lawrence’s cyclotron accelerator - gerry's notes · 1931: cyclotron 1940: betatron 1947:...

Lawrence’s

Cyclotron Accelerator and Its Developments

Gerry Resmi Liyana (1106009910)

Department of Physics Faculty of Mathematics and Natural Sciences

University of Indonesia

Dec 9, 2014

Outline

Introduction

Timeline of Inventions

Classical Cyclotron

Relativistic considerations

Development of cyclotron devices

Notable Examples

Conclusion

References

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Introduction

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Cathode ray tubes ~ late 1800s

Van de Graff ~ 1930

Cockroft and Walton ~ 1920

Earlier accelerators were electrostatic field based

Practical limitations using high voltage:

problem with corona, insulation and design

of vacuum tubes were difficult

Fig 1. Source: http://what-when-how.com

Fig 2. Source: http://cst.mos.org/sln/toe/history.html

Fig 3. Source: http://blazelabs.com/e-exp15.asp

Introduction (cont)

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“It is required a vacuum tube many meters long to accelerate

lighter projectiles (such as alpha particles). Therefore, bending

those particles into a circular path to send them through the

same electrode repeatedly was better.”

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Timeline of Inventions

Timeline of Inventions

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1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

1910: Rutherford

1925: linac

1931: cyclotron

1940: betatron

1947: electron synchrotron

& Synchro-Cyclotron

1930: electrostatic

1952: proton synchroton

1960: functional storage ring

2000: Strijckmans proposes

isochronous cyclotron

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The Classical Cyclotron Accelerator

The Experimental Method

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Connected to

high frequency

oscillator

Peak value

4000 V Electrodes

(Semi circular hollow plates)

B - field

Fig.5 The dees, driven by an RF oscillator, lie

between the poles of a magnet excited by direct current.

Fig.4 Diagram of experimental method for multiple acceleration of ions [Phys. Rev. 40, 19]

http://www.nobelprize.org/nobel_prizes/themes/physics/kullander/

Fields provide

focusing effect!

Experimental Arrangement

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Fig.6 Diagram of apparatus for the multiple acceleration of ions[Phys. Rev. 40, 19]

Fig.7 Tube for the multiple acceleration of light ions – with cover removed [Phys. Rev. 40, 19]

Principle of Operation

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Fig.8 How the cyclotron works. Source: http://www.americanradiohistory.com/Archive-Radio-Craft/1940s/Radio-Craft-1947-Jun.pdf

Governing Relation in Cyclotrons

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B into paper

A positive particle q sees a centripetal force at right angles to the direction of motion:

v

qF

Bvqrr

mv ˆ

2

The angular frequency of rotation

mqB /

Gyrofrequency

qB

m vr

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Relativistic Considerations

Relativistic Considerations

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The relativistic mass can be rewritten as

02

0

2

0

11

mm

c

v

mm

Lorentz factor

The angular frequency of rotation

2

0

1'

c

v

m

qB

m

qB

This modification has the following effect

on the gyrofrequency

For example:

86,0'155.1%50 c

v

14,0'1.7%99 c

v

Proton Energy % Frequency

decrease

10 MeV ~1%

250 MeV ~21%

1.0 GeV ~52%

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How to manage the relativistic change in mass?

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Development of cyclotron devices

Development of cyclotron devices

• There are at least 3 kinds of cyclotrons:

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CLASSICAL CYCLOTRON

SYNCHRO – CYCLOTRON

ISOCHRONOUS – CYCLOTRON

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Classical (Review)

• CLASSICAL: (original)

– Operate at fixed frequency (ω=qB/m) and ignore the mass increase

– Works to about 25 MeV for protons (ϒ=1.03)

– Uses slowly decreasing magnetic field ‘weak focusing’

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Synchro – Cyclotron

Synchro – Cyclotron

• SYNCHRO – CYCLOTRON: let the RF frequency ω decreases as

the energy increases

– ω = ω0/ ϒ to match the increase in mass (m= ϒ m0)

– Uses same decreasing field with radius as classical cyclotron

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ISOCHRONOUS-CYCLOTRON

Isochronous – Cyclotron

• ISOCHRONOUS: raise the magnetic field with radius such that the

relativistic mass increase is just cancelled

– Pick B = ϒ B0 {this also means tat B increases with radius}

– Then ω=qB/m = qB0/m0 is constant

– Field increases with radius – magnet structure must be different!

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Magnet Structure

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Orbit stability is related to the magnetic induction as a function of the radius:

nrrB

1)(

Fig.9 field index n determines magnet structure

Field index n!

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This is used for Isochronous

Orbit Stability

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Fig 10. Radial (a) and axial (b) oscillations about a circular equilibrium orbit (c).

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Orbit Stability (cont)

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Fig 11. Radial forces for a zero field index; also valid in the mid-plane of for any field index

Fig 12. Axially focuussing forces Fz for a positive field index

Fig 13. Axially defocusing forces Fz for a negative field index

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An alpha particle, which has a positive electric charge, experiences Lorentz forces

How to prevent an axial orbit instability for n<0?

The principle of Thomas focusing to solve the axial orbit instability

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Fig 13. Magnet pole of an isochronous cyclotron, i.e. A sector focussed or AVF (azimuthally varying field) cyclotron plane (reproduced with permission of Jhon Wiley & Sons. Ltd from Strijckmans K. Charged particle accelerators. In;

Z.B. Afassi, editor. Chemical analysis by nuclear methods. Chichester (UK), 1994)

Fig 14. Thomas force acts always towards the median plane. The dot means that the particle has a velocity component from the paper and the cross that the particle has a velocity component towards the paper. (Heikkinen, Pauli, 1994)

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Positive and Negative ions

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Actually, the cyclotron can be used to accelerate not only the positive but also negative ions

For the positive ions For the negative ions

Axial orbit instability for n < 0 with the positive ions Axial orbit stability for n < 0 with the negative ions

Fig 15. Whether the “magnetic structure for n < 0” causes the axial ion orbit instability or not, it depends on the charge on the ion (positive or negative). “The magnetic structure for n < 0” doesn’t cause the axial orbit instability for the negative ions.

(a) (b)

Fz

Fz Fz

Br

Br Fz

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Notable Examples

Notable Examples

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Fig 15. SRC Cyclotron at RIKEN laboratory in Japan.

Source: http://www.nishina.riken.jp/facility/RRC_e.html Fig 16. One of the TRIUMF’s Cyclotrons.

Source: http://www.triumf.ca/headlines/current-events/new-milestone-for-tc-99m-production

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CONCLUSION

• E. O. Lawrence invented cyclotron which operate at fixed frequency (ω=qB/m)

and ignore the relativistic change in mass

• The relativistic change in mass was solved by:

Bohm and Foldy

o By raising the magnetic field with radius such that the relativistic mass increase is just cancelled

Strijckmans

o By decreasing RF frequency ω as the energy increases

• Initiated a big science, a new way of doing science

– Tevatron, LHC, etc

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References

• Lawrence, E. O., Livingston, M. S. Production of high speed light ions witout the use of

high voltages. Physical Review 40, 19- 35, Apr. 1, 1932.

• D. Bohm, L. Foldy. Theory of the synchro – cyclotron. Physical Review 72, 649, 1947.

• Strijckmans K. The isochronous cyclotron: principles and recent developments.

Comput Med Imaging Graph 2001; 25: 69 – 78.

• Heikkinen, Pauli. CYCLOTRONS. University of Jyvàskylâ, Accelerator Laboratory,

Jyvàskylâ, Finland (1994)

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References (cont)

• Pictures:

– http://what-when-how.com

– http://cst.mos.org/sln/toe/history.html

– http://blazelabs.com/e-exp15.asp

– http://www.nobelprize.org/nobel_prizes/themes/physics/kullander/

– http://www.americanradiohistory.com/Archive-Radio-Craft/1940s/Radio-Craft-1947-Jun.pdf

– http://www.nishina.riken.jp/facility/RRC_e.html

– http://www.triumf.ca/headlines/current-events/new-milestone-for-tc-99m-production

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