Ball, J. B.

Fischer, K. N.

Hudson, E. D.

Lord, R. S.

Mallory, M. L.

Mann, J. E.

Martin, J. A.

McNeilly, G. S.

Mosko, S. W.

Riedinger, L. L.

Robinson, R. L.

UNT (University of North Texas) Digital Library

By acceptance of this article, the publisher r recipient acknowledges the V. S., Government's right to retain a nonexclusive, royalty-free license in and to anycopyright covering the article.A SEPARATED-SECTOR CYCLOTRON POST-ACCELERATOR FOR THE OAK RIDGE HEAVY ION LABORATORYS. W. Mosko, E. P. Hudson, R. S. Lord, M. L. Ma]lory, J. E. Mann, J. A. Martin, G. S. McNeillyJ. Ii. Ball, K. N. Fischer, L. L. Riedinger, R. L. RobinsonOak Ridge National Laboratory , Oak Ridge, Tennessee, U.S.A.AbstractA separated sector cyclotron post-accelerator ,is proposed for the Oak Ridge Heavy Ion Laboratory.The SSC accepts beams from either ORIC or the 25 MVtandem electrostatic accelerator and extends themaximum particle energy to 75 MeV/u for A less than40 and to at least 10 MeV/u for A greater than 40.The SSC has a field-radius product of 2540 kG-cm,a 4-sector configuration, and azimuthal pole widthof 52°. RF acceleration of up to 1 MV per turn isobtained with two resonators in opposite valleys.An RF tuning range of 6 to 14 MHz accommodatesacceleration on harmonics 2 through 11. Concentricsecond harmonic resonators are provided foroptimizing phase acceptance.IntroductionIn 1969 a new accelerator facility was proposedat Oak Ridge for accelerating all heavy ionspecies to a minimum energy of 7.5 MeV/u using aseparated sector cyclotron with a 16 MV tandemelectrostatic injector accelerator and a compactcyclotron as an alternate injector1). Later, theminimum energy was raised to 10 MeV/u, theexisting ORIi: cyclotron became the alternateinjector cyclotron, and desired tandem potentialwas increased to 20 MV 2> 3). Finally, in 1974,construction was authorized for a 25 MV tandemelectrostatic accelerator at the ORIC facility1*).The new tandem will operate in both a stand-alonemode, and as an injector accelerator for ORIC.The tandem-ORlC raci.lity is still short of thegoal of 10 MeV/u for ions beyond mass 100.Therefore, a separated sector cyclotron, SSC,post accelerator is now planned which extends themaximum ion energy as illustrated in Fig. 1. Theheaviest ions through uranium will be acceleratedto about 10 MeV/u, and lighter ions through mass 40will be accelerated to about 75 MeV/u. The new jt.; f Z'-^'CSSC configuration is similar to that described in %-/•>'.•?.;•'• •'•19722), but it is somewhat more compact due to *"'"'•higher ion injection energy and subsequent highercharge state. Fig. 2 shows a layout of the heavyion laboratory as it will appear when the tandemaccelerator is completed. Fig. 3 shows how thelaboratory will look when the SSC is added. Beamsfrom the tandem can be injected into ORIC, the SSC,or used directly. Beams from ORIC can be useddirectly or injected into the SSC.A separated sector cyclotron post-acceleratoris proposed for the Oak Ridge Heavy Ion Laboratory.The SSC accepts beams from either ORIC or the 25 MVtandem electrostatic accelerator and extends themaximum particle energy to 75 MeV/u for A less than'10 and to at least 10 MsV/u for A greater than 40.The SSC has a field-radius product of 2540 kG-cm,a 4-sector configuration, and azimuthal pole widthof 52°. RF acceleration of up to 1 MV per turn isobtained with two resonators in opposite valleys.An RF tuning range of 6 to 14 MHz accommodatesacceleration on harmonics 2 through 11. Concentricsecond harmonic resonators are provided foroptimizing phase acceptance.IntroductionIn 1969 a new accelerator facility was proposedat Oak Ridge for accelerating all heavy ionspecies to a minimum energy of 7.5 MeV/u using aseparated sector cyclotron with a 16 MV tandemelectrostatic injector accelerator and a compactcyclotron as an alternate injector1). Later, theminimum energy was raised to 10 MeV/u, theexisting ORIC cyclotron became the alternateinjector cyclotron, and desired tandem potentialwas increased to 20 MV 2» 3). Finally, in 1974,construction was authorized for a 25 MV tandemelectrostatic accelerator at the ORIC facility1*) .The new tandem will operate in both a stand-alonemode, and as an injector accelerator for ORIC.The tandem-ORIC facility is still short of thegoal of 10 MeV/u for ions beyond mass 100.Therefore, a separated sector cyclotron, SSC,post accelerator is now planned which extends themaximum ion energy as illustrated in Fig. 1. Theheaviest ions through uranium will be acceleratedto about 10 MeV/u, and lighter ions through mass 40will be accelerated to about 75 MeV/u. The newSSC configuration is similar to that described in19722), but it is somewhat more compact due tohigher ion injection energy and subsequent highercharge state. Fig. 2 shows a layout of the heavyion laboratory as it will appear when the tandemaccelerator is completed. Fig. 3 shows how thelaboratory will look when the SSC is added. Beamsfrom the tandem can be injected into ORIC, the SSC,or used directly. Beams from ORIC can be useddirectly or injected into the SSC.The CyclotronA plan view of the cyclotron is shown inFig. 4. It is a 4 pole separated sector configura-tion with an effective pole width of 52 degrees.Work supported by the U.S. ERDA under contract withthe Union Carbide Corp.- NOTICE-This repori was prepared as an account o( worksponsored by ih« Uniied States Government. Neiiheithe United Stitei nor the United States EnergyReiearch and Development Administration, nor any oftheir employees, nor any of their ooitrracKvi,subcontractors, or their employeei, maket anywarranty, express or Implied, or aaume* any legalliability or responsibility for the accuracy, compkienesiot usefulne» of any information, apparaiui, product oiprocess discloied, or represents that its we would notinfringe privately owned tights.I ' iTwo of the valleys contain RF cavities, and theothers contain injection and extraction components,the injection beam line, and beam diagnosticsinstrumentation. The machine dimensions fromedge to edge are 10 m on the magnet yokes, and 17m on the RF cavities. Cyclotron characteristicsarc listed in Table 1. The variable injectionradius and respective range for energy ratio aredue to unique combinations of injection energy,ion charge, and RF synchronization with ORIC.Table 1. Cyclotron CharacteristicsMAXIMUM ENERGY, MeV/uUranium (23<nj43+)Carbon (l2C6+)MAXIMUM Bp, kG-cmENERGY CONSTANT, k, (E = kq2/A)ORBIT FREQUENCY, MHz10 MeV/u ions75 MeV/u ionsMAXIMUM MAGNETIC FIELD, kGORBITAL MAGNET FRACTIONNUMBER OF SECTORSENERGY RATIO, Ef/E.jRADIUS RATIOINJECTION RADIUS, PATH/2TT, cmEXTRACTION RADIUS, PATH/2TT, cm107525403102.466.49150.60415-73.88-2.6b73-107283Ion energy capability is further illustratedin Fig. 5. Ion energy and respective orbitfrequency are shown as a function of averagemagnetic field and mass to charge ratio. Themaximum average magnetic field is a result of the15 kG maximum hill field and the 0.6 orbitalmagnet fraction. The latter term is defined asthat fraction of an orbit path which lies withinthe magnet sector. The span of orbit frequenciescovered by the RF system for harmonic numbers 2through 7 is also noted.Magnet SystemThe effective sector angle of 52° was chosento provide strong axial and radial focusing ofthe ion beam without encountering resonances dueto magnet periodicity or field imperfections.The relation of axial and radial oscillation,v, vs vr, is shown in Fig. 6 for a 10 MeV/u uranium(Z38y«t3+) a m l a 7 5 M e Vy u c a r b o n (12C5+-) ;beam u s i n g a15 kG hill field. These data were derived frommodel magnet measurements as described;elsewherein these proceedings by Hudson, et al.5jj The openvalleys provide sufficient space for the accelerat-ing (RF) system so that the pole t̂ p aperture needs-The magnet system characteristics are listed inTable 2.Table 2. Magnet System CharacteristicsNUMBER OF SECTORS 4SECTOR ANGLE, degrees 52OVERALL HEIGHT, cm 488OVERALL DIAMETER, cm 1000STEEL WEIGHT, m tons 1450MAIN COIL COPPER WEIGHT, m tons 20MAIN COIL EXCITATION POWER, kW 300NUMBER OF TRIMMING COIL PAIRS PER SECTOR 30TRIMMING COIL EXCITATION POWER, kW 300GAP BETWEEN POLES, cm 10GAP AVAILABLE FOR BEAM, cm 7The RF SystemThe RF system is designed to provide a highrate of energy gain and a large ion beam pulsewidth concurrent with good ion beam quality. Thehigh rate of energy gain is required for reducingcharge exchange losses and for providing good orbitseparation at both injection and extraction radii.The large beam pulse width is obtained with 2ndharmonic flat-topping of the RF acceleration waveform. The RF system tuning range is approximately6 to 14 MHz. Referring to Fig. 5, it can be seenthat operation in the 5th harmonic mode covers theenergy range of about 2 through 12 MeV/u. Higherenergy, as is possible with light ions, requires 2nd,3rd and 4th harmonics. When ORTC serves as theinjector, only odd harmonics are usable.Characteristics of the RF system arc listed inTable 3. The cavities are quarter wave coaxialstructures extending radially from the cyclotron asshown in Fig. 4. The dees and respective groundplanes are cone shaped. Each 15 degree azimuthallywide harmonic dee is located concentrically withina 30 degree azimuthally wide fundamental dee.Electrode clearances are sufficient to hold about250 kV on the fundamental dee. Half as muchclearance is used on the harmonic dee to obtaintransit time factors in the harmonic acceleratinggaps which are equal to those in the respectivefundamental gaps. RF voltage profiles for thedees are shown in Fig. 7. As is typical withradial resonators, the RF voltage decreases withincreasing radius; however, this effect isminimized through transmission line shaping. Thevoltage on the harmonic dee falls off moreseverely than that on the fundamental dee, butthe net RF potential (fundamental potential minusthe harmonic potential) is nearly constant withrespect to radius. Whan transit time factors arealso considered, Fig. 8, the actual potentialeasesubstantially with respect to radius. Consequently;the accelerating system will cause a slight beampulse phase contraction rather than an expansion asone might otherwise expect with a radial RFsystem.Table 3. RF System CharacteristicsNUM3ER OF CAVITIESWIDTH OF DEE, degreesTUNING RANGE, MHzCOARSE TUNINGFINE TUNINGMINIMUM ELECTRODE CLEARANCE, cmRF VOLTAGE, peak, kVRF EXCITATION POWER PER CAVITY, kWAMPLITUDE STABILITYPHASE STABILITY, degreesVacuum SystemFundamentalFrequency2306-14Shorting2ndHarmonic21512-23PlaneTrinroer Capacitors7.62502001 pp l(r>± 0.13.810050The vacuum system characteristics are listedin Table 4. The base operating pressure, 1 x 10~7Torr, is sufficient to avoid significant beam lossthrough charge exchange processes as determinedfrom cross section estimates6'7). The systemvolume includes pole tip vacuum tanks, valleyvacuum tanks, and the RF cavities. In order toachieve the required pressui'e within a reasonabletime with a rather large variety of residual gases,a combination of oil diffusion pumps and heliumcooled cryopumps is used. Fore pumping isaccomplished with a combination of Roots blowers,and oil-sealed mechanical pumps. The system ispumped down to a pressure of 1 x 10 ^ Torr inapproximately one hour prior to starting up thediffusion pumps and cryopumps.Table 4. Vacuum System CharacteristicsOPERATING PRESSURE 1.0 X 10~7 torrSYSTEM SURFACE AREA 7.0 x 106 cm2SYSTEM VOLUME 9 5 j 0 0 0 s.PUMPING SPEEDA i r 140,000 A/secWater vapor 1,000,000 */secPUMPDOWN TIME < 15 h rReferences1. J. A. Martin, et al., "A Heavy-Ion AcceleratorFacility featuring a Separated-SectorIsochronous Cyclotron," Fifth InternationalCyclotron Conference, Butterworths, 1971.2. J. A. Martin, et al., "A Proposed NationalHeavy-Ion Accelerator at Oak Ridge," SixthInternational Cyclotron Conference, AmericanInstitute of Physics, 1972.3. E. D. Hudson, et al., "A Multi-AcceleratorSystem for Heavy Ions," IEEE Trans, onNucl. Sci., NS-20, No. 3, (1973).4. R. S. Lord, et al., "The Oak Ridge IsochronousCyclotron as a Booster for a 25 MV Tandem,"Proceedings of this conference.5. E. D. Hudson, et al., "Magnet Model Studiesfor Separated Sector Heavy Ion Cyclotrons,"Proceedings of this conference.6. The Oranitron, UCRL 16828, July 1966.7. C/j. Schmelzer, "Study of a Variable EnergyHeavy Ion Linear Accelerator," Proceedings ofthe 1968 Proton Linear Accelerator Conference,Brookhaven National Laboratory reportBNL-50120, p. 735, (1968).Figure CaptionsFig. 1. Maximum ion energy as a function of ionmass. The ion beams are stripped tooptimum charge state prior to accelerationin the final stage.Fig. 2. A plan drawing of the heavy ion laboratoryshowing the ORIC, the tandem electrostaticaccelerator, experimental areas, and thebeam transport system.Fig. 3. A plan section drawing of the heavy ionlaboratory showing the ORIC, the tandemelectrostatic accelerator, experimentalareas, the beam transport system, and thenew SSC with required additional beamtransport system, and new experimental area.Fig. 4. Plan view of the cyclotron.Fig. 5. Final ion energy from the SSC as related•to orbit frequency and as a function ofmagnetic field and mass to charge ratio.The span of the RP tuning range is with'respect to orbit frequency for severalvalues of harmonic number.I3. I-. D. Hudson, et al., "A Multi-Accelerator.T.ystem for Heavy Ions," IEliF. Trans, onNucl. Sci., NS-20, No. 3, (1973).4. K. S. Lord, et al., "The Oak Ridge IsochronousCyclotron as a Booster for a 25 MV Tandem,"Proceedings of this conference.5. H. D. Hudson, ct al., "Magnet Model Studiesfor Separated Sector Heavy Ion Cyclotrons,"Proceedings of this conference.6. The Omnitron, UCRL 16S28, July 1966.7. Ch. Sehwelzer, "Study of a Variable EnergyHeavy Ion Linear Accelerator," Proceedings ofthe 1 i>t>S Proton Linear Accelerator Conference,Brookhaven National Laboratory reportBNL-50120, p. 735, (1968).Figure CaptionsFig. 1. Maximum ion energy as a function of ionmass. The ion beams arc stripped tooptimum charge state prior to accelerationin the final stage.Fig. 2. A plan drawing of the heavy ion laboratoryshowing the OKIC, the tandem electrostaticaccelerator, experimental aveas, and thebeam transport system.Fig. 3. A plan section drawing of the heavy ionlaboratory showing the OKIC, the tandcinelectrostatic accelerator, experimentalareas, the beam transport system, and thenew SSC with required additional beamtransport system, and new experimental area.Fig. 4. Plan view of the cyclotron.Fig. 5. Final ion energy from the SSC as relatedto orbit frequency and as a function ofmagnetic field and mass to chiirgo ratio.The span of the RF tuning range is withrespect to orbit frequency for severalvalues of harmonic number.Fig. 6. Focusing characteristics of the SSC magnetas calculated from model data. The datawere taken from a 1/4 scale model magnet , / 5 " -and smoothed.Fig. 7. The RF accelerating potential profile for e*ck acci/tr"*.?!** jop.Fig. 8. Voltage gained per orbit(kv)for various J 'orbit harmonic numbers. The data fromFig. 7, net RF gap potential, is multipliedby 4 and corrected for transit time effects.Higher energy gain per turn with reducedbeam pulse phase width is available whenthe second harmonic cavities are turned off.ORNL-DWG 75-2794R40 80 120 160ION MASS lomu)200 240I:ig. 1. Maximum ion energy as a function of ionmass. The ion beams arc stripped tooptimum charge state prior to accelerationin the final stage.i:ig. 2. A plan drawing of the heavy ion laboratory;;in.wiiij; iho auic, dio t.-nulcni eloctrostatic,-iccelcrator, experimental areas, and thebeam transport system.Fig. 3. A plan section drawing of the heavy ionlaboratory showing the ORIC, the tandem0 80 120 160 200ION MASS (omu)240Fig. 1. Maximum ion enei";:y as a function of ionmass. The ion beams are stripped tooptimum charge state prior to accelerationin the final stage.Fig. 2. A plan drawing of the heavy ion laboratorysViowhm tl\c OklC, the tandem electrostaticaccelerator, experimental areas, and thebeam transport system.Fig. 3. A plan section drawing of the heavy ionlaboratory showing the ORIC, the tandemelectrostatic accelerator, experimentalareas, the beam transport system, and thenew SSC with required additional beamtransport system, and new experimental area.anuK'fO maw V^.JL'ttmaCVGH l»i,\Ef^ ..,,„ N^ ,-'-fFig. 4. Plan view of the cyclotron.P -nus ooo cP U)O 31 C K\ s,* +/ £\ *fnpcoUSoI t lort'scg.o•ocO 'r tCO2-^,r tO, C?53O"^ot-Jt/sOcSor tactu3¥2P(3M 1VIS|*--r»srr̂oaM"™*s.V.V.r+or4fc;9=ft•^Pr*Wi-Or*OOCr t—O-gc• - ;pCPVSP* t isortH "O13C• t i3i—'^ . .O32o^<or t^ *(5C/inPus•-Io»—ipr toCD—imOc1 ™o! -<00AVERAGE MAGNETIC FIELD (kG)CDnoMAXIMUM FREQUENCYNo ioOoCDo<?om—>'aio-<<o3)r-DWGeni9688350300 -250 -ORNL-DWG 75-9686200 -oa< 150cr100 —50 —0—11ol111 r1_ jflEAN ORBITLAST ORBIT—^j-^£r~FUNDAMENTAL RF POTENTIAL ' ^ ^ ^ ^ - ^ . ^—28-20_12~I• NET 1111H _TiIHARMONIC11 1 IRF POTENTIAL—~«, = 141!MHz\—1 - i ^ _ ~ —(2nd) RF POTENTIAL 1| |1 1 I I I" — .\X/^ 14I—^ = 6 MHz^ = 10 MHZMHz12 MHz20 MHz>8 MHz800700ozoccLUa.a 500uio< 400oa30050 100 150 200 250 300ORBIT RADIUS ON VALLEY CENTER LINE (cm)350 400Fig. 7. The RF accelerating potential profile for cyf-ORNL-DWG 75-9687ANY FREQUENCY,6-14 MHz= 5,6,7/",= 14 MHz, />=/ , = 6 MHz , A = 9/,= 14MHz, A=314 MHz, /?=2o< 150a:UJ_iUJoo<100500800700COCEoLJa.UJ6 0 0500< 400t-oa.30020014 MHzI IHARMONIC (2nd) RF POTENTIALI I/2 = 12 MHzfz= 20 MHZ/2=28 MHz50 100 150 200 250 300 350ORBIT RADIUS ON VALLEY CENTER LINE (cm)4 0 0F i g . 7 . The RF a c c e l e r a t i n g p o t e n t i a l p r o f i l e f o r a<f> ct_t_ck--»'.V-•••0RNL-DWG 75-9687ANY FREQUENCY,6-14 MHz/ , = 6 MHz, A=9/,= 14 MHz,/7=3= 14 MHz,50 100 150 200 250 300ORBIT RADIUS ON VALLEY CENTER LINE (cm)350Fig. 8. Voltage gained per orbit(kVjfor variousorbit harmonic numbers. The data fromFig. 7, net RF gap potential, is multipliedby 4 and corrected for transit time effects.Higher energy gain per turn with reducedbeam pulse phase width is available whenthe second harmonic cavities are turned off.

Separated-sector cyclotron post-accelerator for the Oak Ridge Heavy Ion Laboratory

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Separated-sector cyclotron post-accelerator for the Oak Ridge Heavy Ion Laboratory

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