Non-scaling FFAG rings for cancer hadron therapy offer reduced physical aperture and large dynamic aperture as compared with scaling FFAGs. The variation of tune with energy implies the crossing of resonances during acceleration. Our design avoids intrinsic resonances, although imperfection resonances must be, and can be, crossed. We consider a system of three non-scaling FFAG rings for cancer therapy with 250 MeV protons and 400 MeV/u carbon ions. Hadrons are accelerated in a common RFQ and linear accelerator, and injected into the FFAG rings at .. .. . H+/C6+ ions are accelerated in the two smaller/larger rings to 31 and 250 MeV/68.8 and 400 MeV/u kinetic energy, respectively. The lattices consist of doublet cells with a straight section for RF cavities. The gantry with triplet cells accepts the whole required momentum range at fixed field. This unique design uses either high temperature super-conductors or super-conducting magnets reducing gantry size and weight. Elements with variable field at beginning and at end set the extracted beam at the correct position for a range of energies

Keil, Eberhard

Sessler, Andrew M

Trbojevic, D

CERN Document Server

Hadron Cancer Therapy Complex Employing Non-scaling FFAG Accelerator AndFixed Field Gantry DesignNon-scaling FFAG rings for cancer hadron therapy offer reduced physical aperture and large dynamicaperture as compared with scaling FFAGs. The variation of tune with energy implies the crossing ofresonances during acceleration. Our design avoids intrinsic resonances, although imperfection resonancesmust be, and can be, crossed. We consider a system of three non-scaling FFAG rings for cancer therapywith 250 MeV protons and 400 MeV/u carbon ions. Hadrons are accelerated in a common RFQ and linearaccelerator, and injected into the FFAG rings at v/c = 0.1294.  H+/C6+ ions are accelerated in the twosmaller/larger rings to 31 and 250 MeV/68.8 and 400 MeV/u kinetic energy, respectively. The latticesconsist of doublet cells with a straight section for RF cavities. The gantry with triplet cells accepts thewhole required momentum range at fixed field. This unique design uses either high temperaturesuper-conductors or super-conducting magnets reducing gantry size and weight. Elements with variablefield at beginning and at end set the extracted beam at the correct position for a range of energies.EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHCERN   -   AB DepartmentGeneva, SwitzerlandJune 2006AbstractCERN-AB-2006-0471) Lawrence Berkeley National Laboratory, Berkeley, CA 29720, USA,2) Brookhaven National Laboratory, Upton, New York 11973, USAE. Keil, A. Sessler1), and D. Trbojevic2)CERN, Geneva, SwitzerlandPresented atEPAC'06, Edinburgh, UK, June 26-30, 2006HADRON CANCER THERAPY COMPLEX EMPLOYING NON-SCALINGFFAG ACCELERATOR AND FIXED FIELD GANTRY DESIGNE. Keil , CERN, Geneva, Switzerland, A.M. Sessler , LBNL, Berkeley CA, USAD. Trbojevic , BNL, Upton NY, USAAbstractNon-scaling FFAG rings for cancer hadron therapy offerreduced physical aperture and large dynamic aperture ascompared with scaling FFAGs. The variation of tune withenergy implies the crossing of resonances during accelera-tion. Our design avoids intrinsic resonances, although im-perfection resonances must be, and can be, crossed. Weconsider a system of three non-scaling FFAG rings for can-cer therapy with 250 MeV protons and 400 MeV/u car-bon ions. Hadrons are accelerated in a common RFQand linear accelerator, and injected into the FFAG ringsat     . H+/C6+ ions are accelerated in thetwo smaller/larger rings to 31 and 250 MeV/68.8 and 400MeV/u kinetic energy, respectively. The lattices consist ofdoublet cells with a straight section for RF cavities. Thegantry with triplet cells accepts the whole required momen-tum range at fixed field. This unique design uses either hightemperature super-conductors or super-conducting mag-nets reducing gantry size and weight. Elements with vari-able field at beginning and at end set the extracted beam atthe correct position for a range of energies.INTRODUCTIONCancer proton therapy exists today in many medicalfacilities and many more are being built throughout theworld. These facilities consist of cyclotrons (often a scal-ing FFAG) or synchrotrons. In this paper we consider non-scaling FFAG. The advantages of non-scaling FFAG withrespect to synchrotrons are the fixed magnetic field andpossibilities of higher repetition rates for spot scanning.With respect to cyclotrons the advantage is very much re-duced magnet weight and ease of changing the final energy.Because of the possibility of changing energy and locationwith each spot (having a repetition rate of about 100 Hz)the cancerous tumor can be carefully scanned in three di-mensions. We have worked on the subject before [1, 2].ACCELERATOR COMPLEXThe facility consists of three rings with 36 cells each,circumferences 34.56 m, 43.2 m and 51.84 m, shown inFig. 1. The cell lengths  , 0.96 m, 1.2 m, 1.44 m, are inthe ratio 4:5:6. Tab. 1 shows the beam parameters. The Eberhard.Keil@t-online.de Work supported by the U.S. Department of Energy under ContractNo. DE-AC02-05CH11231. Supported by the U.S. Department of Energy under Contract No. DE-AC02-98CH10886maximum kinetic energies at extraction are 250 MeV forH+ and 400 MeV/u for C6+. In Ring 2, the values of are the same for H+ and C6+. Acceleration changes themby a factor of three. All rings can be operated at constantexcitation for both species. In Tab. 1, the particle speeds are equal in the 1-Inj column of Ring 1 for H+ and in the2-Inj column of Ring 2 for C6+ rings. Hence, both speciescan be accelerated in the same system of RFQ and linearaccelerator. The lattices are very similar. Transfer of thebunches from the buckets in one ring to buckets in the nextring is possible, since all RF systems operate at 1.3 GHz.LatticesWe adopt doublets of combined function magnets forfocusing. The straight section space for the RF cavities,0.3 m, and the gap between the magnets, 0.1 m, are thesame in all rings. The phase advances stay well below thesystematic half integral resonance at 	   	   at thelower edge of the energy range.-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12Distance [m]-8-6-4-202468Radius [m] Carbon (69-400 MeV/n)Proton 31 & Carbon 69 MeV/nProton (6.9-31 MeV)Figure 1: Schematic layout of the ringsWe adjust the bending angles such that the path lengthvariation  with Æ approximately vanishes to first or-der at the reference energy. Its remaining variation is pre-dominantly quadratic. This is achieved by bending thebeam away from the machine centre in the horizontally fo-cusing F magnets [3]. The variation of the time of flightwith Æ of the non-relativistic H+ and C6+ ions is dom-inated by the variation of their speed . All rings havesimilar lattice layout and orbit functions. Maximum -functions and dispersion  are roughly proportional to  .In Ring 3, we have 	   m, 	   m, 	    mm.Table 1: Beam parameters of H+ and C6+ in rings 1, 2, 3. Identical particle parameters at n-Extr and (n+1)-Inj.Particle H+ C6+Ring 1-Inj 1-Extr 2-Inj 2-Extr 2-Inj 2-Extr 3-Inj 3-ExtrKin. en./u/MeV 7.951 30.97 30.97 250 7.8934 68.801 68.801 400 0.1294 0.2508 0.2508 0.6136 0.1294 0.3645 0.3645 0.7145/Tm 0.4083 0.8107 0.8107 2.432 0.8107 2.432 2.432 6.3472The vertical aperture radiusis determined by the am-plitude of the vertical betatron oscillations. As in PIMMS[4], we assume normalised emittances     m and    m for H+ and C6+, respectively. For a pes-simistic estimate of , we use the highest value of inthe acceleration range at distance  along a cell, and thelowest momentum error. We allow for three RMS beamradii within . We calculate the contribution of the hori-zontal betatron oscillations to the horizontal apertureina similar manner. We then look for the maximum and min-imum horizontal offsets  at distance  along a cell, andin the same ranges of Æ. We subtract three times thehorizontal RMS betatron beam radius from the minimumoffset  to find the minimum horizontal aperture , andadd three times the horizontal RMS betatron beam radiusto the maximum offset  to find the maximum horizontalaperture . We arrive at the apertures of the F and Dmagnets shown in Tab. 4. Ring 3 has the largest apertureof the three rings, because the cells are the longest. Thevertical aperture in Ring 2 and the minimum horizon-tal aperture are determined by the C6+ ions, while themaximum horizontal aperture is due to the H+.Table 2: RF system parameters at    GHz, initialand final harmonic numbers and , initial step ,number of turns, maximum circumferential voltage Ring  turns  /MV1 H+ 1158 598 8 289 0.112 H+ 747 298 25 116 2.42 C6+ 1448 507 27 253 0.613 C6+ 619 309 19 81 10.8AccelerationWe adopt jumping the harmonic number  [5]. The en-ergy gain in a turn  is adjusted such that the change in causes a change of the revolution period by an integralnumber of RF cycles, and hence corresponds to an inte-gral step  in . Since    , and   , it follows that    , where is the rest energy of the particle. Hence, the smallest is achieved with     and large . At fixed , increases rapidly during acceleration. Its variation can bereduced by starting acceleration with   , graduallydecreasing , and switching to     towards theend. Tab. 2 shows the main parameters of the RF systems,and how  decreases during acceleration, since the revolu-tion period decreases because of the increasing speed .The number of turns is significantly smaller than the dif-ference  , because of the initial step   ,and much smaller than in a synchrotron. The energy gainper turn varies by less than a factor of two, but is muchlarger than in a synchrotron. The high rate of accelerationensures fast crossing of the resonances. The bunches arearranged in a train. The train occupies a fixed time interval , which is a small fraction of the revolution period inRing 1 and in Ring 2 for C6+. This fraction of the revolu-tion period grows during acceleration.Table 3: Extraction kicker parametersRing 2 3Kick angle/mrad 10.7 6.1Rise time/ns 80 80Aperture width/mm 33 46Aperture height/mm 21 15Kicker length/m 0.2 0.2Kicker field/T 0.13 0.19Injection and ExtractionExtraction happens in two stages: (i) A full-aperture fastkicker magnet in the longer straight section deflects the ex-tracted beam such that it is outside the circulating beamone or more cells downstream. The energy of the extractedbeam can be varied in steps at most equal to the voltage in Tab. 2 by accelerating for a variable number of turns.We operate all rings with about 200 bunches, and leaveabout 1/3 of the circumference free for the extraction kickerrise time in Ring 3 and Ring 2 for H+. There, the extrac-tion kickers have the most demanding parameters shownin Tab. 3. The extraction kicker in Ring 1 and all injec-tion kickers have longer rise times. (ii) A septum mag-net deflects the extracted beam further, such that it missescomponents downstream, and sends it into a transfer line.Injection uses similar components in reverse order.Table 4: Magnet parameters, aperture in mm, field  in T.Magnet F DRing 1 2 3 1 2 3Min hor apert -12 -16 -23 -6 -9 -8Max hor apert 12 22 34 6 12 20 at min apert -0.5 -0.9 -1.9 0.8 1.6 3.2 at max apert -0.3 -0.4 -0.6 0.7 1.3 2.6Vert half apert 5 8 6 8 12 8MagnetsTab. 4 shows the apertures and the fields of the combinedfunction magnets, assumed to be sector magnets. The mini-mum and maximum values of the horizontal aperture in theF and D magnets are calculated from tables in the mannerdiscussed in the section above. The gradients in the com-bined function dipoles cause a variation of the magneticfield across the horizontal aperture, quantified in the rowslabelled Field at min/max hor aperture. The fields do notchange sign inside the horizontal aperture.In Ring 1, the fields are below 1 T. The maximum fieldin Ring 2, 1.6 T, occurs in the D magnets at the minimumhorizontal aperture, i.e. at its radially inside edge. Themagnets in these rings are conventional iron-dominatedmagnets. They may be excited either by resistive room-temperature coils, or by coils made of high-temperaturesuper-conductor [6]. The maximum field in Ring 3 also oc-curs in the D magnets at the minimum horizontal aperture.At about 3.2 T, it is in the range of easy super-conductingmagnets. Suitable combined function magnets can be ar-rived at by scaling from the super-conducting magnets inthe proposed proton transport line for the J-PARC neutrinoexperiment [7].0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18Distance [m]-12-11-10-9-8-7-6-5-4-3-2-101Radius [m]End of the gantryAxis of rotationr = 5.27 mr = 5.27 mFigure 2: Schematic layout of the gantryGANTRYThe beam is assumed to have equal emittances   .In the fixed transport line from the accelerators to the ro-tating gantry, it is matched to equal -functions,    , and       at the junction. A 0.3 m longstraight matching insertion consists of two quadrupoles andtwo drift spaces, and rotates with the gantry. It matchesthe round beam at the end of the transfer line to the gantrycells at any rotation angle. The gantry cells consist of non-scaling FFAG cells of combined function dipoles, arrangedin the order FDDF. The bending angle of a cell is .The bending angles of the F and D magnets are adjustedsuch that       at the centre of the D magnet.There, the curvature can be changed without harm to thematching of -functions and dispersion at    .At the reference energy with Æ   , the maximum -functions are less than 1.63 m. The dispersion varies in therange     mm. Fig. 2 shows a schematic layout.The first eight cells bend the beam away from the axis ofrotation. The remaining seventeen cells have the oppositecurvature, and bend the beam back towards the axis of ro-tation. The distance between the end of the gantry and theaxis of rotation, as well as the maximum distance betweenthe gantry and the axis of rotation, about 9 m in Fig. 2,can be varied by changing the number of cells. A simi-lar gantry is in [8]. The gantry can transport particles withmomentum errors up to Æ   . With one excitationof the magnets it transports C6+ ions with kinetic energiesbetween 195 and 400 MeV/u. With about 40% of that ex-citation it transports H+ with kinetic energies between 118and 250 MeV. A system of deflecting and focusing magnetsat the end of the gantry compensates for lateral beam off-sets, allows scanning, and achieves the desired beam size.CONCLUSIONSIn this paper we have exhibited a design of a non-scalingFFAG and fixed field gantry. We have designed a seriesof rings producing 250 MeV protons or 400 MeV carbon,designed an acceleration scheme, considered injection andextraction, developed a matched into the gantry, and pre-sented a compact gantry design. The complex facility de-sign is now ready for detailed engineering and costing.REFERENCES[1] E. Keil, A.M. Sessler, D. Trbojevic, PAC (2005) 1667.[2] D. Trbojevic, E. Keil, A. Sessler, Pres. at Internat. Symp. onUtilisation of Accel., 5 to 9 June 2005, Dubrovnik, Croatia.[3] E. Keil, A.M. Sessler, Nucl.Instr.Meth. A538 (2005) 159.[4] P.J. Bryant (ed.), CERN-2000-006, Vol. 2 (2000).[5] A.G. Ruggiero, BNL Doc. C-A/AP/237 (2006)[6] R. Gupta et al., PAC (2005) 3018.[7] T. Nakamoto et al., PAC (2005) 495.[8] D. Trbojevic et al., EPAC (2006) WEPCH180.

Hadron cancer therapy complex employing non-scaling FFAG accelerator and fixed field gantry design

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