Breakdown positioning in CLIC prototype RF accelerating structures
Breakdown positioning in CLIC prototype RF accelerating structures CLIC workshop 2016 R. Rajamäki*, W. Farabolini, J. Giner Navarro, T. Argyropoulos, B. Woolley, W. Wuensch 19. 01. 2016 *Aalto university / CERN
Introduction • What? • Localize BDs in RF accelerating structures • Why? • Structure diagnostics • Breakdown studies • How? • RF power and phase • Directional coupler • Structure vibrations • Accelerometer • Electron emission • Faraday cup • Spectrometer • Photons • PMT/ camera • X-ray
Experimental setup • Current DUTs and BD diagnostics • TD 26 CC (Xbox-1) • RF power and phase • accelerometers • T 24 open (Xbox-2) • RF power and phase • Faraday cups • Electron spectrometer • accelerometers Directional RF power couplers Accelerometers TD 26 CC T 24 open
RF power signals RF only (no beam) Breakdown (no beam) Previous pulse Filling time • Two methods for time delay estimation 1. Falling edge of TRA and rising edge of REF 2. Correlation in tails of INC and REF • Time delay converted to cell location by knowing group velocity in structure
BD positioning using RF power and phase Correlation method Edge method Rising edge of reflection Falling edge of transmission Phase difference
Structure diagnostics (1/2) TD 26 CC y-axis projection BD cell map x-axis projection
Structure diagnostics (2/2) T 24 open y-axis projection BD cell map x-axis projection
Method comparison (1/3) Falling edge of transmission Correlation method Edge method Rising edge of reflection Why is there a discrepancy?
Method comparison (2/3) i. BD position (Correlation method) ii. BD position (edge method) iii. Difference of methods
Method comparison (3/3) 1. 3. 2. Observations: 1. Methods are generally in agreement 2. Non-symmetric spread 3. Peak of correlation method What about possible expanations?
Breakdown migration? ii. Mainly upstream migration Downstream migration iii. Upstream migration Possible migration scenario Courtesy of W. Farabolini
Long absorption period? a. b. c.
Spatio-temporal correlations i. iii. Vertical lines = artefacts of conditioning algorithm Breakdowns arriving shortly after each other occur close to each other.
Conclusions •
Extra
Converting time delay into cell # Measured time delays Group velocity profile of TD 26 CC
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