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Power is first carried from ambient temperature to about
77�K via conventional copper leads or via vapor cooled
leads.
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The conventional lead is connected to our specially designed
high temperature superconducting composite leads.
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The cold end of the lead is then connected either to a
copper wire or to a low temperature superconducting wire
that is joined to the magnet.
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NOTE: The critical current is the amount of
current a HTSC lead can carry before loosing its superconducting
properties |
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�Projected Helium Consumption |
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�MarkeTech
HTSC Leads vs. Conventional Vapor-Cooled Leads |
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Current Rating
(Amperes) |
He Consumption MarkeTech lead*
(litres/hr) |
He Consumption
Vapor-Cooled lead** (litres/hr) |
Savings
(litres/hr) |
% |
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20 |
0.05 |
0.07 |
0.02 |
28 |
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100 |
0.19 |
0.32 |
0.13 |
41 |
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150 |
0.24 |
0.48 |
0.24 |
50 |
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200 |
0.29 |
0.64 |
0.35 |
55 |
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300 |
0.39 |
0.96 |
0.57 |
59 |
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500 |
0.59 |
1.60 |
1.01 |
63 |
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1000 |
1.10 |
3.20 |
2.10 |
66 |
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1500 |
1.60 |
4.80 |
3.20 |
66 |
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*Lead consisting of conventional He vapor cooled lead from
ambient to 77K and HTSC to 4K |
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**Reported values for conventional He vapor cooled leads |
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Key Applications for MarkeTech HTSC leads
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MRI Magnet Systems
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Superconducting Magnetic Separators
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High Energy Particle Accelerators
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SMES Systems
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Large Superconducting Magnet Systems
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Superconducting Generators and Motors
For nearly any application where high currents are being
conducted from a region of 77�K to colder regions, MarkeTech
leads can reduce coolant costs.
Superconducting magnet systems requiring current from 100 to
more than 1000 amps can benefit from the significantly
reduced helium consumption provided by our HTSC leads.
MarkeTech can help you design a complete current lead system
to accommodate your design and performance requirements for
low temperature superconducting applications.
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The Effect of Temperature and Magnetic Field on
Critical Current |
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Size and Grade |
Minimum self field
critical current* |
Approx. critical current*
(77K) at longitudinal** magnetic field |
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Diameter
(mm) |
Length
(mm) |
Grade |
77 K |
64 K |
25 mT |
50 mT |
100 mT |
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7 |
70 |
1 |
60 A |
120 A |
20 A |
13 A |
8 A |
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7 |
70 |
2 |
100 A |
200 A |
33 A |
20 A |
13 A |
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10 |
80 |
1 |
100 A |
200 A |
30 A |
20 A |
12 A |
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10 |
80 |
2 |
170 A |
340 A |
50 A |
30 A |
20 A |
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| � |
12 |
80-160 |
1 |
150 A |
300 A |
50 A |
33 A |
20 A |
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| � |
12 |
80-160 |
2 |
250 A |
500 A |
90 A |
33 A |
20 A |
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12 |
80-120 |
3 |
370 A |
740 A |
180 A |
110 A |
70 A |
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18 |
80-120 |
1 |
300 A |
600 A |
120 A |
80 A |
50 A |
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| � |
18 |
80-120 |
2 |
450 A |
900 A |
200 A |
120 A |
80 A |
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18 |
80-120 |
3 |
750 A |
1500 A |
430 A |
300 A |
190 A |
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26 |
120 |
1 |
600 A |
1200 A |
270 A |
180 A |
110 A |
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| � |
26 |
120 |
2 |
900 A |
1800 A |
450 A |
270 A |
180 A |
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| � |
26 |
120 |
3 |
1500 A |
3000 A |
1000 A |
720 A |
450 A |
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* Values at 64 K and at double magnetic field are twice
higher than the values at 77 K. |
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** Respective values at transversal magnetic field are
lower by approximately 20%. |
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Conductive Heat Leak Per Pair Between
Temperatures
(Values without vapor cooling. If cooled in vapor the
values are substantially lower) |
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Diameter
(mm) |
Length
(mm) |
Grade |
77K - 4K |
64K - 4K |
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7 |
70 |
1,2 |
0.08 W |
0.05 W |
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10 |
80 |
1,2 |
0.10 W |
0.07 W |
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12 |
80 |
1,2,3 |
0.17 W |
0.12 W |
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12 |
120 |
1,2,3 |
0.10 W |
0.07 W |
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12 |
160 |
1,2 |
0.07 W |
0.05 W |
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18 |
80 |
1,2,3 |
0.40 W |
0.30 W |
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18 |
120 |
1,2,3 |
0.20 W |
0.16 W |
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26 |
120 |
1,2,3 |
0.60 W |
0.40 W |
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Fabrication of Leads |
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In order to ensure a quality lead, we begin by fabricating our
own BSCCO ceramic powders under carefully controlled laboratory
conditions. The powder is then isopressed around a mandrel and
fired under strict time, temperature procedures. Following the
firing of a silver conductive band, each tube is checked for
critical current, temperature characteristics. |
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These tubes are produced in several standard diameters and
lengths. In addition, we offer three material grades, which are
selected based on the final design specifications.
Bare leads with silvered ends are available for the
customer to attach their own metal conductors and
final fabrication design, however, most prefer that
Marketech supply a complete package, ready for
installation. We have three standard composite HTSC
lead options. |
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Composite Current Leads |
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We begin by soldering flexible copper braid to the warm end of
the tube and either a copper braid or a low temperature SC wire
to the cold end. This is normally encased in either a G-10
Fiberglass tube or a NiCu or stainless steel tube. |
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Superconducting Current Leads in G-10 Fiberglass Casing |
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The entire ceramic lead and a short portion of the metal leads
are secured in a G-10 fiberglass tube with epoxy and sealed with
fiberglass end caps. This ensures the completed assembly is
protected environmentally as well. |
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Superconducting Safety Current Leads in Metal Casing |
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Superconducting Bi based 2223-phase tubes are encased in either
a SS or a CuNi casing for protection against mechanical strains
and any accidental operating temperature increase. |
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Design Criteria for HTSC Leads to Minimize
Heat Leak |
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Electrical Load The first criteria to consider
is the maximum expected electrical load. Increasing the load
requires a larger ceramic tube to be used. The heat leak is
directly proportional to the cross section of the ceramic.
Length The heat leak is inversely proportional
to the length of the ceramic tube. The longer the tube, the
lower the heat leak. The design should accommodate the longest
length of tube possible.
Temperature The critical current for a given
lead is significantly changed by the warmest temperature the
lead will see. The critical current at 50K will be as much as
4.4 times the 77K value and just 50% the 77K value at 90K. The
operating temperature will affect the size of ceramic tube
required.
Also, the temperature drop from warm to cold end will also
affect the amount of heat leak. The heat leak from 64K to 4K is
about 70% that of the heat leak from 77K to 4K.
Magnetic Field The critical current of all
ceramic superconductors is affected by both the self field and
external fields generated by the magnet and whether the external
field is parallel or perpendicular to the lead. Knowing this
information is important in the proper design of the size of the
lead. For example, a 50-mT field parallel to the lead will
reduce the critical current by 80% at 77K. The effect of
perpendicular or transverse fields will be about 20% lower.
This effect is normally at least partially off set by the fact
that the regions of higher magnetic fields closer to the magnet
are generally also colder, which raises the critical current.
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