############################################################################## # Flags: nomenu, noprompt, nomessage, # ############################################################################## # section: -lcharge # ############################################################################## # ----- Parameters of a line charge: ------ # # charge = 0.0 -- [As] # # shape = gaussian -- gaussian | triangular | table # # tablefile= -none- # xtable = 1.0 -- [m] # # sigma = undefined -- [m] # # isigma = 6 -- number of sigmas to use. # # xposition = 0.0 -- [m] # # yposition = 0.0 -- [m] # # direction = +z -- +z, -z # # soffset = 0.0 -- [m] # # ----- other parameters: ------ # # ds = auto -- [m] # # shigh = auto -- [m] # # showdata = no -- ( yes | no ) # # napoly = yes -- ( yes | no ) # # naccuracy= 10.0e-6 -- wanted acc for poisson-eq in Napoly alg. # # ignoretem= yes -- should be "yes" for Wx, Wy # ############################################################################## # ?, nextcharge, return, help # ##############################################################################
In this section one specifies the properties of one or several relativistic line charges. When computing with the conventional algorithm, ie. not with the windowwake algorithm, one can specify up to 100 linecharges, each with a different charge, different position, different distribution and different direction of flight. When using the windowwake algorithm, all charges must go in positive z-direction, and they must have the same shape. They may differ in their positions and charge. Once the properties of a linecharge are specified, one switches to the next linecharge with the command '-nextcharge'.
The standard usage of this section is to compute wakepotentials. When a inonzero charge is specified, and a time domain computation is performed, the wakepotentials are computed as the potential that is seen by witness particles that are traveling in positive z-direction.
charge:
shape:
gaussian, triangular and table.
tablefile:
sigma is then ignored.
xtable:
sigma:
isigma:
-windowwake it might be useful to specify
isigma=3. Then the length of the computational window extends from
-3*isigma before the center of the charge up to shigh behind the center of the charge.
xposition, yposition:
direction:
soffset:
soffset has the effect that the charge travels
later through a given plane.
ds:
auto" or a positive real.
If "ds= auto", a value of "spacing/2" is used
("spacing" is defined in -mesh).
When napoly= yes, the value for ds is fixed to c*dt,
where c is the velocity of light and dt is the used timestep.
This parameter is not very useful. Please ignore it.
shigh:
auto" or a positive real.
If "shigh= auto", a value of "20 * sigma" is taken.
showdata= [yes|no]:
napoly= [yes|no]:
napoly= yes, near the z-borders of the computational volume,
a integration of the wakefield similiar to the Napoly-integration is
performed. This option should be set to napoly= yes for scraper-like
structures.
One can keep the option set even
if it is no needed, as GdfidL checks whether such a integration is useful.
If it is not, it is not done.
naccuracy= SMALL-NUMBER:
ignoretem= [yes|no]:
ignoretem=yes, the term
nextcharge:
-lcharge
xpos= 0
ypos= 0
charge= 1e-12
sigma= 1e-3
ds= 0.1e-3
shigh= 100e-3
Example
An example for a table file describing a charge shape is given below.
# -lcharge # shape= table, tablefile= Bunch1.txt # xtable= 1e-6, charge= 1e-12 # # Everything behind a '#' is ignored. # Lines in the tablefile may be empty, or they may # contain two (or more) numbers. # The first number is a position, the next number is # a relative charge. What follows behind these two numbers is ignored. # # bunch1 (linac entrance) # s[microns] No. of macro-particles # ________________________________________________ 0, 0 1 -1.32067 2 -1.10711 3 -0.894051 4 -0.6815 5 -0.469454 6 -0.25791 7 -0.046869 8 0.16367 9 0.373709 10 0.583247