Yarba, V A

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Particle Accelerators, 1990, Vol. 26, pp. 131-139Reprints available directly from the publisherPhotocopying permitted by license only© 1990 Gordon and Breach, Science Publishers, Inc.Printed in the United States of AmericaTHE IHEP UNK PROJECT. STATUS AND DEVElOPMENTV.A.YarbaInstitute for High Energy Physics, 142284, Serpukhov,Moscow region, USSRAbstractlex (UNK) hasexample l - 3 ). Itup to 3 TeV andsently, the 1stbeing built.The project of the IHEP Accelerating and Storage Comp-repeatedly been reported and discussed (see, forenvisages a possibility to accelerate in the UNK protonsprovide collisions of 6 TeV c.m.s. energy beams. Pre-phase of the machine, the fixed-target accelerator, is1. OPERAT ION IN THE ACCELERAT ION MODEFigure 1 shows the cross sectional view of the UNK tunnel and the equip-ment placed in it. The presently existing 70 GeV proton synchrotron,whose intensity is planned to be upgraded up to 5-1013 ppp, will injectprotons into the UNK. The U-70 beam will be injected into the 1st phaseof the UNK, the 600 GeV conventional machine (UNK-1)~ which will be thebooster for the 2nd phase, superconducting accelerator UNK-2. The UNKcircumference is 14 times as large as that of U-70, which will make itpossible to stack in UNK an intensity of 6.]014 during multiple (up to12 times) injection. The beam accelerated in U-70 is prebunched in itat a UNK frequency of 200 MHz. On stacking within 72 sec the beam isaccelerated in UNK-1 up to 400 GeV and transferred by single-turn injec-tion into UNK-2 to be accelerated further up to 3 TeV. The UNK-2 cycleis as follows: 40-s field rise, 40-s flattop and 40-s drop.FIGURE 1 Cross section of the tunnel with the equipment placedthere.131132 V.A. YARBAThree modes of beam extraction from UNK-2 are foreseen: 40-s slowresonance extraction, 2-3-ms fast resonance extraction of up to 10 pul-ses and fast single-turn extraction. Fast resonance extraction may takeplace simultaneously with slow one. The operating resonance of the slowextraction system is chosen to be 3Qr =110.Resonance extraction leads to 1-2% of beam loss at the septum ofthe 1st extraction device, electrostatic deflector4 . The secondariesproduced in the septum matter irradiate the superconducting elementsdownstream in the straight section for extraction. To reduce the radia-tion-induced heating of the magnets placed close to the extractionsystems special measures 5 enabling one to bring the radiation effectdown to the tolerable level have been elaborated. With an uncertaintyin the extraction efficiency taken into account, the temperature reser-ve in the critical current of the magnet coils placed in the radiationareas is chosen to be at least 0.5 K.To protect the equipment during emergency situations fraught witha feasible beam loss the beam is aborted onto the external absorber.2. roLLID ING BEAMS IN THE UNKFigure 2 presents the UNK lattice. To arrange 6 TeV c.m.s. p-p colli-sions, two superconducting rings, UNK-2 and UNK-3, placed in the samehorizontal plane and intersecting in Matched Straight Sections (MSS),2, 3, 5, 6 will be used. MSS2 will house the experimental colliding beamfacility, the Universal Calorimeter Detector (UCD) , MSS3 will be usedfor the experimental internal jet target facility (NEPTUN experiment)and MSS5 will house another colliding beam facility, a track strimmerdetector. The systems of '~orward't injection, acceleration, beam losslocalization and beam abort systems will be put in MSS1, while thosefor beam extraction from UNK-2 and transfer from UNK-1 into UNK-2 andUNK-3 will be placed in MSS4.MS 5-1'1M55-1U-70FIGURE 2 UNK lattice in the pp-mode.THE IHEP UNK PROJECT 133In the p-p mode, the beam is stacked according to the same patternas in the acceleration one. The U-70 beam is injected into UNK-1 12 ti-mes to fill its orbit in succession. After that the stacked beam is ac-celerated up to 400 GeV and transferred into UNK-2 to be retained therefor some time. Then the stacking procedure is repeated but the beam isinjected into UNK-1 in the "backward" direction with the help of thesystem of injection into MSS6 with the field polarity reversed. On ac-celeration in UNK-] up to 400 GeV the beam is transferred into UNK-3.The final stage is the simultaneous acceleration of protons in UNK-2and UNK-3 up to 3 TeV and making them collide. The parameters of pp col-liding beams are presented in Table ]. As is seen from this Table, verystringent requirements are imposed on the U-70 beam intensity and emit-tance. At present, both transverse and longitudinal phase volume of theU-70 beam exceed the required value.Table I The Parameters of Colliding Beams in the UNKParameterIntensityNumber of bunchesNumber of particles per bunchRMS transverse emittance, mm mradRMS longitudinal bunch emittance,MeV/s~mRMS bunch length, cmBunch-to-bunch distance, mStacking time, hBeam-beam tune shift(per 1 intersection)fl-function in intersection, mFree space for the detector, mLuminosity, cm- 2s-]Number of events per collisionRMS beam diameter, mmp3020200.06p pp1.5.10]3 2.4.]0]466 86002 1011 2.8 10]05 530 1020 12297 1.50.2 0.23 10- 4 1 10- 3] ]+20 +20] -103 ] 4-10321 0.30.08 0.08This necessitates the following major upgrading of U-70:- replacement of the corrugated vacuum chamber for a smooth onewith a view to bring the value of the longitudinal coupling impedancedown to 10 Olun;- replacement of the ring electromagnet power supply system;- upgrading the field correction system;- development of the charge exchange injection system;- decrease of the injection and extraction mismatches by about anorder of magnitude.With all these measures accomplished, the luminosity attainablemay be as high as 4.1032 cm- 2s- l .The colliding beam mode imposes heavier demands on the UNK as com-pared with the fixed-target operation, which entails rather stringentrequirements on the vacuum chamber impedance, the noise level of theaccelerating systems and beam injection and transfer mismatches.To have a fairly small beam spot at the collision point the compli-cated schemes of the straight sections have been developed. Figure 3shows the beam shaping scheme for collisions in MSS2. The beam intersec-134 V.A. YARBAtion angle is 1 mrad. The section is transparent for the circulatingbeam, has a unity transfer matrix and zero dispersion at the intersec-tion point.eM(208040·160 l-------J.-------L-------'------I.~OO-a tOO J(J(J JOO ¥ MFIGURE 3 Optic system of a section for pp colliding beams.~ -functions in the ppcollision section.FIGURE 4200 m"'1m rnfoO 150w un50aIoM'/z706050403020Vi, VfxfaFigure 4 shows the cyclewise variation of the -functionsin MSS2. The dashed lines denote particle acceleration andstacking. As is seen, the maximum values of the amplitude flUlctions inthe section actually do not exceed those in the regular part of thelattice. This makes it possible to construct the MSS beam line havingthe acceptance equal to that in the regular part, while keeping thedimensions of the magnet element apretures reasonable. After accelera-tion of the beams up to the maximum energy their emittances are reducedby a factor of 7.5 which allows one to increase by the same factor thevalues of -functions. Retuning will be carried out by varying thecurrents of a few quadrupole lenses of the straight section. The solidlines of fig.4 show the -functions for the colliding mode. For thephases, j3~=j3~=1 m in the section centre. The optics of UNK-2 and UNK-3THE IHEP UNK PROJECT 135contain some common elements in the straight section. The lifetime ofpp-beams should be at least ] hour.This year IHEP has considered a possibility to use the CERN p sour-ce (the AAC) together with the UNK complex to make pp collisions in theUNK. Figure 5 shows this possible scheme. The beam accelerated in U-70is extracted onto th~ external target. The 3.5 GeV p beam produced thereis transferred into the AAC.MSS~FIGURE 5 Layout of pp complex.Changeover to the harmonic number of 24 is planned to be made inU-70 in order to match its bunch-to-bunch distance with the wave lengthof the AAC accelerating field. After conversion, the p bunches fill 3buckets out of 6 of the AAC. The U-70 intensity should be at least2.6']013 ppp. The field flattop is produced at 50 GeV within which 3neighbouring bunches are extracted 8 times, each at an interval of 2.4s,and then the field is reduced to the injection level. In this case, thecomplete cycle of U-70 is 22 s. With a conversion ratio of 2 10- 5 andstacking efficiency of 50% (which seems reasonable), the number of pstacked at each extraction is 3.3-]07 and a stacking rate is 4.3 10]0~.Thus, the time of stacking p in the AAC is about 18 hours.The optimum number of bunches of each type in the UNK is 66. In thiscase,a pair of bunches colliding close to the centres of the MSS's pro-duces 1 event. To facilitate the operation of injection and beam abortsystems a 1.5-km section of the beam is left unfilled with particles.Particles are stacked in the UNK in the following way. A 2~1011 protonbeam is accelerated in U-70 up to 65 GeV to be transferred into UNK-1.This operation is repeated 66 times, whereupon the beam is acceleratedin UNK-] up to 400 GeV and transferred into UNK-2 within a single turngA part of the p beam core stacked in the AAC and containing 9.]0- pis formed into a bunch accelerated in U-70 and UNK-] up to 400 GeV andtransferred into UNK-2. This operation is also repeated 66 times. As aresult, the p beam having the same structure as the p one is producedin UNK-2. After acceleration of the two beams up to 3 TeV the accelera-ting fields are phase shifted, which provides the collision of bunches136 V.A.YARBAat the relevant points of the MSS's. The colliding beam lifetime shouldbe about 24 hours.Table 1 presents the parameters of pp colliding beams. Comparingthem with those of pp colliding beams one can see that the maximum lu-minosity attainable in pp collisions is appreciably higher than thatattainable in p~ ones. The time for stacking an ~ beam is considerablylonger. This requires a larger lifetime of collisions which, in itsturn, requires a higher reliability of the whole acceleration complex,separation of the p and p beams with electrostatic separators, reduc-tion of the level of the RF acceleration system noise, etc. On the otherhand, for the pp mode to be realized, an additional superconductingring will be needed, which might interfere into the collider timeschedule.3. THE DEVELOPMENT OF SUPERCONDUCTING MAGNETSThe superconducting machine will contain 2176 dipoles and 474 quadrupo-lese The operating field of SC magnets is chosen to be 5 T. To attaina high efficiency of resonance extraction, the region of a good borefield should be at least +3 em. The basic parameters of SC magnets havebeen chosen proceeding from these requirements.The cold-iron design has been chosen for serial production of mag-nets. A few 1-m models of this type used to tryout the production tech-nology were manufactured. After that two full-scale prototypes were ma-nufactured and tested. The maximum field, 6.5 T, is attained actuallywithout training, which is well above the operating one.J2IIIFIGURE 6 Cross section of a cold-iron SC dipole: 1 - coil,2 - stainless steel col-lars, 3- yoke, 4- heliumvessel, 5 - single-phasehelium pipe, 6 - ion pipe,7 - nitrogen shield 8 - su-perinsulation, 9 - vacuumvessel, 10 - suspensions,1] -extension rods, 12-single phase helium chan-nels, ]3 - two-phase heliumchannel.Figure 6 shows the cross sectional view of a SC-dipole magnet. Itsbasic unit is a two-layer shell-type coil collared with the help ofstainless steel collars. The coil assembly and iron yoke arA placed intothe helium vessel cooled by single-phase helium flow a part of whichgoes through the coil and another one branches into a bypass channelto exchange heat with a two-phase helium flow going through the innerTHE IHEP UNK PROJECT 137pipe. The helium vessel is fixed to the warm vacuum vessel with the helpof titanium-alloy vertical suspensions and horizontal extension rods.Longitudinal motions are hampered by the anchor extension rods fixingthe central cross section and allowing a free motion of dipole end partsin thermal cycles.The 1st layer of the coil consists of 34 turns and the 2nd one con-tains 2] turns. The zebra-type cable consists of ]9 strands, each 0.85 romin diameter, 9 of which are coated with a Sn+5% Ag solder. A strand con-tains 89]0 filaments, each 6~m in diameter. The critical current densi-ty in the 5 T field at 4.2 K is 2.3.]05 A/cm2 .Figure 7 presents the results on measuring the basic harmonics offield nonlinearities across the 3.5 em radius. They are in a good agre-ement with the calculations and fulfil the requirements imposed on thefield quality.Cs 0/ --............./--C7 0Cg 01 2 3 4I,KAFIGURE 7 Nonlinearities versus bore field.The heat load on the cryogenic helium system calculated from theresults on measuring static heat leaks and ac loss in the dipole coilin the accelerator and collider cycles is 35 kW. This value is aboutthe same for either mode.The superconducting quadrupole is at the stage of operational deve-lopment.4. STATUS OF THE CONSTRUCTION OF THE UNKFigure 8 shows the undeground structures and status of boring the tunnel.By the 1st of July 16.6 km had been bored. The construction of thesouthern part of the ring tunnel and of the injection line are beingcompleted. Here work is being done on the preparation for assemblingthe equipment, the construction of the surface technological buildings138 V.A.YARBAfor the equipment of the power supply, cryogenic and monitoring systemsis being completed.THE UNDERGROUND CONSTRUCTIONS OF UNK AND THEIR STATUS.THE BORE D SECTIONS OF THE UNK TUNNEL ARE SHOWN IN DARK.FIGURE 8 Undeground structures of the UNK and status of boringthe tunnel.The mass production of the equipment for UNK-l is going on. Thewhole electromagnet and vacuum equipment for the 2.7 kIn injection linebetween U-70 and the UNK is actually ready.Magnets of the warm ring are being supplied (there are about 300magnets supplied), about 10000 m of the vacuum chamber are also ready.The equipment for the acceleration and ring magnet power supply systemsis developed and its production has started. The tests will be done andthe equipment prepared in .a special 10000 m2 building, where test faci-lities are now being constructed. The electromagnetic equipment willstart to be assembled this year.The superconducting dipole has actually been developed and triedout. The production lines for the serial manufacturing of SC magnetsare now being prepared. An experimental string consisting of 100 magnetsand serviced by the standard cryogenics will be assembled in the tunnelin 1990-1991. The whole cryogenic equipment is developed and producedat the scientific and industrial corporation "Cryogenmash".5. CONCLUSIONSThe scope of the construction work on the UNK has been expanded. Ordersfor the production of all standard equipment have been placed with in-dustry. Some nonstandard equipment is manufactured at the IHEP workshop.Orders for the equipment of UNK-2 are being placed with the industry.Next year a batch of 100 standard SC magnets will be produced. The cour-se of the work confirmes the feasibility of finishing the constructionof the machine in 1993 and putting into operation the 1st phase and itsexperimental facilities in 1994.REFERENCESTHE IHEP UNK PROJECT 1391. V.I.Balbekov et ale Proceed. of XII Intern. Conf. on High EnergyAccel. - Batavia, 1983, p. 40.2. A.I.Ageyev et ale Proceed. of XIII Intern. Conf. on High EnergyAccel. - Novosibirsk, 1987, v. 2, p. 332.3. K.P.Myznikov. Proceed. of Workshop on the Experimental Program atthe UNK. - Serpukhov, lHEP, 1988, p. 13.4. A.N.Akimov, I.S.Baishev et ale Protection of Superconducting Magnetsagainst Irradiation during Fast Resonance Extraction from the UNK.European Accelerator Conference, Rome, 1988.5. I.S.Baishev, A.I.Drozhdin et ale Protection of Superconducting Mag-nets of the UNK a,gainst Irradiation, ta lk at this Conference.

The Ihep Unk Project: Status And Development

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