Niobium Coating of Copper Cavities by UHV Cathodic Arc: progress report
In collaboration withA. Andreone, Università di Napoli “Federico II”, and INFN-Na
G. Lamura, CNR-INFM “Coherentia”, and INFN-NaGroup of Prof. M. Sadowski, SINS Poland,
also support and collaboration from:CEA-Saclay, CERN, Cornell University, DESY, Jefferson Lab,
Legnaro INFN-LNL…
L. Catani, A. Cianchi, D. Digiovenale, J. Lorkiewicz, Prof. S. Tazzari, INFN-Roma "Tor Vergata", ItalyRoberto Russo, Istituto di Cibernetica del CNR and INFN-Na, Napoli, Italy
JLab 22-25 July 2008
Outline
Summary of the Vacuum arc discharge
Results using the UHV arc sources
The cavity deposition
The new deposition system
Summary and Conclusion
JLab 22-25 July 2008
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 plasmaUsing pulsed bias it ispossible to coat "no flat" surfaces
pulsed bias
Monteiro, J.Vac.Sci.Technol A17(1999)1094
JLab 22-25 July 2008
Discharge (hot spot) sustained in the vaporof the cathode material (no working gas) Arc spot moves on the Nb cathode at 10m/sNiobium is fully ionizedmultiply charged ions +2,+3... (mean value forNb +3)
Average energy of Niobium ions about 130eV (tunable with bias)Minimum Arc Current is 60ACathode voltage is ≈ 35VBase vacuum ≈ 10-10 mbar (10-8 Pa)Main gas during arc is Hydrogen (≈10-7 mbar)Voltage Bias on samples 20-100V
Nb Cathodeduring arc
Photo t =0.1s
Photo t =1s
DC Vacuum Arc discharge
JLab 22-25 July 2008
Planar arc configuration: sample production and deposition parameters study
(1)
(7)
(10)
(3)
(5)
(6)
(4)
(8)
(9)
(7)
(2)
(1) The cathode(2) Water cooled copper support (3) Water cooled stainless steel anode(4) Port for the arc ignition (5) Magnetic coil (6) Additional magnetic Helmholtz coil(7) Sample holder (8) Rotating shutter(9) Electrically insulation(10) CF100 pumping port
Cathode-substrates distance 50cm
JLab 22-25 July 2008
0 20 40 60 80 1000.01
0.1
R(T
)/R(3
00K
)
Temperature (K)
Results(I): high RRR obtained (up to 100)
0 20 40 60 80 1000.01
0.1
R(T
)/R(3
00K
)
Temperature (K)
Niobium deposited by sputteringat Room Temperature
0 20 40 60 80 1000.01
0.1
R(T
)/R(3
00K
)
Temperature (K)
Niobium deposited by sputteringat Temperature higher than 100C
0 20 40 60 80 1000.01
0.1
R(T
)/R(3
00K
)
Temperature (K)
Niobium deposited by sputteringat Temperature higher than 200C
Results on Nb film deposited by UHVCA on sapphire and copper at low temperature (<100C)
10
100
30
RRR R(300K)R(10K) =β
JLab 22-25 July 2008
Results (II): Good Nb film Morphology
FEG-SEM images:Thanks to Dr. R.PoliniDip. ChimicaUniv. Roma ”Tor Vergata”
JLab 22-25 July 2008
Results (III):X-Ray diffraction analysis
The best fit using all peaks gives a lattice parameter between 0.3299nm and 0.3313nm. These values are similar to the bulk 0.3306nm and in agreement with Tc measurement.The niobium films produced by arc deposition are less stressed than in the sputtering case (UHVCA Δa⊥/a ⊥ < ± 0.2% Sputtering Δa⊥/a ⊥ = 0.636 ± 0.096 %)
20 40 60 80 10010
100
1000
10000
100000Nb on Copper
Cu Kα
c.p.
s
2θ20 40 60 80 100
10
100
1000
10000
100000Nb on Sapphire
Cu Kα
Al2O3Al2O3
Al2O3
Nb(222)Nb(310)
Nb(220)Nb(211)
Nb(200)
Nb(110)
Inte
nsity
(cps
)
2Θ (degree)
0 5 10 15 20 25
0.02
0.04
0.06
0.08 Sputtering UHVCA
β co
sθ/λ
[nm
-1]
4sinθ/λ [nm-1]
b)
R. Russo, Meas. Sci. Technol. 18 (2007) 2299
Williamson-Hall plot
JLab 22-25 July 2008
Results (IV):The multiangle sample holder: good sample quality also at high angles
Deposition angles between the cathodeand the substrate were 0, 30, 45, 60, 75, 90 RRR was higher then 30 for angles up to 60 degrees
0 15 30 45 60 75 900
10
20
30
40
β 10(R
300K
/R10
K)
Angle (deg)
JLab 22-25 July 2008
Result (V): Deposition rate >100nm/minalso at high angles of deposition
Niobium thickness distribution on sapphire samples as a function of incidence angle at
different substrate bias values
0
100
200
300
400
500
600
0 20 40 60 80 100
incidence angle (degree)
depo
sitio
n ra
te
(nm
/min
) bias -23Vbias -40Vbias -60Vbias -80V
JLab 22-25 July 2008
Results (VI): Good morphology at high angles
0 30 45
60 75 90
FEG-SEM images (tilted view 35o) thanks to Dr. R. Polini
JLab 22-25 July 2008
Result (VII): Grain size and morphology can be controlled by using a Pulsed Bias
DC Bias -60V Pulsed bias 10 KHz 30%
Pulsed bias 10 KHz 30%DC Bias -60V
JLab 22-25 July 2008
pump
B
B
B
B
How to deposit a cavity: the plasma transport monitored by thermal map
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)
Equator
Iris
Iris
Equator
Iris
Equator
JLab 22-25 July 2008
pump
B
B
B
B
Cavity deposition system with a single UHV arc source
Using such system 2 cavities have been coated at the end of 2007. 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.
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)
ARC source
Vacuum pump
Laser to ignite arc
JLab 22-25 July 2008
The system equipped with two arc sources was commissioned (May 2008)
ARC source
ARC source
Laminar flow
Lasertrigger
pumpport
Cavityposition
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.
JLab 22-25 July 2008
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 presentThe CF100 flanges are almost parallel making possible to mount the cavity on the deposition system and try to coat it)
JLab 22-25 July 2008
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.
JLab 22-25 July 2008
Schematic drawing of a filtered deposition system
anode
cathodecathode
anode
pumping port
cut-off valve
T-typefilter
cut-off valve
isolator isolator
rotating platform with 3 coils
1-cell cavity
plasma beam guidingcoils
pumping port
T-typefilter
This configuration is more complex and it will reduce the deposition rate by a factor 3 at least
JLab 22-25 July 2008
Summary and conclusion
Superconducting thin Nb films with bulk material properties have been obtained using UHVCAthe Niobium film structure can be controlled using a pulsedbiasThe plasma transport in the cavity cell with the scanningcoils has been optimised and first cavities coatedThe two cathodes deposition system was mounted and tested We are ready to deposit the first cavity using the two cathode system
JLab 22-25 July 2008
Acknowledgement
The project is financed and supported by INFN and VI European Program "CARE" (contract number RII3-CT-2003-506395).
many results could not be achieved and future results will not be achieved without the help and assistance from many of you:
THANK YOU