Construction of a Compact 12 MeV Race-track Microtron at...
Transcript of Construction of a Compact 12 MeV Race-track Microtron at...
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Construction of a Compact 12 MeV Construction of a Compact 12 MeV RaceRace--track Microtron at the UPCtrack Microtron at the UPC
Yuri Kubyshin, Vasiliy ShvedunovYuri Kubyshin, Vasiliy Shvedunov(on behalf of the project team)(on behalf of the project team)
Novembre 10, 2011
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Talk outline
1. UPC* project of 12 MeV RTM 2. 12 MeV Race-Track Microtron (RTM)
2.1 Design requirements and main characteristics2.2 Magnets2.3 Accelerating structure2.4 Beam dynamics 2.5 RF system 2.6 E-gun2.7 Vacuum chamber and vacuum system2.8 Control system
3. Summary and concluding remarks- Status of the project- Further steps
*UPC = Universitat Politècnica de Catalunya
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UPC project of 12 MeV RTM
Race-track microtron (RTM): Principle of operation
Injection
Extraction• RTM is a machine with beam recirculation
• Pulsed RTMs are optimal for medium and high beam energies (10-100 MeV) and relatvely low pulse beam current 10- 100 mA (average current < 100 µA)
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,2
ec
EB s
RTM: Principle of operation
Linac
n
n+1l
For ultra-relativistic particles, 1n
BecE
cl
cR
clT n
nn
n
nn 2
2222
● Time of revolution on the nth orbit:
● Resonance (synchronicity) conditions:
RFnn TTT 1
ZTT RF , ,1
sE is the energy gain per turn (of the synchronous particle)
Magnetic field in the end magnets:●
● Narrow longitudinal acceptance
● High monochromaticity of the output beam
320 s
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2004 Concept of a compact RTMB.S. Ishkhanov, V.I. Shvedunov et al. RuPAC-2004
UPC project of 12 MeV RTM
2005 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)
2006-2007 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)
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Introperative Radiation Therapy
Example: Intensive use of LIAC for IORT at the Instituto Europeo di Oncologia, Milan
Mobetron(IntraOp Medical Inc.)
NOVAC7(ENEA, Hitesis, Info&Tech)
IORT is a therapy technique consisting in administration, during a surgical intervention, of a single and high radiation dose 10-20 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 IORTdedicated compact electron accelerators are needed.
UPC project of 12 MeV RTM
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2008-2009 Technical design of the RTM systems.Purchase of standard components. Tenders and placing orders for manufacturing of non-standard components.
2009-2010 Delivery of the E-gun, vacuum chamber, accelerating structure, supporting platform.
2010-2011 Tests of RTM systems: RF, vacuum, control system, etc.
UPC project of 12 MeV RTM
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General layout12 MeV UPC RTM
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Accelerator head
IORT complex
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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 20-30 Gy/min, dose stability-Low dark currents-Low parasitic radiation-Compact design, low weight-Low energy consumption
12 MeV RTM
Solution:
RTM
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12 MeV RTM: General layout of the accelerator head
1. Electron gun2. Accelerating structure (linac)3. End magnet 14. End magnet 2
5. Horizontally focusing quadrupole
6. Extraction magnets7. Extracted beam
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Beam energies 6, 8, 10, 12 MeVOperating wavelength / frequency 5.25 cm / 5712 MHzSynchronous energy gain 2 MeVRF and E-gun pulse length* 3 µsPulse repetition rate* 1 – 250 HzEnd magnet field 0.8 TKinetic energy at the injection 25 keVPulsed beam current at RTM exit 5 mAPulsed RF power < 750 kWRTM dimensions 670x250x210 mmRTM head weight <100 kg
Main characteristics
12 MeV RTM: Main characteristics
* The E-gun and RF source (magnetron) are fed by a common modulator
1Harmonic number:
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12 MeV RTM: Main characteristicsTo 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 mbar (in-vacuum solution).
64 1010 Pa
● , extraction energies: 6, 8, 10, 12 MeV
● Pulse current
● Low duty factor / average beam current: 50 nA – 5 µA
● Pulse beam power , then ,
in any case
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MeVE 12max mAI pulse 5
35 1010 kWPbeam 60
MWPRF 1
kWPRF 900800
12 MeV RTM: Main characteristicsEnergy and current: motivated by the IORT application (dose rate: 10-20 Gy/min)
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12 MeV RTM: End magnets
Medianplane
REPMmaterial
Main specifications:♦ Uniform field region induction with accuracy ~ 0.1%
This is achieved by precise magnetization and tuning of the permanent magnet blocks.
♦ Field uniformity This is achieved by the steel magnetic properties and accuracyof the parts machining.
TB 7987.0
%075.0
♦ 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
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12 MeV RTM: End magnets
♦ Problem of strong vertical defocusing by the end magnet fringe field
Requirement: Vertical focusing with focal power (orbit length) in order to get stable transverse oscillations
Solution: Reverse pole to compensate the focusing by the fringe field.
F1
Main pole, V
Reverse pole, V
Median plane
0
1
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Solution of the fringe field problem (Babich, Sedlacek, 1967):
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12 MeV RTM: End magnets
♦ Linac bypass problem
Solution: First orbit closure, beam reflection and subsequent second acceleration in the linac
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Method of beam reflection from the end magnet after 1st acceleration.(Alvisson, Eriksson, 1976)
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12 MeV RTM: End magnets 4-pole design
AA
Facet 2x2 mm 2 everywhere
z
y1 32 4
The idea is to decouple the vertical focusing and beam reflection problems by incorporating two dipoles into the magnetic system
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
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-50 -25 0 25 50 75 100 125
-0.8
-0.6
-0.4
-0.2
0.0
0.2Bs2 = 0.239 T
Bs1 = -0.239 T
B1 = 0.116 TM
agne
tic F
lux
Den
sity
B, (
T)
longitudinal coordinate z, (mm)
B0 = -0.7986 T
12 MeV RTM: End magnets 4-pole design
Optimal field profile
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-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0 2 4 6 8 10 12 14
E (MeV)
1/F
(m-1)
Focal power
1 432
2 MeV
12 MeV RTM: End magnets 4-pole design
(PAC-2007)
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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.
12 MeV RTM: End magnets
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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
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Main specifications:♦ Standing wave bi-periodic π/2 on-axis coupled accelerating structure
♦ C-band structure,
♦ 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
12 MeV RTM: Accelerating structure (linac)
MHzf 5712
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Parameters to optimize:
● (max. shunt impedance, min. beam losses, min. overstrength factor, etc.)
● 0.4 <β<0.8 for the short cell● number of β=1 cells
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
gtLR cb ,,,
12 MeV RTM: Accelerating structure (linac)
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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=8500
0
10
20
30
40
50
0 20 40 60 80 100
z (mm)
E z (M
V/m
)
12 MeV RTM: Linac2D optimization
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12 MeV RTM: Linac3D optimization with HFSS (CIEMAT) and ANSYS (SINP+UPC) codes
ca RR ,
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
3. Estimation of RF power losses and total RF power required
4. Calculation of the coupling window parameters of the feeding waveguide
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Results:
β=1
● Resonant frequency 5712 MHz● Quality factor Q=9860● Total pulsed power dissipated in the structure walls 600 kW ● Cell coupling● Coupling factor ● Shunt impedance
2c
12 MeV RTM: Linac3D optimization with HFSS (CIEMAT) and ANSYS (SINP) (EPAC-2006)
3D linac modelmMRs /100
%10k
Test Cavity 1 Discs machined
Cavity tests at the CIEMAT test stand
Linac construction (CIEMAT)12 MeV RTM: Linac
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Linac brazed (at CERN) and fixed on a support and the supportingplatform (at UPC)
Linac construction (CIEMAT)12 MeV RTM: Linac
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Q0 βc f (MHz)Experimental value(after brazing) 9075 1.50 5713.5
Theoretical value 9493 2.0 5714.1
Electromagnetic characteristics (CIEMAT)
E-field before (blue line) and after (red line) the brazing
12 MeV RTM: Linac
With this data and parameters of the components of the RF system the magnetron must provide 850 kW of RF power.
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12 MeV RTM: Beam dynamics
Z0MZ0M S
dLdS
Lq
~2 MeV
Llinac
1st2d3d4th5th
4 MeV6 MeV8 MeV
10 MeV12 MeVM1 M2
Ld
Position for longitudinalacceptance calculations at 1.917 MeV
Position for transverseacceptances calculations at 25 keV
25 keV beam
2 MeV beam, linac exit 9.1550
2 MeV beam, linac entrance 82.45inj
For a relativistic beam the maximum acceleration takes place atat the linac entrance, for the asymptotically synchronous particle at 77.9º
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Simulations performed with RTMTRACE (SINP)
6.61max
5.1730
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Longitudinal acceptance and beam emittance at 1.92 MeV
Horizontal acceptance at 25 keV
12 MeV RTM: Beam dynamics
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Longitudinal capture efficiency is about 20%
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E ~ 4 MeV E ~ 12 MeV
06.0
250
EE
keVE
007.0
80
EE
keVEEnergy spread:
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ScandiNova modulator
CPI Magnetron SFD-313
12 MeV RTM: RF system
(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
Linac
WR187 waveguide system
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12 MeV RTM: RF system
General scheme with the Automatic Frequency Control (AFC) system (mechanical tuning of the magnetron) and Low Power RF (LPRF) control (magnetron frequency pulling)
(1) magnetron ----(4) 4-port circulator with loads ----(6) dual loop coupler----(11) phase shifter
4
6
Linac
11
AFC
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Parameter ValueOperating frequency 5712 MHzRF and E-gun pulse length 3 µsPulse repetition rate 1-250 HzMagnetron anode voltage 36 kVMagnetron anode current 60 AModulator output pulse power 2.2 MWMagnetron output pulse power ≤ 1 MW
12 MeV RTM: RF system
RF system operation parameters
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♦ RF source: SFD-313 magnetron of CPI
Frequency 5.45-5.85 GHzPeak power output 1 MWAnode voltage 36 kVAnode current 60 AHeater 5V @ 19A Air cooledMechanically tunable ♦ M1 Modulator of ScandiNova
Cathode pulse voltage -36 kVPulse current 60 APulse width 2-4 µsRepetition rate 1-250 HzPulse top flatness < 0.5%Amplitude stability 1 %
12 MeV RTM: RF system
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Stand for high power RF tests (UPC)
12 MeV RTM: RF system
Preliminary measurements by two methods give a value of the magnetron pulse power 700-800 kW.
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Results of RF test runs performed in 2010-2011
Shape of the HV pulse Frequency spectrum of the RF pulse
12 MeV RTM: RF system
Failure of a power supply unit of the modulator in June 2011 has produced an unplanned pause in the tests.
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12 MeV RTM: Electron gun
On-axis gun with off-axis cathode
Electron trajectories in the vertical plane are bent by a focusing electrode.
I = 25 mA, U=25 kV
CathodeAnode (linac wall)
Focusing electrode
At z=15 mm σ < 1 mm, σ’ < 5 mrad
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Beam images at the distance 15 mm and 30 mm from the anode edge
Measured emittances: H 1.4 mm·mradV 2.2 mm·mrad
(PAC’11; NIM 2010)
E-gun was designed (CST code), constructed and optimized at SINP. Now it is installed at the supporting platform inside de vacuum chamber (UPC)
12 MeV RTM: Electron gun
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12 MeV RTMGeneral setup
Accelerator head
Vacuum chamberPumping tube
Ion pump
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12 MeV RTM: Vacuum chamber and pumping /supporting tube Vacuum to maintain:
mbar610
Port for a turbomolecular pump (pre-pumping; MINITASK, 40 l/s)
Supporting platform
Ion pump (VACION / MINIVAC, 50 l/s)
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12 MeV RTM: Vacuum chamber and pumping /supporting tube
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Deformations study and mechanical design were performed with ANSYS code (UPC).
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Technical design of various elements (UPC)
Mechanism for moving the extraction magnets
End magnets on adjustment rails
12 MeV RTM: Vacuum chamber and pumping /supporting tube
Supporting platform with linac installed
12 MeV RTM: Vacuum chamber and pumping /supporting tube
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12 MeV RTM: Vacuum chamber and pumping /supporting tube
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Vacuum box pumping out 19-22 July 2010
1,E-08
1,E-07
1,E-06
1,E-05
1,E-04
1,E-03
1,E-02
1,E-01
1,E+00
1,E+01
1,E+02
1,E+03
1 10 100 1000 10000
t (min)
p (m
bar)
MiniTask19 July
Ion pump 19-20 July
MiniTask20 July
Ion pump 20-22 July
•Vacuum tests carried out in 2010•Measured pressure curves
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
12 MeV RTM: Vacuum chamberVacuum tests of the chamber + tube assembly
Vacuum tests with chamber heating (November 3, 2011)
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12 MeV RTM: Control system
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107
240.
9
103
10
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Target 2
Target 3
Target 1
5 0
Linac
End magnet 1
End magnet 2
Linac axis
Exiting beam
Target 4
Main sources of radiation of the IORT complex:(1)Applicator + patient (2)RTM
The radiation from the RTM is generated by parasitic electron beam losses.
Model: targets generating parasitic losses
Total beam losses ~ 80-90% of the initial E-gun current
12 MeV RTM: Radiation issues
Simulations of stray radiation and shielding with PENELOPE were performed by -F. Verdera (2008)-Mª.A.Duch, C. de la Fuente (IPAC 2011)
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Ceiling
Floor
RTM
Tumor
Exitwindow
5000
107
240.
9
103
10
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Target 2
Target 3
Target 1
5 0
Linac
End magnet 1
End magnet 2
Linac axis
Exiting beam
Target 4
Pb
5 cm
5 cmPb12 cm
Shielding proposal
12 MeV RTM: Radiation issues
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12 MeV RTM: Test bench
3D design of the RTM test bench (UPC)
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
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Summary and concluding remarks
Summary and concluding remarks2. Plan for 2011-2012 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)
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This project is an example of fruitful collaboration between Russian and Spanish groups.