1. THE HIE-ISOLDE SUPERCONDUCTING CAVITIES:
Surface Treatment And Niobium Thin Film Coating
Giulia Lanza

2. HIE linac staged installation
3 stages installation
1.2 MeV/u
3 MeV/u
5.5 MeV/u
10 MeV/u
From: M. Pasini
VSC Seminar
Sergio Calatroni

3. Quarter Wave Resonators (QWRs)
Low-β cavity
High-β cavity
101.28
f (MHz) 50
Inner Cond. Diam (mm) 90
195
Outer Cond Diam (mm)
300
Nb\Cu technology
VSC Seminar
Giulia Lanza

4. QWR cavities production sequence:
Machining and EB welding
Warm RF test for frequency measurement
Chemical polishing (SUBU) and passivation
Low pressure ultrapure water rinsing
Coating
RF warm and cold test (TRIUMF, later on at CERN)
VSC Seminar
Giulia Lanza

5. SURFACE TREATMENTS
VSC Seminar
Giulia Lanza

6. SUBU Sulfamic acid (H3NO3S) 5 g/L, H2O2 5% vol,
n-butanol C4H10O 5% vol,
di-ammonium citrate (C6H14N2O2) 1 g/L
Chemical polishing is carried out at 72 °C and is preceded and followed by washing with a diluite solution of sulfamic acid
VSC Seminar
Giulia Lanza

7. SUBU Sulfamic acid (H3NO3S) 5 g/L, H2O2 5% vol,
n-butanol C4H10O 5% vol,
di-ammonium citrate (C6H14N2O2) 1 g/L
Chemical polishing is carried out at 72 °C and is preceded and followed by washing with a diluite solution of sulfamic acid
VSC Seminar
Giulia Lanza

8. In a class 100 clean room with ultrapure water at 6 bar
Low pressure rinsing
In a class 100 clean room with ultrapure water at 6 bar
VSC Seminar
Giulia Lanza

9. NEW FACILITY FOR QWR
COATING

10. INFN-LNL experience Bias Diode Sputtering
The bias technique is highly reliable: over 40 QWRs are installed and working at LNL
VSC Seminar
Giulia Lanza

11. The coating system
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12. Mounting sequence
VSC Seminar
Giulia Lanza

13. The coating system
VSC Seminar
Giulia Lanza

14. The cathode assembly
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15. Bias Diode Sputtering
-80 V
Cavity
-700 V
Cathode
Grids
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16. Bias Diode Results
After min the plasma disappeared from the outer part of the cathode.
Non homogeneous distribution of the plasma.
Different sputtering rate was measured: after 2 hours of sputtering a thickness of 250nm was measured on the inner antenna while there was no measurable film on the outer wall.
Even in the inner part the sputtering rate was too low (2 nm/min).
VSC Seminar
Giulia Lanza

17. Magnetron sputtering
Multilayer coil : calculations were run to simulate the axial magnetic
field and optimize the coil heights
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18. Magnetron sputtering
Cavity
-500 V
Cathode
Coil
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19. Magnetron Results Stable plasma, Improvements on the thickness,
Parameters
test 8
test 9
test 10
test 11
test 13
Pressure (mbar)
0.015
0.01
Cathode I 3
Coil I 50 40
Time (min)
240
410
420
Stable plasma,
Improvements on the thickness,
More homogeneous distribution of the plasma between the external wall and the internal antenna.
VSC Seminar
Giulia Lanza

20. XRF measures
Good ratio between the film thickness on the external wall and on the inner conductor. Due to geometrical factors, this ratio cannot not be lower than four
VSC Seminar
Giulia Lanza

21. Residual Resistivity Ratio
On the bottom part of the cavity the magnetic field is perpendicular to the cathode surface
VSC Seminar
Giulia Lanza

22. New idea
-500 V
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23. Higher ionization efficiency where E ┴ B
New idea E E B B B
Higher ionization efficiency where E ┴ B
VSC Seminar
Giulia Lanza

24. Outlook Coating parameters optimization
Copper cavity coating at the end of October
RF measure at TRIUMF
Study of the low β cavity coating ( 200 mm)
Safety improvements on the system for chemical treatments
Set up a standardize procedure for the QWRs series production and possible industrialization
VSC Seminar
Giulia Lanza

25. thanks…

26. Why superconducting linac?
SC linacs maintain beam quality for energy variable machines
The maximum effective voltage can be applied to lighter masses so to have a higher final energy.
SC linacs provide the highest flexibility of operation
Quarter waver cavities already well-known in several labs
Nb/Cu technology chosen over bulk-Nb for mechanical stability (reduction of microphonics and sensitivity to He bath pressure), no magnetic shielding (simpler cryostat), lower cost
VSC Seminar
Sergio Calatroni