New Development of VPI Process for Large Superconducting Coils

Plasma Science & Technology, Vol.5, No.4 (003)New Development of VPI Proces for Large Superconducting CoilsPan Wanjiang (潘皖江), Wu Songtao (武松游), Cui Yimin (崔益民)04 AInstitute of Plasma Pyics, Chine Acadeny of Sene, Helei 2303,ChinaAbstract High vacum is rquired for Vacum Pessure Impregnation (VPD) procs oflargecoils w in crogmie The delets such as dry spots and over ridh rsis sold be minineinilarge sperconducting coils wed. Both saling probles ascited with the mold and over richresin problems are elimninated by using vacum bag molddesign of vacum mold.Keywords: superconducting coils, vacum pesure impregnation, vacum bag methodPACS: 85.25.L2 The construction of a long1 Introductionmodel of PF coil and itsA tokamak project of plysis experiment device ofinsulationsHT-7U using superconducting coils was undertakenby Institate of Plasmna Physics, Chinese Academy ofThe long model of PF coil is designed as a lineSciences .The project is to develop the scientific basisof 1270 mm long whose section is the same as thatfor an economic, clean and continuously operatingof the real CS coil being a round-shaped structure,tokamak fusion reactorl. One of the most impor-with 453 mm in height, 1422 mm in outer diametertant parts of HT-7U is its magnet system consistingand 1100 mm in inner diameter. Fig. 1 shows theof 16 magnet coils in the toroidal field (TF) systemdesign of the CS coil winding consisting of 120 turnsand 7 pairs of maguet coils in the poloidal field (PF)of cable in-conduit conductor (CICC) arranged in asystem with 3 pairs of central solenoid coils (CS)6-turn x 20-turn natrix, with every 6-turn a pan-located symmtrically on horizontal mid-plane andcake, totaling 20 pancakes. The external sectionalcentral line among the 7 pairs of PF coils. Now thedimensions of the conductor is 20.4 mm x 20.4 mm.engineering design and its first coil have been com-The wound conductor is half-lapped by a dry E-glasspleted. As insulating systemn is critical to magnettape and kapton, forming a 1 mm insulation layercoil properties especially for superconducting fusionbetween every two turns. The 1 mm thick pancake-experiment devices, this paper details the feasibilityto- pancake insulation is made by inserting an 1 mmof VPI (Vacuumn Pressure Impregnation) of the HT-thick dry E-glass tape between pancakes. After the7U PF coil insulating system by VPI experiment ofapancakes are placed well, the outside of the coil willlong model, the section of which is the sane a8 thatbe half-lapped with a 5 mm thick dry E-glass tapeof real coils.as ground insulation.中国煤化工YHCNMH G1877Pan Wanjiang et al. : New Development of VPI Process for Largc Superconducting CoilsSilcone tapeGrund Iuato(1 mmJeonductor (2cmmx 20mm]RTV 627众众立农众众众工Release tape]Layer ruao(nom)Glassyarn filerMold plateBr你江尔字453mmSprue boardFig.1 lustration of a part section of a CS coilResin inletFig.3 The section of the bag moldEmergency,甜line.pressure iletValve/PumpResin dutletprogram. Half-lapped layers of dry glass tape haveHeatervent tankbeen used for both the turn/turn and groundwallinsulation. It was found that shimming and seal-100p0oσ0001ing of the mold was more dificult and more costlythan anticipated in the former VPI experiment ofToolTF coils. The bag mold process minimized costs andrednced problems associated with machined moldssuch as uniforn compression, mold fabrication tol-Resininlet。00000000erances and sealing issues. Fig. 2 shows the sketchof the equipment for PF coil impregnation program,including the vacun system, nitrogen pressure sup-ply, the epoxy mixing equipment, the heater and theFig.2 The sketch of equipmcnl for RF colt impregna-bag mold. The bag mold for the long model of PPtion programcoil is 1320 mm long whose outer walls were fab-ricated with steel plate. The upper & lower moldplates were bored for ports of epoxy entry & exit.3Description of the bag moldFig. 3 shows the secion of the bag mold. The spruefor long model of CS coil .boards for epoxy distribution were fabricated withaluminum,the surface of which was brushed withA tolal of 14 coil stacks will be fabricated on HT-release agent. The long model was first halfapped7U, comprising 7 PF coil stacks, with the largest onea layer of polytetrafuoroethylene release tape whichexceeding 6700 mm diameter. This fabricatiorn pro-was attached directly to the sprue boards up andgran is required to mix and handle a huge quantity中国煤化工cc with another half-of epoxy ever used at a single time for a fusion-rclatedrubber (3M Co.), atYHC NMH G'1878Plasma Science & Technology,VoL.5, No.4 (2003)Table 1. Resin specification for vcum-resure-impreggnation of cs model coilComponentsComponents proportion (by weight)Commercial trade designationDGEBF60YDF-175PPGDE .10PG-207DETD (cure agent)1ETHACURE 10009/7°C+19C0.80.778°C+1"C .0.6-y60°CS 0.40.3|50C0.2个- 40fc0.1.-200 02004006008001000120014001600Time/minFig.5 The imprcgnated long modelFig.4 The viscosity of the inpregnating epoxyfor CS coil is described as follows:a. The temperature of the mold is raised andlast the mold plates were assembled. The RTV 627heated up to 80 °C.was then poured into the mold. After the mold wasb. The glass tape in the mold is degassed and acompletely flled the syster was checked for leaks.vacuum of 5 Pa to 10 Pa is maintained for 8 h.At the end all of the epoxy entry and exits were in-c. Vacuum is applied to model assembly whilestalled, and the mold was then ready to be piped.decreasing temperalure down to 40。C to removeboth air and adsorbed moisture from glass fabric ofthe model.4 Vacuum pressured. The epoxy resin and harden are individuallypre-heated up to a temperature of 40 "C to lowerimpregnation processtheir viscosity.e. The mixing tank for epoxy is maintained at aAll TF coils and PF coils on HT-7U will be imprcg-temperature of 40。C and a vacum of5 Pa to 10nated with epoxy by vacum and pressure. Tablel isP:the resin specification for VPI of long model for CSf. After mixing and degassing for approximatelycoil.4 hours, the epoxy is introduced to the long modelFig. 4 shows that the viscosity of impregnatedmold by a resin inlet on the supply tank maintainedepoxy used is less than 0.15 Pa-s and the epoxy resinunder 35.5 kPa of dry nitrogen.has a long usable life at 40 °C that is suitable fou中国煤化工how evidence ofimpregnation. The VPI program of the long modelCnk is removed.YHCNMH G1879Pan Wanjiang et al. : New Development of VPI Process for Large Superconducting Coilsh. The pressure on vent tank is raised to 20.3vantages include:kPa and the fuid is Imoved to within 76.2 mm ofa. Any discontinuities due to workmanship ormold.variations in the density of fiberglass matrix arei. The pressure remnove and a vacuum of 5 Pa ~smoothed and the concentration of stress is elimi-10 Pa is applied to vent tank. Rcpeat this step untilnated.there is no evidence of bubbles in the lines.b. Secondary operations of machining the fin-j. 35.5 kPa is applied on vent tank until theished coil are considerably reduced.epoxy resin will be gelled.C. The RTV bag allows the finished coil to beThe resin cure procedures are:easily removed from the mold.a. The resin is gelled at 78°C(士3 °C) for 24 h.d. Consistent fAuid-dynamic resistance is reb. The resin is cured at 130°C (士5 °C) for 12sulted from the isotropic uniformity of pressure inhthe vacuum bag.The cured long model is removed from the mold.Fig.5 shows that the cured long model is transparentin appcarancewithout obvious defect. The impregna-Referencestion quality will be evaluated as below1 WuS T, WengP D, et al. The project of HT-7U5 Conclusionsand its progress. MT-15, Oct, 1997, Beijing, 20 ~24It is reasonable to use bag mold for large coil2 Evans Dave, Canler s J. A new resin systemfor the impregnation and bonding of large mag-impregnation. The bag mold process mininizednet coils. Rutheford Laboratory Internal Report,costs and reduced problems associated with ma-1999chined rnolds such as uniform compression, mold fab-(Manuscript received 13 February 2003)rication tolerances and sealing issues. Additional ad-E mail address of Pan Wanjiang: wjpan@ipp.ac.cn中国煤化工MYHCNMHG1880