Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers
Some features of accelerating section field computation presented by the development of power and HOM couplers for TESLA linear collider are considered. The devices mentioned produce electromagnetic field asymmetry in the beam area, thus causing transverse kick. For this kick and its influence on be...
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| Date: | 2001 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2001
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| Cite this: | Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers / M.V. Lalayan, D.V. Kostin, N.P. Sobenin, V.I. Shvedunov, A.A. Zavadtzev, M. Dohlus // Вопросы атомной науки и техники. — 2001. — № 3. — С. 138-140. — Бібліогр.: 5 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860028943927607296 |
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| author | Lalayan, M.V. Kostin, D.V. Sobenin, N.P. Shvedunov, V.I. Zavadtzev, A.A. Dohlus, M. |
| author_facet | Lalayan, M.V. Kostin, D.V. Sobenin, N.P. Shvedunov, V.I. Zavadtzev, A.A. Dohlus, M. |
| citation_txt | Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers / M.V. Lalayan, D.V. Kostin, N.P. Sobenin, V.I. Shvedunov, A.A. Zavadtzev, M. Dohlus // Вопросы атомной науки и техники. — 2001. — № 3. — С. 138-140. — Бібліогр.: 5 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | Some features of accelerating section field computation presented by the development of power and HOM couplers for TESLA linear collider are considered. The devices mentioned produce electromagnetic field asymmetry in the beam area, thus causing transverse kick. For this kick and its influence on beam under acceleration parameters estimation the dynamics modelling calculations were done. 3D-simulation code MAFIA was used for field computation. These data were further used in beam dynamics calculations by means of TRMTrace code. Standing wave mode was simulated while considering HOM couplers, and travelling wave in case of power couplers. Transverse kicks and focussing forces are calculated for one HOM coupler design and two coaxial FM couplers.
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| first_indexed | 2025-12-07T16:51:23Z |
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ELECTROMAGNETIC FIELDS AND BEAM DYNAMICS SIMULATION
FOR THE SUPERSTRUCTURE OF TESLA LINEAR COLLIDER
CONSIDERING FIELD ASYMMETRY CAUSED BY HOM AND POWER
COUPLERS
M.V. Lalayan, D.V. Kostin, N.P. Sobenin, V.I. Shvedunov1, A.A. Zavadtzev2, M. Dohlus3
MEPhI (Technical University),
1 Scientific Research Institute JAF of the Moscow State University,
2 RTI Russian Academy of Science,
3 DESY (Germany)
Some features of accelerating section field computation presented by the development of power and HOM couplers
for TESLA linear collider are considered. The devices mentioned produce electromagnetic field asymmetry in the
beam area, thus causing transverse kick. For this kick and its influence on beam under acceleration parameters esti-
mation the dynamics modelling calculations were done. 3D-simulation code MAFIA was used for field computa-
tion. These data were further used in beam dynamics calculations by means of TRMTrace code. Standing wave
mode was simulated while considering HOM couplers, and travelling wave in case of power couplers. Transverse
kicks and focussing forces are calculated for one HOM coupler design and two coaxial FM couplers.
PACS numbers: 29.27.Bd, 71.15.Pd
1 INTRODUCTION
The superstructure layout according TESLA collider
scheme proposal [1] is shown in Fig. 1, where one could
see the FM coupler along with HOM couplers position.
Estimation of the transverse kick seen by a particle
moving through asymmetry field regions was based on
field components obtained by MAFIA electromagnetic
modelling code. Then the values of field components
were exported to RTMTRACE code, and by means of it
the dynamics calculations of the beam under accelera-
tion were performed.
Fig. 1. Superstructure layout with FM and HOM
couplers positions.
For correct beam dynamics simulation while moving
through accelerating structure one must consider the
electromagnetic fields in relatively long part of it. To
avoid excessive memory consumption and long compu-
tation time the full superstructure model was divided
into separate parts with computation followed by fields
merging. The following elements were used: cavity end
cell with drift tube and input coupler attached, two half-
cells and drift tube with HOM coupler, and cavity mid-
dle cell. Latter two elements computation was done in
SW mode using MAFIA’s eigenvalue solver module. In
the input coupler region the electromagnetic wave is
travelling, and in order to make a correct evaluation one
have to apply another approaches.
a) FM3 b) FM5
Fig. 2. End cell with two types of input couplers.
Fig. 3. Two half-cells and HOM coupler.
2 TW FIELDS COMPUTATION
Two different ways were used to solve this task -
two standing waves combining method and the one
based on time-domain computation.
Models used in each case were the same in order to
make the results comparable. Considerable attention
was put to obtain model’s azimuthal symmetry in order
to eliminate pretended field unsymmetry effects. But
quadrupole effects could not be completely eliminated
because of MAFIA’s way of rounded borders approxim-
ation with straight lines.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №3.
Серия: Ядерно-физические исследования (38), с. 138-140.
138
2.1 Two standing waves combining method
Travelling wave in coaxial input coupler could be
treated as two standing waves interferention. To get the
correct simulated fields vales it is sufficient to apply
two types of boundary – magnetic and electric one in
coaxial line, provided the reference plane position in
line is chosen correctly. For this task one could only
deal with eigenvalue problem, solvable by many well-
developed codes, for example by E module of MAFIA.
Reference plane coordinate is to be chosen so that
the frequencies fe, fm, and operating frequency fo were
equal (fe = fm = fo), where fe – frequency corresponding
to electrical boundary conditions in reference planes 1
and 2, fm - the same for magnetic ones.
Reference plane 1
reference
plane 2
Fig. 4. Input coupler model with reference planes
positions showed.
At the second stage travelling wave fields in input
coupler are computed. This computation uses two fields
components: Еx,y,z
(e) , Bx,y,z
(e) for electrical boundary con-
ditions in reference planes, and Еx,y,z
(m) , Bx,y,z
(m) for mag-
netic ones, obtained by two MAFIA runs. The following
normalising procedure is essential: the Еz мах
(е) и Еz мах
(m)
components maxima along coaxial line inner conductor
surface (at z = r) are to be equal. After this the field
amplitude and phase of travelling wave in coaxial wave-
guide calculation became possible.
( ) ( ) 2)m(
z,y,x
2)e(
z,y,xz,y,x EEE +=
=ϕ )e(
z,y,x
)m(
z,y,x
z,y,xE E
E
arctg
( ) ( ) 2)m(
z,y,x
2)e(
z,y,xz,y,x EBB +=
=ϕ )e(
z,y,x
)m(
z,y,x
z,y,xB B
B
arctg
In order to make an Еx,y,z and Bx,y,z amplitudes corres-
pond to some power P transmitted along the waveguide
the second normalisation is to be done. In the reference
plane 1 vicinity one should calculate the following
factor
( )
r
RlnP120
rrz,y,0xEz
2
⋅
⋅===α
and then divide all Еx,y,z and Bx,y,z amplitudes by it.
2.2 Method using MAFIA T3 module for TW fields
calculation
Model used for calculations consisted of one cell
with magnetic boundary placed at the iris, drift tube and
the coaxial coupler, all having the geometry like corres-
ponding TESLA ones. Drift tube was long enough to the
field considerably decayed along it.
Because of very small coupling the only way to
solve this problem using MAFIA is to reverse the power
flux. The field excitation was realised by two currents.
They are high-frequency Gaussian pulse modulated sine
with determined pulse width of 300 MHz. At the first
stage the frequency of this signal has been chosen equal
to 1300.0 MHz, which is close to yet unknown reso-
nance frequency.
Excitation currents pass the cell parallel to the beam
axis with each having 45 degrees off the symmetry
plane with the displacement equal to the drift tube radi-
us (see Fig. 6). Two beams were used during the calcu-
lation because in the task description for MAFIA it is
not allowed to have magnetic boundary and beam on the
same plane. Otherwise we could have used only one
beam passing the model along cavity axis.
As it was already mentioned, at the first stage of
computation the excitation pulses frequency was chosen
just close to resonance, and signal propagating along the
coaxial line was of interest. This signal was obtained by
placed in coaxial line virtual monitor – special MAFIA
means for calculation data storing during the time integ-
ration loop.
Having pulse length determined one could get excit-
ation pulse length (tpuls), and take into account for the
later treatment only part of output signal, in the region
from about 1.2 ⋅ tpuls to 3 tpuls. Applying harmonical ana-
lysis to this signal we could determine the exact reson-
ance frequency of excited oscillations, those apparently
became free after excitation pulse ended. This was done
by determining a complex function
( ) ( ) t*fest*2*ie*
f*4
1tAitAf,tC
est
est
π−
−⋅+= ,
where A(t) is the output signal, fest is the estimation for
the resonant frequency.
Proper choose of this estimation gives us a constant
argument of C(t, fest). During the second MAFIA run
fields in the entire volume were monitored after the ex-
citation pulses pass. Signal decreasing has substantially
low rate, so one could put the amplitude to be constant
in some short time period. Using special MAFIA means
having resonant frequency known online vector Fourier
transformation was performed, thus providing us travel-
ling wave fields.
3 BEAM DYNAMICS CALCULATION
While beam dynamics calculating transverse kick
could be treated as following [4]:
)yxxy(S)yyxx(Q
)yyxx(FyDxDp
0000
000y0xt
++−+
++++=∆
where tp∆ - transverse kick, 00 , yx
- unit vectors for
horizontal and vertical plane, x, y - initial particles dis-
placements, Dx, Dy - dipole kick components, F, Q, S -
azimuthal, quadruple and skew quadrupole focussing
strengths, all but F are energy-independent. Thus the
simulation results obtained for some energy could be
applied to the cases having other beam energy. All the
simulation were done assuming the particles are elec-
trons with charge sign taking into account. Beam energy
139
on particles phase with respect to field dependence al-
lows us to derive a transverse kick to maximal accelera-
tion phase relation. For the estimation HOM and FM
couplers shares in transverse kick independent simula-
tions were done for the superstructure having five
identical HOM couplers and the one with input coupler
of different constructions.
Fig. 5 illustrates simulation done by the RTMTrace
code for the energy of particles leaving superstructure
(a) dependence on their initial phase along with dipole
momentum (b) computed for the input coupler construc-
tion #5 and both dependencies approximation by cosine
function.
a. b.
Fig. 5.
In Table 1 the simulation results for HOM couplers
and two variants of input coupler are presented.
Table 1. Transverse kick dipole components and quad-
ruple focussing strengths for different couplers.
Coupler type Dy0,
KeV/s
ϕDy0 Q0,
KeV/s/m
ϕQ0
HOM, SW 6.7±0.1 3930 212±7 2180
FM #3, SW 1.4±0.1 1250 40±7 2930
FM #3, TW 2.3±0.1 1290 69±7 2910
FM#5a TW 11.7±0.1 930 337±7 2660
In order to make these results easily comparable
they were normalised for the same energy gain by the
superstructure equal to 60 MeV having initial particle
energy of 100 MeV. Besides in each case the reference
plane for particles phase definition was placed with its
offset of the first cell centre corresponded to maximum
acceleration at ϕ = 180o.
For input coupler #3 the simulation results for TW
and SW calculations are presented. These cases have
close transverse kick phase values, but 1.6 to 1.7 times
differ in its amplitude. Taking into account an asymmet-
rical field component high sensitivity to the reference
plane position in the input coupler simulations using
SW mode we assume these results of less accuracy and
exclude them from further analysis.
Transverse kick caused by the input coupler was es-
timated also by travelling wave field integrals using
MAFIA code means. Transverse kick absolute value
calculated using the integral for field normalisation ac-
cording to Table 1 data is 2.37 KeV for coupler #3
which is pretty close to Dy0 values. It is worth to be men-
tioned that only a dipole kick component could be es-
timated using integrals along the beam axis calculation.
For asymmetric component role studying the trans-
verse kicks and focussing strengths corresponding to a
particle phase of maximal acceleration are of significant
interest. These data are presented in Table 2.
Table 2. Transverse kick dipole components and
quadruple focussing strengths for different couplers
Coupler type Dx0,
KeV/s
Dy0,
KeV/s
Q0,
KeV/s/m
S0,
KeV/s/m
HOM, SW -1.1±0.1 -5.6±0.1 167±7 14±7
FM, #3, TW – 1.4±0.1 -25±7 –
FM, #5a, TW – 0.6±0.1 23±7 –
4 CONCLUSIONS
Input coupler #5 has the largest transverse kick amp-
litude and quadrupole focusing strength, but at the phase
corresponding to maximal acceleration these parameters
values for HOM couplers are greater than for input
ones. For example trajectory tilt angle at the end of su-
perstructure caused by HOM couplers for the beam in-
jected along it axis will be about 50 µrad and focal dis-
tance about 6⋅105m. Transverse kick caused by couplers
to the particles bunch under acceleration couple be par-
tially compensated with beam correctors. Most danger-
ous with respect to emittance dilution is the kick de-
pendence on the particles position in the bunch. Trans-
verse kick dependence on particle phase in the bunch
could be evaluated: dDy/dϕ = –Dy0sin(ϕ+ϕDyo). This
value for three couplers mentioned in Tables 1 and 2 is
3.6, 1.8, 11.7 KeV/s/rad, respectively. Assuming the
bunch having the length of 1 mm at the superstructure
entrance (phase length of 0.027 rad) one could estimate
transverse kick in bunch occupied region, dσDy = 0.097,
0.049 and 0.320. To make normalised mean-squared re-
spective emittance growth we could use the following
expression [5]: dεn,y/εn,y = dσDy/σpy. Impulse mean-
squared scattering for the bunch to be injected in
TESLA collider is σpy ≅ 1.5 KeV [5]. So, the relative
transverse emittance growth after the superstructure
passing by a bunch in maximal acceleration phase is 6,
3, 21% and of this reason the input coupler construction
#5 is less suitable.
REFERENCES
1. J.Sekutowicz et al. Superstructure for TESLA //
Phys.Rev.Special Topics, 1999, v. 2, p. 062001.
2. V.I.Shvedunov et al. PTMTRACE // VINITI. 1989,
N 183-В89.
3. M.Dohlus, S.G.Wipf. Numerical investigations of
waveguide input couplers for the TESLA super-
structure // Proceedings of EPAC, 2000, Vienna,
Austria, p. 2096-2099.
4. Z.Li, J.J.Bisognano and B.C.Yunn. // Proc. of
PAC’93, p. 179.
5. M.Zhang and Ch.Tang. TESLA 98-17.
140
|
| id | nasplib_isofts_kiev_ua-123456789-79258 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T16:51:23Z |
| publishDate | 2001 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Lalayan, M.V. Kostin, D.V. Sobenin, N.P. Shvedunov, V.I. Zavadtzev, A.A. Dohlus, M. 2015-03-30T08:03:16Z 2015-03-30T08:03:16Z 2001 Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers / M.V. Lalayan, D.V. Kostin, N.P. Sobenin, V.I. Shvedunov, A.A. Zavadtzev, M. Dohlus // Вопросы атомной науки и техники. — 2001. — № 3. — С. 138-140. — Бібліогр.: 5 назв. — англ. 1562-6016 PACS numbers: 29.27.Bd, 71.15.Pd https://nasplib.isofts.kiev.ua/handle/123456789/79258 Some features of accelerating section field computation presented by the development of power and HOM couplers for TESLA linear collider are considered. The devices mentioned produce electromagnetic field asymmetry in the beam area, thus causing transverse kick. For this kick and its influence on beam under acceleration parameters estimation the dynamics modelling calculations were done. 3D-simulation code MAFIA was used for field computation. These data were further used in beam dynamics calculations by means of TRMTrace code. Standing wave mode was simulated while considering HOM couplers, and travelling wave in case of power couplers. Transverse kicks and focussing forces are calculated for one HOM coupler design and two coaxial FM couplers. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers Расчет электромагнитных полей и динамики электронов в суперструктуре линейного коллайдера TESLA с учетом асимметрии полей в устройствах ввода мощности и вывода высших типов волн Article published earlier |
| spellingShingle | Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers Lalayan, M.V. Kostin, D.V. Sobenin, N.P. Shvedunov, V.I. Zavadtzev, A.A. Dohlus, M. |
| title | Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers |
| title_alt | Расчет электромагнитных полей и динамики электронов в суперструктуре линейного коллайдера TESLA с учетом асимметрии полей в устройствах ввода мощности и вывода высших типов волн |
| title_full | Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers |
| title_fullStr | Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers |
| title_full_unstemmed | Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers |
| title_short | Electromagnetic fields and beam dynamics simulation for the superstructure of TESLA linear collider considering field asymmetry caused by HOM and power couplers |
| title_sort | electromagnetic fields and beam dynamics simulation for the superstructure of tesla linear collider considering field asymmetry caused by hom and power couplers |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/79258 |
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