PAC2013 - List of Authors (Raubenheimer, T.O.)

Paper

Title

Page

Simulation of an X-band Hard X-ray FEL with LCLS Injector

264

Y. Sun
ANL, Argonne, USA
P. Emma
LBNL, Berkeley, California, USA
T.O. Raubenheimer
SLAC, Menlo Park, California, USA

In this note, it is briefly discussed the accelerator design and start-to-end 3D macro particles simulation (using {\small ELEGANT} and {\small GENESIS}) of an X-band RF driven hard X-ray FEL with LCLS injector. A preliminary design and LiTrack 1D simulation studies were presented before in an older publication~[chris]. In numerical simulations this X-band RF driven hard X-ray FEL achieves/exceeds LCLS-like performance in a much shorter overall length of 350 m, compared with 1200 m in the LCLS case. One key feature of this design is that it may achieve a higher final beam current of 5 kA plus a uniform energy profile, mainly due to the employment of stronger longitudinal wake fields in the last X-band RF linac~[tor].

MOPHO15

X-band FEL Driver Linac Design with Optics Linearization

273

Y. Sun
ANL, Argonne, USA
P. Emma
LBNL, Berkeley, California, USA
T.O. Raubenheimer, J. Wu
SLAC, Menlo Park, California, USA

In this paper, a compact hard X-ray FEL design is proposed with a single bunch charge of 250 pC, which is based on all X-band RF acceleration and two stage bunch compression. It eliminates the need of a harmonic RF linearization section by employing optics linearization in its first stage bunch compression. Emittance growth in the horizontal plane due to CSR is investigated and minimized, to be on a similar level with the LCLS. An electron bunch distribution at the linac end is taken as the input for an FEL simulation in GENESIS, with a beam energy of 7 GeV. At an FEL radiation wavelength of 0.15 nm, a saturation length of roughly 40 meters can be achieved by employing an undulator with a period of 1.5 cm. Without tapering, an FEL radiation power above 10 GW is achieved with a photon pulse length of 50 fs, which is LCLS-like performance. The overall length of the accelerator plus undulator is around 250 meters which is much shorter than the LCLS length of 1230 meters.

WEOBA1

Initial X-band Photoinjector Performance at SLAC

C. Limborg-Deprey, C. Adolphsen, M.P. Dunning, C. Hast, R.K. Jobe, H. Li, T.J. Maxwell, D.J. McCormick, T.O. Raubenheimer, S.P. Weathersby
SLAC, Menlo Park, California, USA

Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515
The X-Band Test Area (XTA) at SLAC is an all X-Band compact RF photoinjector that can produce short, high current electron bunches. Computations have shown that the peak bunch brightness should exceed that from S-Band RF photoinjectors by a factor of four. This improved performance principally comes from the high (200 MV/m) peak fields that can be sustained on the gun cathode. During the first three months of XTA commissioning, 20 pC electron bunches have been routinely generated with the gun cathode operating at greater than 200 MV/m while the dark current levels have been low. The electron bunches are accelerated to 70 MeV in a one-meter long, travelling-wave, X-band structure after the gun (a newer version of this structure should allow acceleration to more than 100 MeV). This paper reviews progress to date including measurements of the bunch properties and the bunch-to-bunch stability. The lengths of the 20 pC bunches have been measured with a transverse X-Band deflection cavity to be 250 fs rms, as expected from simulations. Transverse emittance in the range of 0.9 mm-mrad have been measured. A path to reach expected low transverse emittance numbers is described.

Slides WEOBA1 [2.840 MB]

WEPBA19

Wakefield Calculations for Septum Magnet in LCLS-II

928

K.L.F. Bane, T.O. Raubenheimer
SLAC, Menlo Park, California, USA

Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.
In LCLS-II, a fast kicker and Lambertson-type septum magnet will be installed just upstream of the undulator region, in order to allow electron bunches to be directed to either of two undulators. In the envisioned scenario both undulators receive bunches with the same current profile and the same energy which will be between 7–13.5 GeV. The kicker is used to separate the two trajectories vertically in the septum by 7 mm and thus the high current beams travel close to septum metallic walls and the short-range resistive wall wakefields can become a limitation. This paper will analyze the impact of the longitudinal and transverse wakefields on the LCLS-II performance.

Paper	Title	Page
MOPHO12	Simulation of an X-band Hard X-ray FEL with LCLS Injector	264
	Y. Sun ANL, Argonne, USA P. Emma LBNL, Berkeley, California, USA T.O. Raubenheimer SLAC, Menlo Park, California, USA
	In this note, it is briefly discussed the accelerator design and start-to-end 3D macro particles simulation (using {\small ELEGANT} and {\small GENESIS}) of an X-band RF driven hard X-ray FEL with LCLS injector. A preliminary design and LiTrack 1D simulation studies were presented before in an older publication~[chris]. In numerical simulations this X-band RF driven hard X-ray FEL achieves/exceeds LCLS-like performance in a much shorter overall length of 350 m, compared with 1200 m in the LCLS case. One key feature of this design is that it may achieve a higher final beam current of 5 kA plus a uniform energy profile, mainly due to the employment of stronger longitudinal wake fields in the last X-band RF linac~[tor].

MOPHO15	X-band FEL Driver Linac Design with Optics Linearization	273
	Y. Sun ANL, Argonne, USA P. Emma LBNL, Berkeley, California, USA T.O. Raubenheimer, J. Wu SLAC, Menlo Park, California, USA
	In this paper, a compact hard X-ray FEL design is proposed with a single bunch charge of 250 pC, which is based on all X-band RF acceleration and two stage bunch compression. It eliminates the need of a harmonic RF linearization section by employing optics linearization in its first stage bunch compression. Emittance growth in the horizontal plane due to CSR is investigated and minimized, to be on a similar level with the LCLS. An electron bunch distribution at the linac end is taken as the input for an FEL simulation in GENESIS, with a beam energy of 7 GeV. At an FEL radiation wavelength of 0.15 nm, a saturation length of roughly 40 meters can be achieved by employing an undulator with a period of 1.5 cm. Without tapering, an FEL radiation power above 10 GW is achieved with a photon pulse length of 50 fs, which is LCLS-like performance. The overall length of the accelerator plus undulator is around 250 meters which is much shorter than the LCLS length of 1230 meters.

WEOBA1	Initial X-band Photoinjector Performance at SLAC
	C. Limborg-Deprey, C. Adolphsen, M.P. Dunning, C. Hast, R.K. Jobe, H. Li, T.J. Maxwell, D.J. McCormick, T.O. Raubenheimer, S.P. Weathersby SLAC, Menlo Park, California, USA
	Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515 The X-Band Test Area (XTA) at SLAC is an all X-Band compact RF photoinjector that can produce short, high current electron bunches. Computations have shown that the peak bunch brightness should exceed that from S-Band RF photoinjectors by a factor of four. This improved performance principally comes from the high (200 MV/m) peak fields that can be sustained on the gun cathode. During the first three months of XTA commissioning, 20 pC electron bunches have been routinely generated with the gun cathode operating at greater than 200 MV/m while the dark current levels have been low. The electron bunches are accelerated to 70 MeV in a one-meter long, travelling-wave, X-band structure after the gun (a newer version of this structure should allow acceleration to more than 100 MeV). This paper reviews progress to date including measurements of the bunch properties and the bunch-to-bunch stability. The lengths of the 20 pC bunches have been measured with a transverse X-Band deflection cavity to be 250 fs rms, as expected from simulations. Transverse emittance in the range of 0.9 mm-mrad have been measured. A path to reach expected low transverse emittance numbers is described.
	Slides WEOBA1 [2.840 MB]

WEPBA19	Wakefield Calculations for Septum Magnet in LCLS-II	928
	K.L.F. Bane, T.O. Raubenheimer SLAC, Menlo Park, California, USA
	Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515. In LCLS-II, a fast kicker and Lambertson-type septum magnet will be installed just upstream of the undulator region, in order to allow electron bunches to be directed to either of two undulators. In the envisioned scenario both undulators receive bunches with the same current profile and the same energy which will be between 7–13.5 GeV. The kicker is used to separate the two trajectories vertically in the septum by 7 mm and thus the high current beams travel close to septum metallic walls and the short-range resistive wall wakefields can become a limitation. This paper will analyze the impact of the longitudinal and transverse wakefields on the LCLS-II performance.