Glukhikh, V A

Grachev, M I

Lobashev, V M

Matveev, V A

Severgin, Yu P

Stavisky, Yu Ya

Titov, V A

CERN Document Server

Particle Accelerators, 1990, Vol. 27, pp. 51-58Reprints available directly from the publisherPhotocopying permitted by license only© 1990 Gordon and Breach, Science Publishers, Inc.Printed in the United States of AmericaEXPERIMENTAL AREA OF HOSCOW MESON FACTORYH. I. GRATCHEV, V. H. LOBASHEV, V. A. MATVEEV,Yu. Ya. STAVISSKYInstitute for Nuclear Research of AS USSR, Moscow,v. A. GLUKHIKH, Yu. P. SEVERGIN, V. A. TITOVEfremov Scientific Research Institute forElectrophysical Equipment, Leningrad, USSR.~b~t~act The beam channeling, the protonring, the neutron source, pion and muon beamsMoscow meson factory are discussed.INTRODUCTIONstorageat theThe I-st stage of the experiaental area of Moscow mesonfactory (fig.l) uses the linear accelerator! whichaccelerates H- ion beam and proton beam (one of them can bepolarized) simUltaneously with peak current 50 mA to peakenergy 600 MeV and the beam channeling. The main featuresof this facility design for the nuclear and the particlephysics experiments at the intermediate enezgies, the solidstate physics experiments and other applications are:(1) the particles energy may be continuously variable;(ii) two or aore proton beams may be used simultaneouslyat independently variable intensities;(iii) the macroscopic duty factor of the proton beams maybe varied fro. a continuous beam to a pulsed beamwith the current 10-20 A;(iv) short-pulsed beam with variable frequency in theregion from 0.1 to 2 MHz is available.BEAM CHANNELINGThe linear accelerator has an 1 % duty factor. Theacceleration of H ions is crucial for obtaining multiplebeams and multiturn charge-exchange injection to PSR(Proton storage ring). The beam channeling during theaccelerating cycle injection into PSR and obtaining ofmultiple beams are shown in fiq.2~At first, main H- beam is divided into four pencil protonb~ams Ht,H;,H;,H: and remaining H- by stripping of part ofH beam by the carbon foIls before each of the dividerdoublets (the pairs of the equal dipolar magnets of theopposite polaritYl and the polarized proton beam H+as it isshown in fig.2. H and the proton beams have been separated[297]/5152/[298] M. I. GRATCHEV ET AL.FIGURE 1 Layout of the I-st stage of the experimentalarea of Moscow meson factory. 1 - muon beam for ~SRtechniques, 2 - muon beam, 3 - low energy pion beamand spectrometer with AE/E = 10-9 ,4 - high energy pionbeam 5, - polarized proton and neutron beams, 6- ~ - econversion search, 7 pion X-rays search inhydrogen, deuterium and light nuclei, 8 neutronsource.in vertical plane at 1 em and 2 em at the exit of thedivider doublet. The remainder of the H beam is used forinjection into PSR, it is shaped by the stripping foils.H-and the proton beams are transported via one beam pipe.The focusing cells are used for transporting all beams. Itconsists of four equal alternate gradient quadrupoles (inour case two quadrupole doublets) and makes the minus unitmatrix transportation available for H- and the protonbeams.PROTON STORAGE RING (f1q.3)2The time structure of the ion beams after the linearaccelerator is determined by the construction features. Toshape the time structure and to keep average current forvarious experiments the proton storage ring is used as acompressor or a stretcher. Receiving a 100 ~s beam pulsefrom the proton linac the PSR as a compressor delivers330 ns (or smallez) pulse current of the proton beam forthe neutron source, the PSR as a stretcher delivers thecontinuous beam for the meson targets or fast repetitionpulsed beam for the muon experiments. Extraction of aproton beam from PSR is carried out during a pause of thetime structure of the linear accelerator. The PSR is builtMOSCOW MESON FACTORYuuuuo ))1 ]))2 )])3 J)])lf[299]/53FIGURE 2 Beam channeling diagram. PSR protonstorage ring, NS - neutron source, 0 - focusing cells,T - pion production targets, MS - septum-magnets, DO -divider doublets, CF - carbon foils.in the beam channeling as a part of the beam layout.Compressing of the beam is achieved by the one-turnextraction as soon as the filling process is finished. Theinitial time structure is shaped to provide an azimuthalvoid (bunch structure) to exclude the beam losses duringthe rise time of the kicker magnet field. In this case thering magnet structure is adjusted as an isochronous onei.e.Ct = Y -2 (1),where a is a lIoaentua compaction factor, y is theenergy.There is no necessity to use RF system to keep the bunchstructure. Similar storage idea h~s been proposed andexperimentally studied at the CERN The condition (1)might be maintained in our case only approximately becausea-values is deviated along bunch. In our case the magnitudeof deviation is Aac = 0.018 for linear density of theparticles 3·10~~ m-~, it corresponds to extension of thelength of the bunch to 2 • in 100 PS, it is the negligibleby comparison with 75 •.For stretchinq mode operation tbe aecbanism of theextraction particles by reduction of the particles momentumtransmitted (pass) through target is chosen (£ig.3)4 Inthe half of the period structure where this particles willbe displaced relative to a closed orbit the splitter magnet54/[300] M. I. GRATCHEV ET AL.____________________________--y'7__~__:=__-7FIGURE 3 The proton storage ring. 101 108 th~mine dipole magnets: B = 1.45 T, aperture 20x12 emHOR x VERT, bending angle = 45°; 1Q1 lQ15 thequadrupoles: 0 = 20 em, length = 0.4 m, G = 4.5 Tim;lSP - the sextupoles: 0 = 20 em; 2B1 - 2B8 - the bumpmagnets for injection; 3K - the kicker magnet for theone turn extraction ; DT slow extraction tarqetjIB - circulating beam; AS - the extraction beam instretcher mode; Kn - septum of the splitter magnet.is set for bending the circulation beam. The magnitude ofthe displacement is~r = .·AP/Po (2),where • is the dispersion function.The magnet structure is chosen as to optimize both theseparation between the closed orbit and the extracted beamand the losses of the particles due to interaction with thetarget. We have chosen this mechanism extraction becausefor the case of the incoherent coulomb shift of thebetatron oscillation -0.09 resonance mechanism extractioncan't be implemented effectively. Extraction time isdetermined by the bump magnets which shifts the beam ontothe target.The essential characteristics of the storage ring are asMOSCOW MESON FACTORY [301]/55A\%mmamKwtmmsJ.JTD/revcRl.mradcm.Dlradcm.mradT·mnscm.mradcm.mradmmfollows:Orbit circumference (Circulation period) •. 102.8 m (430 ns)Number of storage turns................... 240Maximum intensity per. pulse 3·10~9stored beam emi ttance. . . • • . . . • . . . . • . . . . • .. 3nMax incoherent tune shift(smooth approx,).-O.09Peak current ..............•....•.......... 11Momentum compaction fa.tor 0.371Kicker-magnet strength .•.................. 0.02Kicker-magnet ri;s time 100Radial emittanci4 2nAxial emittance ...•...•.•••...•..•........ 6nTarget thickness (carbon) ••..•............ 4.4Relative momenta decrease -0.002Dispersion function magnitude at thetarget azimuth 11.3extractor splitter magnet azimuth 0~-function magnitude at thetargei.azimuth .....•..•..••.•••...... 6Sp iII time . . . . . . .••. • . . . • . . • • . . . . . . . . . •. 8. 5Beam expansion rate 3The depth of beam penetration into thetarget .........••.........••....••... 0.3Maximum heat deposition in the target ... 1Intensity 10s5 for the nuclear••interaction in the target .••....... 1Intensity 105s at splitter magnet 0.2Emittance of.~he extracted beamradial••.....•.................•.•.. 0.5axial . • . . . . . • . . . . . • . • . . . . . . . . • . • •. 7•• - only for compress mode operation- only for stretcher mode operationNEUTRON SOURCE (Fig.4)5The proton dziven spallation neutron sources are preferableFIGURE 4 Proton drivenspallation neutronsource1 the proton beams;2 - the quasistationaryneutron source;3 - the pulsed neutronsource56/[302] M. 1. GRATCHEV ET AL.to the reactors. They are ecology safe and can be optimizedfor the kind of the neutron scattering experiments (Fig.4).The neutron source consists of two high-Z high densitytargets for neutron production. First target is used forthe pulsed neutron source with the system of the thin lightwater moderators. Second target is used for thequasistationary source with the heavy water moderator andwith the liquid deuterium moderator. The neutron beams passvia the channels, penetrating through the steel and theconcrete shielding into the experimental hall and along theexternal neutron beam pipes. The parameters of the neutronflux for the uranium targets are given in the table.TABLE Neutron beam parameters for the uranium target.KindofneutronsAveragedensityn/ca sPeakdensityn/cm 5PulsedurationI-'SRemarksFastThermalCold 4e10~S3elO~46 e 10· 66 e 10 1 (110~52 elOi.410~9100 Channel within target40 At H20-moderator surface4000 Channel withinDzO-moderator5000 At LDz-moderator surface0.3 Channel within target0.3 Into solid angle 4n0.3 Neutrons at energy100-2l5eV, emitted intosolid angle 2 ster 3cmthickness H20-moderatorsurface3.5 At H2O-moderator surface• for proton storage ring.PION AND MUON BEAMS (Fig.l)Two pion channels are being constructed. The beamline 4(Fig.l) has been designed for the experiments in the momen-tum range of the pions from 200 to 520 MeV/c. Maximum pionintensitr at the exit of the channel is 10·i. s-~ for n+ or2·10~os- for n-when the momentum spread is AP/Po = 5 % ,thepion-generation carbon target size is 2 e 2 e 100 mm3 andthe proton current beam is 1 mAe The momentum resolutionof the channel corresponds to ~/Po = 0.3 % .The beamline 3is the low energy pion channel and the spectrometer. It isplanned to carry out the pion-nuclear interactionMOSCOW MESON FACTORY [303]/57experiments at the pion energy from 10 to 100 HeV with theenergy resolution S 100 KeV and the angular resolution ~ 50mrad. The beamline 3 will be used in two modes:(i) dispersion mode, when the spectrometer compensates thedispersion of the channel;(ii) achromatic mode ,when the beam spot size at the targetbefore spectrometer will be 2 am in comparison with100 11m in (1).The dispersion plane of the beaml1ne Is vertical, thescattering plane is horizontal, angular range of pouitlonof spectrometer being from OOto 145°. Compensation of thesecond order aberrations is used.Three muon channels are under construction. Characteristicfeature of them is a use of the superconducting solenoids.One of those (6 in fig.1)6 is the ultra-high intensity lowenergy muon source for p - e conversion search and someother experiments. The designed p-stop rate is O.7·10~~s-t+ tt -tand p stop rate is 10 5 at the detector system when ~heaverage beam current is 100 I-JA. The proton beam is injectedinto the 5uperconducting solenoid. A compound target of thetungsten or the molybdenum separate plates is used forproduction of the low energy pions. The pions are capturedby the magnetic field, decay in fliqht and the muons arepushed with high efficiency backward due to the magneticfield gradient.Two muon channels (1 and 2 in fig.l) are used for "decay"muon production in traditional scheme. They use one pionpxoduction target. The front end of the channell consistsof a "shell" magnet and a quadrupole doublet and views thetarget at an angle of 150 0 from the proton beam direction.For "decay" muon production this system selects pions witha momentum 120 HeV/c and focuses (delivers) them into the8 m decay section of the 5 T superconducting solenoid. Forthe "surface" muon beams these elements are tuned to themomenta of about 30 HeV/c and the field in the solenoid isdecreased. The "shell" magnet with the various gradient ofthe field along the beam axis captures the pions in thesolid angle 100 mster, the momenta spread is 10\ .The extraction part of the channel delivers the muon beamsto two experimental areas with the following parameters:the momenta is (30 - 1&0) HeV/c, the momenta spread is10 \ , the intensity is 2-10° s-~ for ~+ and 5-10· s-~ for~-, using the beam spot size of 10 ca. The extraction partis not frosted and must be fitted for each kind of theexperiments. This channel will be predominantly used by theexperimentalists using the muon spin rotation techniques.The front end of the channel 2 views the target at theproton beam direction and delivers the pions of bothcharges into one 8 m, 5 T superconductinq solenoid. Thefront end of the channel consists of two quadrupoledoublets separated by four bending magnets and a quadrupolepole lens. They form two achromatic channels for positiveand negative pions and use the common head and exitquadrupole doublets. Designed parameters of the front endof the channel 2 are: pion momenta is 200 HeV/c, capture58/[304] M. 1. GRATCHEV ET AL.solid angle is 50 mster, the momenta spread is 10% Theextraction part consists of two legs for positive andnegative muons. The .ain parameters of the muon beams are:the muon momenta is 110 HeV/c, the momenta sDread is 10 % ,~ -~ + 0 -~ -the intensity is 8-10 s for ~ and 2-10 s for ~, usingthe beam spot size of 9 em.REFERENCES1. v. D. Bu~lakov et ale Proc. of the 1984 Linear Accel.Conf., Darmstadt, 1984, p. 9.2. H. I. Gratchev et al. Proc. of the XIII Int. Conf. onHigh Energy Accel. , Novosibirsk, 1987, p. 264.3. Ca~pi R. et al. IEEE TRANSACTIONS ON NS, 1981, v. 28,IN 3, p. 2389.4. O. A. Gusev et al. Proc. of the XIV Int. Conf. on HighEnergy Accel. , Tsukuba, 1989.5. Yu. H. Bulkin et ale Proc. of a Conf. on NeutronScattering in the 'Ninetines. International AtomicEnergy Agency, Vienna, 1985.6. R. H. Djilkibaev, V. H. Lobashev. Journal of Nuclearphysics v. 49, (2), 1989, p. 622, (in russian).A. I. Botchkarev at al. In Proc.: Programmaexperimentalnyh issledovanli na mesonnoi fabrike IYaIAN SSSR. Trudy W Vsesoyusnogo seminara, Moskwa, 1987,p. 131 (in russian).

Experimental Area Of Moscow Meson Factory

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