Successfully passed the tests of the first cryogenic superconducting magnet for Russian Collider

The project NICA — project to create a Super-collider based nuclotron High Energy Physics Laboratory, Joint Institute for Nuclear Research.

From 16 to 20 May in the High Energy Physics Laboratory conducted tests of the first cryogenic superconducting magnet for booster Nuclotron, the future of the intermediate ring accelerator. As you know, the NICA project includes a series of rings — the ring booster, which passes the intermediate acceleration, then the beam is injected into the Nuclotron-M, and then sent to the collider consisting of two opposing rings. We asked Hamlet IG Khodzhibagiyan, chief engineer, winner of the Prize of the Government of the Russian Federation in the field of science and technology in 2010, to tell about the trials of the first dipole magnet for booster Nuclotron stories and create unique Dubna superconducting magnets.

G. Hamlet, tell me what is happening here, in case 203-A, to stand trial for cryogenic superconducting magnets?

Here are tested full-scale prototype dipole magnet for booster Nuclotron. After we performed a series of tests and find out what characteristics we are satisfied in this magnet, and which need to be aligned with the specified requirements, the necessary changes will be made in the design and started mass production of the magnets. It is planned to create 40 dipole magnets, length of 2.2 meters, with an aperture width of 130 mm and a height of 68 mm for the location of the beam chamber. In order to reduce the size of the magnet and heat when it is operating in the pulsed mode of the magnet coil is made single and curved accelerator of 14.1 m, weight about 850 kg magnet.


A.R.Galimov, G.G.Hodzhibagiyan and V.N.Karpinsky — discussion of the next phase of testing.

Where was it made?

First it was developed in our laboratory, and then the yoke parts were manufactured in the NGO "Atom", and the assembly and finishing are produced in our laboratory workshops. The superconducting magnet coil cable and manufactured in VBLHEP on special equipment.

But this will not last forever. After a series of tests and magnet design improvements will be put into production. The yoke of the magnet is completely manufactured in the industry — "NPO" Atom ", JSC" VNITEP ", JSC" SMZ "or at another plant, and winding — in VBLHEP. In addition to the dipole magnets for the booster Nuclotron to design and fabricate and 48 quadrupole magnets. Currently, the yoke of the quadrupole magnet is collected and made his finishing on the milling machine.

What is the difference between these types of magnets?

The dipole magnet produces a magnetic field directed vertically. A charged particle passing in such a field, deflected in the horizontal plane and held ponderomotive (electromagnetic) forces in a circular orbit. A quadrupole magnet used to focus a beam of charged particles.

G. Hamlet while you wait for the next delivery of liquid helium, tell me, what is this type of Nuclotron magnets, how do they differ from the others?

The project started in Nuclotron LHE in the early 70’s, and at first it was planned to build the so-called magnet-type Cos. Until now, all of superconducting magnetic systems of circular accelerators, except Nuclotron made on this type of magnets — Tevatron (the world’s first superconducting accelerator) in the United States, HERA in Germany, RHIC in the United States, LHC at CERN … There were unrealized projects — UNK in Russia and the SSC project in the U.S., but they were all based on the same type of magnets Cos, the first of which was made in the name of Fermi Lab, USA. In contrast to the magnets of this type, we have been offered in Dubna, brought to the working conditions and use of a fundamentally different type of magnet — it is called in the West "superferrik" or magnet type Nuclotron. Until recently, for superconducting synchrotrons anywhere except in Dubna, they are no longer used. Only now, in Germany, in Darmstadt, the new project involves the creation of FAIR at GSI superconducting synchrotron SIS100 magnets of the type Nuclotron.

How do they differ from, say, the traditional?

If a conventional understand conventional "warm" magnets, working at ambient temperature, the fact that instead of copper in a superconducting magnet coil. This idea in 1973 brought in LHE Igor Shelaev. The magnet yoke is made of iron and has the shape of a window frame. The winding of the cable is made of rectangular cross-section of the superconducting wires twisted and wrapped with insulating material. Such a superconductor is called the Rutherford-type cable. In 1974, our laboratory has been made and at the same cryogenic bench tested on a model-type window frame magnet with a superconducting coil and immersion cooling system, that is a magnet immersed in a bath of boiling helium. Of these magnets in the LHE was made synchrotron SPIN model, which served as a school create Nuclotron. Relatively easy to manufacture and inexpensive magnet for SMES accelerator housed in a complex and unreliable cryostat with a large amount of liquid helium inside the collapsible helium vessel. In order to simplify the cooling system of the magnet in 1978, Anatoly Alexeyevich Smirnov suggested using magnets such as window frame tubular superconducting cable. In the manufacture of cable Rutherford type superconducting wire is wound in a spiral around a cylindrical parts (tube section) and then bundle of twisted wires rolled into rolls, giving the rectangular cross section of the cable. AASmirnov offered after winding wires to solder them on the phone to her and to pass through the channel helium cooling tube. This offer was accepted, and we began to model magnets. As a result of research and design optimization was developed magnet type Nuclotron having a yoke at 4.5 K in the form of a window frame of transformer steel sheet and coil of tubular superconductor cooled by the flow of two-phase helium. To reduce the dynamic tube heat release cable is made of nickel silver and tube heat contact with the wires soldered in place using the provided binding wire.

Magnet type Nuclotron have one major limitation — the magnetic field in the aperture should not exceed the value of 2 T due to the saturation of the iron core, which forms the field in the gap. The traditional type of superconducting synchrotron magnets Cos, a field in which the aperture is formed by winding it possible to have a greater value of the field. Thus, in the magnets Tevatron, HERA and RHIC, the magnetic field in the aperture of about 5.4 T and the LHC, and even higher — 8 T. Maximum limit of the field can be considered as a drawback of our magnets. And then go only advantages. And the main advantage of the magnet type Nuclotron are good conditions for its cooling the superconductor magnets allow working with a record rate of change of the field up to 8 T / c and above with minimum (about 8 percent) of the degradation of the critical current. The magnet is relatively easy to produce (we do Nuclotron magnetic system almost exclusively by JINR Experimental Workshop and laboratory workshops). Simply for good quality field in the aperture, as it is formed of iron yoke instead precision winding type magnets as in Cos, and many other advantages.

If you do not mind, let’s explain why there is liquid helium is used and why it is he?

Because superconductivity exist under certain conditions. Primarily, this low temperature. Just recently we celebrated the centenary of the discovery of superconductivity. It was opened at the temperature of liquid helium to the mid 80’s newly discovered superconductors have a
n operating temperature close to the temperature of liquid helium at atmospheric pressure — 4.2 K. The alloys of which began to make superconducting magnets were discovered in the 60’s years. This is primarily NbTi, which is made of a superconducting cable Nuclotron and all other superconducting synchrotron at the moment, then Nb3Sn. In 1986 was opened so-called high-temperature superconductivity exists at a temperature close to the boiling point at atmospheric pressure of nitrogen (80 K). For her future, of course. In the future, these will replace the low-temperature superconductors, but they are very expensive and have some physical and technological characteristics that constrain their widespread use. Although high-temperature superconductivity is developing very rapidly, but applied to the magnets of accelerators we are still guided by the low-temperature superconductivity. How Nuclotron, so booster and NICA collider will be created with the use of superconductor niobium-titanium.


Cryogenic testing full-scale prototype of the superconducting dipole magnets for the booster NICA.

And what are the benefits given technology, when helium is fed into the receiver coil?

The fact that we have only liquid helium cryostat in the tube instead of the heavily simplified the design. No need to make a helium vessel remains in the cryostat vacuum jacket only and heat shield. Thus far easier cryogenic safety is ensured in the event of an emergency. Seen, probably, a report on TV about the emergency situation at the LHC. Then, as a result of the transition from the superconducting magnets to the normal state, and because of a failure in the system of energy evacuation occurred a sharp rise in pressure helium cryostat helium vessel depressurization, and a lot of helium "spilled" out. We can say, it was an explosion due to sharp changes in the density of helium (helium in liquid form has a volume of 700 times less than at room temperature). For the type of magnets Nuclotron such effects are excluded in case of emergency — a small amount of helium is inside the tube channel, allowing the pressure of over 100 bar.

As the technology is further developed?

At the beginning of 1979 was a test of the first tubular magnet. At first superconductor cable soldered with solder to the tube. Then, in order to reduce energy losses and increase efficiency, we have abandoned the soldering decided to fix the wire on tube through the shroud of German silver wire and improved on the design of the magnet. The first experiments have shown a very good cooling condition of the conductor.

This has given the advantages that are not available today from other superconducting magnets for synchrotrons. The State Prize was awarded, including, for the benefit of this type of magnets Nuclotron — the opportunity to work with a high repetition cycle, or with a large rate of change of the field, which is many times larger than the magnet-type Cos.

In our case, the superconductor is pressed against the tube with helium, that is, the cooling channel is separated from the superconductor nickel silver metal wall. Therefore, the heat which occurs in the superconductor when the pulsed change of the field "flows" to the fluid through a metallic wall. In Rutherford type conductor cable on coated insulation has a thermal conductivity which is many times smaller than the metal. A metal wall, in this case the cooling takes place is many times better. Experimentally, we have determined that we can work on large (8 T / c) rates of change of the field and the critical current of the cable is reduced by only a few percent. In the magnet-type Cos, if you set a rate of change of the field, the cable will overheat and the critical current in the magnet is reduced by several times.

You mentioned the cooperation with German colleagues …

In 1999 we were approached by experts from GSI (Darmstadt), who were interested in superconducting magnets, able to work with a large rate of change of the field. The modeling and experimental study of superconducting magnets for the synchrotron SIS100. Together with our German colleagues we were able to improve the performance of the magnet type nuclotron improve the quality of the magnetic field in the aperture and significantly reduce heat dissipation in the magnet at high rates of change in the field. Heat dissipation in the magnet — that is what defines the operational costs of the magnet system. To remove 1 W of heat at the helium level, it is necessary to spend about 300 watts on the compressor shaft. As a result of studies conducted in the past 10 years, was twice the current density is increased structural tubular cable developed a prototype magnet SIS100 with curved single-layer winding, which led to the further miniaturization of the magnet. Currently SIS100 magnet is in preparation for mass production.

Magnets for the complex NICA, apparently, also improved?

The yoke of the magnet collider NICA.
Of course. Reduced heat dissipation, winding configuration changed (at Nuclotron was a two-layer, single-layer and is now for NICA and SIS100). Magnet booster NICA curved, with a fairly small radius of curvature — 14 meters, a dipole magnet for SIS100 radius of curvature of 52 meters. Curved magnets difficult to manufacture and test, but they are smaller — if the magnet is made from two-layer winding line, as before, the cross section of the magnets would have turned out much better than it is now. That is, as I said, we continue to minimize the size of the magnet, and therefore the heat in them.

G. Hamlet, never about himself did not mention … When you are connected to this work?

I graduated from the Bauman Higher Technical School in 1973, it was at this time began to develop magnets for Nuclotron. Under this program, and I was invited to work as I was finishing the cryogenic department. I got in very good hands — in the department Alexander G. Zeldovich, cryogenic Zeldovich school is well-known in the world, in the sector Zababakhin Dyachkova, while the young doctors of science (he is 39, he defended his doctoral dissertation), very talented cryogenic. Then, of course, had to work with colleagues from other departments. I was a young man, but I gradually began to be invited to discuss important issues. I remember, for example, how the decision, from which the magnets to build SPIN model superconducting accelerator. At the moment, this setting apart the — she worked as a model and as an acting accelerator and has not been started, in part because of a very complex cryogenic system.

Ends your production break, the next phase of testing will. In conclusion, I want to ask about your young colleagues. Well you work with them?

Young people have little, but it’s nice that it’s there. More recently, there was a time when young people in the lab almost was not. There is a new thing — an interesting, lively — the project NICA, and started coming young professionals. Not everything here is delayed, but who remain — it is interesting!

PS While the interview goes to press, there were test results: "From 16 to 20 May completed an important milestone towards the creation of complex NICA — conducted successful cryogenic testing full-scale prototype of the superconducting dipole magnets for the booster NICA. After a brief training received nominal current of 9690 A, taken thermo-physical and hydraulic characteristics of the magnet when it is operating in cycles with different amplitudes and rates of change of the field in the working aperture. "We congratulate and thank the team of Hamlet IG for the detailed explanation of what’s behind these dry formulations of information.

Interviewed by Galina MYALKOVSKAYA

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