a15 superconductors - · pdf fileessence of the previous slides. testardi, 1975 literature:...

A15 Superconductors:Alternative to Nb for RF CavitiesS.M. Deambrosis*^, G. Keppel*, V. Palmieri*^, V. Rampazzo*^,

C. Roncolato*, R.G. Sharma°, F. Stivanello*

Padova University, Material Science Dept

* INFN - Legnaro National Labs^ Padua University, Science faculty, Material Science Dept

° Nuclear Science Centre, New Delhi

Outline

• Theory: Surface Resistance

– Mo-Re system: Deposition Technique and Results

– V3Si: Thermal Diffusion in Reactive SiH4 Atmosphere

– Nb3Sn: Liquid solute diffusion tecnique

– 6 GHz cavities: RF Measurements

• Conclusions and future plan

Zn = 1 − iσnδ

= 1 − iρnδ

σ1-iσ2 in place of σn

Surface Impedance and Surface Resistance

For a normal metal in the normal regime:σn = 1 / ρn = dc conductivity at T

δ = skin depth

As derived by Nam, for T < Tc / 2, Rs can be approximated by:

2

1

3

2

12n

ns

n

RR σ

σ

σσ

⎛ ⎞⎜ ⎟⎝ ⎠

=

Extension to Superconductors:

( ) ( ) ( )1 2

n

f E f E g E dEσσ

ωω

∞+

∆

= + +⎡ ⎤⎣ ⎦∫ hh

( ) ( ),

2 1 1 2n

f E g E dEω

σσ

ωω

∆−

∆ − − ∆

= − +⎡ ⎤⎣ ⎦∫h

hh

In the framework of the BCS theory, for ω < 2 ∆, the complex conductivity of a superconductor is:

Mattis and Bardeen Integrals

The two integrals σ1/σn and σ2/σn are easily numerically calculated.

In the normal skin effect regime, for ħω << 2 ∆

( )2/

/1

2

ln1

B

B

B

K T

K T

n

K T

eeσ

ωσ−

−∆

∆

∆⎡ ⎤⎢ ⎥ ∆⎢ ⎥=⎢ ⎥+⎢ ⎥⎣ ⎦

h

2 tanh2n BK T

σσ

πω∆ ∆

=

( )( )TOeARR TKn

n

nBCS

B ,,12

123

ωρσσ

πω

∆+=⎟⎠⎞

⎜⎝⎛

∆≅

∆−h

RBCS

Then, if T < Tc / 2

Empirically, Rres is found to be dependent on ρn too.

For low rf losses,

a high TC value is not sufficient

A metallic behaviourin the normal state is mandatory

Essence of the previous slides

Testardi, 1975

Literature: Mo-Re system

Mo38Re62

Mo40Re60Mo65Re35


A – Sputtering v ~ 500 Å/min, deposition T = 1000 °C, B – Sputtering v ~ 1000 Å/mindeposition T = 1200 °C, C – Mo-Re bulk samples

Gavaler et al.

Mo-Re system: deposition tecnique

Magnetron Sputtering at high T

3 Target Compositions

Mo75Re25

Mo38Re62

Mo60Re40

26 SPUTTERING RUNS

11 samples SETS

More than 60 samples

Annealing treatment

Mo75Re25

Mo75Re25: XRD Spectra

44,49 64 ,49 84 ,49 104 ,49 124 ,49 144 ,49

0

20

40

60

80

100

Rel

ativ

e In

tens

ity

An g o lo 2 ϑ (g ra d i)

(110)

(200)

(211)

(220)(310)

(222)

(321)

Film XRD Spectrum

Deposition T = 633°C, Annealing t = 15 minutes

Target XRD Spectrum

11,0 11,2 11,4 11,6 11,8 12,0 12,2-0,002

0,000

0,002

0,004

0,006

0,008

0,010

0,012

0,014

0,016

R (Ω

)

T (K)

Tc = 11.398K∆Tc = 0.009KRRR = 1.57

Mo75Re25: A Superconductive Transition Curve

Deposition T = 633°C Annealing t = 15 min

0 5 10 15 20 25 3011,2

11,3

11,4

11,5

11,6

11,7

11,8

11,9T c (

K)

Annealing time (minutes)

Deposition T = 750°C Deposition T = 800°C

Mo75Re25: Tc vs Annealing Time

0 Gauss

Mo75Re25: R vs T at Increasing H

4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0 9,5 10,0 10,5 11,0 11,5-0,002

0,000

0,002

0,004

0,006

0,008

0,010

0,012

0,014

0,016R

(Ω)

T (K)


40 000 Gauss

8 9 10 11 12-0,0372

-0,0370

-0,0368

-0,0366

-0,0364

-0,0362

-0,0360

-0,0358

M' (

emu)

T (K)

Mo75Re25, Cu: Deposition T = 680°C, no annealing

A Mo75Re25 Film Deposited on Cu

Tc = 11.18K∆Tc = 0.08K

A Mo75Re25 Film Deposited on Nb

8 9 10 11 12

-0,028

-0,026

-0,024

-0,022

-0,020

-0,018

-0,016

-0,014M

' (em

u)

T (K)

Mo75Re25, Nb: Deposition T = 725°C, Annealing t = 15 min

Tc = 11.03K∆Tc = 0.08K

Nb

Mo75Re25

11,8 11,9 12,0 12,1 12,2 12,3 12,4

0,000

0,005

0,010

0,015

0,020

R (Ω

)

T (K)


Deposition T = 750°C Annealing t = 60 min

Tc = 12.00K∆Tc = 0.041KRRR = 1.88

0,0 0,5 1,0 1,5 2,0

0,05

0,06

0,07

0,08

0,09∆

T c (K

)

Annealing time (h)

Deposition T = 800°C Deposition T = 850°C

Mo60Re40: ∆Tc vs Annealing Time

Lines of equal RBCS. At T = 4.2 K, f = 500 MHz, s = 4

RBCS depends on ∆ and ρn

Nomogram

Mo60Re40 (Tc = 12.13, RRR =1.3, ρn ~ 30µΩcm ),

Mo75Re25 (Tc = 11.82, RRR =1.71, ρn ~ 10µΩcm).

9.0 9.5 10.0 10.5 11.0 11.5

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

T (K)

R (Ω)



Tc = 9.47K∆Tc = 0.029KRRR = 1.11

• Annealing treatments give surprising results: >Tc,<∆Tc

• Tc is higher than 12K (Mo60Re40)

• Long range order is very important so ∆Tc becomes one of the most meaningful parameters. A sharpsuperconducting transition corresponds to a high ξ0.


• We deposited more than 100 films

• RBCS is around 16 nΩ (Mo75Re25, Mo60Re40)

V3Si: RRR vs Silicon content

Preliminary results on cosputtering of V3Si films by the facing-target magnetron technique

Y. Zhang, V. Palmieri, R. Preciso, W. Venturini, Legnaro National Laboratory, ITALY

Schematic diagram of the facing-target magnetron.

V target Si target

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

13.5 14.0 14.5 15.0 15.5 16.0 16.5

sample5-9RR

K

Superconducting transition of a V3Si sample

RR

R

Thermal diffusion of V3Si filmsY. Zhang, V. Palmieri, W. Venturini, F. Stivanello, R. Preciso, Legnaro National Laboratory, ITALY

40h20h900ºC300W1.2·10-4mbar

Anneal in vacuum

Diffuse in silane

TemperatureHeat powerSilane pressureDiffusion

Parameters:

There is room to improve the film quality by higher thermal diffusion temperature or by longer annealing time in vacuum.

2.5

3.0

3.5

4.0

4.5

14.5 15.0 15.5 16.0 16.5 17.0

Bulk Vanadium, sample No.13-2V

K

AC inductive measurement:Tc ~ 16.0K ∆Tc < 0.4K

6.0

9.0

12.0

15.0

18.0

10.0 15.0 20.0 25.0 30.0Silicon content ( % at. )

800oC

500oC

Reactive sputtered V3Si filmsY. Zhang, V. Palmieri, W. Venturini, R. Preciso, Legnaro National Laboratory - INFN, Italy

a bSurface of two annealed samples under SEM: Grain size, (a) 0.2µm, (b) 0.5µm

Beforeannealing

After annealing

T c(K

)

Tcs of 17 K and RRR values of 18 have been

recovered by annealing in SiH4 atmosphere

No matter how good the initialsuperconducing properties of the film are

We are ready to apply the thermal diffusionmethod to 6 GHz cavities


Wuppertal: Nb3Sn cavity (1.5 GHz) obtained trough Snvapour phase diffusion (’90s)

Nb3Sn: Liquid solute diffusion

Linearfeedtrough

Coolingwater jacket

Furnace

Liquid Sn

Nb3Sn: Used System

Nb3Sn: Phase Diagram

Nb3Sn

<Tc phases

930°C

Nb3Sn: SEM Image

20 µm

Nb3Sn

Nb

0 2 4 6 8 10 12 14 16 18 20

0

5

10

15

20

25

30 Nb3Sn n°4: 970°C, 30min+6h

Sn a

t.%

Depth (µm)

Nb3Sn: Sn at.% vs Depth

Nb3Sn Nb

20 40 60 80 100 120 140 1600,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0R

elat

ive

Inte

nsity

Angle 2θ

Nb3Sn n°4: T=970°C, 30min+6h

(200)

(210)

(211)

(222)(320)

(321)

(400)

(420)(421)

(332)(520)

(521)(440) (600)

(611)

(622)

(630)

Nb3Sn: XRD

0 2 4 6 8 10 12 14 16 18 20-0,026

-0,024

-0,022

-0,020

-0,018

-0,016

-0,014

-0,012M

' (em

u)

T (K)

Nb3Sn n°8: T=1000°C, 2h+14h

Tc = 17.3 K∆Tc = 0.1 K

Nb3Sn: A Superconductive Transition Curve

Nb

Nb3Sn

Nb3Sn Process Parameters:

T = 970°CDipping time = 1hAnnealing time = 1h

Nb3Sn Surface Treatment:

Pure HCl (55-66°C) for 15 minutes

Nb3Sn: A 6 GHz Cavity

• Liquid Sn wets the Nb surface and bulk diffusion starts

• No nucleation sites on Nb are required

• Fast growth of Nb3Sn layer due to bulk diffusion

• Uniformity of Nb3Sn film ensured and stoichiometrymantained

• We can avoid Nb-Sn low Tc phases:- manteining T > 930°C during the experiment- reducing T very fast at the end of the process

• A possible Sn outer layer has to be removed: we are ableto get rid of it by prolonged post annealing


6 GHz seamless cavities

obtained by the spinning technique:

And now?

We can produce a large amount of samples but it isdifficult to measure their RF resistance

• are made from scrap material

• do not need welding (even for flanges)

• are directly measured inside a Liquid He dewar

• Mechanical polishing

• Chemical polishing

3. Q Factor Measurement

• A15 obtainment

6 GHz Cavities

1. Spinning Technique

2. Surface Treatments

6 GHz Cavities: Q Factor Measurement

Nb3Sn

V

Conclusions

Nb

From scrap material and by a seamless technique

we are planning

A 6 GHz CAVITIES MASS PRODUCTION TO

INVESTIGATE A15 INTERMETALLIC COMPOUNDS

The end

A atoms form linear chains: they are parallelto the 3 crystallographic directions [100], [010], [001]

Stoichiometry ~ A3B

B

A

A15 Compounds Structure

TM

noTM

TM

Mo75Re25 Cavity (MIT 1978)

K. Agyeman, I. M. Puffer, J. A. Yasaitis and R. M. Rose, “Superconducting Mo0.75Re0.25 cavities at X-band”

Mo60Re40

A.Andreone, A.Barone, A.Di Chiara, G.Mascolo, V.Palmieri, G.Peluso, U.Scotti, 1988


6 GHz Cavities: Mechanical Polishing

6 GHz cavities: Chemical Polishing

a15 superconductors - · pdf fileessence of the previous slides. testardi, 1975 literature:...

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