the clic pets on/off operation. principles and design
DESCRIPTION
THE CLIC PETS ON/OFF OPERATION. PRINCIPLEs and design. 4 th X-band Structure Collaboration Meeting – 4 th May 2010 Alessandro Cappelletti for CLIC collaboration. INTRODUCTION. International Linear Collider. Technical Review Committee Second Report (2003 ) - PowerPoint PPT PresentationTRANSCRIPT
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THE CLIC PETS ON/OFF OPERATION.
PRINCIPLES AND DESIGN4th X-band Structure Collaboration Meeting
– 4th May 2010
Alessandro Cappelletti for CLIC collaboration
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INTRODUCTION
Reliability• In the present CLIC design, an entire drive beam section must be turned off on any fault (in
particular on any cavity fault). CLIC needs to develop a mechanism to turn off only a few structures in the event of a fault
International Linear Collider. Technical Review CommitteeSecond Report (2003)
CLIC feasibility issues, Ranking 1.
During the machine operation, the accelerating structure and/or PETS will suffer from a number of RF breakdowns.
Currently we have little information about the actual behavior of the structures at a very low (by design: <3x10-7 /pulse/meter) breakdown trip rate, thus it might be necessary to switch off the single structure/PETS and re-process it.
In order to maintain the operation efficiency, we want to perform the off switching very fast between the pulses (20 msec).
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BASELINE ON/OFF CONCEPTWITH EXTERNAL COMMUTATION AND INTERNAL RECIRCULATION
With the proposed method the complete suppression of the RF delivery to the accelerating structure can be achieved.
The RF power produced in the PETS itself will be significantly reduced for the cases #2 and #3.
The case #3 was chosen as a base line due to the best efficiency and lowest cost.
The method requires the development of a special RF high power switch.
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PRINCIPLE ILLUSTRATION
r(t)
t
r(t)
Single-bunch response
ON Every t0=Db/c, a new signal reaches the output section and adds up to the previous ones.
r(t)
t
Multi-bunch response
…
…
RTT
r(t)
t
Single-bunch response
OFF
The s.b. response is made of signal reflections. The m.b. response, after an initial power build-up, saturates to a fractionof the “ON” power.
r(t)
t
Multi-bunch response
We consider the signals envelopes at the reflector section, in a dispersion-free approximation.
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INTERNAL RECIRCULATION
PETS OFF
PETS ON
Tunable reflector
0 2 108
4 108
6 108
8 108
1 107
1.2 107
1.4 107
1.6 107
1.8 107
0
0.5
1
time. sec
PE
TS
pow
er
0.25
Ramped pulse example for the beam loading compensation.
0 2 108
4 108
6 108
8 108
1 107
1.2 107
1.4 107
1.6 107
1.8 107
0
0.5
1
time, sec
PE
TS
po
wer ON
OFF
0.25
P
ETS
p
ow
er
P
ETS
p
ow
er
Time [s]
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REFLECTOR DESIGNS
Bulky, expensive; high field concentration; testing needed, success not guaranteed.
#2#1
TE10 TE20 TH01
Original idea by S. Kazakov (KEK)
10.85mm stroke
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LIMITS OF DESIGN #2
0 20 40 60 80 1000
0.5
1
1.5
Power build-up RF phaseCoupleroutput
Time [ns] Time [ns]
SINGLE BUNCH RESPONSE
Log(Time [ns])
High surfacefield
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LIMITS OF DESIGN #2
0 20 40 60 80 1000
0.5
1
1.5
Power build-up RF phaseReflector ONoutput
Time [ns] Time [ns]
SINGLE BUNCH RESPONSE
Log(Time [ns])
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REFLECTOR: DESIGN #3
extremely broad band (~4 GHz) low surface electric field (< 45
MV/m) reduced actuators stroke (~l/4) contact-free
Radiation
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REFLECTOR: DESIGN #3
2 4 6 8 10 1250
40
30
20
10
0
Reflected
Transmitted
Stroke 7.7 mm
RF p
ow
er
[dB
]
Gap width [mm]2 4 6 8 10 12
200
100
0
100
200
90
0
RF p
hase
[deg]
Gap width [mm]0 3 6 9 12 15
0
50
100
0.1
0.15
0.2
0.25
Gap width [mm]
Max E
[M
V/m
]
Max H
[M
A/m
]
E
H
130 MW
0 20 40 60 80 1000
0.5
1
1.5
Time [ns] Time [ns]Log(Time [ns])
Power build-up RF phaseReflector ONoutput
SINGLE BUNCH RESPONSE
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SIMULATED SIGNALS
PETS output (steady state)
Structure input
ON
OFF
Stroke 7.7 mm
0.26
Piston position [mm]
OFF, full-6dB
Transmission=0 dB (ON)
-1 dB
-3 dB Str
oke
7.7
m
m
Time [ns]
Pow
er
(to
str
uctu
re)
Norm
alize
d
pow
er
Pow
er
(fro
m
PETS
)
Time [ns]
Transmission=0 dB (ON)
-1 dB
-3 dB-6dB
OFF, full
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TBTS:
- PETS current configuration (recirculation)
1.0 m long PETS
- PETS RF network modification (internal recirculation – ON/OFF option)
1.0 m long PETS
variable reflector(analog to attenuator)CLIC design
variable short circ.(analog to phase shifter)CLIC design
End 2009/10
PETSvariable reflectorCLIC design
CLIC referenceIntegratedShort circuit
- The ON/FF feasibility demonstration will require full (22.8 A) current.
3-10A
23 A
Variable reflector
THE ON/OFF FEASIBILITY DEMONSTRATION
BUILDING IN PROGRESS!
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The PETS ON/OFF mechanism design was firstly based on HFSS simulations.
However, that approach alone is unfit to deal with the flexibility of the entire system and the computational load it would generate.
A mathematical model of the whole device has been developed. It allows: to get a numerical/analytical representation of any component we need to
include into the RF network;
to perform an in-depth signal analysis to investigate the transmission and reflection issues and the resulting power production;
to tune up some parts of the system without resorting to time-consuming simulations;
to quickly adapt the model to any configuration we may want to test.
PULSE PROPAGATION MODEL. INTRODUCTION
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Each device is characterized by its transfer function. A cascade of two-port devices is still equivalent to a
two-port device (e.g.: inserting waveguide chunks). The signals can be analyzed at chosen sections (PETS,
reflector).
THE RF COMPONENTS
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1
2
)(tx
x(t) is constructed analytically
An input/output equation is needed to model the system
)(ty
THEORETICAL APPROACH
1 2
3
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1 2
3
1
2
)(tx
s
N
k
kpspncc SSSDSSfXfY ,31
0,11,11,12,21 )()1)(()(
)(ty
PETS outputSystem
output c: coupler pnc: PETS with no
choke s: system p: PETS
MATHEMATICAL MODEL
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SOFTWARE IMPLEMENTATION
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Note: for each reflector configuration, a waveguide of optimized length should be introduced
0 20 40 60 80 1000
0.5
1
0 20 40 60 80 100
0.5
1
It is possible to test and verify the phase modulation schemes used in the bunch recombination concept.
Power (to structure)
Power (from PETS)
POWER BUILD-UP
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THE SIMULATED SIGNALS
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The whole PETS ON/OFF study is overall at a well advanced stage.
The proposed model provides a relatively easy-to-implement algorithm for simulating the pulse propagation in the ON/OFF system.
Alternative configurations can easily be tested and the results can be discussed with the beam dynamics section.
An improved design of the coupler will result into signals affected by lower reflection levels.
… questions?
CONCLUSIONS