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ILC Wakefest Workshop, Dec 11-13, 2007
WakeFest Summary 2
Subject Areas
• Wakefield with cavity imperfection
• Beamline HOM absorber
• Large system simulation
• Multipacting simulation
A total of 9 talks
Modeling Imperfection Effects on Dipole
Modes in TESLA Cavity
Liling Xiao
Advanced Computations Department, SLAC
1. TESLA Cavity Dipole Mode Measurement Data
Dipole mode frequencies shift and Qext scatter
TTF module 5: 1st/2nd dipole band
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1600 1650 1700 1750 1800 1850 1900
F (MHz)
Qe
xt
1.E+03
1.E+04
1.E+05
1700 1701 1702 1703 1704 1705 1706
1st band 6th pair
1.E+04
1.E+05
1.E+06
1877 1878 1879 1880 1881 1882
2nd band 6th pair
• Omega3Po Measured data in colour
x
z
2. TESLA Cavity Imperfection Model
Red: ideal cavity, Blue: deformed cavity
Distorted mesh for the cavity imperfection model
a) Cell length error
b) Cell radius error
c) Cell surface deformed
d) Elliptical cell shape
1st ILC Workshop at KEK
A. Matheisen
TDR cavity with elliptical cell shape
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.60E+09 1.65E+09 1.70E+09 1.75E+09 1.80E+09 1.85E+09 1.90E+09
F (Hz)
Qex
t
2nd band: 6th pair
1.E+04
1.E+05
1704.0 1705.0 1706.0 1707.0 1708.0
F (MHz)
Qex
t
defor cell1 along xdefor cell4 along xdefor cell1 and 4 along xidea cavity
• ideal cavity
O elliptically deformed cell shape cavity
Example 2: Cell shape elliptical deformed (dr=0.25mm)
- cause mode polarization change and mode splitting
Elli. deformed cavity
1st band 6th pair 2nd band 6th pair
ideal cavity
1.E+03
1.E+04
1.E+05
1787.0 1787.5 1788.0 1788.5 1789.0 1789.5 1790.0
defor cell1 along x
defor cell4 along x
defor cell1 and 4 along x
idea cavity
x
y
Beamline HOM Absorber
Talks:
• Beamline HOM Absorber – Oleg Nezhevenko, FNAL
• Beamline HOM absorber simulation using T3P – Liling Xiao, SLAC
T.Higo, et al, IId ILC Workshop
8
O.N.
Absorption efficiency estimations.
Simple model of HOM absorber: the ring has the length of 50mm, internal diameter of 90 mm, and the thickness of 10mm (DESY style).
9
O.N.
S. Nagaitsev 10
•Overall Plan: Test ILC RF units•3 CM, Klystron, Modulator, LLRF•Move A0 Injector to provide ILC like beam
•New bldg: diagnostic, new cryo plant•ILC Twin tunnel design to allow 2nd RF unit and to study tunnel layout and maintenance issues
Bunch Compressor
ILC RF unitDiagnosticsGun
CC I,II
Laser
3rd har
Test Area
~ 22 M72 M
Existing Building
New Building
New ILC like tunnel
2nd ILC RF unit
Test Areas
new 300 W cryo plant
RF Equipment
RF Unit Test FacilityRF Unit Test Facility
10
O.N.
• Simulation Results
1) 3D single cavity with beamline absorber (εr=15, σeff=0.6s/m)
A Gaussian bunch with σz=10mm, Q=3.2nc on axis.
3.5million mesh elements, 2nd basis function run on Franklin at Nersc.
512 processors 24000 time steps within 12 hours
Copper coated wall
TM0n modes
L.X.
One bunch Q=3.2nc, bunch length=10mm
Loss factor (V/pc)=3.566V/pc
Lossy dielectric conductivity σeff=0.6(s/m)
Dielectric constant εr=15, Within 45ns
Total Energy Generated by Beam (J) 3.65e-5
Energy stored in cavity (J) 3.25e-5 (FM mode energy=2.06e-5J)
Energy leaked out HOM coupler ports (J) 4.05e-7
Energy propagated into beam pipe (J) 2.11e-6
Energy dissipated in the absorber (J) 2.4e-6
Energy loss on the copper absorber beampipe wall (J) 6.6e-10 (cold copper conductivity=350ms/m )
Energy stored in cavity
3.0E-05
3.5E-05
4.0E-05
4.5E-05
5.0E-05
5.5E-05
6.0E-05
0 10 20 30 40 50
t (ns)
Ene
rgy
(J)
@6.6ns, exciting bunch just left the structure
Absorption
Left beampipe
Right beampipe
Up stream HOM
Down stream HOM
Monopole Single Passage Losses
K-loss=6.86v/pc for 10mm, Total Energy=7.02e-5 (J)absorber (εr=15, σeff=0.6s/m)
Energy absorption/Total HOM energy
Energy leaked into Left beampipe/Total HOM energy
Energy leaked into right beampipe /Total HOM energy
Large System Simulation
Talks:
• Multi-cavity trapped mode simulation – Cho Ng, SLAC
• Globalised scattering matrix simulation in ILC cavities and modules – Ian Shinton, Manchester University
• Large scale 3D wakefield simulations with PBCI – Sascha Schnepp, T.U. Darmstadt
3rd Dipole-Band Trapped Modes in Cryomodule
C.N.
1.0E+05
1.0E+06
1.0E+07
1.0E+08
1.0E+09
1.0E+10
1.0E+11
1.0E+12
1.0E+13
1.0E+14
2.5770 2.5772 2.5774 2.5776 2.5778 2.5780 2.5782 2.5784F (GHz)
Kic
k F
act
or
(V/C
/m/m
od
ule
)
K_X
K_Y
Kx[y]=Ky[x]_amp
Kx[0]_amp
Ky[0]_amp
• Modes above cutoff frequency are coupled throughout 8 cavities• Modes are generally x/y-tilted & twisted due to 3D end-group geometry• Both tilted and twisted modes cause x-y coupling
TDR 8-Cavity Module
1.0E+03
1.0E+04
1.0E+05
1.0E+06
1.0E+07
2.577 2.5775 2.578 2.5785F (GHz)
Qex
t
Cryomodule 3rd Dipole-Band Mode - Qext and Kick
C.N.
Trapped Mode using Omega3P
Trapped mode
• TM-like mode localized in beampipe between 2 cavities
• Frequency = 2.948 GHz, slightly higher than TM cutoff at 2.943 GHz
• R/Q = 0.392 ; Q = 6320• Mode power = 0.6 mW (averaged)
Electric field
TM mode
C.N.
Introduction
1. Wake field simulations in arbitrary 3D-geometry
3D-codes3D-codes
2. Accurate numerical solutions for high frequency fields
(quasi-) dispersionless codes(quasi-) dispersionless codes
3. Utilizing large computational resources for ultra-short bunches
parallelized codesparallelized codes
4. Specialized algorithms for long accelerator structures
moving window codesmoving window codes
There is an actual demand for:
S.S.
ILC-ESA collimatorILC-ESA collimator #8
s /
Wz
/ [V
/ p
C]
-4 -3 -2 -1 0 1 2 3 4-100
-80
-60
-40
-20
0
20
40
60 / z = 2.5 / z = 5 / z = 10 / z = 15
Convergence vs. grid step
bunch size 300μm
no. of grid points ~450M
no. of processors 24
simulation time 85hrs
Moving window:3 mm length
S.S.
TESLA / HOM couplerTESLA 9-cell cavity
-15 -10 -5 0 5 10 15 Ez / [kV /m]
bunch length 1mm
bunch charge 1nC
cavity length 1.5m
no. of grid points ~760M
no. of processor cores
408
simulation time ~40hrs
bunch
-5 -4 -3 -2 -1 0 1 2 3 4 5-15
-10
-5
0
5 PBCI ECHO2D
Wz /
(V
/ p
C)
s /
S.S.
Multipacting Simulation
Talks:
• Multipacting simulation for the SNS cavity using Analyst – I. Gonin, FNAL
• Multipacting simulation using parallel code Track3P – Lixin Ge, SLAC
• TTF-III coupler processing and multipacting simulation using MAGIC – Faya Wang, SLAC
Enhanced Counter Function (20 impacts)
1,E+02
1,E+03
1,E+04
1,E+05
0 5 10 15 20 25 30 35
Eacc(MV/m)
1069
MP IN SNS CAVITY I.G & L.G.
Analyst Track3P
Models simulated using Analyst and Track3P are different!
Egap ~ 3.8 V/m;
MP in ILC HOM coupler: notch gap
Enhanced Counter Function (20 impacts)
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
0 0.5 1 1.5 2 2.5 3
Eacc (MV/m)
FE mesh, ~1 million second order elements
Emax ~ 48.1 V/m
= Egap / Eacc ~ 0.16
Enhanced Counter Function (20 impacts)
0
500
1000
1500
2000
2500
0 50 100 150 200 250 300 350
kV/m1.73mm
Enhanced Counter Function for gap 1.73mm and 1.3GHz
EMP_analytical ~ 200 kV/m Eacc= EMP / ~ 1.25 MV/m
Analyst results
Emax ~ 3.8 V/m
HOM coupler
1-D
3-D
Z94_02_Aug24_06
1.0E+10
1.2E+10
1.4E+10
1.6E+10
1.8E+10
2.0E+10
0.0E+00 5.0E+06 1.0E+07 1.5E+07 2.0E+07 2.5E+07 3.0E+07
Test: Q vs. Eacc
MP in the gap
Good correlation between 1D, 3D&measurements
I.G.
6.25mm
20mm
Delta as a function of RF input power and Multipacting order
Cold Coax in TTF-III Coupler
300mm
L.G.
Ion Pump
Ion Pump
e-pickup
PM
PM
F.W.
0 200 400 600 800 1000 1200 14000
50
100
150
Cu
rre
nt o
f Io
n P
um
e: u
A
Forward power: kW
0 200 400 600 800 1000 1200 1400
-100
-50
0
Ele
ctro
n s
ign
al:m
V
electron signal amplitude
vacuum level
600mm long straight SS coax section test results
600mm long straight Copper plated SS coax section test results
Strong MP around 300kW!
F.W.TTF-III coupler processing
0 200 400 600 800 1000 1200-100
-80
-60
-40
-20
0
Forward RF power to coax: kW
ele
ctro
n s
ign
al a
mp
litud
e fr
om
e-p
icku
p: m
V
20us50us100us200us400us
0 200 400 600 800 1000 1200 1400
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Power forward into straight coax section: kW
Ele
ctro
n s
ign
al:
-V
RF processing result of ramping RF from 20us pulse to 400us
20us RF pulse
50us
100us200us
400us
Stainless Steel Coax Tube Copper plated S/S Coax Tube
100 200 300 400 500 6000
1
2
3
4
5
6
7
RF power: kW
Sp
ace
Ch
arg
e a
t Sa
tura
tion
: arb
.u.
sey
max=1.5
seymax
=1.3
Magic Simulation
200 400 600 800 10000
0.2
0.4
0.6
0.8
1
RF Input Power (kW)
Re
lativ
e A
mp
litu
de
of E
lect
ron
Sig
na
l: a
rb.u
.
Track3P simulation (indicated by dashed lines) is independent of SEY.
F.W.