IPAC2013 - List of Authors (Hao, H.)

Paper	Title	Page
MOPEA078	Commissioning and Operation of Wiggler Switchyard System for Duke FEL and HIGS	267
	Y.K. Wu, M.D. Busch, M. Emamian, J.F. Faircloth, H. Hao, J.Y. Li, S.F. Mikhailov, V. Popov, G. Swift, P.W. Wallace, P. Wang, J. Yan FEL/Duke University, Durham, North Carolina, USA A.L. Wu USTC/NSRL, Hefei, Anhui, People's Republic of China
	Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033. To enable the Duke storage ring FEL to operate in VUV with adequate gain, a major storage ring upgrade was carried out in 2012 to install two additional helical FEL wigglers with a wiggler switchyard system. Using the switchyard, a quick changeover can be made between two planar OK-4 wigglers and two helical OK-5 wigglers in the middle of the FEL straight section. This system preserves the linear polarization capabilities of the Duke FEL and gamma-ray beams at the High Intensity Gamma-ray Source (HIGS), while enabling VUV FEL operation with a higher gain using a longer FEL with as many as four helical wigglers. The wiggler switchyard upgrade was completed in Summer 2012, followed by a rapid and successful commissioning of the Duke storage ring, FEL system, and HIGS. In this paper, we will present the results of accelerator and light source commissioning with the wiggler switchyard. We will also present preliminary results of operating the OK-5 FEL in different configurations. With the wiggler switchyard, we are well positioned to realize the operation of a VUV FEL below 190 nm and production of Compton gamma-ray beams above 100 MeV in circular polarization.

TUPEA074	Protection of VUV FEL Mirrors using Soft Orbit Bump at Duke FEL/HIGS facility	1301
	S.F. Mikhailov, H. Hao, J.Y. Li, V. Popov, P.W. Wallace, Y.K. Wu FEL/Duke University, Durham, North Carolina, USA
	Funding: This work is supported in part by the US DoE grant # DE-FG02-97ER41033 The Duke FEL and High Intensity Gamma-ray Source (HIGS) facility is operated with an electron beam from 0.24 to 1.2 GeV and a photon beam from 190 to 1060 nm. Presently, the energy range of the gamma-beam is from 1 MeV to about 100 MeV, with the maximum total gamma-flux of more then 10¹⁰ gammas per second around 10 MeV. Production of high intensity, high energy gamma-beams of 60 to 100 MeV, using UV-VUV mirrors of 240 to 190 nm, requires high energy, high current electron beams of 0.9 to 1.05 GeV. Synchrotron radiation damage to the FEL mirrors becomes crucial for VUV FEL operation at or below 190 nm. The edge radiation (ER) from the End-of-Arc (EOA) bending magnet, instead of the radiation of FEL wigglers, is the dominant cause of a rapid degradation of the downstream FEL mirror. In this work, we describe a further development of the “soft” orbit bump concept to significantly reduce the radiation exposure to the mirror from the EOA dipole magnet. The bump uses designated "soft" orbit correctors with magnetic field limited to produce a radiation with a critical wavelength close or below the FEL wavelength.

TUPWO061	Design of a Soft Orbit Bump for FEL Mirror Protection at Duke FEL/HIGS Facility	2006
	H. Hao, J.Y. Li, S.F. Mikhailov, Y.K. Wu FEL/Duke University, Durham, North Carolina, USA
	Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033. In an oscillator Free-Electron Laser (FEL) with a high energy electron beam, it is critical to minimize harmful high-energy radiation on the downstream FEL mirror in order to increase its lifetime. At the High Intensity Gamma-ray Source (HIGS) facility at Duke University, effort has been devoted to developing a variety of techniques to reduce the amount of radiation on the FEL mirror. One of the most effective methods was the use of a set of adjustable in-vacuum apertures to block harmonic radiation from FEL wigglers. In recent studies, it was determined that the edge radiation from the end-of-the-arc bending magnet is the main source of UV/VUV and x-ray radiation which causes mirror damage. To mitigate this effect, a soft orbit bump is designed to change the displacement and angle of the electron beam around the end-of-the-arc area. This soft orbit bump is developed using the multi-objective optimization technique. Calculation shows the soft orbit bump can significantly reduce the flux of high energy photons on the FEL mirror. Study is also performed to determine the impact of this orbit bump on the injection, beam lifetime, and the FEL and gamma-ray operation at HIGS facility.

THPEA057	Compensation Schemes for Operation of FEL Wigglers on Duke Storage Ring	3270
	J.Y. Li, H. Hao, S.F. Mikhailov, V. Popov, W. Wu, Y.K. Wu FEL/Duke University, Durham, North Carolina, USA
	Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033. The Duke FEL is the photon driver for the High Intensity Gamma-ray Source (HIGS). To extend the capabilities of the FEL and HIGS to higher photon energy regions, a FEL wiggler switchyard system was developed in the recent years. This system was installed and commissioned in 2012. The FEL wiggler switchyard is used to change between two planar OK-4 wigglers and two helical OK-5 wigglers in the middle of the FEL straight section in a short period of time (a few days). With a total of six electromagnetic wigglers, the Duke FEL can be operated in a number of wiggler configurations and with a wide range of magnetic fields. The operation of uncompensated FEL wigglers can cause significant changes to the electron beam closed orbit and magnetic lattice. To maintain a sufficiently large dynamic aperture for an efficient injection and good beam lifetime, a set of complex compensation schemes, including magnetic field and lattice compensation, have been developed for the operation of the FEL wigglers. This paper reports the overall architecture and performance of the FEL wiggler compensation schemes and their implementation in the accelerator controls system using the feedforward mechanism.

Paper

Title

Page

Commissioning and Operation of Wiggler Switchyard System for Duke FEL and HIGS

267

Y.K. Wu, M.D. Busch, M. Emamian, J.F. Faircloth, H. Hao, J.Y. Li, S.F. Mikhailov, V. Popov, G. Swift, P.W. Wallace, P. Wang, J. Yan
FEL/Duke University, Durham, North Carolina, USA
A.L. Wu
USTC/NSRL, Hefei, Anhui, People's Republic of China

Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033.
To enable the Duke storage ring FEL to operate in VUV with adequate gain, a major storage ring upgrade was carried out in 2012 to install two additional helical FEL wigglers with a wiggler switchyard system. Using the switchyard, a quick changeover can be made between two planar OK-4 wigglers and two helical OK-5 wigglers in the middle of the FEL straight section. This system preserves the linear polarization capabilities of the Duke FEL and gamma-ray beams at the High Intensity Gamma-ray Source (HIGS), while enabling VUV FEL operation with a higher gain using a longer FEL with as many as four helical wigglers. The wiggler switchyard upgrade was completed in Summer 2012, followed by a rapid and successful commissioning of the Duke storage ring, FEL system, and HIGS. In this paper, we will present the results of accelerator and light source commissioning with the wiggler switchyard. We will also present preliminary results of operating the OK-5 FEL in different configurations. With the wiggler switchyard, we are well positioned to realize the operation of a VUV FEL below 190 nm and production of Compton gamma-ray beams above 100 MeV in circular polarization.

TUPEA074

Protection of VUV FEL Mirrors using Soft Orbit Bump at Duke FEL/HIGS facility

1301

S.F. Mikhailov, H. Hao, J.Y. Li, V. Popov, P.W. Wallace, Y.K. Wu
FEL/Duke University, Durham, North Carolina, USA

Funding: This work is supported in part by the US DoE grant # DE-FG02-97ER41033
The Duke FEL and High Intensity Gamma-ray Source (HIGS) facility is operated with an electron beam from 0.24 to 1.2 GeV and a photon beam from 190 to 1060 nm. Presently, the energy range of the gamma-beam is from 1 MeV to about 100 MeV, with the maximum total gamma-flux of more then 10¹⁰ gammas per second around 10 MeV. Production of high intensity, high energy gamma-beams of 60 to 100 MeV, using UV-VUV mirrors of 240 to 190 nm, requires high energy, high current electron beams of 0.9 to 1.05 GeV. Synchrotron radiation damage to the FEL mirrors becomes crucial for VUV FEL operation at or below 190 nm. The edge radiation (ER) from the End-of-Arc (EOA) bending magnet, instead of the radiation of FEL wigglers, is the dominant cause of a rapid degradation of the downstream FEL mirror. In this work, we describe a further development of the “soft” orbit bump concept to significantly reduce the radiation exposure to the mirror from the EOA dipole magnet. The bump uses designated "soft" orbit correctors with magnetic field limited to produce a radiation with a critical wavelength close or below the FEL wavelength.

TUPWO061

Design of a Soft Orbit Bump for FEL Mirror Protection at Duke FEL/HIGS Facility

2006

H. Hao, J.Y. Li, S.F. Mikhailov, Y.K. Wu
FEL/Duke University, Durham, North Carolina, USA

Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033.
In an oscillator Free-Electron Laser (FEL) with a high energy electron beam, it is critical to minimize harmful high-energy radiation on the downstream FEL mirror in order to increase its lifetime. At the High Intensity Gamma-ray Source (HIGS) facility at Duke University, effort has been devoted to developing a variety of techniques to reduce the amount of radiation on the FEL mirror. One of the most effective methods was the use of a set of adjustable in-vacuum apertures to block harmonic radiation from FEL wigglers. In recent studies, it was determined that the edge radiation from the end-of-the-arc bending magnet is the main source of UV/VUV and x-ray radiation which causes mirror damage. To mitigate this effect, a soft orbit bump is designed to change the displacement and angle of the electron beam around the end-of-the-arc area. This soft orbit bump is developed using the multi-objective optimization technique. Calculation shows the soft orbit bump can significantly reduce the flux of high energy photons on the FEL mirror. Study is also performed to determine the impact of this orbit bump on the injection, beam lifetime, and the FEL and gamma-ray operation at HIGS facility.

THPEA057

Compensation Schemes for Operation of FEL Wigglers on Duke Storage Ring

3270

J.Y. Li, H. Hao, S.F. Mikhailov, V. Popov, W. Wu, Y.K. Wu
FEL/Duke University, Durham, North Carolina, USA

Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033.
The Duke FEL is the photon driver for the High Intensity Gamma-ray Source (HIGS). To extend the capabilities of the FEL and HIGS to higher photon energy regions, a FEL wiggler switchyard system was developed in the recent years. This system was installed and commissioned in 2012. The FEL wiggler switchyard is used to change between two planar OK-4 wigglers and two helical OK-5 wigglers in the middle of the FEL straight section in a short period of time (a few days). With a total of six electromagnetic wigglers, the Duke FEL can be operated in a number of wiggler configurations and with a wide range of magnetic fields. The operation of uncompensated FEL wigglers can cause significant changes to the electron beam closed orbit and magnetic lattice. To maintain a sufficiently large dynamic aperture for an efficient injection and good beam lifetime, a set of complex compensation schemes, including magnetic field and lattice compensation, have been developed for the operation of the FEL wigglers. This paper reports the overall architecture and performance of the FEL wiggler compensation schemes and their implementation in the accelerator controls system using the feedforward mechanism.