Recent high-gradient results, rf testing, places and plans Steffen Döbert, CLIC Workshop, 17.10.2008 • Test facilities • High gradient results • Future testing program For more detailed high gradient results please see: The x-band structure design and testing workshop: June 2007 http://indico.cern.ch/conferenceDisplay.py?confId= 15112 The High-Gradient workshop, October 2006 http://hg2006.web.cern.ch/HG2006
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Recent high-gradient results, rf testing, places and plans Steffen Döbert, CLIC Workshop, 17.10.2008 Test facilities High gradient results Future testing.
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Recent high-gradient results,rf testing, places and plans
Steffen Döbert, CLIC Workshop, 17.10.2008
• Test facilities
• High gradient results
• Future testing program
For more detailed high gradient results please see:
The x-band structure design and testing workshop: June 2007
Klystron Test stand 12 GHz, 200950 MW-150 MW, 500 ns
X-band test facilities at SLAC
• NLCTA: 3 Test Stations: 2x50 MW into SLEDII, 300 MW , 240-400 ns, fully automated conditioning
• Klystron Lab: 2 single Klystron test stands 2x50 MW into SLED II ASTA bunker
X-band Test Facilities at KEK
Single Klystron (50 MW) test stand up and running
NEXTEF: Available from fall 2007, 2x50 MW, 400 ns, 24/7 operation
Reached nominal 30 GHz CLIC values :
150 MV/m 70 ns
Overview of 30 GHz results
Molybdenum shows higher gradient but different slope
HDS performs worse than round brazed structure
New Materials for High-Gradient
Copper has still the best performance at low break down rate
HDS4vg2.6_thick_150degC40vg8_pi/2
Recent 30 GHz results
Structure P (MW)
E (MV/m)
PT1/3/C (wue)
C30vg4.7 20.2 92 7.5
HDS60vg8.0 16.1 61 5.6
HDS60vg5.1 13.3 75 5.5
C40vg7.4_pi/2 19.2 65 6.2
HDS4vg2.6_thick
7.5 67 2.8
All data at 70 ns pulse length and 10-3 breakdown rate
Summary of 30 GHz results
Hybrid damped structures (HDX) at x-band
Frequency scaling
Scaled structures show very similar performance
HDS-type structures show consistently limited performance
A reference structure for CLIC from NLC
Length: 53 cm
Phase advance: 120 deg
Group velocity: 3 %
a/: 0.13
Es/Eacc: 2.2
Pin (65 MV/m):41 MW
Coupler: mode luncher
Preparation: H-brazing,diamond
turning
Tests of old NLC structures at short pulses
T53vg3MC can be used as a first reference for the new CLIC parameters
CLIC goal
Structure P (MW)
E (MV/m)
PT1/3/C (wue)
T53vg3MC (50ns) 118 110 18
T53vg3MC (100ns)
107 105 20
H75vg3 (150 ns) 155 97 27
HDX11vg5 (70 ns)
59 60 9
All data around ~10-6 breakdown rate
Summary of 11 GHz results
Pulse Length Dependence
Conclusions on recent structure tests
Current CLIC design within experimentally demonstrated region
27 wue have been measured (Design used 18)
120 MW input Power for 100 ns into first cell of T53
Hybrid Damped Structures show performance deficit (short phase advance, slots, quadrants and milling)
Copper is still the best material to make accelerating structures (Molybdenum still has some potential, shallow slope seen in previous experiments could be due to iris clamping, slow processing as usual)
Exactly scaled structures seem to perform independent of frequency (therefore 30 GHz test are still meaningful)
Structure manufacturing technology seems to play an important role Damping has to be integrated and tested
Structure Program Philosophy
1. Gradient program (highest priority):Demonstrate a CLIC prototype structure:
(100 MV/m,300ns, 12 GHz, damping)
2. General high gradient R&D (high priority):Find the universal breakdown theory, P/C, phase advance,
materials Try to do that with simple and clear experiments (single cells)