FEL2012 - List of Authors (Reiche, S.)

Paper

Title

Page

Growth Rates and Coherence Properties of FODO-lattice based X-ray Free Electron Lasers

25

S. Reiche, E. Prat
PSI, Villigen PSI, Switzerland

Most hard X-ray Free Electron Lasers are designed with a super-imposed FODO lattice to focus the electron beam for optimum performance of the FEL. Theory predicts an optimum value of the beta-function, where the induced axial velocity spread starts to counteract the increased rho-parameter due to higher electron density. However in a FODO lattice the electron beam envelope varies significantly and disrupts the coupling of the electron beam to the radiation field. This is particularly relevant for hard X-ray FELs, where the radiation mode is smaller than the electron beam size. In this presentation we study the impact of the FODO cell length and the beta-function variation on the FEL gain length and growth of the coherence properties for SASE FELs.

Slides MOOC02 [2.776 MB]

MOPD35

Detailed Modeling of Seeded Free-electron Lasers

101

S. Reiche
PSI, Villigen PSI, Switzerland
M. Carlà
UNIFI, Sesto Fiorentino (FI), Italy

Seeding schemes for Free Electron Lasers have mostly a strong impact on the electron distribution by either a conversion of an energy modulation into a current modulation with high harmonic content (HGHG seeding) or an over-compression of this energy modulation to induce energy bands (EEHG seeding) or smear out any bunching in the electron beam (self-seeding). Most codes follow an approach to use thin electron slices, which are carefully generated to provide the correct shot-noise but which also prevents them from mixing and re-sorting the macro-particle distribution. The FEL code Genesis 1.3 has been modified to allow resolution of each individual electron. Using this approach the correct shot noise at all frequencies is provided and permits "re-binning" of the particles to the 3D radiation grid at any time. The results for self-seeding and HGHG seeding are discussed.

MOPD36

Dark Current Studies for SwissFEL

105

F. Le Pimpec, A. Adelmann, S. Reiche, R. Zennaro
PSI, Villigen PSI, Switzerland
B. Grigoryan
CANDLE, Yerevan, Armenia

Activation of the surrounding of an accelerator must be quantified and those data provided to the official agencies, This is a necessary step for obtaining the appropriate authorization to operate such accelerator. The SwissFEL, being a 4th generation light source, will produce more accelerated charges, which are dumped or lost, than any conventional 3rd generation light source, like the Swiss Light Source. We have simulated the propagation of a dark current beam produced in the photoelectron gun using tracking codes like ASTRA and Elegant for the current layout of the SwissFEL. Detailed experimental study have been carried out at the SwissFEL test facilities at PSI (C-Band RF Stand and SwissFEL Injector Test Facility), in order to provide necessary input data for detailed study of components using the simulation code OPAL. A summary of these studies are presented.

MOPD37

Switchyard Design: Athos

109

N. Milas, S. Reiche
PSI, Villigen PSI, Switzerland

The SwissFEL facility will produce coherent, ultrabright and ultra-short photon pulses covering a wavelength range from 0.1 nm to 7 nm, requiring an emittance of 0.43 mm mrad or better. In order to provide electrons to the soft X-ray beam line a switchyard is necessary. This beamline will switch the electron bunch coming from the SwissFEL linac, with an energy of 3.0 GeV, and transport it to Athos. The switchyard has to be designed in such a way to guarantee that beam properties like low emittance, high peak charge and small bunch length will not be spoiled. In order to keep the switchyard as versatile as possible it can work for a range of values of R56 from isochronous up to 6 mm, when the bunch is stretched by a factor two, and also be able to transport the beam in the so called "large bandwidth" mode. In this paper we present the schematics for the switchyard, discuss its many modes of operation, sextupole correction scheme and positioning of energy collimator for machine protection.

TUPD21

Self-Seeding Design for SwissFEL

281

E. Prat, S. Reiche
PSI, Villigen PSI, Switzerland
D.J. Dunning
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

The SwissFEL facility, planned at the Paul Scherrer Institute, is based on the SASE operation of a hard (1-7 Å) and soft (7-70 Å) X-ray FEL beamline. In addition, seeding is foreseen for the soft X-ray beamline (down to a wavelength of 10 Å), and it is currently also under consideration for the hard X-ray beamline. We have investigated two methods, Echo-Enabled Harmonic Generation (EEHG) and self-seeding for each of the two FEL beamlines. Presently we consider self-seeding the most robust and lowest risk strategy for both lines. The paper discusses our considerations and presents the design of self-seeding implementation for the soft and the hard X-ray beamlines including the layout and simulation results.

WEPD68

UCLA Seeded THz FEL Undulator Buncher Design

527

S.C. Gottschalk, R.N. Kelly
STI, Washington, USA
C. Joshi, S. Tochitsky
UCLA, Los Angeles, California, USA
S. Reiche
PSI, Villigen PSI, Switzerland

UCLA is planning to build a THz user facility. One is a seeded THz FEL tunable in the range of 0.5 - 3 THz or even 3-9 THz in an optical klystron configuration. Another* relies on microbunching at 340 micron using a 3.3 cm undulator or even driving the FEL with an electron beam from a laser-plasma accelerator. These FEL's make use of a 2.1m long pre-buncher, chicane and shorter, 110cm long radiator. Chicane requirements are modest. A round copper waveguide with 4.8mm ID will be used. We will describe the magnetic design and measured performance of the gap tunable undulators, mechanical design of the entire system, vacuum boxes, waveguides and expected operational approaches. Both undulators have 33mm periods and curved poles for two-plane focusing. Discussions will be included on issues associated with fabricating, sorting and shimming curved pole undulators. A new optimization method will be described that was used to meet magnetic requirements with a minimum volume of magnetic material.
*S. Tochitsky et al, "Seeded FEL Microbunching Experiments at the UCLA Neptune Laboratory", Advanced Accelerator Conference 2010

THPD19

Technical Overview of SwissFEL Undulator Line

583

R. Ganter, M. Aiba, H.-H. Braun, C. Calvi, A. Fuchs, P. Heimgartner, E. Hohmann, R. Ischebeck, H. Jöhri, B. Keil, N. Milas, M. Negrazus, S. Reiche, S. Sanfilippo, T. Schmidt, S. Sidorov, P. Wiegand
PSI, Villigen PSI, Switzerland

Starting after Linac 3 at z ~ 430 m (z = 0 being the gun photocathode position), the so-called Aramis Hard-X ray undulator section extends over 170 m, from the energy collimator to the electron beam dump. Electrons enter the undulator section with a maximum energy of 5.8 GeV, a slice emittance below 0.43 μm and a peak current of 3 kA with 200 pC of charge. A prototype of the in-vacuum undulator (U15) is currently under assembly. Most of the other beamline components have been designed and for some of them prototypes are already ordered (quadrupoles, beam position monitors, phase shifters, alignment quadrupoles; mechanical supports; safety components). The paper will describe how constraints like temperature drifts, stray magnetic field, wakefields, beam losses, costs are taken into account for the design of components and building (undulators are however described in details in a companion paper).

Paper	Title	Page
MOOC02	Growth Rates and Coherence Properties of FODO-lattice based X-ray Free Electron Lasers	25
	S. Reiche, E. Prat PSI, Villigen PSI, Switzerland
	Most hard X-ray Free Electron Lasers are designed with a super-imposed FODO lattice to focus the electron beam for optimum performance of the FEL. Theory predicts an optimum value of the beta-function, where the induced axial velocity spread starts to counteract the increased rho-parameter due to higher electron density. However in a FODO lattice the electron beam envelope varies significantly and disrupts the coupling of the electron beam to the radiation field. This is particularly relevant for hard X-ray FELs, where the radiation mode is smaller than the electron beam size. In this presentation we study the impact of the FODO cell length and the beta-function variation on the FEL gain length and growth of the coherence properties for SASE FELs.
	Slides MOOC02 [2.776 MB]

MOPD35	Detailed Modeling of Seeded Free-electron Lasers	101
	S. Reiche PSI, Villigen PSI, Switzerland M. Carlà UNIFI, Sesto Fiorentino (FI), Italy
	Seeding schemes for Free Electron Lasers have mostly a strong impact on the electron distribution by either a conversion of an energy modulation into a current modulation with high harmonic content (HGHG seeding) or an over-compression of this energy modulation to induce energy bands (EEHG seeding) or smear out any bunching in the electron beam (self-seeding). Most codes follow an approach to use thin electron slices, which are carefully generated to provide the correct shot-noise but which also prevents them from mixing and re-sorting the macro-particle distribution. The FEL code Genesis 1.3 has been modified to allow resolution of each individual electron. Using this approach the correct shot noise at all frequencies is provided and permits "re-binning" of the particles to the 3D radiation grid at any time. The results for self-seeding and HGHG seeding are discussed.

MOPD36	Dark Current Studies for SwissFEL	105
	F. Le Pimpec, A. Adelmann, S. Reiche, R. Zennaro PSI, Villigen PSI, Switzerland B. Grigoryan CANDLE, Yerevan, Armenia
	Activation of the surrounding of an accelerator must be quantified and those data provided to the official agencies, This is a necessary step for obtaining the appropriate authorization to operate such accelerator. The SwissFEL, being a 4th generation light source, will produce more accelerated charges, which are dumped or lost, than any conventional 3rd generation light source, like the Swiss Light Source. We have simulated the propagation of a dark current beam produced in the photoelectron gun using tracking codes like ASTRA and Elegant for the current layout of the SwissFEL. Detailed experimental study have been carried out at the SwissFEL test facilities at PSI (C-Band RF Stand and SwissFEL Injector Test Facility), in order to provide necessary input data for detailed study of components using the simulation code OPAL. A summary of these studies are presented.

MOPD37	Switchyard Design: Athos	109
	N. Milas, S. Reiche PSI, Villigen PSI, Switzerland
	The SwissFEL facility will produce coherent, ultrabright and ultra-short photon pulses covering a wavelength range from 0.1 nm to 7 nm, requiring an emittance of 0.43 mm mrad or better. In order to provide electrons to the soft X-ray beam line a switchyard is necessary. This beamline will switch the electron bunch coming from the SwissFEL linac, with an energy of 3.0 GeV, and transport it to Athos. The switchyard has to be designed in such a way to guarantee that beam properties like low emittance, high peak charge and small bunch length will not be spoiled. In order to keep the switchyard as versatile as possible it can work for a range of values of R56 from isochronous up to 6 mm, when the bunch is stretched by a factor two, and also be able to transport the beam in the so called "large bandwidth" mode. In this paper we present the schematics for the switchyard, discuss its many modes of operation, sextupole correction scheme and positioning of energy collimator for machine protection.

TUPD21	Self-Seeding Design for SwissFEL	281
	E. Prat, S. Reiche PSI, Villigen PSI, Switzerland D.J. Dunning STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	The SwissFEL facility, planned at the Paul Scherrer Institute, is based on the SASE operation of a hard (1-7 Å) and soft (7-70 Å) X-ray FEL beamline. In addition, seeding is foreseen for the soft X-ray beamline (down to a wavelength of 10 Å), and it is currently also under consideration for the hard X-ray beamline. We have investigated two methods, Echo-Enabled Harmonic Generation (EEHG) and self-seeding for each of the two FEL beamlines. Presently we consider self-seeding the most robust and lowest risk strategy for both lines. The paper discusses our considerations and presents the design of self-seeding implementation for the soft and the hard X-ray beamlines including the layout and simulation results.

WEPD68	UCLA Seeded THz FEL Undulator Buncher Design	527
	S.C. Gottschalk, R.N. Kelly STI, Washington, USA C. Joshi, S. Tochitsky UCLA, Los Angeles, California, USA S. Reiche PSI, Villigen PSI, Switzerland
	UCLA is planning to build a THz user facility. One is a seeded THz FEL tunable in the range of 0.5 - 3 THz or even 3-9 THz in an optical klystron configuration. Another* relies on microbunching at 340 micron using a 3.3 cm undulator or even driving the FEL with an electron beam from a laser-plasma accelerator. These FEL's make use of a 2.1m long pre-buncher, chicane and shorter, 110cm long radiator. Chicane requirements are modest. A round copper waveguide with 4.8mm ID will be used. We will describe the magnetic design and measured performance of the gap tunable undulators, mechanical design of the entire system, vacuum boxes, waveguides and expected operational approaches. Both undulators have 33mm periods and curved poles for two-plane focusing. Discussions will be included on issues associated with fabricating, sorting and shimming curved pole undulators. A new optimization method will be described that was used to meet magnetic requirements with a minimum volume of magnetic material. *S. Tochitsky et al, "Seeded FEL Microbunching Experiments at the UCLA Neptune Laboratory", Advanced Accelerator Conference 2010

THPD19	Technical Overview of SwissFEL Undulator Line	583
	R. Ganter, M. Aiba, H.-H. Braun, C. Calvi, A. Fuchs, P. Heimgartner, E. Hohmann, R. Ischebeck, H. Jöhri, B. Keil, N. Milas, M. Negrazus, S. Reiche, S. Sanfilippo, T. Schmidt, S. Sidorov, P. Wiegand PSI, Villigen PSI, Switzerland
	Starting after Linac 3 at z ~ 430 m (z = 0 being the gun photocathode position), the so-called Aramis Hard-X ray undulator section extends over 170 m, from the energy collimator to the electron beam dump. Electrons enter the undulator section with a maximum energy of 5.8 GeV, a slice emittance below 0.43 μm and a peak current of 3 kA with 200 pC of charge. A prototype of the in-vacuum undulator (U15) is currently under assembly. Most of the other beamline components have been designed and for some of them prototypes are already ordered (quadrupoles, beam position monitors, phase shifters, alignment quadrupoles; mechanical supports; safety components). The paper will describe how constraints like temperature drifts, stray magnetic field, wakefields, beam losses, costs are taken into account for the design of components and building (undulators are however described in details in a companion paper).