10.131 ZTRANSVERSE—A simulation of a single-pass broad-band or functionally-specified
transverse impedance.
A simulation of a single-pass broad-band or functionally-specified transverse impedance.
Parallel capable? : yes
GPU capable? : no
Back-tracking capable? : no
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| Parameter Name | Units | Type | Default | Description |
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| CHARGE | C | double | 0.0 | Deprecated—use CHARGE
element |
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| BROAD_BAND | | long | 0 | broad-band impedance? |
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| RS | Ohm∕m | double | 0.0 | shunt impedance
(Rs=Ra/2=V /(2*P)) |
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| Q | | double | 0.0 | cavity Q |
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| FREQ | Hz | double | 0.0 | frequency
(BROAD_BAND=1) |
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| INPUTFILE | | STRING | NULL | name of file giving impedance
(BROAD_BAND=0) |
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| FREQCOLUMN | | STRING | NULL | column in INPUTFILE
containing frequency |
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| ZXREAL | | STRING | NULL | column in INPUTFILE
containing real impedance for
x plane |
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| ZXIMAG | | STRING | NULL | column in INPUTFILE
containing imaginary
impedance for x plane |
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| ZYREAL | | STRING | NULL | column in INPUTFILE
containing real impedance for
y plane |
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| ZYIMAG | | STRING | NULL | column in INPUTFILE
containing imaginary
impedance for y plane |
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| BIN_SIZE | S | double | 0.0 | bin size for current histogram
(use 0 for autosize) |
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| INTERPOLATE | | long | 0 | interpolate wake? |
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| N_BINS | | long | 128 | number of bins for current
histogram |
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| MAX_N_BINS | | long | 0 | Maximum number of bins for
current histogram |
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| SMOOTHING | | long | 0 | Use Savitzky-Golay filter to
smooth current histogram? |
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| SG_ORDER | | long | 1 | Savitzky-Golay filter order for
smoothing |
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| SG_HALFWIDTH | | long | 4 | Savitzky-Golay filter
halfwidth for smoothing |
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A simulation of a single-pass broad-band or functionally-specified transverse impedance.
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| Parameter Name | Units | Type | Default | Description |
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| DX | M | double | 0.0 | misalignment |
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| DY | M | double | 0.0 | misalignment |
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| FACTOR | | double | 1 | Factor by which to multiply x
and y impedances. |
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| XFACTOR | | double | 1 | Factor by which to multiply x
impedance. |
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| YFACTOR | | double | 1 | Factor by which to multiply y
impedance. |
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| WAKES | | STRING | NULL | filename for output of wake |
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| WAKE_INTERVAL | | long | 1 | interval in passes at which to
output wake |
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| WAKE_START | | long | 0 | pass at which to start to
output wake |
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| WAKE_END | | long | 9223372036854775807 | pass at which to stop to output
wake |
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| START_ON_PASS | | long | 0 | The pass on which the
impedance effects start. |
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| RAMP_PASSES | | long | 0 | Number of passes over
which to linearly ramp up the
impedance to full strength. |
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| 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). |
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| HIGH_FREQUENCY_CUTOFF1 | | double | -1 | Frequency at which
smoothing filter is 0. If
not given, defaults to
HIGH_FREQUENCY_CUTOFF0. |
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| X_DRIVE_EXPONENT | | long | 1 | Exponent applied to x
coordinates of drive particles |
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| Y_DRIVE_EXPONENT | | long | 1 | Exponent applied to y
coordinates of drive particles |
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| X_PROBE_EXPONENT | | long | 0 | Exponent applied to x
coordinates of probe particles |
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A simulation of a single-pass broad-band or functionally-specified transverse impedance.
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| Parameter Name | Units | Type | Default | Description |
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| Y_PROBE_EXPONENT | | long | 0 | Exponent applied to y
coordinates of probe particles |
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| BUNCHED_BEAM_MODE | | long | 1 | If
non-zero, then do calculations
bunch-by-bunch. |
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| START_BUNCH | | long | -1 | In bunched beam mode, if
non-negative, starting bunch
number for computations |
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| END_BUNCH | | long | -1 | In bunched beam mode, if
non-negative, ending bunch
number for computations |
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| ALLOW_LONG_BEAM | | long | 0 | Allow beam longer than
covered by impedance data? |
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| 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 |
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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
 | (169) |
where i = 
, 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
 | (170) |
where Rs is the shunt impedance in Ohms∕m, Q is the quality factor, and ωr is the resonant
frequency.
When providing an impedance in a file, the user must be careful to conform to these conventions. In
addition, the units of the frequency column must be Hz, while the units of the impedance components
must be Ohms/m. At present, elegant does not check the units for correctness.
Other notes:
- The frequency data required from the input file is not ω, but rather f = ω∕(2π).
- 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.
- Impedance data can be created from a wake function using the script trwake2impedance,
which is supplied with elegant. This script also illustrates how to scale the data with the
frequency spacing. The script uses sddsfft, which produces a folded FFT (f ≥ 0) from a
real function. The folded FFT representation involves multiplying the non-DC terms by 2.
elegant expects this and internally multiplies the DC term by 2 as well.
- 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.
- Wake output is available only in the serial 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.