Beam Physics, Linac Lattice Peter N. Ostroumov
Content n Project X parameters n Basic concepts for the Linac design – RFQ and MEBT – Front end up to 420 Me. V, 325 MHz – High energy section, ILC based, 1300 MHz n Linac structure and base technology – Power fan-out to multiple cavities – SC accelerating structures above 10 Me. V n Choice of lattice parameters – 325 MHz Front End linac – High energy section n Some results of beam dynamics simulations n Conclusion Project X Workshop Beam Physics, Linac Lattice November 21, 2008 2
Main parameters Parameter HINS PD Project X-2007 Particle Species Project X - 2008 H-minus Output Beam Energy 8 Ge. V 8 -Ge. V Beam Power, Pulsed Average 200 MW 2. 0 MW 72 MW 360 k. W 160 MW 1. 0 MW Particles per Pulse 1. 56 1014 5. 625 1013 1. 56 1014 Pulse Repetition Rate 10 Hz 5 Hz Beam Pulse Length 1 msec 1. 25 msec Pulse Beam Current, Average Peak 25 m. A 40 m. A 9 m. A 14. 36 m. A 20 m. A 32 m. A Particles per Linac bunch 7. 58 108 2. 73 108 7. 58 108 Chopping at 2. 5 Me. V - 6% at 89 k. Hz for 700 ns RR/MI abort/extraction gap - 33% at 53 MHz Project X Workshop Beam Physics, Linac Lattice November 21, 2008 3
Our approach for the 8 -Ge. V Linac n RF power fan-out from one klystron to multiple cavities n Two-frequency Linac option to produce multi-Ge. V hadron beams: – 1300 MHz ILC cavities above ~1. 2 Ge. V – Use S-ILC cavities (beta=0. 81) in the energy range ~400 Me. V-1. 2 Ge. V – Spoke loaded SC cavities operating at 1300/4=325 MHz n Front End: 325 MHz. One klystron (J-PARC type) feeds multiple cavities n Below 10 Me. V: use the RFQ and 16 RT-CH n Apply SC solenoid focusing to obtain compact lattice in the front end including MEBT n RFQ delivers axial-symmetric 2. 5 Me. V H-minus beam n Minimize beam losses by appropriate design Project X Workshop Beam Physics, Linac Lattice November 21, 2008 4
Linac Structure Major Linac Sections 325 MHz 1300 MHz Being installed in the Meson Lab SSR-2 0. 05 2. 5 10 0. 065 2. 5 10 Project X Workshop 32 33 Beam Physics, Linac Lattice 123 110 418 410 November 21, 2008 5
Accelerating cavities ( not to scale) NC spoke SC single spoke b. G=0. 81, 7 -cell, 1300 MHz Project X Workshop Beam Physics, Linac Lattice Triple-spoke cavitiy ILC, 9 -cell November 21, 2008 6
RF power fan-out n ILC RF power distribution, similar system in the front end – Power couplers in the ILC cavities must be re-designed to handle higher power – Front end: fast ferrite phase shifters, high power n Number of klystrons – Seven (7) 2. 5 MW JPARC klystrons operating at 325 MHz – 23 10 MW ILC klystrons operating at 1300 MHz Project X Workshop Beam Physics, Linac Lattice November 21, 2008 7
Radio Frequency Quadrupole n Basic PD requirements: – Cost-effective – Produce axially-symmetric beam – Small longitudinal emittance n Design features – No emittance growth – Strong transverse focusing ( 0 43 ) – Limiting current 140 m. A – Acceleration efficiency is 96 % for 45 m. A – Short, 3 meters n Output radial matcher Project X Workshop Beam Physics, Linac Lattice November 21, 2008 8
Focusing by SC solenoids n To provide stability for all particles inside the separatrix, the defocusing factor FODO FDO n n should be below ~0. 7 SC solenoids in the NC section from 2. 5 Me. V to 10 Me. V – Solenoids decrease the length of the focusing period (~0. 5 m) – Small beam size, aperture of the cavities is 18 mm Other advantages of solenoids compared to typical FODO – Acceptance is large for the same phase advance as for quads. – Less sensitive to misalignments and errors. The most critical error in quads – rotation about the longitudinal axis – does not exist – Beam quality is less sensitive to beam mismatches FNAL PD: cryogenics facility is available, major part of the linac is SC The 325 MHz Front End up to 420 Me. V – Long cryostats house up to ~(9 -11) SC cavities and solenoids – Apply quads above 100 Me. V, required for H-minus beam focusing Project X Workshop Beam Physics, Linac Lattice November 21, 2008 FO 9
Cavity parameters and focusing lattice CH S-ILC SSR-1 ILC-1 SSR-2 TSR ILC-2 Project X Workshop Beam Physics, Linac Lattice November 21, 2008 10
Voltage gain per cavity Project X Workshop Beam Physics, Linac Lattice November 21, 2008 11
Front end, Linac Lattice n MEBT and NC section, short focusing periods, adiabatic change from 50 cm to 75 cm RFQ n 2 CM of SSR-1: Minimize the inter-cryostat drift space, LCRYO = 6. 85 m n 3 CM of SSR-2: Provide a drift space by missing the cavity, LCRYO = 9. 4 m n 7 CM of TSR: Provide an extra drift space inside the cryostat, LCRYO = 10. 9 m Project X Workshop Beam Physics, Linac Lattice November 21, 2008 12
High energy section, n Squeezed ILC section, LCRYO = 12. 6 m n Additional focusing quad is located between the cryostats, LCRYO = 12. 6 m ILC-1 ILC-2 Project X Workshop Beam Physics, Linac Lattice November 21, 2008 13
Beam Dynamics Simulations n The major workhorse is TRACK, recently Parallel-TRACK n “Zero-current” tune were created using TRACK routines in 3 D-fields n The tuned lattice was simulated with ASTRA for detailed comparison Project X Workshop Stability chart for zero current, betatron oscillations - TRACK - ASTRA Beam Physics, Linac Lattice November 21, 2008 14
Variation of lattice parameters along the linac n 0 90 n k. T 0, k. L 0 adiabatic despite of many lattice transitions with different types of focusing and inter-cryostat spaces, cavity TTF n Beam matching in the lattice transitions is very important to avoid emittance growth and beam halo formation Project X Workshop Beam Physics, Linac Lattice November 21, 2008 15
Hofmann’s chart for the PD Front End n Avoid strong space charge resonances (white area) n Provide equipartitioning of betatron and synchrotron oscillation temperatures along the linac, primarily in the front end Project X Workshop Beam Physics, Linac Lattice November 21, 2008 16
Beam envelopes, 45 m. A RFQ entrance, 43. 25 m. A in the linac 325 MHz 1300 MHz Project X Workshop 325 MHz Beam Physics, Linac Lattice 1300 MHz November 21, 2008 17
Error studies n The most comprehensive error studies have been performed for the HINS proton driver – Slightly higher beam current n Error simulations – Random, multiple seeds – For the static errors, correction is applied in each seed – Dynamic errors are not corrected n Type of errors Typical errors – Misalignments Error Value Distribution – Dynamic errors of RF Cavity (front end) 0. 5 mm Uniform and focusing field Elliptical 1. 0 mm Solenoids Uniform Quads, displacement of ends 0. 15 mm Uniform Quads, rotation 0. 5 mrad Uniform RF field jitter 1. 0%, rms Gaussian RF phase jitter Project X Workshop 0. 3 mm 1. 0 , rms Gaussian Beam Physics, Linac Lattice November 21, 2008 18
High statistics simulations for 8 -Ge. V, 100 seeds with all errors Envelopes Project X Workshop RMS emittances Beam Physics, Linac Lattice November 21, 2008 19
High statistics simulations for 8 -Ge. V, beam losses We have data for 10 M particles for 100 seeds, total =1 B particles Beam Losses (W/m) Project X Workshop Beam Physics, Linac Lattice November 21, 2008 20
Conclusion and Outlook n Accelerator physics is well advanced n Iterate beam physics with engineering design, cost optimization – Cryomodule design – Alignment errors and tolerances – RF distribution system – RF errors, include realistic LLRF, transient analysis – Specs to beam diagnostics system – Beam losses n Failure modeling n Linac tuning, start-up Project X Workshop Beam Physics, Linac Lattice November 21, 2008 21
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