JSC “State Scientific Center RF
TRINITI”
1
16 Т dipole
for VLHC
Prof. E.Yu.Klimenko
It is a 2D-proposal. Some features are obvious, some are tested and used in my practice,
others need studying.
2
Introduction
There are a lot of new dipole projects for LHC upgrading
[1- 5]. Most of them require new Nb3Sn wire development
with the current carrying capacity (CCC) as high as 1500
A/mm2 in 15 T, to be used in a multishell design.
Here another possibility is discussed:
What a new dipole design must be developed to achieve
the desired aim with an existing wire with CCC as low
as 500 - 1000 A/mm2.
The aim is: A dipole 15 m in length with 16 T in 50 mm
aperture. A pair of the dipoles must be confined in a
cylindrical iron yoke of 700-750 mm in diameter.
The new design should have no restrictions on shell
number.
3
I was deeply impressed by prof. R. Flükiger’s presentation at
FCC Week, Rome (I), 11-14.4.20 (What happened to the Nb3Sn Bronze
Route?)
We both consider a bronze Nb3Sn wire as the most suitable
material for VLHC dipoles.
He hopes to reach jc(16 T)=1500 A/mm2 at APC wire.
I will show that the 16 T dipole may be made with existing
Nb3Sn wire.
4
Properties of modern bronze Nb3Sn (R. Flükiger)
This presentation uses “(Nb-Ta)3Sn alloyed” option.
It was successfully used “ITER” option in our previous presentation.
5
The basic idea:
To obtain the necessary J = (1.27 – 2.54)e7 A/m at
sacrifice of high jc in lower field (to use cables of
various cross section) . It is so called “ winding
optimization”
6
The first optimized SC magnet [9]
The winding optimization is not any newcomer. We used it as long as 1967.
Inner diameter = 200 mm
The figures in the circles
denote number of SC wires
in electroplated conductors.
7
The main points of the proposal:
1. Optimization of the winding.
(That means: Several types
of Roebel conductor are used with different numbers of wire in each.
So the current density is higher in low field sections of the winding.)
2. A laminar type winding
(the turns are adhesive bonded
to rigid strong sheets providing their fixation along whole length of
the conductor and direct force transferring to the mechanical
structure)
3. Elliptical shape of the dipole cross section for
homogeneous field generation.
8
Optimization of the winding.
Thickness ratio of optimized and
nonoptimized windings depends on
maximum generating field. The effect
is more distinct in the vicinity of
critical field.
Magnetic field distribution in a pair of
parallel infinite plates carrying current.
The current in the left plate is
homogeneous (jc(20 T)) , the current
distribution in the right plate is optimized.
(It was assumed jc=1.3e9 - 5.8e7*B A/m2)
9
Laminar type winding
Comparison of hysteresis loops of
laminar (upper) and usual (lower)
windings [6]. The laminar winding is
much more rigid and generates less
heat.
A multilayer winding made with a
conductor having soft insulation can’t be
rigid. It generates heavy excitations. So it
is prone to degradation and training.
Laminar winding rigidity is provided by a force
structure. A conductor is adhesively bonded to
the structure. It is reliably fixed and unloaded.
The film adhesive (VK-36) strength to shifting is
about 100 MPa.
10
Some examples of laminar windings [6-8]
The laminar windings are free of training and degradation, as a rule. Sometimes there were
no noise at a diagnostic bridge.
The manufacturing technique is well developed.
11
Nb3Sn wires used for estimations
Not so complete refinements will allow
transforming of commercially produced
ITER conductor into VLHC one.
If Steckly parameter >>1
Stability criteria E<Ej=hPTc/nIj
Wire stability is determined with smoothness of
transition (the less “n” , the higher stability).
Copper quality and quantity do not affect on
conductor stability [ 11 ].
The copper channels are useful for
preventing temperature rise in the bronze
that is a cause of instability growth [ 12 ].
They are not necessary in the flat wire
(New)
Previous
New
Diameter
1.5
0.5x3.5
Bronze/copper ratio
2.45:1
1:1
RRR
80
80
n
<30
<30
Filaments number
12 000
12000
Filaments diameter,
mcm
6.0
6.0
Twist pitch, mm
25
25
12
Single Dipole design
6 types of
conductors
Y-force support
Conductor
X-force support
Magnetic field of
elliptical shell is more
than of circular one by
13%
(c/b=1.3)
6 types of Roeble cables
Previous option
New one
13
Why does the New dipole has the same dimensions as previous one
in spite of much higher jc of the conductor?
The Force Structure of New one is more advanced. It could be done
more compact but without hope to work properly.
14
Magnetic field map of a single dipole, Io=33.3 kA
6
7
5
6
8
9
10
8
11
8
9
10
5
0,15
7
2
15
3
5
87
9
11 10
5
9
6
6
11
-0,1
1
78 6
5
11
12
15
6
6
5
7
10
10
-0,15
9
14
1
12
14
15 14
5
-0,1
13
1121
10
98
67
4
3
2
-0,05
8
12
8
0
15
0,05
54
87
9
10
11
12
13
6
14
0,1
7
-0,05
0
0,05
0,1
15
Magnetic Field in aperture, Io=33.3 kA
0,05
0,05
0,001
0, 2
0,03
15
0,02
,9
0,02
-0,0
05
01
,
15
0,01
- 0,0
0,00
1
15,913
15
,4
,005
-0,001
-0
15
,9
0,01
0,04
4
,9
15,905
0,03
15
15,
0,04
5
90
15,903
0,001
-0,01
-0,03 -0,02 -0,01
15,4
15,913
,4
15
,9
15
15
,9
0
0,01
0,02
0,03
0,00
1
-0,03
-0,04
B
5
0,04
0, 2
-0,03 -0,02 -0,01
1
-0,00
-0,005
15,905
-0,03
-0,04
-0 ,0 0
-0,02
0,001
-0,02
001
-0,
05
,9
15
15,9
-0,01
0,001
0
15,9
15,903
0
0
0,01
B
x
0,02
0,03
0,04
16
Pair of dipoles in iron yoke
A pair of elliptical
dipoles are arranged
well with an iron
yoke of 600-720 mm
in diameter.
17
Cryostat surface B=1.7 T
Cryostat surface B=0.5 T
Without yoke
With 720 mm yoke
Magnetic field rises due to second dipole straw field (1.7 T) and an yoke (~2 T).
So the 16 T dipole winding will be made more compact.
18
Single dipoles parameters
Parameter
Previous
Units Previous New
Nb3Sn wire option
ITER
Nb-Ta alloy
Bronze/Cu
2,45:1
1:1
Wire cross section
1.5 dia
0.5x3.5
Roeble cond. (n wires)
8 -36
12-60
248x315
246x324
Number of shells
6
6
Number of layers
80
34
Number of turns
342
158
Dipole ellipse axis
mm
Max. current
kA
15
33.3
Inductivity
mH
38.6
7.67
Stored energy
MJ/m
4.34
4.25
Aperture field
T
15.97
15.913
Max.field
T
16.11
16.7
Field quality (Bx(35 mm)
T
5.0E-4
5.0E-3
Operating temperature
K
4.2
4.2
Metal cross section
mm2
15 112
12 488
Conductor mass
kg/m
~150
~125
New
19
-7.39 MN/m
Forces in the single dipole at 33.3 kA
(upper quater)
The total pressure in the
median plane is 76.2 MPa
13.75 MN/m
The closed circles are related to continuous
plates and designate tensile stress. The open
ones to plates laying in the plane of aperture.
Their sum (2.65 MN/m) is held by shear stress
(25.7 MPa) on the borderplane of the winding
rest.
The forces are high clearly but not hopeless.
More detailed structural analysis requires information on
composite mechanical properties. It needs experimental studying.
20
Structure elements
Indirect cooling.
High heat conductive composite on a base of
fiberglass and copper wires may be used as
structural material. It provides sufficient strength
and absence of eddy loss.
High electrical strength allows use bare conductors
providing that Y-supports are insulated.
Temperature conductivities comparison
of the composite and its components
Some of the structural X-plates contain protective heaters
21
Free addition
An option of quadrupole laminar winding
with 50 mm aperture.
22
Without Yoke
With yoke
Bm=10.9, G=204.1
Bm=12.6, G=226T/m
3.7 kA
23
Conclusion
1.
There is an alternative to unlimited increasing requirements to
superconductor current carrying capacity. It is modified VLHC
dipole design.
2.
The laminar winding dipole coupled with optimized winding
allows solving VLHC problems with the modern commercially
produced conductors. It is important that losses in these
conductors are very low.
3.
The manufacturing technique of the laminar windings is
developed in TRINITI . However a new element of the
technique must be developed. It is mounting of force structure
at heat treated dipole.
4.
16 T is not the upper limit of this type dipoles.
24
Bibliography
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2. E.Todesco, Conceptual design of 20 T dipoles for High-Energy LHC, CERN-2011-03, EuCard Conf. 2011-001,
pp 20-26.
3. P. McIntire, 20 T dipoles and Bi 2212: the path to the LHC energy upgrate, CERN-2011-03, EuCard Conf. 2011001, pp 70-74.
4. M.Sorby, Cosine-theta configuration for SC Dipole, (presentation), Eurocircol annual meeting, Orsay,
November 19-20 2015.
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accelerator dipole model. https://www.researchgate.net/publications/287506235.
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v30, N1, pp.41-45
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