggler, harmonic radiation from a helical wiggler is peaked off-axis, and using a helical wiggler can significantly improve the FEL mirror lifetime. With a helical wiggler. However, the off-axis harmonic radiation from helical wigglers can still cause serious damage to the downstream mirror or limit the maximum beam current for FEL operation due to UV-VUV power loading on the mirror. At Duke FEL lab, we have developed a mechanism to control the off-axis harmonic radiation from the helical wigglers by using a set of motorized, water-cooled, in-vacuum apertures. These apertures can reduce the harmonic power load on the downstream mirror by one order of magnitude. With these apertures, operation with high electron beam currents becomes feasible for stable, high power UV-VUV lasing. In this work, we report the effectiveness of the apertures in reducing the wiggler harmonic radiation under various operation conditions and for different configurations of the Duke FELs.
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| MOPPH069 |
A Pass-by-Pass Gain Measurement Technique for Oscillator FELs
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139 |
| |
- S. F. Mikhailov, S. Huang, J. Li, V. Popov, Y. K. Wu
FEL/Duke University, Durham, North Carolina
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We present a new pass-by-pass gain measurement technique for a storage ring FEL Typically, the FEL oscillator gain is obtained by measuring the growth of the envelope of an optical macropulse using a slow photo-detector. While successfully used for low-gain FEL operation at Duke FEL laboratory for many years, this technique does not provide the information on the optical power growth from pass to pass. In addition, this method was not adequate for measuring higher gains of distributed optical klystron FELs. We have developed a new gain measurement technique based upon the direct measurement of the optical energy in micropulses. Using fast photo-detectors, the growth of an FEL macro-pulse can be recorded from pass to pass. This new gain measurement technique provides a powerful tool to study the details of the FEL gain process, including the onset of the FEL lasing. In the work, we describe this new gain measurement technique in detail and compare it with the old technique. Using fast photo-detectors with a sub-nanosecond time response, this new technique can be adopted for many oscillator FELs, including those driven by super-conducting linacs.
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