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ZTRANSVERSE

A simulation of a single-pass broad-band or functionally-specified transverse dipole impedance.
Parallel capable? : yes
Parameter Name Units Type Default Description
CHARGE $C$ double 0.0 beam charge (or use CHARGE element)
BROAD_BAND   long 0 broad-band impedance?
RS $Ohm$ double 0.0 shunt impedance (Ra=2*Rs)
Q   double 0.0 cavity Q
FREQ $Hz$ double 0.0 frequency (BROAD_BAND=1)
INPUTFILE   STRING NULL name of file giving impedance (BROAD_BAND=0)
FREQCOLUMN   STRING NULL column in INPUTFILE containing frequency
ZXREAL   STRING NULL column in INPUTFILE containing real impedance for x plane
ZXIMAG   STRING NULL column in INPUTFILE containing imaginary impedance for x plane
ZYREAL   STRING NULL column in INPUTFILE containing real impedance for y plane
ZYIMAG   STRING NULL column in INPUTFILE containing imaginary impedance for y plane
BIN_SIZE $S$ double 0.0 bin size for current histogram (use 0 for autosize)
INTERPOLATE   long 0 interpolate wake?
N_BINS   long 128 number of bins for current histogram
MAX_N_BINS   long 0 Maximum number of bins for current histogram
SMOOTHING   long 0 Use Savitzky-Golay filter to smooth current histogram?
SG_ORDER   long 1 Savitzky-Golay filter order for smoothing
SG_HALFWIDTH   long 4 Savitzky-Golay filter halfwidth for smoothing
DX $M$ double 0.0 misalignment

A simulation of a single-pass broad-band or functionally-specified transverse dipole impedance.
Parameter Name Units Type Default Description
DY $M$ double 0.0 misalignment
FACTOR   double 1 Factor by which to multiply x and y impedances.
XFACTOR   double 1 Factor by which to multiply x impedance.
YFACTOR   double 1 Factor by which to multiply y impedance.
WAKES   STRING NULL filename for output of wake
WAKE_INTERVAL   long 1 interval in passes at which to output wake
WAKE_START   long 0 pass at which to start to output wake
WAKE_END   long 9223372036854775807 pass at which to stop to output wake
START_ON_PASS   long 0 The pass on which the impedance effects start.
RAMP_PASSES   long 0 Number of passes over which to linearly ramp up the impedance to full strength.
HIGH_FREQUENCY_CUTOFF0   double -1 Frequency at which smoothing filter begins. If not positive, no frequency filter smoothing is done. Frequency is in units of Nyquist (0.5/binsize).
HIGH_FREQUENCY_CUTOFF1   double -1 Frequency at which smoothing filter is 0. If not given, defaults to HIGH_FREQUENCY_CUTOFF0.
X_DRIVE_EXPONENT   long 1 Exponent applied to x coordinates of drive particles
Y_DRIVE_EXPONENT   long 1 Exponent applied to y coordinates of drive particles
X_PROBE_EXPONENT   long 0 Exponent applied to x coordinates of probe particles
Y_PROBE_EXPONENT   long 0 Exponent applied to y coordinates of probe particles

A simulation of a single-pass broad-band or functionally-specified transverse dipole impedance.
Parameter Name Units Type Default Description
BUNCHED_BEAM_MODE   long 1 If non-zero, then do calculations bunch-by-bunch.
GROUP   string NULL Optionally used to assign an element to a group, with a user-defined name. Group names will appear in the parameter output file in the column ElementGroup





This element allows simulation of a transverse impedance using a ``broad-band'' resonator or an impedance function specified in a file. The impedance is defined as the Fourier transform of the wake function

\begin{displaymath}
Z(\omega) = \int_{-\infty}^{+\infty} e^{-i \omega t} W(t) dt
\end{displaymath} (100)

where $i = \sqrt{-1}$, $W(t)=0 for t<0$, and $W(t)$ has units of $V/C/m$. Note that there is no factor of $i$ in front of the integral. Thus, in elegant the transverse impedance is simply the Fourier transform of the wake. This makes it easy to convert data from a program like ABCI into the wake formalism using sddsfft.

For a resonator impedance, the functional form is

\begin{displaymath}
Z(\omega) = \frac{-i\omega_r}{\omega} \frac{R_s}{1 + iQ(\frac{\omega}{\omega_r} - \frac{\omega_r}{\omega})},
\end{displaymath} (101)

where $R_s$ is the shunt impedance in $Ohms/m$, $Q$ is the quality factor, and $\omega_r$ is the resonant frequency.

When providing an impedance in a file, the user must be careful to conform to these conventions.

Other notes:

  1. The frequency data required from the input file is not $\omega$, but rather $f = \omega/(2 \pi)$.
  2. The default smoothing setting (SG_HALFWIDTH=4), may apply too much smoothing. It is recommended that the user vary this parameter if smoothing is employed.
  3. Using the broad-brand resonator model can often result in a very large number of bins being used, as elegant will try to resolve the resonance peak and achieve the desired bin spacing. This can result in poor performance, particularly for the parallel version.

Bunched-mode application of the impedance is possible using specially-prepared input beams. See Section 6 for details. The use of bunched mode for any particular ZTRANSVERSE element is controlled using the BUNCHED_BEAM_MODE parameter.


next up previous
Next: Examples Up: Element Dictionary Previous: ZLONGIT
Robert Soliday 2014-03-21