2 nd collaboration meeting on X-band Accelerator Structure Design and Test-Program Structure fabrication Comparative analysis of disk and quadrant manufacture G. Riddone Acknowledgement: S. Atieh, A. Samoshkin, M. Taborelli, R. Zennaro

Structure fabrication G. Riddone, 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 rpm) - positioning accuracy of the machine tools is 1 to 5 µm Disk-type structure (  = 35 to 80 mm) –Turning - carbide or diamond (on copper only) tools (ball nose mills) –Milling Accuracy requirements Accuracy of manufacturing Surface quality Summary of what seems to be feasible Accuracy requirements Accuracy of manufacturing Surface quality Summary of what seems to be feasible

Accuracy requirements x x x x x x G. Riddone, e.g. CLIC_G, 120⁰  df/dB~ 1 MHz/  m,  d  /dB~ 1 ⁰ /  m) (B= radius of the cell) e.g. CLIC_G, 120⁰  df/dB~ 1 MHz/  m,  d  /dB~ 1 ⁰ /  m) (B= radius of the cell)

Quadrant structures G. Riddone, Avoid steps and kinks on the surfaces (field enhancement  ) Ra should be around ¼ of the skin depth to preserve electrical conductivity Frequency matching or tuning

Octant structures G. Riddone,

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 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,

Achieved shape accuracy (quadrant/octants) G. Riddone,

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 machining TEMPERATURE Thermal expansion of the piece Temperature stability, dynamics of the machine tool POSITIONING 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,

Surface quality (str. in quadrants) Ra= Ra= Diamond milling Conventional tools milling 0.01 mm G. Riddone, mm

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  m 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 Disks: machining by diamond turning Adding damping features  Needs milling (no circular symmetry) with smooth transition between milled and turned surfaces. Relative positioning at  m 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,

Disk dumped structures G. Riddone,

Assembly by brazing Bookshelfing: assembly on a slope V-bench gives “tilted” discs Smaller and random error: assembly on vertical V-bench as 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,

Recrystallization after thermal treatment (vacuum brazing cycle at 820 C) Ra = 0.05 m Surface quality (str. in disks, Cu OFE) G. Riddone, mm 1 mm 0.1 mm

Disk undamped structure (prototype) 11WNSDvg1Cu G. Riddone,

Achieved accuracy (prototype) Specification 11WNSDvg1Cu G. Riddone,

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 – Turning Ø 35 mm, accuracy < +/-1 μm Ø 80 mm, accuracy < +/-1.5 μm Ra_best = μm –Milling Accuracy < +/- 2.5 μm Ra_best = 0.05 μm –Assembly by brazing (vertical assembly better): < +/- 2.5 μm G. Riddone,

G. Riddone,

Effect on thermal treatment Solvent cleaned Vacuum baked 750C x 1h Milled surface (carbide tools) 10 µm G. Riddone,

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 G. Riddone,

G. Riddone,

High speed milling machine tool Diamond fly-cut G. Riddone,