2nd collaboration meeting on X-band Accelerator Structure Design and Test-Program
Structure fabrication
Comparative analysis of disk and quadrant manufacture
G. Riddone
13.05.2008
Acknowledgement: S. Atieh, A. Samoshkin, M. Taborelli, R. Zennaro
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Structure fabrication
G. Riddone,13.05.2008
• Quadrant-type structures (50 to 300 mm)• Octant-type structures (300 to 1000 mm)
– Milling- technology used so far: CNC milling, at high cutting speed (spindles at 20000-50000 rpm)- positioning accuracy of the machine tools is 1 to 5 µm
• Disk-type structure (f = 35 to 80 mm)– Turning - carbide or diamond (on copper only) tools (ball nose mills)– Milling
Accuracy requirementsAccuracy of manufacturing Surface quality
Summary of what seems to be feasible
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Accuracy requirementsMachining Ass. Alignm. Oper.
SHAPE
Shape of an Iris dephasing lower efficiency x -Tuning ±0.001 high local 1
Shape of the matching I ris mismatching lower efficiency x -Tuning ±0.001 high local 2LONGITUDINAL
Expansion of the structure due to the heat dissipation dephasing lower efficiency x
-Thermal elongnation compensated (isotropic) ±0.005 mm low
thermal elongation 3
Relative position of the quadrant or the tilt of the discs.
transverse kick
RF induced transverse kick x x
-Disk tecnology (?)- Average shape assembly ±0.001 mm high bookshelf 4
TRANSVERSE
Relative position of the quadrant wakefieldbeam induced
transverse kick x x- Average shape assembly ±0.005 mm low
maybe allignement
problem 6
Expansion of the structure due to unsymmetric heat dissipation wakefield
beam induced transverse kick x
-Symmetric deformation design ±0.005 mm high bending 5
Thermal isotropic expansion dephasing lower efficiency x-Very accurate water temperature control ±0.1 C° high
Frequency variation of the
structures 10
Supporting of the accelerating structure wakefield
beam induced transverse kick x x x
-Accurate Reference interfaces in structures ±0.005 mm low
structure axis wrto beam axis 9
TILT
Tilt of the full structuretransverse kick
RF induced transverse kick x
-Reference points in the structures
±0.03 mradlow
tilt of full structure 7
Deformation of supporttransverse kick
RF induced transverse kick x Active cooling system
±0.03 mradlow
Support interference 8
CauseCriticality Comments SchemeMagnitude of
tollerance (mm) Item Effect of the item Performance Solution
x
xx
x
x
x
G. Riddone,13.05.2008
e.g. CLIC_G, 120⁰ df/dB~ 1 MHz/mm,
d/dB~ 1 ⁰ /mm)(B= radius of the cell)
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Quadrant structures
G. Riddone,13.05.2008
Avoid steps and kinks on the surfaces (field enhancement b)Ra should be around ¼ of the skin depth to preserve electrical conductivity
Frequency matching or tuning
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Octant structures
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• machining by 3D milling (carbide or diamond tools)• alignment of the quadrants by pins or balls and gooves (plastic deformation of copper) difficulty in controlling the gap between quadrant, errors in the groove
• assembly by brazing or by bolting• damping implemented in the design
160 mm
Quadrants/octants: machining by milling
300 mm
30 GHz 11.4 GHz
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Achieved shape accuracy (quadrant/octants)
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Possible sources of errors in 3D milling
TOOL ERRORS• Error on tool diameter, tool length, tool run-out: dynamic
dimensions• Error on tool shape• Tool flexure (larger tools at 11.4 GHz should be favorable)• Tool consumption during machiningTEMPERATURE• Thermal expansion of the piece• Temperature stability, dynamics of the machine toolPOSITIONING ERRORS• Positioning accuracy (originated from geometric, cutting
force, dynamic loading) of the machine tool (machine tool with higher nominal accuracy give better surface finish)
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Surface quality (str. in quadrants)
Ra=0.02-0.2Ra= 0.2-0.4
Diamond millingConventional tools milling
0.01 mm 0.01 mm
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1 mm 1 mm
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Disks: machining by turning and milling• Disks: machining by diamond turning• Adding damping features Needs milling (no circular symmetry) with smooth
transition between milled and turned surfaces. Relative positioning at mm level is necessary! alignment of the damping waveguides is necessary: wake-fields are used by BPM
• Alignment of the disks on V-shaped marble before assembly in a stack: use external “cylinder” surface as reference.
• Assembly by vacuum brazing or by bolting
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Disk dumped structures
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Assembly by brazing
Bookshelfing: assembly on a slopeV-bench gives “tilted” discs
Smaller and random error: assembly on vertical V-benchas a tower
5 μm
The type of error depends on the assembly procedure
Achieved accuracy for brazing assembly of disc structures: better than 5 µm
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Recrystallization after thermal treatment (vacuum brazing cycle at 820 C)Ra = 0.05 mm
Surface quality (str. in disks, Cu OFE)
G. Riddone,13.05.2008
0.01 mm1 mm
1 mm 0.1 mm
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Disk undamped structure (prototype)11WNSDvg1Cu
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Achieved accuracy (prototype)
Specification
11WNSDvg1Cu
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Summary – what seems to be feasible
• Structure in quadrants– Milling accuracy for structures up to 500 mm < +/-2.5 μm– Milling accuracy for structures up to 1000 mm < +/-20 μm– Ra_best = 0.05 μm– Assembly is a critical point: accurate assembly method to be
developed (optical methods) • Structures in disks
– TurningØ 35 mm, accuracy < +/-1 μmØ 80 mm, accuracy < +/-1.5 μmRa_best = 0.001 μm
– MillingAccuracy < +/- 2.5 μmRa_best = 0.05 μm
– Assembly by brazing (vertical assembly better): < +/- 2.5 μm
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Effect on thermal treatment
Solvent cleaned
Vacuum baked 750C x 1h
Milled surface(carbide tools)
10 µm
10 µm
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Diamond tools vs. Carbide tools
Low coefficient of friction and smoothness
High thermal conductivity
Low compressibility
Low thermal expansion
- Dimensional stability
- Maintenance of tolerances
- Chips do not adhere to surface
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High speed milling machine tool
Diamond fly-cut
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