Summary Talk Alternative Accelerator for Therapy. Andrew M. Sessler Lawrence Berkeley National Laboratory April 30, 2009

Transcription

1 Summary Talk Alternative Accelerator for Therapy Andrew M. Sessler Lawrence Berkeley National Laboratory April 30, 2009

2 I want to thank the organizers for inviting me to speak We are all well-aware that there is more to a therapy facility than an accelerator. And new accelerator ideas may not even be needed, but they may result, in ways that we can t even envision, to the various desired attributes for a facility (safety, reliability, cost, etc). Therefore they are worth considering, studying, and developing. Disclaimer: None of the work I will describe, and none of the various slides I will show, are my work. I am simply reporting on the work of others and wish to thank them for giving me the slides for this talk. However, just because it isn t my work, doesn t mean that I don t have ideas and opinions that I shall freely express. (Thus is my chance!) Furthermore, there is no time for you to hear the other side, but then you have been hearing that all week. Well, you can make comments after my talk.

3 Accelerator Alternatives RF Linacs (Not presented orally; blame the organizers.) S-Band X-Band Dielectric Wall Accelerators Non-Scaling FFAGs Laser/Plasma Accelerators General Thoughts

4 RF Linacs: S-Band INFN ACLIP Side-Coupled Linac (at Catania): 3 GHz, Side coupled cavities for very low beta. 30 MeV injection; 62 MeV final energy; gradient of 20 MeV/m. Possibly magnetron powered (less expensive than klystrons). Tested at high power (4.0 MW) and in normal operation 2.6 MW. Lots of loss in first module (acceptance too small for incoming beam), but accelerates adequate charge (beam current of 8 na). Innovative side-coupled cavities: One replaces two of the standard ones. Increased shunt impedance and a number of assembly simplifications. R&D: Complete first module: 26 accelerating cells and 26 coupling cells. R&D: Build 5 modules: Length 3.1 m.

5 RF Linacs: S-Band QuickTime and a decompressor are needed to see this picture. Standard Tiles

6 RF Linacs: S-Band s QuickTime and a decompressor are needed to see this picture. Innovative tiles

7 RF Linacs: S-Band s QuickTime and a decompressor are needed to see this picture. The innovative tile

8 RF Linacs: S-Band The TERA Project uses a Cyclinac; i.e. a cyclotron followed by an RF linac. Roughly the transition is at 30 MeV. The project talks of both protons and ions up to carbon.

9 High Gradient Accelerators for Proton Therapy Machines (X-Band) SLAC We propose to apply the results obtained to date by the US high gradient collaboration research for future linear colliders to proton linacs. ( for a review of this effort see talks presented at a recent workshop on the subject at We assume an injection energy of about 70 MeV and a final energy of about 250 MeV Carbon Therapy machine can also make use of this technology At the moment we are considering accelerators operating at the X-band High gradient developments are centered around three major advances Ability to generate ultra-high power ( demonstrated > 500 MW at X- band) Geometrical effects can enhance the gradients substantially New application of materials to linacs

10 Ideas Two ideas are being put forward: ostanding wave accelerator structures with parallel coupling: Each cell is fed separately using a parallel manifold The structures is built from a Cu Ag alloy (other alloys such as CuZr and CuCr are also possible candidates) In this case we depend on the geometry and the newly discovered potential for copper alloys to achieve high gradients to push the average gradients to ~ 70 MV/m. ohigh group velocity structure Group velocity close to the speed of the particle bunch Very short pulse ( 30 ns ) Extremely high power is required (~1 GW) In this case we depend on our ability to generate short ultra-highpower pulses and the short time duration of the pulse to push the gradient.

11 R&D o For the Standing wave accelerator structure approach The developments of the manifold and feeding system The tunability of the phase advance/section to match the fast changing particle velocity will require some effort. Working with copper alloys is not straight forward and there is not yet experience in building linacs using these alloys while preserving there features However, this is a straight forward developments that will certainly lead to a new generation of high gradient linacs. o High group velocity structure Creating this structure is a challenge because of the high group velocities, candidates such as dielectric structures, plane wave transformer structures etc. do not lend themselves easily to high gradient construction. Innovative ideas for fundamental mode couplers are needed, specially for dielectric structures. The extremely high power required can be generated by extrapolation of current technology, but need to be demonstrated. This is rather more involved developments

12 Geometrical Studies 4 different single cell structures: Standing-wave structures with different iris diameters and shapes; a/λ=0.21, a/λ=0.14, a/λ=0.14 (elliptical iris), and a/λ=0.105 and. Global geometry plays a major role in determining the accelerating gradient, rather than the local electric field. Maximum surface Maximum electric surface fields [MV/m] electric fields [MV/m] Accelerating fields [MV/m]

13 First Test of a Vacuum Brazed CuZr Structure Material Studies Clamping Structure for testing copper alloys accelerator structure ( under test) Diffusion bonding and brazing of copper zirconium are being researched at SLAC. The clamped structure will provide a method for testing materials without the need to develop all the necessary technologies for bonding and brazing them. Once a material is identified, we can spend the effort in processing it.

14 Dielectric Wall Accelerators Dielectric Wall Induction Accelerator (Livermore and also SLAC) Stacked pulse-forming lines coupled to the beam through an insulating dielectric wall Multilayer high-gradient insulators. Hope to achieve 100 MeV/m; present design is 25 MeV/m and goes to 75 MeV (in 3 meters) and not on a gantry. Plan is to get to the higher gradient and have the linac rotate and thus simplify beam delivery.

15 We are working with Tomotherapy, Inc. and CPAC to develop a compact proton DWA 200 MeV protons in 2 meters Energy, intensity and spot width variable pulse to pulse Nanosec pulse lengths At least 200 degrees of rotation Up to 50 Hz pulse repetition rate Less neutron dose (neutrons still produced in the patient) System will provide CT-guided rotational IMPT TomoTherapy has licensed the DWA technology from the Lawrence Livermore National Laboratory and CPAC has a Cooperative Research and Development Agreement (CRADA) with LLNL artist's rendition of a possible proton therapy system 15

16 Stacks of Blumleins with independent switch triggers implement the virtual traveling wave* accelerator HGI Blumlein Proton source Laser Focusing Optical fiber distribution system HGI Beam SiC photoconductive switches Monitor Stack of Blumleins * Patents pending 16

17 Dielectric Wall Accelerator s QuickTime and a decompressor are needed to see this picture. A:pulse line, B:fast switch, C: vacuum insulator, D: vacuum

18 Dielectric Wall Accelerator s QuickTime and a decompressor are needed to see this picture.

19 F.A.S.T. Blumlein structure, proton injector and spark proton source Vacuum pump 5-Induction cells 7 Blumleins HGI Spark sources camera Thomson spectrometer 19

20 Dielectric Wall Accelerator s QuickTime and a decompressor are needed to see this picture. Four Blumlein pulser to accelerat a ka of electrons Put at end of ETA (5.5 MeV) Insulator 3.5 cm thick with 1 mil steel layers Insulator/steel = ns pulses Achieved 3-4 MeV/m at beam No damage to insulator Gradient limited by pulser

21 Induction Concentrator Concept* grid switch tube coaxial feeds core Electric field (V/m) grid conductivity (S/m) time (ns) On-axis accelerating field in the middle of each switch tube segment (1 Volt drive per cell) 20 * Patent pending time (ns) 21

22 There are several possible cell topologies employing DSRD s* SLAC approach: SLIM concept *Courtesy of Anatoly Krasnykh, SLAC 22

23 PAMELA (Mostly United Kingdom) : Overview PAMELA(Particle Accelerator for MEdicaL Applications ) aims to design particle therapy accelerator facility for proton and carbon using NS-FFAG with spot scanning Prototype of non-relativistic NS-FFAG (Many applications!! Ex. proton driver, ADSR) Difficulty is resonance crossing acceleration in slow acceleration rate Schedule by end of 2009 : Baseline design 2010 : Refining design (and funding proposal) International collaboration UK, US, Canada, France, CERN,

24 PAMELA : Lattice Challenges: Tune stabilized NS-FFAG lattice Integer resonance crossing must be circumvented. Tune-stabilization by introducing higher order multipole field is required One feasible option : Non-Linear NS-FFAG (simplified scaling FFAG) : B=B 0 (R/R 0 ) k B=B 0 [1+k R/R 0 +k(k-1)/2 ( R /R 0 ) 2 ] * Eliminating higher order multipole 1.7m Beam Kicker (inj) Septum (inj) (1) Energy : 30MeV~230MeV (Proton) (2) Long straight section (~1.7m) (3) Small orbit excursion(~15cm) 2R=12.5m 1m (4) Small tune drift ( <1) (5) Limited multipole (Up to decapole) Kicker (ext) Septum (ext)

25 Betatron tune Tune variation <1 (except 30MeV, vertical, tune drift<0.5) Vertical tune can be easily varied by changing F/D ratio (ex 2% change of F/D shifts vertical tune about 0.5) Vertical tune is sensitive to distribution of fringing field Tracking using realistic field is indispensable for reliable design Now, tracking using realistic 3D field is under preparation. D/F ν v <0.5 Field index: k

26 Beam extraction Advantage : Variable energy extraction Difficulty: Beam handling of horizontally distributed beam Kicker#1 Septum FDF FDF Solution : Vertical Extraction Advantages are. (1) weaker field, (<0.6kgauss 1m: proton ring) (2) good matching with FFAG transport, (3) extraction kicker can be used as injection kicker R&D issues are. (1) Large aspect ratio kicker (Kicker inductance is an uncertainty ) (2) Kicker reliability(ex life time: 10 9 ms 12day) (3) extension to carbon ring (high current PS) 230MeV (B kicker septum

27 RF system Requirement :: 1kHz repetition rate 100kV/turn Available space :: 6 drift space 1.2m (L drift drift ~1.7m) Target energy gain: 16kV/turn/cavity Challenge : high duty cycle, high rate FM, high field gradient One solution : Ferrite loaded cavity (baseline design: ISIS 2nd harm. Cavity) Relatively high Q (~100) with sufficient accelerating field Development has just started Step 1: Ferrite property measurement beam Q-value FM rate dependence (dynamic loss effect) Step 2: Prototyping (budget request is needed) Power dissipation Power density dependence (high loss effect) Phase error problem 1.1m 2 ferrite core layers

28 NS-FFAG Proton Ring 24 doublets 12 cavities Three kickers Circumference = m D=8.56 m r=4.278 m

29 Tunes vs. momentum E k =30.96 MeV MeV

30 Blow up in x, x due to the random errors of third order avoided /12=1032

31 NS-FFAG Acceleration 1. Harmonic jumping (Not so easy) 2. Harmonic jumping and modulating frequency (A bit easier) 3. Correct accelerating phase at each turn Can be done with low Q (about 50) and, therefore, requires large power. Possibly can be done with ferro-electrics, which have a much higher Q (about 1,500), But need R&D. There were posters (4) on this subject.

32 A Three Ring Therapy Facility E. Keil, D.Trbojevic, and me at EPAC 06 and in PRST:A&B 10, (2007) Protons in the inner two, carbon in the outer two. Injection velocity of protons and carbon are the same. Magnetic field increases as one moves out. QuickTime and a decompressor are needed to see this picture.

33 QuickTime and a decompressor are needed to see this picture.

34 NS-FFAG Summary PRO: Comparable to synchrotrons (~C=60m) or smaller size. (Cyclotrons are smaller but require large amount of steel). Fast acceleration rate. Energy scanning simple: single turn extraction at required energy. Fast, and accurate, spot scanning seems very possible. No radiation loss (cyclotrons have unavoidable activation due to the degrader to allow the required energy range). Easy to operate because of the fixed and linear dependence of the magnetic field. Small orbit offsets small aperture. CON: Resonance crossing Lots of edge magnetic field effect Large power for the RF

35 Laser-Driven Proton Treatment Facility Concept 振興調整費 laser pulse compression & conditioning target /ion source spectral enhancement and filtering beam dump and diagnostics Control room gantry not included here patient positioning Protons (ocular melanoma): energy for therapy 40 to 60 MeV (tunable and steerable for spot scanning) maximum proton energy (cutoff) - ~ MeV energy spread at tuned energy 0.1 % to 1 % bunch charge at source (laser target) ~ 1 nc (full spectrum) bunch charge to patient ~ 10-4 nc (~6x10 5 protons) (assume 1 % spread & 10 Hz for 2 minutes) integrated dose ~ 55 Gy (~2x10 10 protons in ~ 30 fractions) Laser at target: wavelength 1030 nm peak intensity - 5x10 20 W/cm 2 peak power TW pulse energy 150 J pulse duration 300 fs repetition rate 10 to 100 Hz

36 振興調整費 Laser-Driven Proton Treatment Facility: R & D Requirements Laser development (i) single shot, high peal power (ii) repetition-rated high average power (iii) pulse tailoring ( cleaning, shaping ) Single shot and repetition-rated proton yield experiments Targetry efficiency, compatible with repetition rate Proton optics compatible with unique features of laser-driven case Beamline designs low (~10 MeV) and higher energy (~60-80 MeV) versions Spot scanning developments Diagnostics/Instrumentation/Controls of laser-driven accelerator - plus noninvasive, redundant single bunch detection - identify direct laser control of proton charge & energy and relation to magnet/collimator control Medical requirements/guidance detail for performance of laser-driven accelerator - medical/biological science and technology focus (PET ) Gantry requirements/design Compactness

37 振興調整費 Some Key Milestones Laser Development - ~ PW single shot capability ~ 10 TW repetition-rated capability (power scaling) ~ 100 TW Targetry - ~ 10 Hz capability, efficiency ~ few % Proton yields - ~ MeV (repetition-rated) ~ MeV (repetition-rated) Stable, repetition-rated proton beam demonstration (low and higher energy) New focus groups Integrated Laser-Driven Ion Accelerator Systems (ILDIAS) and Medical/Biological Science and Technology PET diagnosis of laser-driven proton dose (autonomous) Spot scanning capability

38 The French Consortium: SAPHIR

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40 General Thoughts Let me list some R&D projects which are either needed, or would improve the performance, of existing therapy machines. Advance in situ diagnostic capability. (Generation, and detection, of radioactive species within the tumor by the therapy beam or another beam.) Much work already going on as described in the posters. Much needed! Develop an ion source that can easily give a range of intensities (a dynamic range of about ten) from shot to shot. Also, of course, capture and transport reliability. Now good to a few percent, but feedback may be in order. Learn how to extract from a cyclotron at various energies. (Possible? Add an after-burner?)

41 General Thoughts (Cont) Increase the rep rate of synchrotrons from (about) 30 Hz to (about) 60 Hz. Demonstrate a section of sc, and also a section of permanent magnet, NS-FFAG gantry. Build a high-q rf cavity suitable for a NS-FFAG and demonstrate that its resonant frequency can be changed quickly (10 ns and a few percent). Demonstrate resonance crossing in a NS-FFAG. (This has a BIG effect on the Pamela design; i.e. avoiding resonance crossing. Necessary? Now a large aperture and wide aperture kickers are needed.)

42 General Thoughts (Cont) Demonstrate a gradient of at least 100Mev/m in a dielectric wall accelerator. (Linacs get about 70 Mev/m.) Develop switch packages and the new idea. Build an S-band linac for low (and variable) beta. Build an X-band structure that works for low (and variable) beta. Perform dose studies to determine necessary standoff for spray nozzles (vs parallel beam wide nozzles). Improve slow extraction from a synchrotron. (Or, is it good enough?) Any possibility of fast extraction of one bunch at a time? Make high field (few T?, Nb 2 Sn, 16T??) sc cyclotrons

43 General Thoughts (Cont) Demonstrate, in a laser accelerator, adequate energy and current (10 10 protons per sec), with a few percent variation in energy (and no high-energy tails) and reproducibility from pulse to pulse. (And other things, such as a beam delivery system, measurement facilities, reliability, etc., along with the cost and size of such a complete facility.) Sharpen up the laser pulse, so there is less of a front porch. Develop adequate rep rate and energy. Laser acceleration target development is needed (high rep rate is desired).

44 Thank you for your attention