FEL2013 - List of Keywords (wakefield)

Paper	Title	Other Keywords	Page
MOOCNO02	Multi-Objective Genetic Optimization for LCLS-II X-Ray FEL	emittance, undulator, simulation, linac	12
	L. Wang, T.O. Raubenheimer SLAC, Menlo Park, California, USA
	The Linac Coherent Light Source II (LCLS-II) will build on the success of the world's most powerful X-ray laser, the Linac Coherent Light Source (LCLS). It will add two new X-ray laser beams and room for additional new instruments, greatly increasing the number of experiments carried out each year. Multiple operation modes are proposed to accommodate a variety of user requirements. There are a large number of variables and objectives in the design. For each operation mode, Multi-Objective Genetic Algorithm (MOGA) is applied to optimize the machine parameters in order to minimize the jitters, energy spread, collective effects and emittance. The optimal designs for various operation modes are presented in this paper. The phase and voltage of the linac RF, R56 at the two bunch compressors are optimized. The CSR (coherent synchrotron radiation) can induce large emittance growth, which is minimized by optimizing the phase advance between the compressor and the bend section. The final emittance at the beginning of the undulator is just about 1um and even lower.
	Slides MOOCNO02 [3.046 MB]

MOPSO65	Suppression of Wakefield Induced Energy Spread Inside an Undulator Through Current Shaping	undulator, impedance, electron, FEL	108
	J. Qiang, C.E. Mitchell LBNL, Berkeley, California, USA
	Funding: This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Wakefields from resistive wall and surface roughness inside an undulatory can cause significant growth of beam energy spread and limit the performance of x-ray FEL radiation. In this paper, we propose a method to mitigate such energy modulation by appropriately conditioning the electron beam current profile. Numerical example and potential applications will also be discussed.

MOPSO73	Suface Roughness Wakefield in FEL Undulator	impedance, undulator, electron, FEL	127
	G.V. Stupakov SLAC, Menlo Park, California, USA S. Reiche PSI, Villigen PSI, Switzerland
	Among several wakefield models for the FEL undulator vacuum chamber a simple sinusoidal wall modulation with a small ratio of height to wavelength is especially attractive because of its simplicity [1]. The model neglects a so called resonant mode wakefield and has an (integrable) singularity at the origin which makes difficult its use in practical simulations. In this work we generalize the longitudinal wake of a sinusoidally modulated wall to include the effect of the resonant mode. This also removes the singularity of the wake at the origin. The new wake is used to evaluate the roughness wakefield effect in the undulator of SwissFEL. [1] G. Stupakov, in "Nonlinear and Collective Phenomena in Beam Physics 1998" Workshop, New York (1999), no. 468 in AIP Conference Proceedings, pp. 334–47.

TUPSO01	Corrector Response Based Alignment at FERMI	alignment, quadrupole, FEL, linac	205
	M. Aiba, M. Böge PSI, Villigen PSI, Switzerland D. Castronovo, S. Di Mitri, L. Fröhlich, G. Gaio Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	The components of an FEL accelerator generally need to be beam-based aligned in order to meet the design performance. We are developing new technique, where dipole corrector responses are used instead of orbit difference measurements. When an orbit feedback is running, any change in beam orbit is compensated by the actuators, i.e., the dipole correctors. For example, the spurious dispersion through linac rf structures, which is a source of emittance degradation, is measured through orbit differences for various beam momenta in the conventional way while dipole corrector responses are examined in the new method. The advantages are localization of misalignments, stable measurement as the orbit is kept constant, and automatic averaging and beam jitter filtering by the feedback loop. Furthermore, this method potentially allows us to detect transverse wakefield kicks, which are also an emittance degradation source, by looking into the dipole corrector responses to a change in bunch charge or bunch length. The results from a series of machine development shifts will be presented.

TUPSO03	Dark Current Transport and Collimation Studies for SwissFEL	gun, simulation, emittance, cathode	209
	S. Bettoni, P. Craievich, M. Pedrozzi, S. Reiche, L. Stingelin PSI, Villigen PSI, Switzerland
	In all accelerating cavities a non negligible background of electrons can be generated by field emission (dark current), transported and further accelerated. A careful estimate of the transport of the dark current is crucial in order to minimize radiation damage to the components and activation of the machine. This paper describes the generation and the transport of dark current from the SwissFEL photo injector downstream of the accelerator. The analysis is based on numerical simulations and experimental measurements performed at the SwissFEL Injector Test Facility (SITF). In the simulations the charge distribution is generated by an emission model based on the Fowler-Nordheim equation taking into account the filling time of the cavity and then tracked through the machine. This model has been used to analyze the impact of a low energy collimation system upstream of the first travelling wave accelerating structure on the dark current transport. A slit with several apertures has been installed in the SITF to benchmark the simulations and to verify the impact of the wakefields on the nominal beam.

TUPSO04	Simulations of a Corrugated Beam Pipe for the Chirp Compensation in SwissFEL	undulator, laser, emittance, simulation	214
	S. Bettoni, P. Craievich, M. Pedrozzi, S. Reiche PSI, Villigen PSI, Switzerland
	In short wavelength FEL designs, bunch compression is obtained by making the beam passing through a magnetic chicane with an energy chirp typically of a percent level. At SwissFEL, before injection into the undulator it is foreseen to remove the residual chirp using the wakes in the C-band accelerating structures of the linac. This scheme works well for the hard X-ray undulator line, which includes the largest accumulation of wakefields, but it leaves a residual chirp in the other undulator line for the soft X-ray beam line, midway in the main linac. Another possibility to remove the residual chirp consists in using the longitudinal wakefields generated by a corrugated beam pipe, as recently proposed by G. Stupakov et al. Before planning a dechirper section in a FEL, an experimental verification of the analytical formulae describing the wakefields is crucial. The SwissFEL injector test facility (SITF) fulfils all the necessary criteria to perform such a proof of principle. We are investigating the technical implementation to perform an experiment in SITF in the second half of 2014. In this paper we present the tracking studies performed to optimize the experiment layout.

TUPSO35	The MAX IV Linac as X-Ray FEL Injector: Comparison of Two Compression Schemes	linac, emittance, FEL, electron	294
	O. Karlberg, F. Curbis, S. Thorin, S. Werin MAX-lab, Lund, Sweden
	The MAX IV linac will be used for injections and top up of two storage rings and at the same time provide a high brightness pulses to a short pulse facility (SPF) and an X-ray FEL (phase 2). Compression in the linac is done in two double achromats which implies a positive R56 unlike the commonly used chicane compressor scheme with negative R56. Compression using the achromats scheme requires the electron bunch to be accelerated on a falling RF slope resulting in an energy chirp that longitudinal wakefields will boost along the linac. This permits a stronger compression. In this proceeding we will present how the longitudinal wakefields interact with the bunch compression in the double achromat scheme compared with the chicane compression case. Focus is brought on how the unique MAX IV linac lattice is fully capable to cope with the high demands of an FEL injector. The charge related electron beam jitter in both set-ups will also be investigated.

Paper

Title

Other Keywords

Page

MOOCNO02

Multi-Objective Genetic Optimization for LCLS-II X-Ray FEL

emittance, undulator, simulation, linac

12

L. Wang, T.O. Raubenheimer
SLAC, Menlo Park, California, USA

The Linac Coherent Light Source II (LCLS-II) will build on the success of the world's most powerful X-ray laser, the Linac Coherent Light Source (LCLS). It will add two new X-ray laser beams and room for additional new instruments, greatly increasing the number of experiments carried out each year. Multiple operation modes are proposed to accommodate a variety of user requirements. There are a large number of variables and objectives in the design. For each operation mode, Multi-Objective Genetic Algorithm (MOGA) is applied to optimize the machine parameters in order to minimize the jitters, energy spread, collective effects and emittance. The optimal designs for various operation modes are presented in this paper. The phase and voltage of the linac RF, R56 at the two bunch compressors are optimized. The CSR (coherent synchrotron radiation) can induce large emittance growth, which is minimized by optimizing the phase advance between the compressor and the bend section. The final emittance at the beginning of the undulator is just about 1um and even lower.

Slides MOOCNO02 [3.046 MB]

MOPSO65

Suppression of Wakefield Induced Energy Spread Inside an Undulator Through Current Shaping

undulator, impedance, electron, FEL

108

J. Qiang, C.E. Mitchell
LBNL, Berkeley, California, USA

Funding: This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Wakefields from resistive wall and surface roughness inside an undulatory can cause significant growth of beam energy spread and limit the performance of x-ray FEL radiation. In this paper, we propose a method to mitigate such energy modulation by appropriately conditioning the electron beam current profile. Numerical example and potential applications will also be discussed.

MOPSO73

Suface Roughness Wakefield in FEL Undulator

impedance, undulator, electron, FEL

127

G.V. Stupakov
SLAC, Menlo Park, California, USA
S. Reiche
PSI, Villigen PSI, Switzerland

Among several wakefield models for the FEL undulator vacuum chamber a simple sinusoidal wall modulation with a small ratio of height to wavelength is especially attractive because of its simplicity [1]. The model neglects a so called resonant mode wakefield and has an (integrable) singularity at the origin which makes difficult its use in practical simulations. In this work we generalize the longitudinal wake of a sinusoidally modulated wall to include the effect of the resonant mode. This also removes the singularity of the wake at the origin. The new wake is used to evaluate the roughness wakefield effect in the undulator of SwissFEL.
[1] G. Stupakov, in "Nonlinear and Collective Phenomena in Beam Physics 1998" Workshop, New York (1999), no. 468 in AIP Conference Proceedings, pp. 334–47.

TUPSO01

Corrector Response Based Alignment at FERMI

alignment, quadrupole, FEL, linac

205

M. Aiba, M. Böge
PSI, Villigen PSI, Switzerland
D. Castronovo, S. Di Mitri, L. Fröhlich, G. Gaio
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

The components of an FEL accelerator generally need to be beam-based aligned in order to meet the design performance. We are developing new technique, where dipole corrector responses are used instead of orbit difference measurements. When an orbit feedback is running, any change in beam orbit is compensated by the actuators, i.e., the dipole correctors. For example, the spurious dispersion through linac rf structures, which is a source of emittance degradation, is measured through orbit differences for various beam momenta in the conventional way while dipole corrector responses are examined in the new method. The advantages are localization of misalignments, stable measurement as the orbit is kept constant, and automatic averaging and beam jitter filtering by the feedback loop. Furthermore, this method potentially allows us to detect transverse wakefield kicks, which are also an emittance degradation source, by looking into the dipole corrector responses to a change in bunch charge or bunch length. The results from a series of machine development shifts will be presented.

TUPSO03

Dark Current Transport and Collimation Studies for SwissFEL

gun, simulation, emittance, cathode

209

S. Bettoni, P. Craievich, M. Pedrozzi, S. Reiche, L. Stingelin
PSI, Villigen PSI, Switzerland

In all accelerating cavities a non negligible background of electrons can be generated by field emission (dark current), transported and further accelerated. A careful estimate of the transport of the dark current is crucial in order to minimize radiation damage to the components and activation of the machine. This paper describes the generation and the transport of dark current from the SwissFEL photo injector downstream of the accelerator. The analysis is based on numerical simulations and experimental measurements performed at the SwissFEL Injector Test Facility (SITF). In the simulations the charge distribution is generated by an emission model based on the Fowler-Nordheim equation taking into account the filling time of the cavity and then tracked through the machine. This model has been used to analyze the impact of a low energy collimation system upstream of the first travelling wave accelerating structure on the dark current transport. A slit with several apertures has been installed in the SITF to benchmark the simulations and to verify the impact of the wakefields on the nominal beam.

TUPSO04

Simulations of a Corrugated Beam Pipe for the Chirp Compensation in SwissFEL

undulator, laser, emittance, simulation

214

S. Bettoni, P. Craievich, M. Pedrozzi, S. Reiche
PSI, Villigen PSI, Switzerland

In short wavelength FEL designs, bunch compression is obtained by making the beam passing through a magnetic chicane with an energy chirp typically of a percent level. At SwissFEL, before injection into the undulator it is foreseen to remove the residual chirp using the wakes in the C-band accelerating structures of the linac. This scheme works well for the hard X-ray undulator line, which includes the largest accumulation of wakefields, but it leaves a residual chirp in the other undulator line for the soft X-ray beam line, midway in the main linac. Another possibility to remove the residual chirp consists in using the longitudinal wakefields generated by a corrugated beam pipe, as recently proposed by G. Stupakov et al. Before planning a dechirper section in a FEL, an experimental verification of the analytical formulae describing the wakefields is crucial. The SwissFEL injector test facility (SITF) fulfils all the necessary criteria to perform such a proof of principle. We are investigating the technical implementation to perform an experiment in SITF in the second half of 2014. In this paper we present the tracking studies performed to optimize the experiment layout.

TUPSO35

The MAX IV Linac as X-Ray FEL Injector: Comparison of Two Compression Schemes

linac, emittance, FEL, electron

294

O. Karlberg, F. Curbis, S. Thorin, S. Werin
MAX-lab, Lund, Sweden

The MAX IV linac will be used for injections and top up of two storage rings and at the same time provide a high brightness pulses to a short pulse facility (SPF) and an X-ray FEL (phase 2). Compression in the linac is done in two double achromats which implies a positive R56 unlike the commonly used chicane compressor scheme with negative R56. Compression using the achromats scheme requires the electron bunch to be accelerated on a falling RF slope resulting in an energy chirp that longitudinal wakefields will boost along the linac. This permits a stronger compression. In this proceeding we will present how the longitudinal wakefields interact with the bunch compression in the double achromat scheme compared with the chicane compression case. Focus is brought on how the unique MAX IV linac lattice is fully capable to cope with the high demands of an FEL injector. The charge related electron beam jitter in both set-ups will also be investigated.