Construction of a Compact 12 MeV Race-track Microtron at the UPC

Transcription

1 Construction of a Compact 12 MeV Race-track Microtron at the UPC Yuri Kubyshin, Vasiliy Shvedunov (on behalf of the project team) Novembre 10,

2 Talk outline 1. UPC * project of 12 MeV RTM MeV Race-Track Microtron (RTM) 2.1 Design requirements and main characteristics 2.2 Magnets 2.3 Accelerating structure 2.4 Beam dynamics 2.5 RF system 2.6 E-gun 2.7 Vacuum chamber and vacuum system 2.8 Control system 3. Summary and concluding remarks - Status of the project - Further steps *UPC = Universitat Politècnica de Catalunya 10/11/2011 2

3 UPC project of 12 MeV RTM Race-track microtron (RTM): Principle of operation RTM is a machine with beam recirculation Extraction Pulsed RTMs are optimal for medium and high beam energies ( MeV) and relatvely low pulse beam current ma (average current < 100 µa) Injection 10/11/2011 3

4 RTM: Principle of operation l n+1 Time of revolution on the nth orbit: 2l 2 Rn 2l 2 En Tn 2 c c c ec B n n n Resonance (synchronicity) conditions: T TRF,, Z T 1 n 1 T n T RF Magnetic field in the end magnets: E s 2 E s ec 10/11/ B n Linac For ultra-relativistic particles, n 1 is the energy gain per turn (of the synchronous particle) Narrow longitudinal acceptance 0 32 High monochromaticity of the output beam s,

5 UPC project of 12 MeV RTM 2004 Concept of a compact RTM B.S. Ishkhanov, V.I. Shvedunov et al. RuPAC Technical University of Catalonia (Universitat Politècnica de Catalunya, UPC), Barcelona started a project of design and construction of an RTM based on this proposal Planned application: Intraoperative Radiation Therapy (IORT) Viability study, theoretical design of RTM systems, beam dynamics simulations The project is developed in a collaboration with the Skobeltsyn Institute of Nuclear Physics (SINP) of Moscow State University and CIEMAT (Madrid) 10/11/2011 5

6 UPC project of 12 MeV RTM Introperative Radiation Therapy IORT is a therapy technique consisting in administration, during a surgical intervention, of a single and high radiation dose Gy using electron beams of energies in the range from 4 MeV to 20 MeV directly to the tumor bed/environment thus avoiding damage of healthy tissues. For the development of the IORT dedicated compact electron accelerators are needed. Mobetron (IntraOp Medical Inc.) NOVAC7 (ENEA, Hitesis, Info&Tech) Example: Intensive use of LIAC for IORT at the Instituto Europeo di Oncologia, Milan 10/11/2011 6

7 UPC project of 12 MeV RTM Technical design of the RTM systems. Purchase of standard components. Tenders and placing orders for manufacturing of nonstandard components Delivery of the E-gun, vacuum chamber, accelerating structure, supporting platform Tests of RTM systems: RF, vacuum, control system, etc. 10/11/2011 7

8 12 MeV UPC RTM Accelerator head General layout IORT complex 10/11/2011 8

9 12 MeV RTM General design requirements: -Output energies: between 6 MeV and 12 MeV -Low energy dispersion (< 1%) -Energy stability, repeatability and simple energy regulation -Electron beam dose rate Gy/min, dose stability -Low dark currents -Low parasitic radiation -Compact design, low weight -Low energy consumption Solution: RTM 10/11/2011 9

10 12 MeV RTM: General layout of the accelerator head 1. Electron gun 2. Accelerating structure (linac) 3. End magnet 1 4. End magnet 2 5. Horizontally focusing quadrupole 6. Extraction magnets 7. Extracted beam 10/11/

11 12 MeV RTM: Main characteristics Main characteristics Beam energies 6, 8, 10, 12 MeV Operating wavelength / frequency 5.25 cm / 5712 MHz Synchronous energy gain 2 MeV RF and E-gun pulse length* 3 µs Pulse repetition rate* Hz End magnet field 0.8 T Kinetic energy at the injection 25 kev Pulsed beam current at RTM exit 5 ma Pulsed RF power < 750 kw RTM dimensions 670x250x210 mm RTM head weight <100 kg Harmonic number: 1 * The E-gun and RF source (magnetron) are fed by a common modulator 10/11/

12 12 MeV RTM: Main characteristics To comply with the design requirements the following technical solutions have been implemented: C-band linac (λ = 5.25 cm, f=5712 MHz) Rare-Earth Permanent Magnet (REPM) material as a source of the magnetic field in the magnets Low energy injection and on-axis E-gun Linac bypass. To assure the linac bypass, after the 1st acceleration the beam is reflected back to the linac. Hence, standing wave linac. All elements of the RTM accelerator head are placed inside a vacuum chamber with vacuum Pa 10 mbar (in-vacuum solution). 10/11/

13 12 MeV RTM: Main characteristics Energy and current: motivated by the IORT application (dose rate: Gy/min) E 12MeV, extraction energies: 6, 8, 10, 12 MeV max Pulse current I pulse 5mA Low duty factor / average beam current: 50 na 5 µa Pulse beam power, then P RF kW, 3 P beam 60kW in any case P RF 1MW 6 10/11/

14 12 MeV RTM: End magnets Main specifications: Uniform field region induction B T with accuracy ~ 0.1% This is achieved by precise magnetization and tuning of the permanent magnet blocks. Field uniformity 0.075% This is achieved by the steel magnetic properties and accuracy of the parts machining. The magnetic field is created by permanent magnetic material (REPM: NdFeB). Advantages; a) No power source and coils are needed c) Can be placed in-vacuum b) Complicated field profile can be obtained d) Compact design REPM material Median plane 10/11/

15 12 MeV RTM: End magnets Problem of strong vertical defocusing by the end magnet fringe field 1 Requirement: Vertical focusing with focal power (orbit length) F in order to get stable transverse oscillations Solution: Reverse pole to compensate the focusing by the fringe field. Reverse pole, V 1 Main pole, V 0 Median plane 10/11/

16 Solution of the fringe field problem (Babich, Sedlacek, 1967): 10/11/

17 12 MeV RTM: End magnets Linac bypass problem Solution: First orbit closure, beam reflection and subsequent second acceleration in the linac 10/11/2011 Method of beam reflection from the end magnet after 1st acceleration. (Alvisson, Eriksson, 1976) 17

18 12 MeV RTM: End magnets 4-pole design The idea is to decouple the vertical focusing and beam reflection problems by incorporating two dipoles into the magnetic system 1 A A 3 y everywhere z Facet 2x2 mm 2D iterative calculations: 1. The dipoles are adjusted to get the beam reflection 2. The reverse pole is adjusted to get the required focal power 10/11/

19 12 MeV RTM: End magnets 4-pole design Optimal field profile Magnetic Flux Density B, (T) B 1 = T B s1 = T B s2 = T -0.8 B 0 = T longitudinal coordinate z, (mm) 10/11/

20 12 MeV RTM: End magnets 4-pole design /F (m -1 ) E (MeV) Focal power 2 MeV (PAC-2007) 10/11/

21 12 MeV RTM: End magnets 3D simulations of the end magnet ANSYS simulations (UPC, SINP) Adjusting the magnet geometry and REPM magnetization Optimization of the yoke thickness to minimize the magnet weight without essential saturation (B < 1.3 T) Calculation of detailed distributions of the magnetic field and field uniformity Fixing the position of the end magnets with respect to the linac axis. 10/11/

22 12 MeV RTM: End magnets Recently a new improved design of the magnets which includes a the a tuning of the magnetic field has been performed. (talk by Juan Pablo Rigla) Next step: magnets manufacturing. Main pole tuner 10/11/

23 12 MeV RTM: Accelerating structure (linac) Main specifications: Standing wave bi-periodic π/2 on-axis coupled accelerating structure C-band structure, f 5712MHz Sufficiently large shunt impedance Sufficiently large cell coupling Beam hole radius 4 mm Good capture efficiency for the non-relativistic beam at injection and efficient acceleration of the relativistic beams at subsequent orbits (> 25 %) Sufficient web thickness (>1.5 mm) for cooling 10/11/

24 12 MeV RTM: Accelerating structure (linac) 2D optimization: 1. Optimization of the β=1 cell geometry and definition of the geometry of β<1 cell of different lengths (SUPERFISH ) 2. Beam dynamics optimization of linac parameters for a 25 kev injected beam (RTMTRACE) 3. β<1 cell geometry optimization Parameters to optimize: Rb, L, t, g (max. shunt impedance, min. c beam losses, min. overstrength factor, etc.) 0.4 <β<0.8 for the short cell number of β=1 cells 10/11/

25 12 MeV RTM: Linac 2D optimization Results: Three β=1 cells with the field amplitude 44.8 MV/m, Q=11700 One β=0.5 asymmetric cell with the field amplitude 43 MV/m, Q= Ez (MV/m) z (mm) 10/11/

26 12 MeV RTM: Linac 3D optimization with HFSS (CIEMAT) and ANSYS (SINP+UPC) codes 1. Optimization of the coupling slot parameters of the β=1 cells (high coupling factor, small drop of shunt impedance, reproduce on-axis field) 2. Tuning π/2-mode frequencies to 5712 MHz by adjusting R a, R c 3. Estimation of RF power losses and total RF power required 4. Calculation of the coupling window parameters of the feeding waveguide 10/11/

27 12 MeV RTM: Linac 3D optimization with HFSS (CIEMAT) and ANSYS (SINP) (EPAC-2006) Results: β=1 Resonant frequency 5712 MHz Quality factor Q=9860 Total pulsed power dissipated in the structure walls 600 kw Cell coupling k 10% Coupling factor c 2 Shunt impedance R s 100 M / 3D linac model 10/11/ m

28 12 MeV RTM: Linac Linac construction (CIEMAT) Test Cavity 1 Discs machined Cavity tests at the CIEMAT test stand

29 12 MeV RTM: Linac Linac construction (CIEMAT) Linac brazed (at CERN) and fixed on a support and the supporting platform (at UPC) 10/11/

30 12 MeV RTM: Linac Q 0 β c f (MHz) Experimental value (after brazing) Theoretical value Electromagnetic characteristics (CIEMAT) With this data and parameters of the components of the RF system the magnetron must provide 850 kw of RF power. E-field before (blue line) and after (red line) the brazing 10/11/

31 12 MeV RTM: Beam dynamics 2 MeV beam, linac entrance ~2 MeV Z0M M1 12 MeV 10 MeV 8 MeV 6 MeV 4 MeV inj S 5th 4th 3d 2d 1st Z0M M2 Simulations performed with RTMTRACE (SINP) Position for longitudinal acceptance calculations at MeV dl 2 MeV beam, linac exit L linac L d Lq ds Position for transverse acceptances calculations at 25 kev kev beam max 61.6 For a relativistic beam the maximum acceleration takes place at at the linac entrance, for the asymptotically synchronous particle at 77.9º 10/11/

32 12 MeV RTM: Beam dynamics Longitudinal acceptance and beam emittance at 1.92 MeV Horizontal acceptance at 25 kev Longitudinal capture efficiency is about 20% 10/11/

33 E ~ 4 MeV E ~ 12 MeV Energy spread: E 250keV E 80keV E E E E 10/11/

34 12 MeV RTM: RF system Linac CPI Magnetron SFD-313 (0) modulator (1) magnetron (2) flexible waveguide (3) pressure unit (4) 4-port circulator with loads (5) H-bend with arc detector (6) dual loop coupler (7) rotary joint (8) vacuum window (9) rigid waveguide (10) flexible waveguide ScandiNova modulator WR187 waveguide system 10/11/

35 12 MeV RTM: RF system Linac (1) magnetron ---- (4) 4-port circulator with loads ---- (6) dual loop coupler ---- (11) phase shifter AFC 11 General scheme with the Automatic Frequency Control (AFC) system (mechanical tuning of the magnetron) and Low Power RF (LPRF) control (magnetron frequency pulling) /11/

36 12 MeV RTM: RF system RF system operation parameters Parameter Value Operating frequency 5712 MHz RF and E-gun pulse length 3 µs Pulse repetition rate Hz Magnetron anode voltage 36 kv Magnetron anode current 60 A Modulator output pulse power 2.2 MW Magnetron output pulse power 1 MW 10/11/

37 12 MeV RTM: RF system RF source: SFD-313 magnetron of CPI Frequency GHz Peak power output 1 MW Anode voltage 36 kv Anode current 60 A Heater 19A Air cooled Mechanically tunable M1 Modulator of ScandiNova Cathode pulse voltage -36 kv Pulse current 60 A Pulse width 2-4 µs Repetition rate Hz Pulse top flatness < 0.5% Amplitude stability 1 % 10/11/

38 12 MeV RTM: RF system Stand for high power RF tests (UPC) Preliminary measurements by two methods give a value of the magnetron pulse power kw. 10/11/

39 12 MeV RTM: RF system Results of RF test runs performed in Shape of the HV pulse Frequency spectrum of the RF pulse Failure of a power supply unit of the modulator in June 2011 has produced an unplanned pause in the tests. 10/11/

40 12 MeV RTM: Electron gun On-axis gun with off-axis cathode Anode (linac wall) Cathode Focusing electrode Electron trajectories in the vertical plane are bent by a focusing electrode. I = 25 ma, U=25 kv At z=15 mm σ < 1 mm, σ < 5 mrad 10/11/

41 12 MeV RTM: Electron gun E-gun was designed (CST code), constructed and optimized at SINP. Now it is installed at the supporting platform inside de vacuum chamber (UPC) Beam images at the distance 15 mm and 30 mm from the anode edge Measured emittances: H 1.4 mm mrad V 2.2 mm mrad (PAC 11; NIM 2010) 10/11/

42 12 MeV RTM General setup Vacuum chamber Pumping tube Ion pump Accelerator head 10/11/

43 12 MeV RTM: Vacuum chamber and pumping /supporting tube Vacuum to maintain: 10 6 mbar Ion pump (VACION / MINIVAC, 50 l/s) Port for a turbomolecular pump (prepumping; MINITASK, 40 l/s) Supporting platform 10/11/

44 12 MeV RTM: Vacuum chamber and pumping /supporting tube Deformations study and mechanical design were performed with ANSYS code (UPC). 10/11/

45 12 MeV RTM: Vacuum chamber and pumping /supporting tube Technical design of various elements (UPC) Mechanism for moving the extraction magnets End magnets on adjustment rails 10/11/

46 12 MeV RTM: Vacuum chamber and pumping /supporting tube Supporting platform with linac installed

47 12 MeV RTM: Vacuum chamber and pumping /supporting tube 10/11/

48 12 MeV RTM: Vacuum chamber Vacuum tests of the chamber + tube assembly Vacuum box pumping out July ,E+03 1,E+02 1,E+01 1,E+00 1,E-01 MiniTask 19 July MiniTask 20 July p (mbar) 1,E-02 1,E-03 1,E-04 1,E-05 1,E-06 Ion pump July 1,E-07 1,E-08 Ion pump July t (min) Vacuum tests carried out in 2010 Measured pressure curves Vacuum tests with chamber heating (November 3, 2011) Vacuum obtained: empty vacuum box: 1.2 x 10-7 mbar with parts inside: 3 x 10-6 mbar (2010) 2 x 10-6 mbar (2011) no leakage detected 10/11/

49 12 MeV RTM: Control system 10/11/

50 12 MeV RTM: Radiation issues End magnet 1 Target 2 Main sources of radiation of the IORT complex: (1)Applicator + patient (2)RTM Target 1 The radiation from the RTM is generated by parasitic electron beam losses Linac Model: targets generating parasitic losses End magnet 2 Linac axis Target 3 Exiting beam Target 4 Total beam losses ~ 80-90% of the initial E-gun current Simulations of stray radiation and shielding with PENELOPE were performed by -F. Verdera (2008) -Mª.A.Duch, C. de la Fuente (IPAC 2011) 50

51 12 MeV RTM: Radiation issues End magnet 1 Shielding proposal Target 2 Ceiling 7 Target 1 RTM Exit windo w Linac 103 Tumor Target 3 Floor 5000 End magnet 2 Linac axis 5 0 Exiting beam Target 4 12 cm Pb Pb 5 cm 5 cm 51

52 12 MeV RTM: Test bench 3D design of the RTM test bench (UPC) 10/11/

53 Summary and concluding remarks 1. Project status: All parts except magnets are already received Tests of some systems (linac, RF, vacuum, E-gun) have been carried out or are in progress now 10/1/

54 Summary and concluding remarks 2. Plan for E-gun filament and HV power supply unit assembling Assembly of the RTM test bench After this the systems will be ready for the assembling and one-pass linac HP tests Manufacturing and delivery of magnets RTM assembling on the test bench Getting of a bunker for tests and certifications required for tests with beam First beam Tests, tuning and beginning of commissioning (hopefully in 2012) This project is an example of fruitful collaboration between Russian and Spanish groups. 10/1/