THE HIEISOLDE SUPERCONDUCTING CAVITIES Surface Treatment And Niobium

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

HIE linac staged installation 3 stages installation 1. 2 Me. V/u 3 Me. V/u 5. 5 Me. V/u 10 Me. V/u From: M. Pasini VSC Seminar Sergio Calatroni - 3. 4. 2009 2

Quarter Wave Resonators (QWRs) Low-β cavity High-β cavity 101. 28 f (MHz) 101. 28 50 Inner Cond. Diam (mm) 90 195 Outer Cond Diam (mm) 300 NbCu technology VSC Seminar Giulia Lanza - 9. 10. 2009 3

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 • Low pressure ultrapure water rinsing • RF warm and cold test (TRIUMF, later on at CERN) VSC Seminar Giulia Lanza - 9. 10. 2009 4

SURFACE TREATMENTS VSC Seminar Giulia Lanza - 9. 10. 2009 5

SUBU • Sulfamic acid (H 3 NO 3 S) 5 g/L, • H 2 O 2 5% vol, • n-butanol C 4 H 10 O 5% vol, • di-ammonium citrate (C 6 H 14 N 2 O 2) 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 - 9. 10. 2009 6

SUBU • Sulfamic acid (H 3 NO 3 S) 5 g/L, • H 2 O 2 5% vol, • n-butanol C 4 H 10 O 5% vol, • di-ammonium citrate (C 6 H 14 N 2 O 2) 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 - 9. 10. 2009 7

Low pressure rinsing In a class 100 clean room with ultrapure water at 6 bar VSC Seminar Giulia Lanza - 9. 10. 2009 8

NEW FACILITY FOR QWR COATING

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 - 9. 10. 2009 10

The coating system VSC Seminar 11

Mounting sequence VSC Seminar Giulia Lanza - 9. 10. 2009 12

The coating system VSC Seminar Giulia Lanza - 9. 10. 2009 13

The cathode assembly VSC Seminar 14

Bias Diode Sputtering -80 V Cavity -700 V Cathode Grids VSC Seminar 15

Bias Diode Results • After 20 -40 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 250 nm 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 - 9. 10. 2009 16

Magnetron sputtering Multilayer coil : calculations were run to simulate the axial magnetic field and optimize the coil heights VSC Seminar 17

Magnetron sputtering Cavity -500 V Cathode Coil VSC Seminar 18

Magnetron Results Parameters test 8 test 9 test 10 test 11 test 13 Pressure (mbar) 0. 015 0. 01 0. 008 -0. 015 0. 01 Cathode I 3 3 3 Coil I 50 40 40 Time (min) 240 410 420 410 • Stable plasma, • Improvements on the thickness, • More homogeneous distribution of the plasma between the external wall and the internal antenna. VSC Seminar Giulia Lanza - 9. 10. 2009 19

XRF measures Good ratio between the film thickness on the external wall and on the inner conductor. Due to geometrical factors, this ratio cannot be lower than four VSC Seminar Giulia Lanza - 9. 10. 2009 20

Residual Resistivity Ratio On the bottom part of the cavity the magnetic field is perpendicular to the cathode surface VSC Seminar Giulia Lanza - 9. 10. 2009 21

New idea -500 V VSC Seminar 22

New idea E E B B B Higher ionization efficiency where E ┴ B VSC Seminar Giulia Lanza - 9. 10. 2009 23

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 - 9. 10. 2009 24

thanks…

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 - 3. 4. 2009 26