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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
http://indico.cern.ch/conferenceDisplay.py?confId=15112
The High-Gradient workshop, October 2006
http://hg2006.web.cern.ch/HG2006
D FFD
D F D
D F D D F D
D F D
DF DF DF DF DF DF DF DF DF
D F D
F DF D
D FFFDD
D F DD F D
D F DD F D D F DD F D
D F DD F D
DF DF DF DF DF DF DF DF DF DFDF DF DF DF DF DF DF DF DF DF DF DF DF DF DF DF
D F DD F D
F DF DF DF D
Drive Beam Injector
Drive Beam AcceleratorX 2 Delay Loop
X 4 Combiner
Ring
Probe Beam
Injector
4 A - 1.2 s1.5 GHz, 150 MeV
30 A - 140 ns12 GHz, 150 MeV
16 structures - 3 GHz - 7 MV/m
High Power test fasilities at CERN
Two Beam Test stand 12 GHz, 2008
30 GHz Test stand
Rf power production with CTF3
70 MW, 100 ns
200 MW, 140 ns
TBL, 16*160 MW, 140 ns
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)
3. Fabrication technology for potential cost savings (high priority):Disks, slots, quadrants, surface treatment, procedures
Start with simple structures and experiments (single cells, DC-spark),
eventually we need to go to full structures
30 GHz break down R&D program in CTF3
- HDS4_vg2.6_thick (iris thickness, phase advance, P/C) Finished !
- NDS4_vg2.5_thick (Effect of slots and quadrants) Installed !
- C30_vg4.7_quad (clear experiment for fab. Tech.)
Decision point, see flow chart !
- HDS11_vg2 (clear P/C experiment without other changes)
- HDS4_vg2.6_thick_clean (compares cleaning with previous)
- NDS4_vg3.6_thin (iris thickness in comparison with NDS4_thick)
- C30_vg2.6 (P/C)
- C30_vg8.2 (P/C)
- C30_vg4.7_sb (speed bump)
- C30_vg2_TM02 (vg)
- HDS 11 copper/molybdenum (for better statistics)
New list of planned experiments ordered by priority and reality
30 GHz flow chart
C30_vg2_TM02
HDS4_vg2.6_thick (negative test result)
HDS11_vg2
HDS4_vg2.6_thick_clean
NDS4_vg2.5_thick (under test)
NDS4_vg3.6_thin
Quads or slot are a problem
Quads or slot are not a problem
P/C ok
C30_vg2.6
C30_vg8.2
C30_vg4.7_sb
New ideas if needed
2008
2007
Input for x-bandC30_vg4.7_quad
11 GHz CLIC structure program
11.4 GHz:
- TD18_vg2.4_quad (CERN, VDL, Japanese industry) [2x] (test of P/C, damping, quadrant technology)
- T28_vg2.9 (done by SLAC) (conservative approach)
- T18_vg2.4_disk (SLAC,KEK) [4x] {1 CERN, 2 SLAC/KEK (test 1 at SLAC and 1 at KEK), 1 KEK}
(test of P/C in conservative technology, technology comparison)
Decision point, see flow chart
- T18_vg2.4_quad (CERN) (test of P/C, quadrant technology)
- TD18_vg2.4_disk (CERN, KEK) [2x] (mainly test of damping)
- TD28_vg2.9 (CERN) (back up test of damping if others are not successful)
New list of planned experiments
11 GHz flow chart
TD18_vg2.4 geometry OK
2008
TD18_vg2.4geometry not OK
Disks OKQuads OK+Damp
2009
CLIC prototype disks dampedCLIC prototype TD28 like
CLIC prototype quads damped
Go towards more extreme structures
2010
Input from break down R&D
TD18_vg2.4_quadT28_vg2.9T18_vg2.4_disk
TD28_vg2.9
(T18_vg2.4_quad)
TD18_vg2.4_disk
?
DampingNot OK
TD24vg1.7
TD24vg1.7
Aug
Oct Nov Dec
CTF3 30 GHz
NLCTA
Station 1 11.4 GHz
Pi/2 HDS4_vg2.6_thickheat treated
NEXTEF 11.4 GHz
Sept
Jul
Current structure testing program
HDX11 Cularge grains
C30_vg4.7_quad
NLCTA
Station 2 11.4 GHz
2007
NDS4_vg2.6_thick
T53vg3MC
H60vg3S18 ?
Old Clic vg1.1 ?
Apr-Jun Jul-Sep Oct-Dec
CTF3 30 GHz
NLCTA
Station 1 11.4 GHz
C30_vg2.6
NEXTEF11.4 GHz
Jan-Mar
Current structure testing program
C30_vg8.2
C30_vg2_TM02
NLCTA
Station 2 11.4 GHz
2008
C10vg2.9 [2x]
C10vg0.7 [2x]
C10vg2.2_thick [2x]
T18_vg2.4_disk [1]
TD18_vg2.4
T18_vg2.4_disk [2] TD18_vg2.4_qua
d
PETS 11.4 GHz
HDS11_vg2
TD18_vg2.4_quad
T28_vg2.9
C10vg1.3 [2x]
CLEX 12GHz
T18_vg2.4_disk
PETS 12 GHz
Shut down
Shut down
T18_vg2.4_disk [4]
T18_vg2.4_disk [3]
TD18_vg2.4 TD28vg3
Parameters along the structures
TD18_vg2.4 is more extreme in maximum surface field, pulsed heating and lowest group velocity
Parameters of new structure TD24vg1.7
Structure TD24vg1.7
Frequency: f [GHz] 12
Average iris radius/wavelength: <a>/λ
0.11
Input/Output iris radii: a1,2 [mm] 3.15, 2.35
Input/Output iris thickness: d1,2 [mm] 1.67, 1.00
N. of reg. cells, str. length: Nc, l [mm]
24, 229
Bunch separation: Ns [rf cycles] 6
Luminosity per bunch X-ing: Lb× [m-2] 1.22×1034
Bunch population: N 3.72×109
Number of bunches in a train: Nb 312
Filling time, rise time: τf , τr [ns] 62.9, 22.4
Pulse length: τp [ns] 240.8
Input power: Pin [MW] 63.8
Pin/CtPp
1/3[MW/mm ns1/3] 18
Max. surface field: Esurfmax [MV/m] 245
Max. temperature rise: ΔTmax [K] 53
Efficiency: η [%] 27.7
Figure of merit: ηLb× /N [a.u.] 9.1
Structure Nick-Names
Type No of cells vg (start) special feature
HDS 11 8.3 thick
Constant Imp 30 2.4 thin
Tapered 5 3.6 quad
TDamped clean
Old names New names
- CLIC vg3/1 quadrants damped TD18_vg2.4_quad
- T26vg3MC T28_vg2.9
- CLIC vg3/1 disks undamped T18_vg2.4_disk
- CLIC vg3/1 quadrants undamped T18_vg2.4_quad
- CLIC vg3/1 disks damped TD18_vg2.4_disk
- T26vg3MC disks damped TD28_vg2.9
Scattered Dark Spots
Areas of DiscolorationPatchy breakdown areas along sides of irises
High Current Region
Input Coupler
Iris
Post mortem inspection of HDX11cu
Comparison of 11.4 GHz results
P/C*tp^1/3 [Wu3]
0
5
10
15
20
25
30
2 3 4 5 6
a1 [mm]
P/C
*tp
^1/3
[W
u3
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