CN100477027C - Current lead of superconductive magnet - Google Patents

Abstract

The invention is concerned with the current down-lead of the superconductive magnet, includes the copper down-lead (-) and the groupware of the high-temperature superconductive current down-lead (-), the characteristic is: the indoor temperature end of the copper current down-lead (-) connects with a pair of semiconductor cooling groupware (-) in series in order to form combination current down-lead of the semiconductor cooling groupware (-), the copper down-lead (-) and the high-temperature superconductive current down-lead groupware (-);semiconductor cooling groupware (-) consists of the semiconductor cooling element (- ~ -), copper connecting nose (- ~ -) and the copper compacting plate (- ~ -); the invention can decrease the tie-in temperature between the top of the copper down-lead (-) and the copper compacting plate (- ~ -), reduce the leaking heat to the system from the copper down-lead, reduce the cooling need of the first-level cooling head of the cooling machine, and increase the electrify ability of the current down-lead.

Description

A kind of current feed of superconducting magnet

Technical field

The present invention relates to the conduction cooling superconducting magnet current feed.

Background technology

At the beginning of the eighties of eighties of last century, M.O.Hoenig has proposed to cool off NbSn with refrigeration machine ₃The imagination of superconducting magnet has also been carried out conceptual design to it, but the successful development of real practicability conduction cooling superconducting magnet system then is the thing of the nineties, and this mainly should give the credit to the use of refrigeration machine novel magnetic cool storage material and high-temperature superconductive lead wire.

The conduction cooling superconducting magnet system mainly is made up of superconducting magnet, G-M refrigeration machine, low-temperature (low temperature) vessel, current feed, magnet power supply and control assembly etc.Its core technology is to use secondary G-M refrigeration machine directly to cool off superconducting magnet.Soaking superconducting magnet system than liquid helium has simple to operate, need not complicated liquid helium device, plurality of advantages such as construction and cost of use attenuating, but its deficiency is arranged also, outstanding behaviours is being that G-M refrigeration machine refrigeration power is limited, as the refrigeration machine of SHI-SRDK415D model, be 35W during one-level cold head refrigeration work consumption 50K, and have only 1.5W during the refrigeration work consumption 4.2K of secondary cold head.So for the conduction cooling superconducting magnet system, the heat transfer or the thermal insulation that how to increase or reduce associated components just become the key technology place whether system can succeed in developing.

Pine in every leakage, the leakage heat of current feed has accounted for very great share.The leakage heat of current feed comprises that not only conduction heat also comprises Joule heat.At present, the current feed great majority that using are copper-high-temperature superconducting lead binary combination mode, and the copper lead-in wire is operated between room temperature and the refrigeration machine one-level cold head temperature, and high-temperature superconductive lead wire is operated between one-level cold head and the secondary cold head temperature.Like this, the hot major part of leakage of copper lead-in wire can be taken away by the one-level cold head, and high-temperature superconductive lead wire then is in superconducting state, has eliminated Joule heat; On the other hand, the thermal conductivity of high temperature superconducting materia is very low, can reduce along the conductive heat leakage of lead-in wire.The result who compares in the document, the leakage heat of this composite type electric current lead-in wire, can reduce to and have only original copper current lead-in wire to leak 1/5th to 1/10th level (Wesche and A.M.Fuchs of heat, Design of superconductingcurrent leads, Cryogenics, 1994 Volume 34, Number 2, p.145-154).

Leak heat although present current feed has reduced significantly, it still has following shortcoming:

1, some energising is the conduction cooling superconducting magnet system of hundreds of ampere, the refrigeration work consumption deficiency of refrigeration machine one-level cold head, can't take away the Joule heat of copper lead-in wire fully, thereby cause cold screen temperature to raise, the radiant heat that magnet is accepted is excessive, when serious, may cause the superconducting magnet cisco unity malfunction.

2, energising is the device of last kiloampere, as high-temperature superconductor sample test system, its caloric value far is not that a refrigeration machine can be taken away, and to big like this current feed, a G-M refrigeration machine can only be installed additionally again, will certainly increase input like this, and make system configuration more complicated.

Summary of the invention

For overcoming the shortcoming of prior art, the present invention proposes a kind of new current feed pattern, promptly, form semiconductor refrigerating-copper-high-temperature superconductive lead wire ternary structural compound mode being connected in series the semiconductor refrigerating assembly in copper-high-temperature superconductive lead wire diadactic structure at present.

The technical solution adopted in the present invention is as follows:

The present invention is connected in series a pair of semiconductor refrigerating assembly at the indoor temperature end of former superconducting magnet copper current lead-in wire, utilize the semiconductor refrigerating principle, the temperature that can significantly reduce copper current lead-in wire temperature end reaches about 50K-100K, can reduce the external world and reach 20%-30% to intrasystem leakage heat.

The semiconductor refrigerating assembly mainly is fixed plate by semiconductor refrigerating element, copper wiring nose and copper and forms.The semiconductor refrigerating element is fixed between the plate at copper wiring nose and copper, fixes and is pressed on the vacuum tank cover plate by fastening bolt.

The present invention is according to the semiconductor refrigerating peltier effect theory: P type semiconductor material and N type semiconductor material connect into thermoelectric right, pass to direct current and produce cold.Because the charge carrier potential energy that is had in charge carrier (hole) and N type semiconductor charge carrier (electronics) and the metal copper plate in the P type semiconductor is different, and the transmission and the conversion of energy will inevitably take place on semi-conducting material and sheet metal node.Because the potential energy that has in the P type semiconductor is higher than its potential energy at sheet metal, under External Electrical Field, when contact a is passed through in the hole, need from sheet metal, draw certain heat, in order to improve the potential energy of self, just can enter in the P type semiconductor.Thereby will reduce in this contact a place temperature, form cold junction.When the hole enters another contact b, need unnecessary a part of potential energy to leave contact for, just can enter into sheet metal, at this moment this contact b place temperature can raise, and forms hot junction.

Description of drawings

Fig. 1 is peltier effect and thermoelectric refrigerating unit schematic diagram;

Fig. 2 is application conduction cooling superconducting magnet system construction drawing of the present invention, among the figure: 1 superconducting magnet, 2 cold screens, 3 vacuum tanks, 4 semiconductor refrigerating assemblies, 5 copper currents lead-in wire, 6 one-level cold heads, 7 high-temperature superconductive lead wire assemblies, 8 secondary cold heads, 9 conduction cooling plates, 10 conduction cooling lines;

Fig. 3 is the structure chart of semiconductor refrigerating assembly 4, among the figure: the 3-1 bolt connection assembly, 3-2 is fixed plate, the 3-3 fastening bolt, 3-4 insulating sleeve, 3-5 semiconductor refrigerating element, 3-6 vacuum tank cover plate, the 3-7 insulation cushion, 3-8O RunddichtringO, 3-9 insulating sleeve, 3-10 wiring nose, the 3-11 cooling water pipe, 3-12 fastening bolt, 3-13 insulating sleeve.

Embodiment

The present invention will be further described below in conjunction with the drawings and specific embodiments:

Fig. 1 is peltier effect and thermoelectric cooling schematic diagram.When a N type semiconductor material and P type semiconductor material be unified into thermoelectric to the time, in this circuit, connect direct current after, the transfer of energy just can take place, electric current flows to the joint of P type element by N type element, the absorption heat becomes cold junction; Flow to the joint release heat of N type element by P type element, become the hot junction.

In the temperature-difference refrigerating circuit, introduce the third material and can not change character of circuit, so copper current lead-in wire, high-temperature superconductive lead wire and superconducting magnet can be serially connected in the thermoelectric cooling loop.

The pass of refrigerating capacity and electric current is:

$Q=({\mathrm{\α}}_p-{\mathrm{\α}}_n)T_{1}I-\frac{I^{2}R}{2}-K(\mathrm{Th}-\mathrm{Tc})$

Q: refrigerating capacity (W)

α _P, α _n: Seebeck coefficient (V/K)

T _c: cold junction temperature (K)

T _h: hot-side temperature (K)

I: electric current (A)

R: resistance (Ω)

K＝(λ _pS _p+λ _nS _n)/L

λ _p, λ _n: thermal conductivity (W/mK)

S _p, S _2n: sectional area (m ²)

L: thickness (m)

If the physical dimension of two semiconductor cooling modules, the thermal conductivity conductivity, and Seebeck coefficient equates that all then the maximum temperature difference of hot junction and cold junction can be expressed as:

${(\mathrm{Th}-\mathrm{Tc})}_{\mathrm{MAX}}=\frac{1}{2}\frac{{\mathrm{\&alpha;}}^2}{\mathrm{\&lambda;\&rho;}}{\mathrm{<figure-callout\; id="2"\; label="Tc"\; filenames="C20051013060800101.png"\; state="\{\{state\}\}">Tc</figure-callout>}}^2$

In the formula

ρ: resistivity (Ω m)

λ: thermal conductivity (W/mK)

Fig. 2 is the structure chart of application conduction cooling superconducting magnet of the present invention system.

Superconducting magnet 1 is lifted on the cold screen 2 through 10 cooled machine secondary cold heads 8 coolings of conduction cooling plate 9 and conduction cooling line and through pull bar; Cold screen 2 cooled machine one-level cold heads 6 cool off and are lifted on the vacuum tank 3 through pull bar.

The tie point of copper current lead-in wire 5 and high-temperature superconductive lead wire assembly 7 is installed on the cold screen 2 and by one-level cold head 6 and cools off; High-temperature superconductive lead wire assembly 7 lower ends be installed in after the magnet terminal links to each other on the conduction cooling plate 9 and by 8 coolings of secondary cold head.

The effect of cold screen 2 is to reduce the radiation of 3 pairs of superconducting magnets 1 of vacuum tank to leak heat.

Conduction cooling plate 9 is made by copper product with conduction cooling line 10, its objective is the cold of secondary cold head 8 is conducted to superconducting magnet 1 and high-temperature superconductive lead wire 7.

Semiconductor refrigerating assembly 4 is installed in the indoor temperature end of copper current lead-in wire 5, is fixed between the plate at copper wiring nose and copper, is fixed on by fastening bolt on the cover plate of vacuum tank 3.

For making drawing clear, in Fig. 2 semiconductor refrigerating assembly-loop of copper lead-in wire-high-temperature superconductive lead wire of only having drawn, semiconductor refrigerating assembly 4 herein, both can understand that the P type also is understood to is the N type.

Because high-temperature superconductive lead wire assembly 7 is made of ceramic material, the thermal conductivity under the low temperature is lower 100 times than copper, and resistivity is almost nil under the low temperature, so the leakage heat that is caused by high-temperature superconductive lead wire assembly 7 can be ignored.So for semiconductor refrigerating of the present invention shown in Figure 2, copper current lead-in wire and high-temperature superconductive lead wire combination, available following energy-balance equation is described:

$\frac{d}{\mathrm{dx}}\left(\mathrm{kS}\frac{\mathrm{dT}}{\mathrm{dx}}\right)-I\left(T\frac{\mathrm{d\&alpha;}}{\mathrm{dT}}\right)\frac{\mathrm{dT}}{\mathrm{dx}}+{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="C20051013060800101.png"\; state="\{\{state\}\}">I</figure-callout>}}^2\frac{\mathrm{\&lambda;}}{S}=0$

Symbolic significance is the same in the equation.

Equation is applied to semiconductor refrigerating assembly 4 and copper current lead-in wire 5 respectively, can obtains the go between temperature T at 5 contact places of semiconductor refrigerating assembly 4 and copper current _J

For the simple metal copper of observing the Wiedemann-Franz law, λ (T) ρ (T)=L _0T

L ₀Be Lorentz lorentz's constant, 2.445 * 10 ^-8V ²K ^-2

Then the leakage heat of copper lead-in wire has the form of simplifying most:

$\frac{Q_{\mathrm{OPT}}}{I}=\sqrt{L_0(T_J^2-T_L^2)}$

T _JTemperature for semiconductor refrigerating assembly and copper pigtail splice

T _LBe the temperature of copper current lead-in wire with cold screen contact

Under the effect of semiconductor refrigerating, T _JTemperature reduces, so at magnet current I one regularly, can significantly reduce the hot Q of leakage of copper lead-in wire _OPT

If the magnet operating current has surpassed the maximum operating currenbt of semiconductor refrigerating assembly 4, an amount of semiconductor refrigerating element 3-5 can be installed in semiconductor refrigerating assembly 4.For logical big electric current, a plurality of semiconductor refrigerating element 3-5 use in parallel can be able to be taked to be arranged side by side.The usage quantity of semiconductor refrigerating element 3-5 is relevant with following four factors:

(1) magnet operating current;

(2) refrigeration work consumption of refrigeration machine;

(3) Zhuan Zhi whole leakage heat;

(4) maximum operating currenbt of semiconductor refrigerating element.

Fig. 3 is semiconductor refrigerating assembly 4 (being the I place of a Fig. 2) structure chart.

The specific embodiment of the invention is used a pair of (two) semiconductor refrigerating assembly 4, and a semiconductor refrigerating assembly in a pair of semiconductor refrigerating assembly 4 is then placed N type semiconductor cooling module 3-5 if place P type semiconductor cooling module 3-5 in another assembly.

Semiconductor refrigerating assembly 4 mainly is fixed plate 3-2 etc. by semiconductor refrigerating element 3-5, copper wiring nose 3-10 and copper to be formed,

As shown in Figure 3, the lower surface of the upper surface of semiconductor refrigerating element 3-5 and copper wiring nose 3-10, and the upper surface that the lower surface of semiconductor refrigerating element 3-5 and copper are fixed plate 3-2 all is pressed on the vacuum tank cover plate 3-6 by the first fastening bolt 3-3.The first fastening bolt 3-3 is fixed plate 3-2 by the first insulating sleeve 3-4 and copper and constitutes electric insulation.

Copper wiring nose 3-10 has cooling water pipe 3-11 and is pressed on the vacuum tank cover plate 3-6 by the second fastening bolt 3-12.Between the second fastening bolt 3-12 and the vacuum tank cover plate 3-6 electric insulation sleeve pipe 3-13 is arranged.Copper wiring nose 3-10 relies on the second insulating sleeve 3-9 and insulation cushion 3-7 and vacuum tank cover plate 3-6 to form electric insulation, relies on O RunddichtringO 3-8 to constitute vacuum seal.

Copper is fixed plate 3-2 and copper current lead-in wire 5 relies on bolt connection assembly 3-1 to tighten.

The present invention uses a pair of semiconductor refrigerating element:

P type semiconductor Bi _0.52Sb _1.48Te ₃

N type semiconductor Bi ₂Te _2.4Se _0.6

Technical parameter is: α=0.2x10 ^-3V/K

ρ=1.19x10 ^-5Ω m (resistivity)

λ＝1.5W/mK

s＝144mm ²

L＝2.8mm

The course of work of the present invention is: after superconducting magnet system comprises that current feed assembles, with the vacuum unit system is vacuumized earlier, reach 10 ^-1Behind the Pa, start refrigeration machine each parts of magnet system are cooled off, simultaneously superconducting magnet 1 and whole system are carried out temperature monitoring, when treating that magnet 1 is cooled to 4K, give magnet 1 energising excitation.In the process of magnet energising excitation, because the refrigeration of semiconductor subassembly 4, go between copper 5 upper ends and semiconductor refrigerating assembly 4 joint temperature reduce significantly, thereby have reduced the leakage heat of copper lead-in wire to system, have reduced the demand to refrigeration machine one-level cold head 6 colds.Also we can say, under all constant situation of other conditions,, can greatly improve the energising ability of current feed owing to used semiconductor refrigerating assembly 4.

Claims (2)

1, a kind of current feed of superconducting magnet comprises copper current lead-in wire (5) and the high-temperature superconductive lead wire assembly (7) that is attached thereto, and it is characterized in that the indoor temperature end of copper current lead-in wire (5) is connected in series a pair of semiconductor refrigerating assembly (4); Semiconductor refrigerating assembly (4) mainly is fixed plate (3-2) by semiconductor refrigerating element (3-5), copper wiring nose (3-10) and copper to be formed, and semiconductor refrigerating element (3-5) is positioned at copper wiring nose (3-10) and copper is fixed between the plate (3-2); A semiconductor refrigerating assembly in a pair of semiconductor refrigerating assembly (4) is placed P type semiconductor cooling module (3-5), places N type semiconductor cooling module (3-5) in another semiconductor refrigerating assembly.

2, according to the current feed of the described superconducting magnet of claim 1, it is characterized in that the upper surface of semiconductor refrigerating element (3-5) and the lower surface of copper wiring nose (3-10), and the upper surface that the lower surface of semiconductor refrigerating element (3-5) and copper are fixed plate (3-2) is pressed on the vacuum tank cover plate (3-6) by fastening bolt (3-3) all; First fastening bolt (3-3) is fixed plate (3-2) by first insulating sleeve (3-4) and copper and constitutes electric insulation; Copper wiring nose (3-10) has cooling water pipe (3-11), and is pressed on the vacuum tank cover plate (3-6) by second fastening bolt (3-12); Between second fastening bolt (3-12) and the vacuum tank cover plate (3-6) electric insulation sleeve pipe (3-13) is arranged; Copper wiring nose (3-10) relies on second insulating sleeve (3-9) and insulation cushion (3-7) to form electric insulation with vacuum tank cover plate (3-6), relies on O RunddichtringO (3-8) to constitute vacuum seal; Copper is fixed plate (3-2) and relies on bolt connection assembly (3-1) to tighten with copper current lead-in wire (5).

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