The CIS project and the design of other low energy proton synchrotrons

Transcription

1 The CIS project and the design of other low energy proton synchrotrons 1. Introduction 2. The CIS project 3. Possible CMS 4. Conclusion S.Y. Lee IU Ref. X. Kang, Ph.D. thesis, Indiana University (1998). 1. HIPIOS, 2. duoplasma ion source and cockcroft-walton 3. K15 injector cyclotron 4. K200 cyclotron, 5. Cooler and MeV CIS C=17.36 m K= kev I=0-4 A The (Cooler Injector Synchrotron) CIS, 1/5 of the Cooler circumference is designed to replace the cyclotron for the cooler injector. The facility is composed of a H ion source, 3 MeV RFQ and 4 MeV DTL, and a 200 MeV synchrotron for injection into the Cooler. The 7 MeV H is converted to proton by carbon foil 4.5μg/cm 2 thickness, 6 mm X 22 mm. C=86.8 m C=86.82 m, νx=3.82, νz=4.83

2 Note that this is a low current H- linac with current of the order of 1 ma or less. At the CIS, we achieved a foil thickness of 4μg/cm 2, and thus able to accumulate about 80 turns. This requires a pulse length of 38 μs. 1. At low energy, the effect of multiple scattering and energy straggeling is more important. It would be nice to have a source current at 5 ma so that fewer turns is need to achieve the desired intensity. But 1 ma works. 2. A higher energy injector would minimize space charge and multiple scattering effects. Energy (MeV) Circumference (m) Qx / Qz Cx / Cz Ldipole (m) 2 Edge angle 12º ρ (m) γ T KE _transiition (MeV) β x,max (m)/β z,max (m) D xmax (m) An AccSys Technology Model PL-7 Linac consisting of a 3 MeV RFQ coupled to a 4 MeV DTL is used to pre-accelerate H ions to 7 MeV for strip injection into CIS. Two 350 kw, 425 MHZ rf amplifiers power the Linac, which accelerates variable pulse width H beams with duty factors up to 0.2%. The Linac accepts up to 1.0 π mm mrad (norm), 25 kev H beams and accelerates them to 7 MeV with 1% energy spread and no emittance growth. The circumference is limited by the requirement of the Cooler. We did consider ¼ size of the Cooler, but was consider too expensive for the project. Due to fringe field integral Xiaojian Kang (Ph.D. Thesis, 1998): Betatron tunes of CIS 200 & 225 MeV ramping

3 Effect of trim quads Tune shift vs 4 trim quads CIS working point theory measured point Dipole: Good field region 100 mm X 50 mm at 1.0 T

4 End pack optimization: 1. Effective field length is 2.0 m at ρ=1.273 m, independent of B=0.35 to 1.7 T. 2. Effective edge angle of 12 degree 3. Sextupole component B2<1.0 T/m2. 4. Good field region of 80 mm at 1.7 T and 100 mm at 1.0 T. Measurement vs calculation With end pack optimization

5 Eddy current correction coils 1 turn at a/3 2 turns at 2a/3 Dynamic Aperture (3D magnetic field model) RF system 2-10 MHz h=1, Vsinϕ s <250 V Field at r=0, 10, 35, 69 mm inside the shielding pipe of 70 mm along the beam pipe locations.

6 2 mm shielding pipe Einj (MeV) 7 (p); 5 (d) Emax (MeV) 200 (p); 105 (d) Rep rate (Hz) 1-5 Acceleration time (ms) Bucket area ev-s f (MHz) proton f (MHz) deuteron C12 Injection extraction RF debuncher The momentum spread from the LINAC can be reduced by a de-buncher. We carry out proto-typing, but not implemented because the Cooler was decommissioned shortly after the completion of the CIS Project.

7 Adiabatic capture Injection Horizontal scale 2 ms/div. Top: Signal from wall gap monitor; Bottom: rf voltage from 0 to 240 V in 5 ms. Beam lifetime at 7 MeV: 400 ms Betatron tune measurement vs theory

8 CIS: Circumference = 1/5 C_cooler = m Dipole length = 2 m, 90 degree bend, edge angle = 12 deg. Inj KE= 7 MeV, extraction: 240 MeV Compact medical Synchrotron 5m Ldip=3.0 m ρ=1.91 m Edge_angle=8.5 Circum=28.5 m Qx=1.683 Qz=0.684 KE_tr=369 MeV 3.25m 250 MeV Proton Synchrotron Ldip=2.75 m ρ=1.75 m Edge_angle=10.5 Circum=28.5 m Qx=1.70 Qz=0.68 KE_tr=356 MeV REVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 74, 2540 (2003) L dipole =2.75 m, B max =1.53 T at 300 MeV, Circumference=27.5 m Including FINT=0.5 in the fringe field integral is shown as star symbols. L 1 =3.25m L 2 =5m C=27.5m ρ= m Injection emittances (π mm-mrad) 2. Extraction emittances (π mm-mrad) 2 at 300 MeV

9 2.75m 1.75m 90º 10.5º 50.8 mm MeV Tm T < mm 50.8 mm 2.5m 1.59m 90º 12.5º 50.8 mm MeV Tm T < mm 50.8 mm Dynamical Aperture Dynamical aperture of the CMS accelerator at various energies, where the sextupole field, derived from field strength calculations, is included in obtaining the dynamical aperture.

10 p C 12 A 1 12 Z 1 6 Circum(m) Einj/u (MeV) 7 7 Eext/u (MeV) p (MeV/c)/u Brho (T m) dnu_sc N_sc 1.01E E+10 epsn (μm) 2 2 beta_inj gamma_inj N B (10 11 ) KE inj (MeV) The RF system Beam Injection, acceleration, extraction Requirement of rf voltage in rapid accelerating accelerators p E/u (MeV) Brho (T-m) L_dip (m) 11 C (m) 27.5 f (MHZ) B (T) Vsinϕ (V) Example: The rf cavity of the IUCF cooler injector synchrotron Ferrite loaded cavity Power & Industrial Systems R&D Laboratory, Hitachi, Ltd. Kazuo Hiramoto 0.45 m Diameter of the cavity ~0.55m; Length ~0.6m Q~20, R sh ~1kΩ, V~1 kv, P=1kW. The IUCF cooler injector synchrotron (CIS) is a low energy booster for the IUCF cooler ring. It accelerates protons (or light ions) from 7 MeV to 225 MeV. The cavity is a quarter-wave coaxial cavity with heavy capacitance loading. To make the cavity length reasonably short and to achieve rapid tuning, required for synchrotron acceleration, ten Phillips 4C12 type ferrite rings are used. The μ of the ferrite material is changed by a superimposed DC magnetic field provided by an external quadrupole magnet. The ferrite rings return the magnet flux between the two adjacent quadrupole tips Reliable Operation: Solid-sate Amp; Air Cooling Multiple Power Feeding Impedance matching between RF cavity and RF power source FINEMET Core High complex permeability for Freq. Range 1-10 MHz High Curie temperature

11 Extraction: Fast extraction slow extraction 0.5 to 10 sec Hitachi p x1 At ES At MS At ES At MS Maximize β-function values at both the ES and MS locations! But! the ring is small, one tries to do find the best solution!

12 At ES At MS At ES At MS Find the best locations for Sextupoles! Conclusion: I believe that the compact medical synchrotron made of only 4 dipoles of length 2.75m each with an edge angle of 10.5º is an optimal design for proton proton therapy. The properties of the synchrotron are 1. Kinetic energy of 300 MeV with transition energy above the maximum kinetic energy of proton. A ramp rate of more than 5 Hz 2. The betatron tunes are ν x =1.7, ν y =0.8 suitable for slow extraction. The slow extraction can be facilitated by trim quadrupoles and sextupoles. 3. The injection can come from the H from the RFQ/DTL or from a 19 MeV cyclotron with H- beam. 4. The machine can be scaled down to 250 MeV kinetic energy at a circumference of about 25m with dipole length of 2.5 m each. The machine can be designed to include both fast and slow extractions for easy operation. 5. Develop slow extraction technology. 6. Proton therapy systems (cyclotrons or synchrotrons) are NOT plug-and-play turn-key systems. Adequate manpower is needed to develop operation and clinical treatment plan to achieve its promises in cancer treatment. Parameter Unit LLUMC CIS CMS Purpose Medical Cooler inj. Medical Energy Range T/MeV Cycle time sec Intensity p/burst Ion-source 40keV Duopl. 25keV Duopl. 25keV Cusp Linac energy ( PL-7) MeV Inj.Energy T/MeV Circumference m Number straight sections Length, straight sections M 2/ / /3.25 Number of magnets Magnet length m Magnet bend angle degree Magnet bend radius m Magnetic field flux, max. T Edge angle degree Field flux at injection T Magnet gap cm Pole tip width cm Good field aperture cm 10(H)x5(V) 10(H)x5(V) 10(H)x5(V) Field flux at extraction T Horiz. and vertical Tunes 0.6/ / /0.67 Βx/βz M 5.98/ / /9 Dispersion func., max. m Transition, gamma EXTRACTION slow (1-2 s) fast (50ns) slow (0.5-2s)