1

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

10/11/2011 2

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

124

57

6

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

13

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)

124

57

6

10/11/201113

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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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17

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

32

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%

33

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)

44

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

50

107

240.

9

103

10

26 57

7

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

26 57

7

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.