Download Diapositive 1

Status of Wakefield Monitors
developments for CLIC accelerating
structures
25 Sept. 2009
Franck Peauger, Riccardo Zennaro
Alexandre Samoshkin
F. Peauger
CLIC meeting / 25 Sept. 2009
1
Outline
•
•
•
•
Context and requirements
Time domain simulations of wakefields in AS
Design of WFM RF transition
Integration in the Two-Beam Test Stand
• 180° Hybrid coupler
• Test set-up in CTF3
F. Peauger
CLIC meeting / 25 Sept. 2009
2
Context
 Wakefield Monitors are Beam Position Monitors
integrated to the drive beam Accelerating Structures (AS)
 It allows beam-based alignment of AS to remove
wakefield effects and emittance growth
 Emittance growth is very well improved by aligning the
AS to an RMS accuracy of 5 µm to the beam
F. Peauger
CLIC meeting / 25 Sept. 2009
3
Context
Electron bunch
AS with WFM
Girder
Girder
Movers
D. Schulte
 Wakefield kicks from misaligned AS can be cancelled
by another AS
 One WFM per structure and mean offset of the 8 AS
computed
F. Peauger
CLIC meeting / 25 Sept. 2009
4
WFM dev. plan & requirements
 Step 1 (2009 - 2010): build one WFM prototype and integrate it into a CERN
structure and test on TBTS with CALIFES probe beam
 Step 2 (2010 - 2011): build 2 or 3 structures fully instrumented and test on
TBTS + CALIFES
Parameters
8
CLIC Operation
9
CTF3
(CALIFES+TBTS)
9
Charges per bunch
3.7 x 10
3.7 x 10
0.6 nC = 3.75 x 10
Number of bunches
1 - 312
312
1 – 32 - 226
Bunch length
45 – 70 µm
45 – 70 µm
500 µm / 1.66 ps
Train length
156 ns max
156 ns
150 ns max
Bunch Spacing
0.5 ns
0.5 ns
0.66 ns
Accuracy
5 µm
5 µm
To be measured
Resolution
5 µm
< 5 µm
To be measured
Stability
5 µm
To be measured
Range
± 2 mm
± 100 µm
± 2 mm
Bandwidth
35 MHz
35 MHz
TBD
Beam Aperture
~ 5.5 mm
~ 5.5 mm
~ 5.5 mm
Available length
-
-
-
No
No
No
142812
142812
2/3
Yes
Yes
N.A.
No
No
N.A.
Intercepting device
Quantity
Used in RT Feedback
F. Peauger
CLIC
Commissioning
Machine protection Item
CLIC meeting / 25 Sept. 2009
5
WFM additionnal requirements
 Since there is no place available in the linac, the damping waveguides of the
middle cell are used to measure the beam position inside the structure
 we cannot define the geometry, frequency mode, Q factor … as we do for BPM
 the WFM works necessarily with strong damped modes (Q ~ 10) !!
 The WFM design consists in studying the HOM modes and their sensitivity to a
beam offset, choosing an operating mode, designing an RF transition to couple this
mode and processing the signal
 We must attenuate the 12 GHz high power accelerating signal to -150 dB !!
 The RF transition must not reflect any signal to the cell (typically -20 dB from 10
to 35 GHz)
 The middle cell equipped with the WFM must keep its strong damping
functionality (SiC loads)
 The WFM must be cheap, easy to integrate mechanically in the Two Beam Module
and avoid if possible any major additional machining of the cell
F. Peauger
CLIC meeting / 25 Sept. 2009
6
Wakefield simulation with beam offset
GDFIDL Simulations:
• Five cells meshed (no symmetry) with a
mesh step of 0.1 mm
• volume limited to +/- 15 mm in the X and Y
directions
• PML set at the waveguide extremities
(Xmin, Xmax, Ymin, Ymax, Zmin, Zmax)
• Beam: 1 bunch of 0.6 nC, σz=3 mm with
offset
• Simulation stopped at 6.66 ns.
• Rectangular ports at the end of the damped
waveguides of the middle cell. The two first
modes are selected in GdfidL :
1st port mode:
Fc = 13.3 GHz
E field
F. Peauger
TM
like mode for the beam
2st port mode:
Fc = 21.4 GHz
E field
ydamphaut
xdamphaut
xdampbas
ydampbas
• Total of 90e6 meshs
• Time computation of 9 to 13
hours with 36 hosts on LXCLIC
cluster
/ 25 Sept. 2009
TE like modeCLIC
for meeting
the beam
7
TM like modes with beam offset of 1 mm
Port signal
amplitude
(voltage)
Y+
X- & X+
Beam dx=1mm offset
X+
X-
Y+ & Y-
Time (s)
YPort signal
amplitude
(voltage)
Port signal
amplitude
(voltage)
11.94 GHz
18 GHz = First
dipole-band mode
F. Peauger
CLIC meeting / 25 Sept. 2009
F (Hz)
8
Time (s)
monopole / dipole mode configuration
Monopole mode
Dipole mode
E Field
E Field
Opposite ports signals
are in phase
Opposite ports signal
have opposite phase
When we substract the opposite port signals, the monopole mode is
cancelled and the dipole mode amplitude is increased
F. Peauger
CLIC meeting / 25 Sept. 2009
9
TM modes after 180° perfect recombination
Y+
X-
Recombined port
signal amplitude
(voltage)
Beam
dx=1mm
offset
DX=X+-X-
X+
DY=Y+-YY-
Time (s)
Recombined port
signal amplitude
14.81 GHz
Recombined port
signal amplitude
(voltage)
18.19 GHz
11.95 GHz
F (GHz)
F. Peauger
CLIC meeting / 25 Sept. 2009
Time (s)
10
Variation of beam offset amplitude
Recombined port signal
amplitude DX (voltage)
dx = 1 mm
dx = 0.8 mm
dx = 0.6 mm
dx = -1 mm
Time (s)
F. Peauger
CLIC meeting / 25 Sept. 2009
11
Linearity
Max. amplitude of the
delta signal (voltage)
40
30
20
y = 33.092x + 0.1028
10
0
-1.5
-1
-0.5
0
0.5
1
1.5
Offset dx
(mm)
-10
-20
-30
-40
The 18.2 GHz mode works quite well as a cavity BPM mode !
But we need to design an RF transition that couple this mode, attenuate 12
GHz mode, avoid reflection, allows strond damping, etc…
F. Peauger
CLIC meeting / 25 Sept. 2009
12
RF transition design
Long waveguide with
cut-off above 12 GHz
+ 90° E-bend
Coax coupler designed
to have -10 dB
transmission
55 mm
Load
location
15 mm
F. Peauger
CLIC meeting / 25 Sept. 2009
13
Geometry of WFM RF transition
Damped
waveguide
Antenna
Coaxial waveguide
(K type)
1
2
p
R1
R2
L2
Load
d
a
Cell
L1
Cell axis
F. Peauger
CLIC meeting / 25 Sept. 2009
b
P
1 mm
1
2.92 mm
2
1.27 mm
a
11.25 mm
b
7.011 mm
d
5.625 mm
R1
0.2 mm
R2
>15 mm
L1
70 mm
L2
18 mm
14
RF transition transfer function T(f)
T (f) (S parameters)
-11 dB
3
2
S11
S13
-145 dB
1
S12
12 GHz
F. Peauger
18 GHz
CLIC meeting / 25 Sept. 2009
15
TM modes after RF Transition and 180° perfect recombination
with dx=1mm beam offset
Recombined port
signal amplitude
(voltage)
Y+
U0
X-
U1
DX=X+-XX+
DY=Y+-Y-
YTime (s)
Recombined port
signal amplitude
U1  f   T ( f )  U 0 ( f )
18.14 GHz
13.88 GHz
Given by
HFSS
~ 1 – 3 GHz band pass
CLIC meeting / 25 Sept. 2009
filter around 18.1 GHz16
F (GHz)
F. Peauger
Given by
Gdfidl
Resolution
The power and voltage are linked by:
P U2
Dipole mode 18 GHz:
 Simulation results (at the coax pick-up, after the RF transition)
dx=1mm, q=0.6nC
→
U1 ≈ 1 V
 Extrapolation for the commissioning case (voltage varies linearly with offset and charge)
dx=5µm, q=0.06nC, (s=70µm)
→
U1 = 500 µV
→
U1 = 5 mV
 Extrapolation for the nominal case
dx=5µm, q=0.6nC, (s=60µm)
Accelerating mode 12 GHz:
•For 60 MW input power, there is 3 nW at the coax pick-up, after the RF transition
→ equivalent to UHP = 56 µV
+ Thermal noise and noise from signal processing to be evaluated
F. Peauger
CLIC meeting / 25 Sept. 2009
17
Integration in the Two Beam Test Stand
- Design a support and ensure good electrical contact between the WFM
and the structure
- Must make a hole in U support for the “Y- waveguide”
F. Peauger
CLIC meeting / 25 Sept. 2009
18
Integration in the Two Beam Test Stand
Or
We would like to reserve one available flange (150 mm diameter) for a
special CF flange with four feedthroughs
F. Peauger
CLIC meeting / 25 Sept. 2009
19
180° Hybrid coupler
Hybrid couplers are the special case of a four-port directional coupler that is designed
for a 3dB (equal) power split and a 180 degree phase shift between two output ports
Ring Hybrid Junction
Tapered Coupled Line Hybrid
Magic Tees
When using as a combiner, input signals are applied at port 2 and 3, the sum of the
inputs will be formed at port 1 while the difference at port 4.
In theory: S12 = S13 = -3dB and S11 = S14 = -40 dB
F. Peauger
CLIC meeting / 25 Sept. 2009
20
180° Hybrid coupler
• Two tapered-line directional couplers cascaded
• Excellent phase and amplitude matching
• Realized with a three-layer stripline configuration
• Etched on opposite sides of a thin coupler circuit board,
sandwiched between a pair of equal thickness Duroid boards
F. Peauger
CLIC meeting / 25 Sept. 2009
21
Layout of WFM prototype test with Hybrid
: WFM – transition, qty 4, output connector = K female, UHV compatible
: semi rigide cable, Type?, qty 4, length ≈ 400 mm , input connector = K male, output connector = K female, UHV compatible
: CF flange feedthrough, qty 1, 4 connectors, input connector = K male (vacuum side), output connector = K female, UHV compatible
: Flexible cable, qty 4, length ≈ 30 m , input connector = K male, output connector = K female,
: 180° Hybrid coupler, input connector = K male, output connector = K female
TBTS rack
Scope
Diode
detector
Bandpass
filter
≈ 30 m
Klystron gallery
Front
Back
Accelerating structure
TBTS
Accelerating
structure tank
F. Peauger
CLIC meeting / 25 Sept. 2009
CLEX – beam tunnel
22
Conclusion (1/2)
• The WFM Context, specifications and development program well defined
 with the objective to demonstrate the WFM concept before end of 2010
• We have developed a methodology to run Gdfidl from CEA Saclay on the CERN Cluster,
and couple the results to HFSS simulations
• The TM like mode at 18.2 GHz has been identified and well studied in time domain. It
will be used as classical cavity BPM dipole mode with 180° recombination
• We proposed a simple design of the WFM RF transition which should meet the long list
of requirements
• We would like to investigate TE like modes around 23 GHz. Additional simulations are
required
• But we also would like to freeze the design of the WFM prototype soon in order to start
the mechanical study and procurement of components
• We should not forget to work on the electronic for signal processing
F. Peauger
CLIC meeting / 25 Sept. 2009
23
Conclusion (2/2)
• Important topic for CLIC
• Very interesting R&D program
• Good continuation after CALIFES for CEA Saclay
Thank you for your attention
F. Peauger
CLIC meeting / 25 Sept. 2009
24
Extra - slides
F. Peauger
CLIC meeting / 25 Sept. 2009
25
Wakefield simulation with one symetry
GDFIDL Simulations:
•Five cells meshed with one symetry (half of
the structure is meshed)
• Perfect magnetic boundary condition on XZ
plane
• mesh step of 0.05 mm
• PML set at the waveguide extremities
(Xmin, Xmax, Ymax, Zmin, Zmax)
• Beam: 1 bunch of 0.6 nC, σz=1 mm, offset
Δx = 1 mm
• Simulation stopped at 6.66 ns.
• Rectangular ports at the end of the damped
waveguides of the middle cell. The first
modes is selected in GdfidL so that
longitudinal (TM) modes can be recorded
F. Peauger
Total of 156.8e6 meshs
14 hours with 36 hosts machines lxclic
CLIC meeting / 25 Sept. 2009
26
TM modes responses
Y+
Beam 1mm offset
X-
X+
11.83 GHz
15.15 GHz
F. Peauger
CLIC meeting / 25 Sept. 2009
27
TM modes after 180° perfect recombination
Y+
X-
X+
DX=X+-X-
11.98 GHz
15.19 GHz
18.47 GHz
F. Peauger
CLIC meeting / 25 Sept. 2009
28
RF cable under vacuum
F. Peauger
CLIC meeting / 25 Sept. 2009
29
CF Flange feedthroughs
CF Flange: Dext152mm x2
Flange Size=2.75"CF
Number of feedthrough = 4
Grounded 50-Ohm
Ref. = IFDCG042013
F. Peauger
CLIC meeting / 25 Sept. 2009
Dimensions (inches)
A=0.63
B= 0.92
C=2.75 (69.85mm)
D= 1.38
E=0.87
30
Two Beam Module integration
Vac. Manifold: 30 x 30 mmm²
F. Peauger
CLIC meeting / 25 Sept. 2009
31