THE CLIC PETS ON/OFF OPERATION.

PRINCIPLES AND DESIGN4th X-band Structure Collaboration Meeting

– 4th May 2010

Alessandro Cappelletti for CLIC collaboration

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).

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.

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.

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]

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

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

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])

REFLECTOR: DESIGN #3

extremely broad band (~4 GHz) low surface electric field (< 45

MV/m) reduced actuators stroke (~l/4) contact-free

Radiation

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

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

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!

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

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

1

2

)(tx

x(t) is constructed analytically

An input/output equation is needed to model the system

)(ty

THEORETICAL APPROACH

1 2

3

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

SOFTWARE IMPLEMENTATION

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

THE SIMULATED SIGNALS

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