Design of tunable magnets for 12 MeV Race - Track Microtron - ICCUB

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Design of tunable magnets for 12 MeV Race - Track Microtron

Juan Pablo Rigla Pérez, Yuri Kubyshin and Vasily Shvedunov.

10 November 2011

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1.- Introduction: 12 MeV Race-Track Microtron of the UPC.

2.- End magnet design.3.- End magnet tuning system.

3.1.- Simulation of tuners.3.2.- Tuning ranges and interdependence.3.3.- Tuning procedure.

4.- Summary of the results and conclusions.

IndexJuan Pablo Rigla Pérez

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1.- 12 MeV Race – Track Microtron of the UPC.

Race – Track Microtron components,

(1) Electron gun, (2) Linac, (3-4) End magnets, (5) Quadrupole, (6) Extraction magnet,(7) Extracted beam.

• The Technical University of Catalonia (UPC) , the Skobeltsyn Institute of Nuclear Physics (SINP - Moscow State University) and CIEMAT are building a race-track microtron (RTM).

• A possible future application of this RTM is Intraoperative Radiation Therapy.

Beam energies 6,8,10,12 MeV

Operating frequency 5712 MHz

End magnet field 0.8 T

Maximun beam current <2.5 μA

RTM head dimensions 670x250x210 mm

RTM head weight < 100 kg

Juan Pablo Rigla Pérez

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Supporting platform with linac installed.

Vacuum chamber and pumping tube assembly.

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Juan Pablo Rigla Pérez2.- End magnet design.

• The end magnet function is to provide the beam recirculation in the RTM.• As a source of the magnetic field in the end magnets the rare earth permanent magnet (REPM) material is used (M1-M13).The permanent magnet are necessary because:

1.- Complicated magnetic field profile.2.- Compatible with high vacuum.3.- Permit a compact design.

End magnets

#0#1

#2#3

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End magnet external dimensions.

•The end magnet is formed by: One 180º - dipole (main pole) (0), One reverse field magnet (1) Two additional dipoles (2,3).

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Beam trajectory for first orbit.

• Reverse field magnet: Compensate the defocusing effect by the fringe field.• Additional dipoles: Reflect the first orbit back to the linac axis.

Pole 0Pole 1Pole 2Pole 3

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End magnet field profile in the orbit plane.Juan Pablo Rigla Pérez

Reverse pole

Main pole

Additional pole 1

Additional pole 2

The residual magnetization of REPM blocks are:

BrM1=BrM2=BrM3=1.06 T.BrM4=BrM5=0.0663 T.

Design requeriments,

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0

0 1010 −− −=∆BB

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3,2,1

3,2,1 1010 −− −=∆BB

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3.- End magnet tuning sytem.• The magnetic systems must reproduce the field found in beam dynamics simulations with:

• Field Uniformity:•Absolute field value:•Equality of field of two magnets:

• In electromagnets: the magetic field adjustament is achieved by varying the current in the coils.

• In permanent magnets some tuning mechanisms are used:1.- Magnetization and desmagnetization.2.- Tuning with plungers.3.- Tuning with rotating blocks.

For the tuning of the RTM end magnet we decided to use a system of plungers.

310−

4105 −x410−

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Tuning process.Juan Pablo Rigla Pérez

-V0

+V0

V=0

V0=0

V0=0

∞=µg

0

00 2µ

gBV =

V=0

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3.1.- Simulation of tuners.Juan Pablo Rigla Pérez

• The main pole tuning system consistis of a cylindrical plunger that moves in a channel in the end magnet (M2 block).•To avoid the plunger saturation Vanadium –Permendur material is used.

Hmax=10.0mm

D=20.0mm

The maximum magnetic field variation is .

0,775

0,78

0,785

0,79

0,795

0,8

0,805

0,81

0 1 2 3 4 5 6 7 8 9 10

H (mm)

B0 (T

)

3.1.1.- Main pole tuning system. H

037.00

0 =∆BB

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3.1.2.- Reverse pole tuning system.

Six tuners of 5.0 mm

diameter

Six tuners of 5.0 mm

diameter


0,106

0,108

0,11

0,112

0,114

0,116

0,118

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5

h2 (mm)

B1 (T

)


• Reverse pole tuning: a system of six tuners that moves horizontally to the reverse pole.• The M4 height was reduced to allow the motion of the plungers.

36.5 mm

086.01

1 =∆BB

h2max=5.0mm

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3.1.3.- Additional pole tuning system.Juan Pablo Rigla Pérez

•Additional poles tuning: a system formed by five tuners (diameter 4.5mm) that move vertically in the REPM blocks M7 and M11. • To allow tuners movements we perform a channels in REPM blocks M7 and M11.


0,232

0,234

0,236

0,238

0,24

0,242

0,244

0,246

0,248

1 1,5 2 2,5 3 3,5 4 4,5 5h3 (mm)

B2 (T

)

h3

0473.02

2 =∆BB

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0,116

0,1165

0,117

0,1175

0,118

0,1185

0,119

0,1195

0,12

0,1205

0,121

0,1215

0 1 2 3 4 5 6 7 8 9 10

H (mm)

B1 (T

)

3.2.- Tuning ranges and interdependence.

In the ANSYS simulations it was obtained that a variation of the position of the main pole plunger affects the magnetic field in the reverse pole.

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0,8076

0,8078

0,808

0,8082

0,8084

0,8086

0,8088

0,809

0,8092

0,8094

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5

h2 (mm)

B0 (T

)

And vice versa, a variation of the position of the reverse pole plunger, h2, changes the magnetic field in the main pole.

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3.3.- Tuning procedure.

0,78

0,785

0,79

0,795

0,8

0,805

0,81

0,815

0 2 4 6 8 10 12

H (mm)

|B0|

(T)

By means of ANSYS simulations it was found that the nominal values of the magnet field:

B0=0.79826 T B1=0.116 T

are obtained at the median tuner positions:H=5.0mmh2=2.5mm

for the residual magnetizations:BrM1=BrM2=BrM3=1.0628 T.BrM4=BrM5=0.1278 T.

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4.- Summary results and conclusions.Juan Pablo Rigla Pérez

Pole

Main Pole 0.037

Reverse Pole 0.086

Additional Poles 0.047

• Future work: Once the magnets are manufactured, apply this tuning process.

• The results obtained in the ANSYS simulations are,

• For magnetic field tuning we must use a combination of the demagnetization technique and tuning with plungers. The procedure is the following:- magnetize REPM to maximum level of Br=1.1 – 1.2 T.- measure field level and in 1-2 steps by applying demagnetizing field reduce the field level to the range found in ANSYS simulations with respect to the nominal level.- By moving the plunger, make the most difficult step, to adjust the magnetic field level.

nn BB∆

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Thank You

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Design of tunable magnets for 12 MeV Race - Track Microtron - ICCUB