High Technology Application to Modernization of International Electron-Positron Linear Collider (ILC) B.Sabirov1, A.Basti3, F.Bedeschi3, A.Bryzgalin2, J.Budagov1, P.Fabbricatore3, E.Harms5, S.Illarionov2, S.Nagaitsev5, E.Pekar2, V.Rybakov4, Ju. Samarokov4, G.Shirkov1, W.Soyars5, Yu.Taran1 1-JINR (Dubna, Russia) 2-PWI (Kiev, Ukraine) 3-INFN (Pisa/Genova, Italy) 4-RFNC VNIIEF (Sarov, Russia) 5-FNAL (Batavia, USA) History In 2005 the International Committee for Future Accelerators (ICFA) took a decision to develop an electron–positron linear collider (ILC). In 2006 the JINR (Dubna)–VNIIEF (Sarov)–INFN (Pisa, Italy)–FNAL (Batavia, United States) collaboration established on the initiative of JINR launched their research on the ILC. In 2007 JINR officially joined the ILC Project and proposed the neighborhood of Dubna for the ILC location. In 2009 the collaboration made a bimetallic Ti + SS transition element for modernization of and for reducing of price the ILC cryomodule by the explosion welding method developed at Russian Federal Nuclear Research Center (VNIIEF, Sarov). In 2010 well known Institute PWI (Kiev, Ukraine) joined to collaboration, and in 2011 the firsts prototypes Nb + SS transition elements were made for replacing titanium with stainless in cryomodule vessel for significant reducing of the cryomodule price. 1 Sabirov B, JINR New Trends in High-Energy Physics 2-8 October 2016, Montenegro

At the first stage the collider is supposed to accelerate electron–positron beams to the energy of 0.5 TeV; the total length of the accelerating sections is about 31 km if gradient of Niobium cavity is 31.5 MV/m. 2 Sabirov B, JINR New Trends in High-Energy Physics 2-8 October 2016, Montenegro

Development of cylinder-shaped Ti + SS transition elements. The first stage task was to make a bimetallic transition from the helium supply pipe of stainless steel (SS) to the cryomodule shell of titanium. This would appreciably lower the cost of the accelerator. It was a nontrivial problem: Ti and stainless steel cannot be welded by conventional welding techniques. Colleagues from KEK (Japan) made some attempts to join Ti tubes with Stainless Steel using nontraditional methods: B.Sabirov, “ Production of Bimetallic Transition Tube Elements for the ILC Cryomodule”, in JINR News, p.19, April 2008, Dubna, Russia 3 Sabirov B, JINR New Trends in High-Energy Physics 2-8 October 2016, Montenegro

• Joining by HIP (Hot Isostatic Pressing) KEK Experience • Joining by HIP (Hot Isostatic Pressing) Important concern : diffusion of Fe, Cr and Ni into Ti --> degradation of strength at low temperature Manufacturing samples with the insert materials The following tests performed. Tensile tests at room temperature and liquid nitrogen temperature. Charpy V-notch impact tests at room temperature and liquid nitrogen temperature. Helium leak tests at 2 K. Friction pressure welding Diffusion rates of Fe, Cr and Ni into Ti are less than the rates by HIP. Need to measure the strength of the joint. The manufacturing method of the samples is under investigation. –>> degradation of strength at low temperature Sabirov B, JINR New Trends in High-Energy Physics 2-8 October 2016, Montenegro

Сolleagues from the Russian Federal Nuclear Centre (VNIIEF, Sarov) have mastered a method of welding dissimilar materials by explosion. A batch Ti + SS transition elements of the materials complying with the cryomodule specification (316L stainless steel and G2 titanium) were made by the explosion welding method and tested under extreme conditions at INFN (Pisa, Italy) and FNAL (Batavia, Unated States): thermal cycling at the liquid nitrogen temperature (77 K) and liquid Helium temperature (2K), tests in vacuum and at the pressure of 6 atm, exposure to ultrasound at various temperatures and for various time. The results of the all tests are within the limits of 5·10-10 ÷ 2·10-11 Pa·m3/s. Macroanalysis, microanalysis and a shear test were also carried out. The shear strength was found to be ~250 MPa. As starting of technological research to produce bimetallic billets of tube type parallel circuit for explosion welding was used. Metal strengthening is observed in the welded joint area. The highest material strengthening occurs in a narrow area ~0.5 mm wide near the titanium-steel interface. Thus, the dissimilar cylindrical tubes joined together by explosion welding showed reliable strength and tightness of the joint under extreme conditions of ultralow temperatures I.Malkov et al., “Investigation of the Possibility of Production the Bimetallic Tube Transition Element by Explosion Welding for the Cryomodule of the International Linear Collider”, JINR, E13-2008-109, Dubna, 2008, Russia Sabirov B, JINR New Trends in High-Energy Physics 2-8 October 2016, Montenegro 5

We choose the technology that assumed production of bimetal billet of tube type of Grade 2 titanium (China) and stainless steel TP316/TP316L (Austria) applying joint sleeve from stainless steel 12Cr18Ni10Ti (Russia). To produce this variant of bimetallic transition sample we used parallel scheme of explosion welding as in the first case . Cryomodule assembly with the built-in Ti+SS transition element ( art image of a cryomodule from published the Siemens global calendar 2009) Sabirov B. Explosion Welding: New Design of the ILC Cryomodule// JINR News, 3/2010, p.16, Dubna, 2010. Soyars W. et al. Superfluid Helium Testing of a Stainless Steel to Titanium Piping Transition Joint// Cryogenic Engineering Conference, 2009, Tuscon, Arizona, USA. Sabirov B, JINR New Trends in High-Energy Physics 2-8 October 2016, Montenegro

Redesign of the IV-generation cryomodule for the ILC. Based on the results achieved in welding bimetallic tube elements by the explosion method, the collaboration set about a more complicated task of redesigning the fourth-generation cryomodule by replacing the titanium shell of the helium Dewar vessel with the stainless steel shell. This design must considerably facilitate the construction of the cryomodule and, what is most important, substantially reduce the cost of the accelerator. We began with making an adapter by explosion welding the niobium pipe directly to the stainless steel (SS) disc. . Colleagues from the Russian Federal Nuclear Center (Sarov) did the research and development work that resulted in making a batch of SS-Nb adapters by the explosion bonding technique (EBT). The manufactured adapters have demonstrated excellent mechanical behavior at room and liquid Nitrogen and Helium temperatures, during high-pressure tests and thermal cycling: the leak rate measured at room temperature was ≈10−9 atm∙cm3∙s−1 for all specimens; the metallographic analysis revealed no deviations from the structure of the welded components; microhardness of ≈4.4 GPa was formed in a narrow Nb–SS contact zone 0.2–0.25 mm wide The samples were subjected to crusial tests with imitation of their installing to the working position. To this end, niobium rings were electron beam welded to both ends of the niobium pipes. In the sample a large leak occurred in several places of the Nb–SS joint after the first 3–4 thermal cycles in liquid nitrogen. Nb + SS transition element Sabirov B, JINR New Trends in High-Energy Physics 2-8 October 2016, Montenegro

This is because the welded joint experienced various internal stresses, first, due to the explosion welding, then due to the thermal load at the electron beam welding(niobium melting point is 2460C), and ultimately due to the thermal load at a very low helium temperature of 2K. Superposition of all these residual stresses resulted in plastic deformation, failure of welds, and consequently occurrence of a leak. Neutron-Diffraction Investigation of Internal Residual Stresses Resulting from Explosion Welding. It is well known that many production processes like machining, forging, stamping, rolling, welding, etc., can result in a strong field of residual mechanical internal stresses in the material or product due to its plastic deformation. Measurements were carried out with the POLDI stress diffractometer on the neutron beam from the ISIS reactor of the Paul Scherrer Institute (Switzerland). We only give the ultimate result of residual stress measurements in the bimetallic Ti+SS tube in the process of scanning the titanium-to-stainless . The residual stresses in the bimetallic Ti + SS tube measured during the scanning of the titanium–stainless steel joint are shown in Fig. The residual stress is quite considerable, amounting to ~1000 MPa. Measured (points) and fitted (lines) of the (311) peak residual stresses vs rcorr for the cross-section AB. Sabirov B, JINR New Trends in High-Energy Physics 2-8 October 2016, Montenegro

Improvement of cryomodule design Based on our experience of manufacturing Nb+SS adapters and neutron diffraction investigations them a new design, including a minimal titanium intermediate layer, has been developed and two pilot samples built in collaboration with wellknown Paton Welding Institute in Kiev (Ukraine). In this connection the following adapter manufacture procedure was proposed. First, the stainless steel disc is clad with titanium on both sided by explosion welding, the resulting trimetal is shaped as required (by planishing and turning to the size), and a hole is cut for the niobium pipe. The niobium pipe is inserted in the hole and electron-beam welded to titanium. Advantages of this design are: a) explosion welding of flat pieces is technologically much simpler than welding of pipes and allows joints with quality as much stable as possible; b) the effect of the difference in the linear expansion coefficients of the ensemble components is eliminated. c) expenditure of titanium and niobium decreases; d) possible formation of intermetallic compounds in the explosion weld steel–titanium joint does not affect helium tightness Sabirov B, JINR New Trends in High-Energy Physics 2-8 October 2016, Montenegro

Manufactered samples exposed subsequent treatment: 1.The Vickers microindentation test was performed. . The results of measuring microhardness at a load of 100 g are presented in Fig: 2. The samples were broken along steel–titan interface, which is typical of this pair of metals. The breaking strength was 375 MPa. The samples were subjected to crusial tests with imitation of their installing to the working position. To this end, niobium rings were electron beam welded to both ends of the niobium pipes 3. Thermal cycling with liquid Nitrogen (77K) and liquid helium (4.2K) was performed at the INFN Pisa and Genova, Italy. The test results were positive: helium leak measurements performed in Pisa after the thermal cyclings of two adapters in liquid nitrogen and helium revealed no leaks at a background leak rate of 0.4·10-10 atm·cc/s. As resume the experiment tests of junction of different ingredients with different thermal linear expansion in one assembly shown steady strong and tight connection at several varying extreme temperature conditions. Sabirov B, JINR New Trends in High-Energy Physics 2-8 October 2016, Montenegro

CONCLUSION New bimetallic compositions (Ti + SS; Nb + SS) and trimetallic compositions (SS+ Ti +Nb) produced by the unique explosion welding method open up possibilities of developing new-generation accelerator cryomodules. So the authors sum up the results obtained over the decade from 2006 to 2016 by the international collaboration of JINR(Dubna,Russia), INFN(Pisa/Genova, Italy) VNIIEF(Sarov,Russia), FNAL(Batavia,USA) and PWI(Kiev,Ukraine) The use of stated above manufacturing technology is rather simple for mass-production and appreciably reduces the cost of accelerator. As resume the experiment tests of junction of different ingredients with different thermal linear expansion in one assembly shown steady strong and tight connection at several varying extreme temperature conditions. Investigations have shown that explosion welding allows unique bimetallic/trimetallic components to be made for cryogenic units of accelerators, for research equipment and for civil engineering tasks. Sabirov B, JINR New Trends in High-Energy Physics 2-8 October 2016, Montenegro

THANKS for YOUR ATTENTION!