purification of 6 ghz resonators at extremely high temperatures at

5th Workshop on Thin films and New Ideas for pushing the limit of SRF,
July 18--20, 2012, Jlab, Newport News VA
PURIFICATION OF 6 GHZ RESONATORS AT
EXTREMELY HIGH TEMPERATURES AT
ATMOSPHERIC PRESSURE
A.A. Rossi, S. Stark, R. K. Thakur, N. Visonà
and V. Palmieri
ISTITUTO NAZIONALE DI FISICA NUCLEARE
Legnaro National Laboratories
and University of Padua
There is a plenty of
incredible games to play just
close to the melting point
of Niobium ….
PureNb
NbN2
NbN2a
NbN2b
NbN3
NbN4
NbN5
NbN6
NbN8
NbN8Ox
NbN9
NbN11
NbN12
NbN13
NbN13 3'' BCP
NbN14
8
10
Q
BCSNB
Bulk Nb
6 Ghz @4,2K
7
10
0
1
2
3
EPk(MV/m)
4
5
6
Nb5N6; Nb4N3
d-NbN 1-x; h-NbN (hexagonal);
d’-NbN (hexagonal);
b-Nb2N (hexagonal); g-Nb4N3-x
a-Nb (N) (bcc solid solution)
Niobium
SC 2
SC 1
Vacuum
l1
Hz
l2
Niobium
a
Overlayer
SC 2
SC 1
l1
l2
Vacuum
For a “2 Superconductor system”
Hz
1 10
10
a
Q2
Q
Q( x)
Q
91
1 10
5
10
l120
/a
15
x
Q  Q(1 1 - e
-a l 1
)  Q 2e
-a l 1
 Q1 ( Q 2 - Q1 )e
 Q1  Q e
.
-a l 1
-a l 1
SC 2
SC 1
l1
l2
Vacuum
Hz
Q  Q1 ( Q 2 - Q1 )e
-a l 1
1 10
10
Q2
a
Q( x)
Q
91
1 10
5
10
x
15
20
l1/a
An hypotesis:
Gap and Penetration depth depends on magnetic field
( B )   0 - kB
l
l( B )  l0 
B  ...  l0  aB
B
0
Q  Q1 ( Q 2e
-k 2b
-
Q1 )e
a
( l 1ab )
Q2
QTot
Q1
Q1 (* 1 - e
5
10
15
a
( l 1ab )
20
)
Q2 * e
25
-k 2b
30
e
a
( l 1ab )
35
40
45
b
50
Q  Q1 ( Q 2e
= Q (* 1 - e
1
1 10
a
( l 1ab )
-k 2b
Q1 )e
) + Q2 * e
-k 2b
e

a
( l 1ab )
11
Q2
Why Q increases
( B)
withq1field?
-
a
( l 1ab )
Q2e-k2b
q2( B)
( B)
TheqTmore
l1
Q1
increases
vs field
Q2
Q2 exp ( - k2 B)
Q1
The Q1
more
SC2low
(- t 
 ( Q2- Q1)  exp 

 c 
losses)is involved
1 10
10
5
10
15
20
25
B
30
35
40
45
b
50
Q  Q1 ( Q 2e
= Q (* 1 - e
1
a
( l 1ab )
-k 2b
-
Q1 )e
) + Q2 * e
a
( l 1ab )
-k 2b
e

a
( l 1ab )
1 10
13
1.1 10
12
The ticker is SC 1, the smoother is the Q-rise
qT ( B  0.1)
qT ( B  0.5)
qT ( B  1)
a/l
qT ( B  1.5)
Q2
qT ( B0 2)
O
Q1
0.1
Q2
1
Q2 exp ( - k2 B)
10
1 10
12
 - t Q1

 c 
Q1 ( Q2- Q1)  exp 
11
1 10 1 1011
0.04
2
4
6
8
10
B
12
14
16
18
b
20
20
One of our thermal diffused NbN
Cu sputtering into Nb 6GHz cavity
Cavity
Cathode
Sputtering of a Cu overlayer onto a Nb 6GHz cavity
Didn’t you notice
anything strange?
Sputtering of a Cu overlayer onto a Nb 6GHz cavity
Sketch of the furnace
Exhaust gases
Cavity or Sample
Coil
(250-3000)ºC
Gas
bottle
Pyrometer
Work head
15 KW
Input gas
Power
supply
Low overpressure
• We took a contaminated cavity,
exposed to air for years and with a
Q around 1e+6
• We treated at 2000°C for only a few
tenths of seconds at atmospheric
pressure without using vacuum
• The Q at 1,8 K jumped up for 3
orders of magnitede
We did not act onto RRes.
We acted onto RBCS!!!
CONCLUSIONS
A new treatment of the of
time of the minute, at
temperatures over 2000°C,
without using vacuum, allows
the recovery of performances
of 6 GHz cavities
THANK YOU

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