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
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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
Slide2Introduction
What?Localize BDs in RF accelerating structuresWhy?Structure diagnosticsBreakdown studiesHow?RF power and phaseDirectional coupler
Structure vibrationsAccelerometerElectron emissionFaraday cupSpectrometerPhotons
PMT/ cameraX-ray
Slide3Experimental 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
Slide4RF 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
Slide5BD positioning
using RF power and phase
Edge method
Correlation method
Falling edge of
transmission
Rising edge of
reflection
Phase difference
Slide6Structure diagnostics (1/2)
y-axis projection
x-axis projection
BD
cell
map
TD26CC
Slide7Structure diagnostics (2/2)
y-axis projection
x-axis projection
T24 open
BD
cell
map
Slide8Method comparison (1/3)
Edge method
Correlation method
Falling edge of
transmission
Rising edge of
reflection
Why is there a discrepancy?
Slide9i
. BD position (Correlation method)
Method
comparison (
2/3
)
iii.
Difference of methods
ii. BD position (edge method)
Slide10Method comparison (3/3)
1.
2.
3.
Observations:
Methods are generally in agreement
Non-symmetric spread
Peak of correlation method
What about possible expanations?
Slide11Breakdown migration?
Upstream migration
Downstream migration
i.
ii.
iii.
Courtesy of W. Farabolini
Possible migration scenario
Mainly
upstream
migration
Slide12Long 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.
Spatio-temporal correlations
Vertical lines = artefacts of conditioning algorithm
Breakdowns arriving shortly after
each
other
occur
close to each other.
i
.
ii.
iii.
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
Extra
Slide16Converting time delay into cell #
Measured time delays
Group velocity profile of TD26CC