ICAP2012 - List of Keywords (shielding)

Paper	Title	Other Keywords	Page
TUSDC2	Rapid Integration Over History in Self-consistent 2D CSR Modeling	radiation, simulation	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]

THSDC3	Calculation of Longitudinal Instability Threshold Currents for Single Bunches	simulation, synchrotron, damping, cavity	267
	P. Kuske HZB, Berlin, Germany
	Based on the publication by M. Venturini, et al.[1] a computer program has been written that solves the Vlasov-Fokker-Planck equation numerically on a two dimensional grid. In this code different types of longitudinal interactions and their combinations are implemented like the shielded CSR- as well as the purely resistive and inductive interactions of the electrons within the bunch. The details of the program will be presented in the paper. Calculations have been performed for the 1.7 GeV storage ring BESSY II and the 600 MeV ring MLS. The results are compared with measurements on both rings which were based on the observation of the onset of bursts of coherent synchrotron radiation. Fair agreement is found between theoretical and experimental observations. The theoretical results complement calculations performed by Bane, et al. for the shielded CSR-interaction [2]. The new results emphasize the resistive nature of the CSR-Interaction, especially in regions where shielding effects are small. [1] M. Venturini, et al., Phys. Rev. ST-SB, 8, 014202(2005) [2] K.L.F. Bane, et al., “Comparison of Simulation Codes for Microwave Instability in Bunched Beams“, IPAC 2010, Kyoto, Japan
	Slides THSDC3 [1.006 MB]

Paper

Title

Other Keywords

Page

TUSDC2

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

radiation, simulation

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]

THSDC3

Calculation of Longitudinal Instability Threshold Currents for Single Bunches

simulation, synchrotron, damping, cavity

267

P. Kuske
HZB, Berlin, Germany

Based on the publication by M. Venturini, et al.[1] a computer program has been written that solves the Vlasov-Fokker-Planck equation numerically on a two dimensional grid. In this code different types of longitudinal interactions and their combinations are implemented like the shielded CSR- as well as the purely resistive and inductive interactions of the electrons within the bunch. The details of the program will be presented in the paper. Calculations have been performed for the 1.7 GeV storage ring BESSY II and the 600 MeV ring MLS. The results are compared with measurements on both rings which were based on the observation of the onset of bursts of coherent synchrotron radiation. Fair agreement is found between theoretical and experimental observations. The theoretical results complement calculations performed by Bane, et al. for the shielded CSR-interaction [2]. The new results emphasize the resistive nature of the CSR-Interaction, especially in regions where shielding effects are small.
[1] M. Venturini, et al., Phys. Rev. ST-SB, 8, 014202(2005)
[2] K.L.F. Bane, et al., “Comparison of Simulation Codes for Microwave Instability in Bunched Beams“, IPAC 2010, Kyoto, Japan

Slides THSDC3 [1.006 MB]