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Variable energy beam extraction from the Manitoba cyclotron
NUCLEAR INSTRUMENTS
A N D M E T H O D S 43 0966) 381-382; © N O R T H - H O L L A N D
PUBLISHING
CO.
VARIABLE ENERGY BEAM EXTRACTION F R O M T H E MANITOBA CYCLOTRON J. J. B U R G E R J O N
Department of Physics, University of Manitoba, Winnipeg, Canada Received 29 April 1966
A variable energy external beam is now available from the Manitoba cyclotronl'2). When the University of Colorado reported the extraction of a cyclotron beam by stripping the electrons from H-ions3), it was realized that beams of various energies could be obtained by moving the stripping foil radially. These beams can be made to go through the centre of a bending magnet (combination magnet) by also moving the stripping foil azimuthally4). Recently this method has been applied almost simultaneously to the UCLA 5) and Manitoba cyclotrons. Fig. 1 shows the orbits for nominal proton energies of 25 and 50 MeV in the Manitoba machine. The deflected orbits intersect at an angle of ~ 17°. The combination magnet can be
adjusted to direct a beam of any energy in this range along the beam pipe axis. The combination magnet has 20.4 cm dia. and a gap of 3.8 cm and is of compact and economic design. Because it is close to the cyclotron magnet, the cyclotron magnet vertical yoke was used for its flux return path, fig. 1.This causes a slight inconvenience, as the cyclotron magnet detunes a little when the combination magnet current is changed. With the magnet turned offthere is already a field of 0.48 Wb/m 2, about the right value for a 35 MeV beam. This is caused by flux leaking from the highly saturated vertical yoke. The field only has to be increased to 0.83 Wb/m 2 for the minimum energy and decreased to - 0 . 0 8 Wb/m 2
/////,/ I / / / / / / / / / / /
f "
3.-
//////, I
, ,o ,,.C.E~
Fig. 1. Particle trajectories. 1. Dees; 2. Coupling loop; 3. Trimming capacitors; 4. Beam probes; 5. Hills; 6. Stripping foil; 7. Combination magnet; 8. Quadrupole magnet.
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J. J. BURGERJON At m a x i m u m energy, no beam loss is observed at the stripping foil or along the beam pipe (10 cm i.d. with 7 . 6 c m aperture). At lower energies, beam loss is observed at the exit hole and in the beam pipe, increasing with decreasing energy and reaching a maxim u m of 50% at the lowest energy. The axial emittance is ~ 30 m m . m r a d for all energies, but the radial emittance increases f r o m ~ 120 to > 240 m m . m r a d as the energy is varied f r o m m a x i m u m to minimum. Calculations indicate that this rather high value for the radial emittance and its increase at lower energies is caused by the beam energy spread6). The system has operated reliably for about two months and allows energy changes to be made in a few minutes. The author wishes to thank Dr. K. G. Standing for his encouragement and advice, Dr. B. Hird for super.vising the orbit calculations, Mr. D. G. Peterson for c o m p u t i n g the orbits and Mr. J. Bruckshaw for designing the hardware.
Fig. 2. Combination magnet. 1. Cyclotron magnet vertical yoke; 2. Horizontal yokes; 3. Coils; 4. Gap, through viewing window; 5. Vacuum chamber; 6. Beam exit valve. for m a x i m u m energy. The m a x i m u m power consumption is ~ I kW. Fig. 2 shows a side view o f the magnet and v a c u u m chamber.
References 1) K. G. Standing, J. J. Burgerjon and F. Konopasek, Nucl. Instr. and Meth. 18 (1962) 111. 2) j. j. Burgerjon, F. Konopasek and K. G. Standing, IEEE Trans. Nucl. Sci. NS-12 (1965) 334. 3) M. E. Rickey and R. Smythe, Nucl. Instr. and Meth. 18 (1962) 66. 4) A. C. Paul and B. T. Wright, Bull. Am. Phys. Soc. 8 (1963) 606. 5) B. T. Wright, priv. comm. and paper to be presented at Int. Conf. Isochronous Cyclotrons (Gatlinburg, May, 1966). 6) B. Hird, private communication.
A N D M E T H O D S 43 0966) 381-382; © N O R T H - H O L L A N D
PUBLISHING
CO.
VARIABLE ENERGY BEAM EXTRACTION F R O M T H E MANITOBA CYCLOTRON J. J. B U R G E R J O N
Department of Physics, University of Manitoba, Winnipeg, Canada Received 29 April 1966
A variable energy external beam is now available from the Manitoba cyclotronl'2). When the University of Colorado reported the extraction of a cyclotron beam by stripping the electrons from H-ions3), it was realized that beams of various energies could be obtained by moving the stripping foil radially. These beams can be made to go through the centre of a bending magnet (combination magnet) by also moving the stripping foil azimuthally4). Recently this method has been applied almost simultaneously to the UCLA 5) and Manitoba cyclotrons. Fig. 1 shows the orbits for nominal proton energies of 25 and 50 MeV in the Manitoba machine. The deflected orbits intersect at an angle of ~ 17°. The combination magnet can be
adjusted to direct a beam of any energy in this range along the beam pipe axis. The combination magnet has 20.4 cm dia. and a gap of 3.8 cm and is of compact and economic design. Because it is close to the cyclotron magnet, the cyclotron magnet vertical yoke was used for its flux return path, fig. 1.This causes a slight inconvenience, as the cyclotron magnet detunes a little when the combination magnet current is changed. With the magnet turned offthere is already a field of 0.48 Wb/m 2, about the right value for a 35 MeV beam. This is caused by flux leaking from the highly saturated vertical yoke. The field only has to be increased to 0.83 Wb/m 2 for the minimum energy and decreased to - 0 . 0 8 Wb/m 2
/////,/ I / / / / / / / / / / /
f "
3.-
//////, I
, ,o ,,.C.E~
Fig. 1. Particle trajectories. 1. Dees; 2. Coupling loop; 3. Trimming capacitors; 4. Beam probes; 5. Hills; 6. Stripping foil; 7. Combination magnet; 8. Quadrupole magnet.
381
382
J. J. BURGERJON At m a x i m u m energy, no beam loss is observed at the stripping foil or along the beam pipe (10 cm i.d. with 7 . 6 c m aperture). At lower energies, beam loss is observed at the exit hole and in the beam pipe, increasing with decreasing energy and reaching a maxim u m of 50% at the lowest energy. The axial emittance is ~ 30 m m . m r a d for all energies, but the radial emittance increases f r o m ~ 120 to > 240 m m . m r a d as the energy is varied f r o m m a x i m u m to minimum. Calculations indicate that this rather high value for the radial emittance and its increase at lower energies is caused by the beam energy spread6). The system has operated reliably for about two months and allows energy changes to be made in a few minutes. The author wishes to thank Dr. K. G. Standing for his encouragement and advice, Dr. B. Hird for super.vising the orbit calculations, Mr. D. G. Peterson for c o m p u t i n g the orbits and Mr. J. Bruckshaw for designing the hardware.
Fig. 2. Combination magnet. 1. Cyclotron magnet vertical yoke; 2. Horizontal yokes; 3. Coils; 4. Gap, through viewing window; 5. Vacuum chamber; 6. Beam exit valve. for m a x i m u m energy. The m a x i m u m power consumption is ~ I kW. Fig. 2 shows a side view o f the magnet and v a c u u m chamber.
References 1) K. G. Standing, J. J. Burgerjon and F. Konopasek, Nucl. Instr. and Meth. 18 (1962) 111. 2) j. j. Burgerjon, F. Konopasek and K. G. Standing, IEEE Trans. Nucl. Sci. NS-12 (1965) 334. 3) M. E. Rickey and R. Smythe, Nucl. Instr. and Meth. 18 (1962) 66. 4) A. C. Paul and B. T. Wright, Bull. Am. Phys. Soc. 8 (1963) 606. 5) B. T. Wright, priv. comm. and paper to be presented at Int. Conf. Isochronous Cyclotrons (Gatlinburg, May, 1966). 6) B. Hird, private communication.