Observations from High gradient test of CLIC Prototype Structures

Results from Nextef

Observations in high gradient tests of CLIC Prototype Structuresand associated study activitiesCLIC2013, CERN29 January, 2013T. Higo (KEK)ContentsSummary on CLIC prototypesThe most recent result on TD24R05Comparison Ramping speedsBreakdown ratesHot spotsFurther studies in Nextef2013/1/29CLIC2013, Nextef, KEK, Higo2CLIC2013, Nextef, KEK, Higo

KT-1X-bandKT-2C-bandNextefX-bandABKT1-BNextef Control32013/1/29Nextef for high gradient R&D4

ABControl RF source for ANextef 2013/1/29CLIC2013, Nextef, KEK, Higo

Shield A

Shield BHigh gradient tests of CLIC prototype structuresCollaboration from 2007 --- T18#2 2008 --- 2009 TD18#2 2009 --- 2010 T24#3 2010 --- 2011 IWLC2011 Granada TD24#42011 --- 2012 LWLC2012 ArlingtonTD24R05#22012 --- 2013 CLIC2012 GenevaTD24R05#42013 ---52013/1/29CLIC2013, Nextef, KEK, HigoHigh-gradient test at NextefCLIC2013, Nextef, KEK, Higo62013/1/29Basic studies at shield-BTD24R05 #2TD24_Disk_#4High power components testKT1 to shield-BTD24R05 #4?TD24R05(KEK)?Replace klystronT18_Disk_#2TD18_Quad_#5TD18_Disk_#2Narrow waveguide testKT1NextefKX03 (60cm HDDS)T24_Disk_#34 7 10 1 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10 1 4 7 10 12008 2009 2010 2011 2012 2013Shield-BCLIC prototype testsGLC123451.5Reduce Hp/Ea and DT by reducing corner radius in the cell7

TD24 TD24R05

Alexej Grudiev2012/10/25LCWS2012 (Higo)What to be studied in mind with the most recent test with TD24R052013/1/29CLIC2013, Nextef, KEK, Higo8Prove the CLIC high gradient feasibility Undamped well done in T24

Prove with damped structure Ramping speed BDR at 100 MV/m Evolution of BDR vs time BDR vs Eacc BDR vs width Robustness against long-term operationPreparation always follow our nominal structure fabrication flow2013/1/29CLIC2013, Nextef, KEK, Higo9CLIC test structures; fabrication and testT18 TD18T24TD24TD24R05CLIC2013, Nextef, KEK, Higo

1. T18_Disk_#2

2. TD18_Disk_#2

102013/1/29

3. T24_Disk_#3

4. TD24_Disk_#45. TD24R05 under test nowundampeddampedSLAC/KEK typical fab/test flowDesign for CLIC (CERN)Fabrication of parts (KEK)Bonding (SLAC)CP (SLAC)VAC bake (SLAC)High power test (NLCTA-SLAC)High power test (Nextef-KEK)

112013/1/29CLIC2013, Nextef, KEK, Higo

SLACKEK

11TD24R05 and Comparisonin initial processing122013/1/29CLIC2013, Nextef, KEK, Higo2013/1/29CLIC2013, Nextef, KEK, Higo13

TD24R05#2 Processing history2013/1/29CLIC2013, Nextef, KEK, Higo14

TD24R05 Eacc versus #ACC-BD15Difference in processing speed among 5 disk-stack-type CLIC-prototype structures2013/1/29CLIC2013, Nextef, KEK, Higo

T24T18TD18TD2451ns91ns132nsTD24R05Number if ACC-BDs until reaching the same level in (Tp, Eacc) Speed

1. T24 2. TD24R05 3. T18 4. TD24 5. TD18Still to be revised for better comparison (130126)Breakdown rate in flat pulse operation2013/1/29CLIC2013, Nextef, KEK, Higo162013/1/29CLIC2013, Nextef, KEK, Higo

17TD24R05 less steep as Eacc than TD24.

To be evaluated in a better experimental situation and possibly at later times.2013/1/29CLIC2013, Nextef, KEK, Higo18

T24#4(final)TD24#4(~2000hrs)BDR summary on TD24 comparing to T24Arlington presentation+ typical present2013/1/29CLIC2013, Nextef, KEK, Higo19

Similar to TD24 but deteriorated at 1700hrs during long-pulse?Run 31Run 292013/1/29CLIC2013, Nextef, KEK, Higo20

2013/1/29CLIC2013, Nextef, KEK, Higo21

The same as TD24 in the early stage with hot spots appeared. Curious to see how it goes eventually.

Width dependence measured At time from RF-ON about 1600 hoursBDS vs widthTypical and similar to those before.

Worthwhile to compare among those carefully but this work is underway.

Longer pulse may make the situation bad, as seen in TD24R05.2013/1/29CLIC2013, Nextef, KEK, Higo22Appearance and disappearanceof hot spots2013/1/29CLIC2013, Nextef, KEK, Higo23Hot spots have appeared2013/1/29CLIC2013, Nextef, KEK, Higo24

Run 11706787 hrsBD cell

Run 3121222169 hrs

Run 2717971863 hrsDownstreamUpstreamNo bad cellHot spots localized in each cell2013/1/29CLIC2013, Nextef, KEK, Higo25

Run 31 at 110 MV/m

Run 27 at 100 MV/mOnly downstreamBoth up and down

Run 32 run at 105 MV/mone of the sports disappeared2013/1/29CLIC2013, Nextef, KEK, Higo26DominantBDR = 4.2 X 10 -6A little decreaseddue to disappearance of BD upstream?

Gone?2013/1/29CLIC2013, Nextef, KEK, Higo27

NonBDR increaseTD24R05#2 Processing historyHot spotsSpots appeared after long-pulse operation.They appear and disappear. The appearance may depend on field level, pulse width, etc. We want to see how spots behave in further operation.This is the first time for us to notice such hot spots, out of 5 prototype structures. Some cases known also at SLAC tests.We need to identify the source of such spots and establish the technology to be away from them.2013/1/29CLIC2013, Nextef, KEK, Higo28What to do for linear collider?Evaluate performance and find mechanismJust suppress itMaterial?Inclusion, foreign material, or crystal defects, .Fabrication process?Clean environmentEscape from possible dirty process, .Processing in practiceAny protocol?, gentle processing?, 2013/1/29CLIC2013, Nextef, KEK, Higo29Setups being prepared to study characteristics and mechanismof vacuum breakdowns in RF2013/1/29CLIC2013, Nextef, KEK, Higo30Single-cell studies in preparation or in mindExplore basic research in a simple geometry Center cell is such as the followingStandard: KEK made SLAC testNominal: Heavily-dampedMade of large-grain material Undamped but all-milledAll milled quadrant typeChoke-mode type

2013/1/29CLIC2013, Nextef, KEK, Higo31These are under preparationHG2012 in April 20123

TW

100MV/m31Study with simple-geometriesNeed to identify the breakdown mechanism in the relevant field level and including initial processing stageKey issue toward stable high gradient operation for large-scale machine as CLICStudies with both prototype structures and simpler geometries are neededKEK prepared the second test area (Shield-B) for the latterAlmost ready to start, just waiting for the klystron replacement322013/1/29CLIC2013, Nextef, KEK, HigoStrategy in mind2013/1/29CLIC2013, Nextef, KEK, Higo33

Proceed to evaluate Damped cell Damping aperture shapeMaterial HIP, ..Fabrication Turning vs Milling Heat treatments EtchingGeometry Quad ChokeStart with a single-cell setup in nominal design and nominal fabrication method

34Quad with large Chamfer (R=400mm)with single-cell setupTo understand why quad-type does not perform well under high gradient and possibly cure the problem!? 2013/1/29CLIC2013, Nextef, KEK, Higo

Shield-B

R=400mm(Round Chamfer)0.1mm gapbetweenfacing planesField Enhancement due to the Concave Structure

CopperVacuumNumerically Calculated by the Floating Random Walk Methodwith Accuracies Better than 0.5% For more details, see T. Abe, Study of Surface Field Enhancements due to Fine Structures, presented at the 8th Annual Meeting of Particle Accelerator Society of Japan, 2011 , Paper ID:TUPS086.

|E| or |H|E.g.2013/1/29CLIC2013, Nextef, KEK, Higo35

On-going copper surface evaluation2013/1/29CLIC2013, Nextef, KEK, Higo36

End millBall End millTurning latheScratch by profilemeterTakatomi

Heat deposit by laser and probed with SR light2013/1/29CLIC2013, Nextef, KEK, Higo37SR X-rayDrive laserCrystal evaluation by PF X-ray2013/1/29CLIC2013, Nextef, KEK, Higo38

Laser irradiation -> time dependent angle shift of X-ray Bragg reflection (X. Zhang)Before33nsec delayAfter delayShift corresponds to 300 degCZhangParameters and next experimentExperimental parametersLaser: YAG-Laser, pulse width 6~8ns,10HzPower:0.5mJ/shot~10mJ/shotProbe beam diameter: x-ray: 60mm, laser:100 mmTime resolution:6nsFebruary experimentEvaluate relaxation time of materialIrradiation limit for material to mechanically respondCrystal disruption limit versus power density and cycles of irradiation

2013/1/29CLIC2013, Nextef, KEK, Higo39Efforts to keep and develop RF power source for Nextef2013/1/29CLIC2013, Nextef, KEK, Higo40RF power sourcesModulator Invertor HV supply robustThyratron needs intermittent adjustment or failurePPM KlystronsThree have been used for nearly 10 yearsPulse shortening existsBut survives at 40MW levelFailure in water circuitsNot RF-origin failureDriver for klystronSemiconductor amplifier2013/1/29CLIC2013, Nextef, KEK, Higo41

Effort to re-activate fabrication engineering lead by KEK2013/1/29CLIC2013, Nextef, KEK, Higo42Continue fine parts fabrication +2013/1/29CLIC2013, Nextef, KEK, Higo43DDS 12 GHz damped-detuned cells were madeBy KEKTakatomiAn example

Assembly at KEK and surroundingsAn idea under consideration2013/1/29CLIC2013, Nextef, KEK, Higo44High temperature processingVAC baking eq.Close Stainless steel vesseland extract to clean room?In conclusion2013/1/29CLIC2013, Nextef, KEK, Higo452013/1/29CLIC2013, Nextef, KEK, Higo46KEKStructure fabrication & test @NextefCERN supports for structure fabrication, high power test & system expansionSLAC conducts structure fabrication, high power test & basic researchUS-JapanSLAC/KEKCERN/KEK collaborationCLICUS-HGTsinghua, IHEPStructure design, fabrication & testAsian collaborationCERN/KEK collaboration has kept the base for KEKs R&D toward high gradientMedicalIndustrialHiggs, and othersApplication46SummarySix CLIC prototypes tested at NextefBreakdown rate proven in TD24#4 with CLIC pulse TD24R05 found smoothly processed but hot spots emergedFurther studies in simple setup is almost readyRF power sources are to be reinforcedCLIC high gradient collaboration keeps X-band study at KEK activeKEK further aggressive activities are foreseen after commissioning of SuperKEKB in early 20152013/1/29CLIC2013, Nextef, KEK, Higo47