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 requirements

Machining Ass. Alignm. Oper.

SHAPE

Shape of an I ris 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 2

LONGITUDINAL

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 Scheme

Magnitude of tollerance (mm)

I temEffect of the

itemPerformance Solution

x

x

x

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

G. Riddone,13.05.2008

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Achieved shape accuracy (quadrant/octants) 

G. Riddone,13.05.2008

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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)

G. Riddone,13.05.2008

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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

G. Riddone,13.05.2008

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

G. Riddone,13.05.2008

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Disk dumped structures

G. Riddone,13.05.2008

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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 

G. Riddone,13.05.2008

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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

G. Riddone,13.05.2008

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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

G. Riddone,13.05.2008