Structure Testing Program Thoughts proposals S Doebert R

Structure Testing Program Thoughts & proposals S. Doebert (& R. Corsini)

Parameter Space Electrical surface field Threshold somewhere, but at lower values less correlations < 250 - 300 MV/m Magnetic surface field < 40 deg pulse heating seems safe Input Power Less power is better but very low is not magic (Standing wave), little correlation below 100 MW at x-band true ? relevant ? Pulse Length Shorter is clearly better for performance but bad for efficiency Group velocity Lower seems better, but less correlation below 5 % Phase advance Not a big deal between 120 and 150, for time being 60 deg is worse Aperture As big as possible for the beam and for breakdown ? Iris thickness No evidence for performance, damage seems in favor of thicker irises Length No evidence, kick may be dependent only on single cell Conditioning strategy No evidence, could be relevant for yield of final 10 % of performance I hope for something more (but no miracles) – maybe important for uniformity of structure performance except clic X-band Some Pulse Energy related quantity seems to be important

What can we do 2007: Study Parameter Space at 30 GHz and educated guessing at 11 GHz (focus on copper structures without damping ? ) can we afford to wait ? 2008: Focus on one main geometry, develop damping, optimize structure (Get a reference structure and try to stretch parameters from there) 2009: CLIC prototype structure working 2010: Longer term testing and better statistics Number of tests (optimistic) 2007 2008 2009 2010 sum 30 GHz 6 3 0 0 9 12 GHz 0 1 4 4 9 11. 4 GHz 2 2 8 Stand alone at CERN 0 3 8 8 19 sum 8 9 14 14 45 !

What can we do Number of tests (alternative) 2007 2008 2009 2010 sum 30 GHz 6 3 0 0 9 12 GHz 0 1 4 4 9 11. 4 GHz (SLAC) 2 4 4 4 14 11. 4 GHz (KEK) 1 2 2 2 7 sum 9 10 10 10 39

Consequences and Strategy Need as many tests as possible Do simple experiments with only one parameter changed if possible Separate high gradient and damping (because havebut doubts on HDS, need to(first qualify 4 quadrant technology) sure need to we do that, what about reverse timing damping, then no-damping to cross check) ? Tentative parameters: thicker irises, larger phase advance, lower power, smaller aperture Aim on high gradient demonstration first, optimize efficiency issues more linked than apparent – 100 MV/m basically in hand at zero and damping later efficiency Study beam dynamics limits on aperture to limit parameter space Study damping for round structures Study existing X-band data (get reference structure if possible) in case of success optimize around this structure as a second focus

Experiments Practical remarks: Potential issue – material dependent pulse length scaling can give different optima Material: Focus on copper (faster, less expensive, less unknowns) Keep Moly as reserve for best performing structure to gain some margin) Frequency: 30 GHz is ok for learning , use 12 GHz as much as possible Testing: Stand alone power source is essential Need to built 10 structures/year (can we do it) Manpower for testing ?

Experiments Key Question: Why is our last generation structure not performing as we expected ? (last generation structure: 30 GHz HDS optimized for Es; HDS 60 if you want) P/C (Wuensches) is to high Slots (HDS principle) iris thickness (to small) Phase advance (to low) Fabrication technology (quadrants, milling, heat treatment, cleanness) An ideal program should aim on clarifying this question ! Very reasonable !. . but I personally think there may be other (more important ? ) issues – see last slides

Structures in 2007 30 GHz: (already planned, new) neat comparison Mo/Cu, but also with Cu HDS 60 rev - pi/2 structure (test of short phase advance, fabrication tech. ) - HDS 11 copper/molybdenum (for better statistics) - HDS 11 very small (r=1. 2) (clear P/C experiment without other changes) - Round 3. 5 mm made out of quadrants (clear experiment for fab. Tech. ) - HDS 4_150 deg_thick_r=1. 75 (iris thickness, phase advance, length, P/C) - HDS 4_150 deg_thick_clean (compares cleaning with previous) - NDS 4_150 deg_thick_r=1. 75 (fab. Tech between HDS and NDS quadrants) - NDS 4_ 150 deg_thin (iris thickness in comparison with NDS 4_150 deg_thick) - Coupler test structure (not defined yet) Remarks: Here the order is by priority, rather than by availability - Priority because of input needed to advance in x-band - Study existing NLC couplers to be sure that we really propose something new - HDS 11_150 deg_r=1. 6 or 1. 9 would have been the clearer experiment for phase advance - HDS 11_thick_60 deg_r=1. 6 or 1. 9 would have been the clearer experiment for iris thickness

Comments on 30 GHz program 30 GHz is for learning – concentrate on issues & comparisons rather than performance… …but need at least one good performance structure (>100 MV/m 10 -3 70 ns ? ) – better have a couple potential ones in the list Useless to discuss a detailed list with fixed no of slots: No of slots will change Availability of structures will change Need to react to tests results – priorities will change ! Therefore, all that we have to decide now is: First two/three slots (as far as we can see at present…) Which structures in the pipeline we want to stop, if any Which structures we should add to the pipeline Decide on a (tentative!) priority list for tests Reflect test priorities in fabrication priorities if needed

Structures in 2007 11 GHz: -Test T 53 vg 3 Mc extensively (best hope for reference structure) ( if good, built new T 53 based structure with SLAC) - HDX 11 Molybdenum (more statistics on moly) - New CERN x-band (my favorite parameters: round quadrant if proved at 30 GHz; 120 deg, iris > 1 mm, 2 -1% vg, a/l ~ 0. 1, no damping, tapered up) does not look too different to proposed WDS proto ! -CERN structure for KEK ; round disks brazed, why not same as above or T 53 based if experiment successful, half the length, no damping, tapered up ? …and this is the T 23 proto…

Comments on 11. 4 GHz program Wide consensus on basic geometries to test Controversial issues: Damping / no damping Fabrication: quadrants / disks Number of testing slots and fabrication time critical - how many to build ? Other issues where there is some general agreement Waveguide damping 120 degrees phase advance Stay (initially) above 1% vg

(some ) Open Questions – mainly addressed in 30 GHz testing program The Moly puzzle: what are the “real” damage limit and BDR slope of Mo ? Does the Mo BDR slope evolve during conditioning ? What is its pulse length dependence (1/3 – ½ - 1) ? Influence of heat treatment, clamping or not, conditioning strategy… Pulse length dependence issues Re-check existing data, to better assess PL dependence (see e. g. last SLAC data) Is the PL dependence of the damage limit different from the one at low BDR ? Rise & fill time influence Fast & efficient way to measure PL dependence Are we mainly limited by the first cell ? (influence of structure length, tapering…) What is the source of BDs, especially at low BDR ? (heating process, fatigue…) What happens exactly during the conditioning process ? (measurement of beta crucial)