ICAP2012 - List of Keywords (radiation)

Paper	Title	Other Keywords	Page
TUACI1	Numerical Modeling of Collective Effects in Free Electron Laser	FEL, undulator, simulation, electron	81
	I. Zagorodnov DESY, Hamburg, Germany
	In order to have a free electron laser (FEL) of high performance we need to design and optimize it taking into account the dynamics of electrons and their interactions with each other and with their surroundings. An accurate self-consistent simulation of collective effects in the charged beams remains a challenging problem for numerical analysis. In this paper we consider only the modeling of FEL process in an undulator section. We give a short overview of the numerical methods adopted in different FEL codes. Advantages and drawbacks of these methods will be discussed. Some approaches to improve the accuracy and efficiency of the codes will be presented and the remaining challenges in FEL modeling will be highlighted.
	Slides TUACI1 [2.659 MB]

TUACC2	WAVE - A Computer Code for the Tracking of Electrons through Magnetic Fields and the Calculation of Spontaneous Synchrotron Radiation	electron, undulator, synchrotron, synchrotron-radiation	86
	M. Scheer HZB, Berlin, Germany
	WAVE has been developed since 1990 at BESSY - now Helmholtz-Zentrum Berlin (HZB) - to calculate spontaneous synchrotron radiation for arbitrary magnetic fields. A variety of field models for dipoles, wavelength shifters, and undulators is available. Field maps and tables can be read and written. Many routines to handle magnetic fields are implemented, including simulations of field error e.g. due to misalignment. Coherent radiation of electrons in a bunch and energy losses due to radiation are taken into account. Phase space distribution of electrons are taken into account by various algorithms. Generating functions and linear transfer matrices for particle tracking purposes can be calculated. Subroutines to calculate the effects of insertion devices on the storage ring are included. The program runs in batch mode, controlled by input files, but a simple GUI is also provided. The results are given as ASCII data or binary formats of the programs PAW, ROOT, and HDF5. Parallel runs of WAVE on a cluster are supported. WAVE has been checked and validated with the synchrotron radiation code of the German National Bureau of Standards (PTB) based on Schwinger's formula.
	Slides TUACC2 [3.685 MB]

TUACC3	A Fast Integrated Green Function Method for Computing 1D CSR Wakefields Including Upstream Transients	wakefield, lattice, dipole, synchrotron	89
	C.E. Mitchell, J. Qiang, R.D. Ryne LBNL, Berkeley, California, USA
	Funding: This work is supported under DOE Contract No. DE-AC02-05CH11231. An efficient numerical method for computing wakefields due to coherent synchrotron radiation (CSR) has been implemented using a one-dimensional integrated Green function approach. The contribution from CSR that is generated upstream and propagates across one or more lattice elements before interacting with the bunch is included. This method does not require computing the derivative of the longitudinal charge density, and accurately includes the short-range behavior of the CSR interaction. As an application of this method, we examine the importance of upstream transient wakefields within several bending elements of a proposed Next Generation Light Source.
	Slides TUACC3 [2.060 MB]

TUSCC3	Undulator Radiation Inside a Dielectric Waveguide	vacuum, undulator, insertion, synchrotron	96
	A. Kotanjyan, A.A. Saharian YSU, Yerevan, Armenia
	We investigate the radiation from a charge moving along a helix around a dielectric cylinder immersed in a homogeneous medium. We are mainly concerned with the radiation propagating inside the cylinder. The radiation intensity for the modes propagating inside the cylinder is evaluated by the work done by the radiation field on the charge and by evaluating the energy flux through the cross-section of the cylinder. The insertion of a dielectric waveguide provides an additional mechanism for tuning the characteristics of the undulator radiation by choosing the parameters of the waveguide. The radiated energy inside the cylinder is redistributed among the cylinder modes, the corresponding spectrum differs significantly from the homogeneous medium or free-space results. This change is of special interest in the low-frequency range where the distribution of the radiation energy among small number of modes leads to the enhancement of the spectral density for the radiation intensity. The radiation emitted on the waveguide modes propagates inside the cylinder and the waveguide serves as a natural collector for the radiation.
	Slides TUSCC3 [0.809 MB]

TUSDI1	Modeling of Coherent Synchrotron Radiation Using a Direct Numerical Solution of Maxwell's Equations	vacuum, electromagnetic-fields, dipole, synchrotron	107
	A. Novokhatski SLAC, Menlo Park, California, USA
	Funding: Work supported by Department of Energy DE-AC02-76SF00515 We present and discuss the properties of coherent electromagnetic fields of a very short, ultra-relativistic bunch, which travels in a rectangular vacuum under the influence of a bending force of a magnet. The analysis is based on the results of a direct numerical solution of Maxwell’s equations together with Newton's equations. We use a new dispersion-free time-domain algorithm which employs a more efficient use of finite element mesh techniques and hence produces self-consistent and stable solutions for very short bunches. We investigate the fine structure of the CSR fields. We also discuss coherent edge radiation. We present a clear picture of the field using the electric field lines constructed from the numerical solutions. This approach should be useful in the study of existing and future concepts of particle accelerators and ultrafast coherent light sources, where high peak currents and very short bunches are envisioned.
	Slides TUSDI1 [10.584 MB]

TUSDC2	Rapid Integration Over History in Self-consistent 2D CSR Modeling	simulation, shielding	112
	K.A. Heinemann, D. Bizzozero, J.A. Ellison, S.R. Lau UNM, Albuquerque, New Mexico, USA G. Bassi BNL, Upton, Long Island, New York, USA
	Funding: This work has been supported by DOE under DE-FG-99ER41104 In our self-consistent algorithm for calculating 2D CSR effects we reduce the field calculation to a 2D integral over the 2D charge and current densities of the bunch and their time history. Our code VM3@A (Vlasov-Maxwell Monte-carlo Method @ Albuquerque) implements this in a time stepping algorithm as discussed in PRST-AB 12, 080704 (2009). A major expense is the integration over history at each time step. By going to Fourier space the 2D integral is reduced to a 1D convolution over history. This may on its own have a computational advantage, however, using the kernel compression technique of Alpert, Greengard and Hagstrom [1, 2], we approximate the convolution kernel by a sum of exponentials. This allows a time step to be taken using information only from the previous time step, thus eliminating the integral over history. Of course 2D Fourier transforms must be calculated at each step, these can be done with an FFT (or NFFT). We discuss the flop count for the two approaches. In addition we implement this as an option in VM3@A and compare efficiencies of our new and old approaches in the context of a bunch compressor system for the LCLS. [1] SIAM J. Numer. Anal. 37(2000) 1138. See also PhD thesis at http://web.njit.edu/~jiang/pub.html [2] S. R. Lau, J. Math. Phys. 46, 102503, (2005). Supported by DE-FG02-99ER41104
	Slides TUSDC2 [0.485 MB]

WEP11	Stochastic Response Surface Method for Studying Microphoning and Lorenz Detuning of Accelerator Cavities	cavity, simulation, SRF, insertion	158
	J. Deryckere, H. De Gersem, B. Masschaele, T. Roggen KU Leuven, Kortrijk, Belgium
	Funding: This research is funded by grant KUL_3E100118 and grant KUL_3E080005. The dependence of the eigenfrequencies of a superconductive cavity on its geometry are represented by a stochastic response surface model. The model is constructed on the basis of both information on the eigenfrequencies as on their sensitivities with respect to the geometry. The eigenmodes are calculated using the 2D or 3D finite element method or finite integration technique. The stochastic representation does not only model uncertainties on the geometrical parameters but also inaccuracies of the eigenmode solvers, e.g. due to remeshing. Variations or optimisations of the geometry are carried out on the surrogate model. The model allows an efficient evaluation of microphoning and Lorentz detuning of accelerator cavities.
	Poster WEP11 [0.665 MB]

WEP18	Dynamics of Energy Loss of a Bunch Intersecting a Boundary Between Vacuum and Dielectric in a Waveguide	vacuum, plasma, electromagnetic-fields, wakefield	176
	T.Yu. Alekhina, A.V. Tyukhtin Saint-Petersburg State University, Saint-Petersburg, Russia
	Funding: his research was supported by St. Petersburg State University We analyze radiation of a small bunch crossing a boundary between two dielectrics in a cylindrical waveguide. The total energy of radiation was studied earlier for such problem but dynamics of an energy loss as well as a field structure was not investigated. Meanwhile these questions are of essential interest for the wakefield acceleration technique and for new methods of generation of microwave radiation. Our research is based on original approach used previously for the case of the vacuum-plasma boundary. The principal difference of presented work consists in generation of Cherenkov radiation in dielectric and so-called Cherenkov-transition radiation in vacuum. Algorithms of computations for the field and the energy loss are founded upon certain transformations of integration path. Comparison of analytical results with numerical ones shows a good coincidence. We consider two instances in detail: the bunch is flying from vacuum into dielectric and from dielectric into vacuum. In both cases we compare the energy losses by transition radiation and by Cherenkov one. Our investigation shows, for example, that energy loss can be negative at certain segments of the bunch trajectory. T.Yu. Alekhina and A.V. Tyukhtin, Phys. Rev. E. 83, 066401 (2011)

THACC3	Preliminary Study of Single Spike SASE FEL Operation at 0.26 Nanometers Wavelength for the European XFEL	electron, laser, simulation, FEL	253
	B. Marchetti, M. Krasilnikov, F. Stephan DESY Zeuthen, Zeuthen, Germany M. Dohlus, Y.A. Kot, I. Zagorodnov DESY, Hamburg, Germany J. Rönsch-Schulenburg Uni HH, Hamburg, Germany
	The production of ultra-short (fs or sub-fs long), high power, radiation pulses in the X-ray spectral region, showing a single spike spectrum, represents a challenge for many existent SASE- FELs [1, 2]. In order to realize single spike operation the length of the electron bunch after compression must be extremely small [3] (less than a micrometer) and the consequent degradation of its emittance has not to suppress the radiation production. Several technical restrictions, such as limits of diagnostics for small charges, RF jitter and micro-bunching instabilities play an important role in the choice of the operation working point. In this paper we are going to study the feasibility of single spike or few spikes lasing for bunches with charge of tens of pC in the European XFEL facility giving some preliminary results concerning the choice of the working point. [1] J.B. Rosenzweig et al., NIM A 593 (2008) 39-44 [2] S. Reiche et al., NIM A 593 (2008) 45-48 [3] R. Bonifacio et al., PRL vol. 73 n.1 (1994)
	Slides THACC3 [1.401 MB]

Paper

Title

Other Keywords

Page

TUACI1

Numerical Modeling of Collective Effects in Free Electron Laser

FEL, undulator, simulation, electron

81

I. Zagorodnov
DESY, Hamburg, Germany

In order to have a free electron laser (FEL) of high performance we need to design and optimize it taking into account the dynamics of electrons and their interactions with each other and with their surroundings. An accurate self-consistent simulation of collective effects in the charged beams remains a challenging problem for numerical analysis. In this paper we consider only the modeling of FEL process in an undulator section. We give a short overview of the numerical methods adopted in different FEL codes. Advantages and drawbacks of these methods will be discussed. Some approaches to improve the accuracy and efficiency of the codes will be presented and the remaining challenges in FEL modeling will be highlighted.

Slides TUACI1 [2.659 MB]

TUACC2

WAVE - A Computer Code for the Tracking of Electrons through Magnetic Fields and the Calculation of Spontaneous Synchrotron Radiation

electron, undulator, synchrotron, synchrotron-radiation

86

M. Scheer
HZB, Berlin, Germany

WAVE has been developed since 1990 at BESSY - now Helmholtz-Zentrum Berlin (HZB) - to calculate spontaneous synchrotron radiation for arbitrary magnetic fields. A variety of field models for dipoles, wavelength shifters, and undulators is available. Field maps and tables can be read and written. Many routines to handle magnetic fields are implemented, including simulations of field error e.g. due to misalignment. Coherent radiation of electrons in a bunch and energy losses due to radiation are taken into account. Phase space distribution of electrons are taken into account by various algorithms. Generating functions and linear transfer matrices for particle tracking purposes can be calculated. Subroutines to calculate the effects of insertion devices on the storage ring are included. The program runs in batch mode, controlled by input files, but a simple GUI is also provided. The results are given as ASCII data or binary formats of the programs PAW, ROOT, and HDF5. Parallel runs of WAVE on a cluster are supported. WAVE has been checked and validated with the synchrotron radiation code of the German National Bureau of Standards (PTB) based on Schwinger's formula.

Slides TUACC2 [3.685 MB]

TUACC3

A Fast Integrated Green Function Method for Computing 1D CSR Wakefields Including Upstream Transients

wakefield, lattice, dipole, synchrotron

89

C.E. Mitchell, J. Qiang, R.D. Ryne
LBNL, Berkeley, California, USA

Funding: This work is supported under DOE Contract No. DE-AC02-05CH11231.
An efficient numerical method for computing wakefields due to coherent synchrotron radiation (CSR) has been implemented using a one-dimensional integrated Green function approach. The contribution from CSR that is generated upstream and propagates across one or more lattice elements before interacting with the bunch is included. This method does not require computing the derivative of the longitudinal charge density, and accurately includes the short-range behavior of the CSR interaction. As an application of this method, we examine the importance of upstream transient wakefields within several bending elements of a proposed Next Generation Light Source.

Slides TUACC3 [2.060 MB]

TUSCC3

Undulator Radiation Inside a Dielectric Waveguide

vacuum, undulator, insertion, synchrotron

96

A. Kotanjyan, A.A. Saharian
YSU, Yerevan, Armenia

We investigate the radiation from a charge moving along a helix around a dielectric cylinder immersed in a homogeneous medium. We are mainly concerned with the radiation propagating inside the cylinder. The radiation intensity for the modes propagating inside the cylinder is evaluated by the work done by the radiation field on the charge and by evaluating the energy flux through the cross-section of the cylinder. The insertion of a dielectric waveguide provides an additional mechanism for tuning the characteristics of the undulator radiation by choosing the parameters of the waveguide. The radiated energy inside the cylinder is redistributed among the cylinder modes, the corresponding spectrum differs significantly from the homogeneous medium or free-space results. This change is of special interest in the low-frequency range where the distribution of the radiation energy among small number of modes leads to the enhancement of the spectral density for the radiation intensity. The radiation emitted on the waveguide modes propagates inside the cylinder and the waveguide serves as a natural collector for the radiation.

Slides TUSCC3 [0.809 MB]

TUSDI1

Modeling of Coherent Synchrotron Radiation Using a Direct Numerical Solution of Maxwell's Equations

vacuum, electromagnetic-fields, dipole, synchrotron

107

A. Novokhatski
SLAC, Menlo Park, California, USA

Funding: Work supported by Department of Energy DE-AC02-76SF00515
We present and discuss the properties of coherent electromagnetic fields of a very short, ultra-relativistic bunch, which travels in a rectangular vacuum under the influence of a bending force of a magnet. The analysis is based on the results of a direct numerical solution of Maxwell’s equations together with Newton's equations. We use a new dispersion-free time-domain algorithm which employs a more efficient use of finite element mesh techniques and hence produces self-consistent and stable solutions for very short bunches. We investigate the fine structure of the CSR fields. We also discuss coherent edge radiation. We present a clear picture of the field using the electric field lines constructed from the numerical solutions. This approach should be useful in the study of existing and future concepts of particle accelerators and ultrafast coherent light sources, where high peak currents and very short bunches are envisioned.

Slides TUSDI1 [10.584 MB]

TUSDC2

Rapid Integration Over History in Self-consistent 2D CSR Modeling

simulation, shielding

112

K.A. Heinemann, D. Bizzozero, J.A. Ellison, S.R. Lau
UNM, Albuquerque, New Mexico, USA
G. Bassi
BNL, Upton, Long Island, New York, USA

Funding: This work has been supported by DOE under DE-FG-99ER41104
In our self-consistent algorithm for calculating 2D CSR effects we reduce the field calculation to a 2D integral over the 2D charge and current densities of the bunch and their time history. Our code VM3@A (Vlasov-Maxwell Monte-carlo Method @ Albuquerque) implements this in a time stepping algorithm as discussed in PRST-AB 12, 080704 (2009). A major expense is the integration over history at each time step. By going to Fourier space the 2D integral is reduced to a 1D convolution over history. This may on its own have a computational advantage, however, using the kernel compression technique of Alpert, Greengard and Hagstrom [1, 2], we approximate the convolution kernel by a sum of exponentials. This allows a time step to be taken using information only from the previous time step, thus eliminating the integral over history. Of course 2D Fourier transforms must be calculated at each step, these can be done with an FFT (or NFFT). We discuss the flop count for the two approaches. In addition we implement this as an option in VM3@A and compare efficiencies of our new and old approaches in the context of a bunch compressor system for the LCLS.
[1] SIAM J. Numer. Anal. 37(2000) 1138. See also PhD thesis at http://web.njit.edu/~jiang/pub.html
[2] S. R. Lau, J. Math. Phys. 46, 102503, (2005). Supported by DE-FG02-99ER41104

Slides TUSDC2 [0.485 MB]

WEP11

Stochastic Response Surface Method for Studying Microphoning and Lorenz Detuning of Accelerator Cavities

cavity, simulation, SRF, insertion

158

J. Deryckere, H. De Gersem, B. Masschaele, T. Roggen
KU Leuven, Kortrijk, Belgium

Funding: This research is funded by grant KUL_3E100118 and grant KUL_3E080005.
The dependence of the eigenfrequencies of a superconductive cavity on its geometry are represented by a stochastic response surface model. The model is constructed on the basis of both information on the eigenfrequencies as on their sensitivities with respect to the geometry. The eigenmodes are calculated using the 2D or 3D finite element method or finite integration technique. The stochastic representation does not only model uncertainties on the geometrical parameters but also inaccuracies of the eigenmode solvers, e.g. due to remeshing. Variations or optimisations of the geometry are carried out on the surrogate model. The model allows an efficient evaluation of microphoning and Lorentz detuning of accelerator cavities.

Poster WEP11 [0.665 MB]

WEP18

Dynamics of Energy Loss of a Bunch Intersecting a Boundary Between Vacuum and Dielectric in a Waveguide

vacuum, plasma, electromagnetic-fields, wakefield

176

T.Yu. Alekhina, A.V. Tyukhtin
Saint-Petersburg State University, Saint-Petersburg, Russia

Funding: his research was supported by St. Petersburg State University
We analyze radiation of a small bunch crossing a boundary between two dielectrics in a cylindrical waveguide. The total energy of radiation was studied earlier for such problem but dynamics of an energy loss as well as a field structure was not investigated. Meanwhile these questions are of essential interest for the wakefield acceleration technique and for new methods of generation of microwave radiation. Our research is based on original approach used previously for the case of the vacuum-plasma boundary*. The principal difference of presented work consists in generation of Cherenkov radiation in dielectric and so-called Cherenkov-transition radiation in vacuum. Algorithms of computations for the field and the energy loss are founded upon certain transformations of integration path. Comparison of analytical results with numerical ones shows a good coincidence. We consider two instances in detail: the bunch is flying from vacuum into dielectric and from dielectric into vacuum. In both cases we compare the energy losses by transition radiation and by Cherenkov one. Our investigation shows, for example, that energy loss can be negative at certain segments of the bunch trajectory.
* T.Yu. Alekhina and A.V. Tyukhtin, Phys. Rev. E. 83, 066401 (2011)

THACC3

Preliminary Study of Single Spike SASE FEL Operation at 0.26 Nanometers Wavelength for the European XFEL

electron, laser, simulation, FEL

253

B. Marchetti, M. Krasilnikov, F. Stephan
DESY Zeuthen, Zeuthen, Germany
M. Dohlus, Y.A. Kot, I. Zagorodnov
DESY, Hamburg, Germany
J. Rönsch-Schulenburg
Uni HH, Hamburg, Germany

The production of ultra-short (fs or sub-fs long), high power, radiation pulses in the X-ray spectral region, showing a single spike spectrum, represents a challenge for many existent SASE- FELs [1, 2]. In order to realize single spike operation the length of the electron bunch after compression must be extremely small [3] (less than a micrometer) and the consequent degradation of its emittance has not to suppress the radiation production. Several technical restrictions, such as limits of diagnostics for small charges, RF jitter and micro-bunching instabilities play an important role in the choice of the operation working point. In this paper we are going to study the feasibility of single spike or few spikes lasing for bunches with charge of tens of pC in the European XFEL facility giving some preliminary results concerning the choice of the working point.
[1] J.B. Rosenzweig et al., NIM A 593 (2008) 39-44
[2] S. Reiche et al., NIM A 593 (2008) 45-48
[3] R. Bonifacio et al., PRL vol. 73 n.1 (1994)

Slides THACC3 [1.401 MB]