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Breakdown positioning in CLIC prototype RF accelerating structures Breakdown positioning in CLIC prototype RF accelerating structures

Breakdown positioning in CLIC prototype RF accelerating structures - PowerPoint Presentation

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Breakdown positioning in CLIC prototype RF accelerating structures - PPT Presentation

CLIC workshop 2016 R Rajamäki W Farabolini J Giner Navarro T Argyropoulos B Woolley W Wuensch 19012016 Aalto university CERN Introduction What Localize BDs in RF accelerating structures ID: 778161

edge method breakdown power method edge power breakdown correlation phase time migration structure td26cc methods cell projection axis reflection

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Slide1

Breakdown positioning in CLIC prototype RF accelerating structures

CLIC workshop 2016R. Rajamäki*, W. Farabolini, J. Giner Navarro, T. Argyropoulos, B. Woolley, W. Wuensch19.01.2016

*Aalto university / CERN

Slide2

Introduction

What?Localize BDs in RF accelerating structuresWhy?Structure diagnosticsBreakdown studiesHow?RF power and phaseDirectional coupler

Structure vibrationsAccelerometerElectron emissionFaraday cupSpectrometerPhotons

PMT/ cameraX-ray

Slide3

Experimental setup

Accelerometers

Directional RF power couplers

TD26CC

T24 open

Current DUTs and BD diagnostics

TD26CC

(Xbox-1)

RF power and phase

accelerometers

T24

open

(

Xbox-2

)

RF power and phase

Faraday cups

Electron spectrometer

accelerometers

Slide4

RF power

signals

RF only (no beam)

Breakdown (no beam)

Filling time

Previous

pulse

Two methods for time delay estimation

Falling edge of

TRA

and rising edge of

REF

Correlation in tails of

INC

and

REF

Time delay converted to cell location by knowing group velocity in structure

Slide5

BD positioning

using RF power and phase

Edge method

Correlation method

Falling edge of

transmission

Rising edge of

reflection

Phase difference

Slide6

Structure diagnostics (1/2)

y-axis projection

x-axis projection

BD

cell

map

TD26CC

Slide7

Structure diagnostics (2/2)

y-axis projection

x-axis projection

T24 open

BD

cell

map

Slide8

Method comparison (1/3)

Edge method

Correlation method

Falling edge of

transmission

Rising edge of

reflection

Why is there a discrepancy?

Slide9

i

. BD position (Correlation method)

Method

comparison (

2/3

)

iii.

Difference of methods

ii. BD position (edge method)

Slide10

Method comparison (3/3)

 

 

1.

2.

3.

Observations:

Methods are generally in agreement

Non-symmetric spread

Peak of correlation method

What about possible expanations?

Slide11

Breakdown migration?

Upstream migration

Downstream migration

i.

ii.

iii.

Courtesy of W. Farabolini

Possible migration scenario

Mainly

upstream

migration

Slide12

Long absorption period?

Alternative hypothesis to migration

:

BD absorbs RF power for

before it starts reflecting (missing energy)

Non-stationary reflection coefficient of BD modulates phase

 

a.

b.

c.

 

 

Slide13

Spatio-temporal correlations

Vertical lines = artefacts of conditioning algorithm

Breakdowns arriving shortly after

each

other

occur

close to each other.

i

.

ii.

iii.

 

Slide14

Conclusions

Breakdown positioning using RF power and phaseEdge methodCorrelation methodObserved disagreement between edge and correlation methods + modulations in RF phase across different structuresPossible explanations:

Breakdown migrationPower absorbed by breakdown for

???

Breakdown process shows correlation between position and inter-arrival time

Memory effect of structure

 

Slide15

Extra

Slide16

Converting time delay into cell #

Measured time delays

Group velocity profile of TD26CC