1. presented by Bruno Spataro on behalf of NORCIA experiment at INFN-LNF
Achievements and activities's status on the electroformed X Band structures at INFN-LNF
presented by Bruno Spataro
on behalf of NORCIA experiment at INFN-LNF
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

2. This work is made possible by the efforts :
Contributors
This work is made possible by the efforts :
NORCIA Group, INFN - LNF
SLAC(USA)
KEK (JAPAN)
UCLA (Los Angeles-USA)
UNIVERSITY LA SAPIENZA (Roma)
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

3. SUMMARY Problems related to the Sintered Molybdenum bulk
Electroforming and Electroplating activities
Au-Ni Electroformed cavity at GHz
Characterization of the Mo film
Collaborations : SLAC, KEK, UCLA, UNIVERSITY LA SAPIENZA (ROMA)
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

4. NORCIA (NOvel Researches Challenges In Accelerators)
is the INFN R&D program on ‘multicell resonant structures’ operating at X-Band (10 ÷ 12 GHz)
the MOTIVATION …….
The research project is devoted to the R&D of key components for existing accelerators and for the next generation of accelerators. New technologies are necessary to achieve the multi-TeV energies of future linear colliders, x-ray FELs, etc.
To use in high brilliance photo-injectors (SPARC-phase-2) to compensate the beam longitudinal phase-space distorsion, enhanced by the bunch compression of the acceleration process
To gain know-how in vacuum microwave technologies
Approach :
To study new materials and manufacturing techniques including single and multi-layer surfaces with precision-controlled properties
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

5. Sintered Molybdenum (Bulk)
Guidelines:
How to improve the high power perfomance (e.g. discharge rate) ?
R&D on
material
using material with a higher
fusion temperature
avoiding the device heating at high temperature as done in conventional brazing
R&D on fabrication
techniques
R&D on material
Sintered Molybdenum (Bulk)
Electroplated and Electroforming
R&D on fabrication
techniques
Electron Beam Welding
Molybdenum sputtering
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

6. Drawing of the 3 - cells X-Band structure (SW- 11
Drawing of the 3 - cells X-Band structure (SW GHz) for the breakdown studies
The model was designed at SLAC in order to concentrate the RF field in the mid-cell for breakdown studies
Longitudinal field profile of the
operating π mode - SW structure
Mandrel sketch for the construction of the structure using the electroforming technique
The electroforming approach is a manufacturing method in order to avoid heat treatment of the metal
Comeb - MLT Companies
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

7. Sintered Molybdenum bulk brazed and Electroplated structures [3-cells X Band (SW)]
3 cells Sintered Molybdenum bulk brazed structure issue
[NIM-A-657 (2011) ]
Sintered Mo bulk
Brazed structure
Field profile – π mode
Higher power tests of the brazed model have been carried out at SLAC (V. Dolgashev et al.). As a result:
~300 nm roughness using ‘tungsten carbide’ tools (3 tools for machining the structure)
It is not easy to braze. It is likely to have a gas contamination and an uneven loading stress in the braze region (joints are not completely filled with alloy)
long time for machining
the cavity (Mo bulk is a
hard material)
3 cells Cu (OFHC) Electroplating structure
Higher Power tests of the model have been carried out at SLAC (V. Dolgashev et al.) by giving very promising results
[NIM-A-657 (2011) ]
Electroplated structure
Field profile – π mode
The 3 cells made of Cu are already machined and encapsulated by galvanoplastic technique
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

8. …… Electroforming R&D and Test
Structure mandrel
consists of 5 cells
Fundamental mode response of
Cu-Mo electroformed structure
Some RF devices constructed with
the electroforming technique
RF coupler
and cell
Cross section of a Mo-Cu
electroformed structure
Q0 = 5406
π mode
5 cells mandrel of
a Mo-Cu structure
Another view of the Aluminium mandrel of the RF coupler and cell ready to be electroformed
Mo discs are already machined to
be the iris of the electroformed cell
The Mo discs improve the mechanical properties with the external ribs
RF cells have been obtained after removing the aluminium core with alkaline solution (sodium hydroxide NaOH)
Electroformed of the RF coupler and cell
Next step:
a) to improve the quality of the Cu surface altered by the alkaline solution by depositing silver or gold on the core
b) to improve the Mo surface roughness
(~ 300 nm !!)
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

9. …… Electroforming R&D and Test
Au-Ni flat sample gave a resistivity ~ 1.2 worse than Cu (SLAC- V. Dolgashev et al.)
The flat samples have been prepared using combination of :
PVD Au (200nm)+ Galvanic Gold (3 micron)
COMEB & MLT Companies
Flash adhesion layer PVD or galvanic (Pd, Ni) typically 0.5 micron; E-formed Ni or Cu
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

10. (COMEB and MLT Companies)
Electroformed NORCIA’s prototype of the 3-cells X-Band structure
(COMEB and MLT Companies)
The mandrel’s model for the electroforming
The structure’s mandrel with a 3 µm thick of Au’s coating
Fitting tests between mandrel and CF flanges
Final structure after coating of Ni with a 4 mm thick
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

11. 11.424 GHz cross section of the electroformed cavity (Au-Ni)
Hollow of the iris’s cooling
Iris thickness 2 mm
Hollow wall thickness 0.5 mm
70 nm roughness
Au (3 µm) and Ni (4 mm) coatings
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

12. Iris cooling video of the electroformed Au-Ni structure
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

13. Low level RF tests of the Au-Ni electroformed structure
The main RF parameters of this Au-Ni electroformed structure measured at room temperature are summarized in Table
For each mode a good agreement between the theoretical values of the operating frequencies
The working π mode is about 3.9 MHz off (with untuned devices !)
Qzero of the is π mode a little poor: conductivity has to be improved !!
Table : RF parameters at room temperature of the Au-Ni electroformed structure
Tests of the Longitudinal Electric fields profiles on axis
π – mode
π/2 mode
0 mode
Jim Lewandowski, SLAC
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

14. Breakdown data of the Electroformed-Au-Ni as a function of different length of shaped pulse [SLAC - V. Dolgashev et al.]
400 ns
400 ns
150 ns
150 ns
200 ns
200 ns
During the initial process the electroformed structure run
similarly to electroplated Cu structures of the same geometry
400 ns
The structure performances improve with the accumulated
breakdowns and may be additionally improved after
more processes
150 ns
The gradient at low breakdown rate at 200 ns shaped pulse shows better perfomances than at 150 ns shaped pulse (anomalous behaviour).
200 ns
Data analysis does not show a clear correlation with
RF fields or with the pulse heating for the same
breakdown probability.
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

15. Breakdown data for soft copper and electroformed Au-Ni of the same shape at 200 ns shaped pulse (soft Cu, Electroformed Au-Ni) [SLAC - V. Dolgashev et al.]
Electroformed-Au-Ni
Electroformed-Au-Ni
soft Cu
soft Cu
Electroformed-Au-Ni
Electroformed-Au-Ni
Electroformed-Au
soft Cu
soft Cu
Comparison of the structures with
respect to Maximum-Poynting-vector
soft Cu
This approach allows to compare the results with structures with different shape and geometry
The gradient and pulse heating at low breakdown rate is similar to soft-copper structures of the same type at 200ns shaped pulse
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

16. Autopsy of electroformed Au-Ni [SLAC - V. Dolgashev et al.]
Images of the three cells taken from the high gradient side
Input side of
Coupler cell
High gradient side of
End cell
High gradient side of
Center cell
The images clearly show relevant damages in the End and Center cell
The cell on the left is the input side of the Coupler cell does not show the same damage
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

17. Autopsy of electroformed Au-Ni [SLAC - V. Dolgashev et al.]
Images of the three cells taken from the low gradient side
Cavity side of
Coupler cell
Low gradient side of
Center cell
Low gradient side of
End cell
The images do not show relevant damages compared to the high gradient side
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

18. Autopsy of electroformed Au-Ni [SLAC - V. Dolgashev et al.]
Magnification of the images taken from the high gradient side
High gradient side of
Center cell
High gradient side of
End cell
Gold coating has been almost completely removed in the region of the high-electric field by multiple breakdowns
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

19. Undamaged Gold plating
Autopsy of electroformed Au-Ni, SEM inspection [SLAC- V. Dolgashev et al. ]
Undamaged Gold plating
M - spots
Coupler cell, near 2b diameter, low pulse heating area.
Center cell, near 2b diameter, high pulse heating area.
The plating looks thin
M stands for «Melted»
We see no massive pulse heating damage on the gold coating
We compare that to previously tested copper-on-stainless steel structure which showed massive pulse heating damage to the copper coating
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

20. First conclusions on the electroforming activities
Flat samples resistivity is ~1.2 worse than Cu [SLAC]
We built two structures made of Au-Ni. The field profile and frequency are satisfactory for both sections
Structures resistitivity is ~2.5 worse than Cu [SLAC]. The deposition with the galvanic process occurring at grazing angles affects the film’s compactness (due mainly to the porosity inside the film)
The iris’s cooling with a 2 mm thickness was successful !
The sodium hydroxide (NaOH) removes the Al mandrel but does not affect the Au deposited film. The latter is required to stop the erosion of the mandrel
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

21. Electroformed Gold-Nickel structure issue
We successfully tested at high power one of two structures made with electroforming (a manufacturing method that avoids heat treatment of the metal )
The RF losses in the structure are 60% higher than in copper structure of the same type due to a poor resistivity of the gold coating (no uniform gold coating in high magnetic field areas or diffusion of nickel into gold plating). We did not observe the increase of this loss in flat samples coated with gold in the same manufacturing process [SLAC]
The gradient at low breakdown rate is similar to soft-copper structures at 200 ns shaped pulse and about 20% lower at 150ns shaped pulse (in spite of high RF losses and slow initial conditioning) [SLAC]
We see no massive pulse heating damage on the gold coating [SLAC]
We speculate that the reason for the good performance of the structure is that the gold coating was removed by RF breakdowns, exposing nickel, which in its turn is breakdown resistant
We speculate that with an improved quality of gold coating this type of structure could have better performance than copper
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

22. [COMEB & MLT Companies]
X band Galaxie gun prototype (J. Rosenzweig - UCLA) with cooled irises
manufactured with the electroforming process
Tuners (2 mm diameter)
cooled irises
The tuners can be machined before electroforming or
with the EDM process
[COMEB & MLT Companies]
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

23. From the Sintered Molybdenum (Bulk) to sputtering molybdenum actvities at LNF
Roughness’s investigation of the molybdenum sputtering on a Copper sample with a 70 nm roughness
AFM (Atomic Force Microscopy) shows the surface of a copper sample (70 nm roughness) before molybdenum sputtering
AFM (Atomic Force Microscopy) image of deposited molybdenum (100nm thickness) on a copper sample by sputtering technique
The roughness of the film is comparable to that of the substrate. This indicates that the roughness is determined by the substrate (a factor 3 lower than the 300 nm roughness of the Mo bulk)

24. Enhanced conductivity via thermal annealing (Mo/Sapphire)
Mo coatings with an electrical conductivity comparable to that of copper can be obtained optimizing the thickness and the post-deposition annealing process
We already characterized a series of Mo films coated on insulating substrates. We selected two reasonably thick samples (~300 nm and ~1030 nm depth) annealed at both ~300 °C and ~600 °C in order to study their resistivity as a function of the temperature [Chinese Physics C 36, (2012) and Chinese Physics C 37, (2013)].
XAS (X-ray Absorption Spectroscopy) and X-ray Diffraction (XRD) investigations have been performed at Diamond Light Source (UK), before and after annealing, in order to identify the chemical status of Mo film, to probe the presence of different oxides and control the multiphase nature of these metallic films.
A clear decrease of the resistivity as function of the temperature occurs in both samples. The variation is larger for the sample with a 300 nm thickness that is a factor of 2.5 at 600 0C
300 nm thickness
1030 nm thickness
Annealing: 2 hours
The large observed difference in the resistivity of the Mo films, is mainly associated to the ratio betweem grain and the layer thickness [P. Muecke et al. Acta Mater. 56 (2008)] 677–687]
Surface&Coating Technology 261 (2015);
Mo and MoO2 values available from the literature
Additional studies on growth parameters, post- treatment annealing process are in progress in order to further reduce the resistivity of the Mo films.
Resistivity values of BRN1 and BRN2 samples for different annealing temperatures. These annealed coatings are multiphase metallic films with negligible contributions of disordered oxide phases
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

25. Future activities
Usually coatings with PVD (Physical Vapour Deposition) processes give a much better purity compared to the galvanic one.
We are investigating the coatings of gold made with PVD in order to improve the film's conductivity
We planned to perform two steps for the gold film deposition through the PVD process with an angle, while the mandrel is turning (continuous rotation). This layout may deposit at an angle of ±30 deg growing a layer of Au more homogeneous and with a lower porosities [tests are in progress on dedicated prototypes]
Film deposition onto trenches region (as the iris) with an aspect ratio 3-4 by using the IONIZED MAGNETRON SPUTTERING may improve film structure and density [tests are planned on dedicated prototypes]
Activities on the Electron Beam Welding (EBW)
HG workshop June 16-19,2015- Tsinghua University-Beijing, China

26. A special thanks to the SLAC’s people
and
Thank you very much for your attention
HG workshop June 16-19,2015- Tsinghua University-Beijing, China