An%20overview%20of%20TREDI%20

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An overview of TREDI CSR test cases

• L. Giannessi M. Quattromini

Presented at
Coherent Synchrotron and its impact on the beam
dynamics of high brightness electron
beams January 14-18, 2002 at DESY-Zeuthen
(Berlin, GERMANY)
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TREDI

• is a multi-purpose macroparticle 3D Monte
  Carlo, devoted to the simulation of electron
  beams through

• Rf-guns
• Linacs (TW SW)
• Solenoids
• Bendings
• Undulators
• Quads

where Self Fields are accounted for by means of
Lienard-Wiechert retarded potentials
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SELF FIELDS
Source
R(t)
Target
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Motivations

• Three dimensional effects in photo-injectors
• Inhomogeneities of cathode quantum efficiency
• Laser misalignments
• Multipolar terms in accelerating fields
• 3-D injector for high aspect ratio beam
  production
• . on the way
• Study of coherent radiation emission in
  bendings and interaction with beam emittance and
  energy spread

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History

• 1992-1995 - Start EU Network on RF-Injectors
• Fortran / DOS (PC-386 20MHz)
• Procs VII J.D'Etude Sur la Photoem. a Fort
  Courant Grenoble 20-22 Septembre 1995
• 1996-1997 - Covariant smoothing of SC Fields
• Ported to C/Linux (PC-Pentium
  133MHz)FEL
• 1996 - NIM A393, p.434 (1997) - Procs. of 2nd
  Melfi works. 2000 - Aracne ed.(2000)
• 1998-1999 - Simulation of bunching in low energy
  FEL Added Devices (SW Linac Solenoid - UM)
  (PC-Pentium 266MHz)
• FEL 1998 - NIM A436, p.443 (1999) (not
  proceedings )
• 2001-2002 - Italian initiative for Short ? FEL
• Today Many upgrades - First tests of CSR in
  new version

Contributions from A. Marranca Contributions
from P. Musumeci
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FEL lasing (1998)
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Major upgrade to

• Accomodate more devices (Bends, Linacs,
  Solenoids )
• Load field profiles from files
• Point2point or Point2grid SC Fields evaluation
  (NxN ? NxM)
• Allowed piecewise simulations
• Graphical User Interface for Input File
  preparation (TCL/Tk)
• Graphical Post Processor for Mathematica /
  MathCad / IDL
• Porting to MPI for Parallel Simulations
• Fix Data / Code architectural dependence
• SDDS support for data exchange with FEL codes
• ? Smoothing of acceleration fields (still more
  work required)
• Radiative energy loss
• 5000 lines ? 12.000 lines of code pre/post
  processors

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TREDI FlowChart

• Start
• Load configuration
• init phase space

Charge distribution external fields known at
time t
Adaptive algorithm tests accuracy evaluates
step length ?t
Exit if ZgtZend
Trajectories are intagrated to t ?t
Self Fields are evaluated at time t ?t
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Parallelization
Present Beam
Time
NOW
Particle trajectory 1
Particle trajectory 2
Particle trajectory 3
Particle trajectory k-2
Particle trajectory k-1
Particle trajectory k
Self Fields
..

Node 3
Node 2
Node 1
Node n
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CSR Tests with TREDI

• Problems
• CSR cases are memory and cpu consuming
• ? Parallelization required
• ? very few particles
• (300 particles ? 4h on IBM SP3/16 nodes - 400 MHz
  each)
• The program seems much slower than expected
• The real enemy is the noise
• Analysis and suppression of numerical noise
• Test cases
• Basic - No compression 5 nC - 5 GeV
• 500 MeV - 1.0 nC - Gaussian
• 5 GeV - 1.0 nC/0.5nC - Gaussian

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Collective (coherent) effect
Source
R(t)
Targets
Source
2 Particles interaction incoherent collision
Target
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Effect of Noise (1st bend - no screening)
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Suppression of noise

• Acceleration fields
• Can be very large in high energy cases
• Decrease only with distance as 1/R
• Produce transverse forces

In the case of pure coulomb fields ?
Regularization is obtained by giving
macroparticles a finite size
In the case of radiative fields ? Regularization
is obtained by giving macroparticles a finite
size in momentum space
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Suppression of noise II
The spatial integral is treated applying the
Gauss theorem
The momentum integral can be estimated by
assigning a minimum momentum dispersion
Transverse Electric Field
?? 10-4 ? 104
View angle
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Suppression of noise III
The integral in momentum space with a
Gaussian distribution is CPU time consuming
Alternative Limit angle of influence of
particles to force collective interactions
P impact parameter P0 point like
particles - no smoothing collisions
dominate P1 limited spread particles -
collective effects are dominant Pgt1
spread out macroparticle - reduced interaction
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Effect of impact parameter(Simulation of first
bend - basic case)
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Basic case - P1 - No compression - 5 GeV 1.0 nC
Phase space at exit ? still noisy !
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No compression - 5 GeV 1.0 nCEstimation of
emittance
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No compression - 5 GeV 1.0 nC - ?x10.1 mm-mrad
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No compression - 5 GeV 1.0 nCEmittances
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No compression - 5 GeV 1.0 nC
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Energy variation ??
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No compression - 5 GeV 1.0 nCTransverse rms
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E 5 GeV - Q1 nC
Bunch Length
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Phase space at exit ? still noisy !
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Estimation of emittance
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Emittance vs. z dispersion
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Energy spread
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Phase space at exit with 85 of the charge,
?x2.3 mm-mrad
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E 5 GeV - Q0.5 nC
Bunch Length
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Phase space at exit with 85 of the charge,
?x1.4 mm-mrad
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E 500MeV - Q1.0 nC
Bunch Length
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Emittance at exit - 500 MeV - 1.0 nC ??
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Phase space at exit with 92 of the charge, ?x21
mm-mrad
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Conclusions

• The noise suppression method has reduced the
  effects of SF on longitudinal phase space,
  without being completely effective in the
  transverse phase space
• A rigorous model of fields regularization,
  relying on a realistic momentum dispersion of
  macroparticles will be soon implemented
• The low number of macroparticles in severely
  limiting the reliability of the results
• Diagnostic on fields will be implemented to
  improve insight on the smoothing procedure
• The reason of the slow down of the code must be
  understood
• Before the end of the workshop the 1000 particles
  case will be finished - we will see.