niobium coating of copper cavities by uhv cathodic arc: progress

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


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


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


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


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


Results (II): Good Nb film Morphology

FEG-SEM images:Thanks to Dr. R.PoliniDip. ChimicaUniv. Roma ”Tor Vergata”


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


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)


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


Results (VI): Good morphology at high angles

0 30 45

60 75 90

FEG-SEM images (tilted view 35o) thanks to Dr. R. Polini


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


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


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


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.


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)


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.


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


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


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

niobium coating of copper cavities by uhv cathodic arc: progress

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