Niobium Coating of Copper Cavities by UHV Cathodic Arc: progress report

Transcription

1 Niobium Coating of Copper Cavities by UHV Cathodic Arc: progress report L. Catani, A. Cianchi, D. Digiovenale, J. Lorkiewicz, Prof. S. Tazzari, INFN-Roma "Tor Vergata", Italy Roberto Russo, Istituto di Cibernetica del CNR and INFN- Na, Napoli, Italy In collaboration with A. Andreone, Università di Napoli Federico II, and INFN-Na G. Lamura, CNR-INFM Coherentia, and INFN-Na Group of Prof. M. Sadowski, SINS Poland, also support and collaboration from: CEA-Saclay, CERN, Cornell University, DESY, Jefferson Lab, Legnaro INFN-LNL

2 Outline Summary of the Vacuum arc discharge Results using the UHV arc sources The cavity deposition The new deposition system Summary and Conclusion

3 The UHV cathodic arc no working gas (UHV) Fully ionized niobium (self-sustained plasma) high ion energy (>100eV) possible to apply bias and magnetic field to guide the plasma Usingpulsedbiasitis possible to coat "no flat" surfaces pulsed bias Monteiro, J.Vac.Sci.Technol A17(1999)1094

4 DC Vacuum Arc discharge Nb Cathode during arc Photo t =0.1s Photo t =1s Discharge (hot spot) sustained in the vapor of the cathode material (no working gas) Arc spot moves on the Nb cathode at 10m/s Niobium is fully ionized multiply charged ions +2,+3... (mean value for Nb +3) Average energy of Niobium ions about 130eV (tunable with bias) Minimum Arc Current is 60A Cathode voltage is 35V Base vacuum mbar (10-8 Pa) Main gas during arc is Hydrogen ( 10-7 mbar) Voltage Bias on samples V

5 Planar arc configuration: sample production and deposition parameters study (9) (7) (8) (10) (4) (3) (1) (1) The cathode (2) Water cooled copper support (7) (3) Water cooled stainless steel anode (4) Port for the arc ignition (6) (5) Magnetic coil (6) Additional magnetic Helmholtz coil (7) Sample holder (8) Rotating shutter (9) Electrically insulation (10) CF100 pumping port (5) Cathode-substrates distance 50cm (2)

6 Results(I): high RRR obtained (up to 100) Results on Nb film deposited by UHVCA on sapphire and copper at low temperature (<100C) R(T)/R(300K) 0.1 Niobium deposited by sputtering at Room Temperature RRR R(300K) R(10K) 10 Niobium deposited by sputtering at Temperature higher than 100C 30 Niobium deposited by sputtering at Temperature higher than 200C =β Temperature (K) 100

7 Results (II): Good Nb film Morphology FEG-SEM images: Thanks to Dr. R.Polini Dip. Chimica Univ. Roma Tor Vergata

8 Results (III):X-Ray diffraction analysis Intensity c.p.s (cps) Nb on Sapphire Nb on Copper Al 2 O Nb(110) 3 Al 2 O 3 Cu K Al Cu K α 2 O 3 α Nb(220) Nb(211) Nb(200) Nb(310) Nb(222) β cosθ/λ [nm -1 ] Williamson-Hall plot 0.08 Sputtering UHVCA b) θ 2Θ (degree) sinθ/λ [nm -1 ] R. Russo, Meas. Sci. Technol. 18 (2007) 2299 The best fit using all peaks gives a lattice parameter between nm and nm. These values are similar to the bulk nm and in agreement with T c measurement. The niobium films produced by arc deposition are less stressed than in the sputtering case (UHVCA Δa /a < ± 0.2% Sputtering Δa /a = ± %)

9 Results (IV):The multiangle sample holder: good sample quality also at high angles Deposition angles between the cathode and the substrate were 0, 30, 45, 60, 75, 90 RRR was higher then 30 for angles up to 60 degrees 40 β 10 (R 300K /R 10K ) Angle (deg)

10 Result (V): Deposition rate >100nm/min also at high angles of deposition Niobium thickness distribution on sapphire samples as a function of incidence angle at different substrate bias values deposition rate (nm/min) incidence angle (degree) bias -23V bias -40V bias -60V bias -80V

11 Results (VI): Good morphology at high angles FEG-SEM images (tilted view 35 o ) thanks to Dr. R. Polini

12 Result (VII): Grain size and morphology can be controlled by using a Pulsed Bias DC Bias -60V Pulsed bias 10 KHz 30% DC Bias -60V Pulsed bias 10 KHz 30%

13 How to deposit a cavity: the plasma transport monitored by thermal map Iris Iris pump Equator Equator Iris Equator B B B B Adjusting current in the magnetic coils used to guide the plasma it is possible to control the plasma position inside the cavity cell and to obtain a relatively uniform coating (the red region in the pictures are the hottest points where plasma is hitting the cavity surface)

14 Cavity deposition system with a single UHV arc source Vacuum pump pump Using such system 2 cavities have been coated at the end of Unfortunately deposition has to be done in 2 steps and the cavity has to be open to air between steps. During this operation cavity was contaminated and the second coating suffered from peeling during the HPWR. Laser to ignite arc B B B B ARC source This system demonstrated that it was possible deposit a single cell cavity. Using a two source system it is possible to coat the cavity without opening it to air (peeling should not be present in this case)

15 Laminar flow Laser trigger The system equipped with two arc sources was commissioned (May 2008) ARC source ARC source pump port Cavity position The two source System was tested using a stainless steel tube (in the picture) having the same length of the cavity. Some deposition tests has also been performed using a stainless steel cavity. We added a laminar flow to mount the cavity in clean condition. We do not have cleaning and test facilities (chemistry, HPWR and RF) and we need collaboration and support from other labs.

16 Cu Cavities delivered by other labs Up to now 3 Cu cavities has been delivered to Rome but they were damaged during transportation. First one was from DESY in May 2008, (deformation of cavity cell, CF100 flanges were no more parallel) The second one from CEA-Saclay, in June 2008 (deformation of cavity cell and CF100 flanges were no more parallel) And last one from CERN last week (cavity cell is integer but a huge deformation in the cut-off tube is present The CF100 flanges are almost parallel making possible to mount the cavity on the deposition system and try to coat it)

17 Some remarks In the present configuration the two cathode system has no special filters for macroparticles. We expect to have macroparticles in the iris region of the cavity cell, whereas macroparticles should not be present in the equatorial region. We expect that most macroparticles will be removed by HPWR. If macroparticles will not be removed by HPWR our cavities will be probably (hopefully) limited by field emission. In this case it is possible to use a configuration with two T-type filters as the one sketched in next slide.

18 Schematic drawing of a filtered deposition system pumping port cut-off valve plasma beam guiding coils cut-off valve pumping port isolator 1-cell cavity isolator T-type filter T-type filter anode cathode rotating platform with 3 coils anode cathode This configuration is more complex and it will reduce the deposition rate by a factor 3 at least

19 Summary and conclusion Superconducting thin Nb films with bulk material properties have been obtained using UHVCA the Niobium film structure can be controlled using a pulsed bias The plasma transport in the cavity cell with the scanning coils has been optimised and first cavities coated The two cathodes deposition system was mounted and tested We are ready to deposit the first cavity using the two cathode system

20 Acknowledgement The project is financed and supported by INFN and VI European Program "CARE" (contract number RII3-CT ). many results could not be achieved and future results will not be achieved without the help and assistance from many of you: THANK YOU