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Design Choices in Acceleration of Multi-Pass Linacs: Racetrack vs. Dogbone Configuration

This document discusses the design choices in acceleration configurations for multi-pass linacs, focusing on the comparison between the 'Racetrack' and 'Dogbone' designs. Key aspects include multi-pass linac focusing, orbit separation, and simultaneous acceleration of both positive and negative species. The advantages of the Dogbone configuration, particularly for the 10 GeV two-step setup, are highlighted, including better orbital separation for higher passes and efficiency in RF use. Furthermore, the paper contrasts triplet and FODO focusing schemes regarding their performance in these configurations.

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Design Choices in Acceleration of Multi-Pass Linacs: Racetrack vs. Dogbone Configuration

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  1. Acceleration in RLAs – Design Choices Alex Bogacz • ‘Racetrack’ vs ‘Dogbone’ configuration • multi-pass linacs focusing • orbit separation • simultaneous acceleration of both m+m- species • 10 GeV Two-step-Dogbone RLA • Quadrupole focusing scheme – Triplet vs FODO lattices • multi-pass linac • matching to the Arcs • vertical injection double-chicane ISS Workshop, UC Irvine, August 21, 2006.

  2. mis- focusing factor: 1 + (n-1) DE/E0 E0 n - 1 arcs n arcs E0 + n DE orbit separation factor: [E0 + n DE]/[E0 + (n-1) DE] ≃ n/n-1 n/2 droplets n/2 droplets mis- focusing factor: 1 + n DE/E0 E0 E0 + (n + ½) DE orbit separation factor: [E0 + (n+½) DE]/[E0 + (n-2+½) DE] ≃ n/n-2 ‘Racetrack’ vs ‘Dogbone’ RLA (n-pass) DE/2 total arc length: (2n - 1) pR DE/2 DE total arc length: 2n (7/6) pR ISS Workshop, UC Irvine, August 21, 2006.

  3. m+ m- m- m+ m+ m- m- m- m- m+ m+ m+ m+ m- m- m+ ‘Racetrack’ vs ‘Dogbone’ RLA (both m+ and m- species ) ISS Workshop, UC Irvine, August 21, 2006.

  4. m+ m- m- m- m+ m+ m+ m+ m- m- ‘Racetrack’ vs ‘Dogbone’ RLA (both m+ and m- species ) ISS Workshop, UC Irvine, August 21, 2006.

  5. 0.2 GeV 0.9 GeV 3 GeV 0.6 GeV/pass 10 GeV 2 GeV/pass 10 GeV Two-step-Dogbone RLA 3.33… ext/injenergy ratio 3.0 GeV to 10 GeV 0.9 GeV to 3.0 GeV 1.5 GeV to 5.0 GeV ISS Workshop, UC Irvine, August 21, 2006.

  6. 0.2 GeV 0.9 GeV 3 GeV 0.6 GeV/pass 10 GeV 2 GeV/pass 10 GeV Two-step-Dogbone RLA 3.33… ext/injenergy ratio 3.0 GeV to 10 GeV 0.9 GeV to 3.0 GeV 1.5 GeV to 5.0 GeV ISS Workshop, UC Irvine, August 21, 2006.

  7. m- m- m+ m+ Injection double-chicane m+ m- ISS Workshop, UC Irvine, August 21, 2006.

  8. FODO vs Triplet focusing structure • The same length • The same phase advance per cell (Dfx= 900 = Dfy) FODO Triplet • Advantages: • much weaker quads (~3 times) • shorter quads (total) • easier chromaticity correction • Advantages: • longer straight sections • smaller vertical beta-function • uniform variation of betas and dispersion ISS Workshop, UC Irvine, August 21, 2006.

  9. Multipass linac - Triplet vs FODO focusing (900 phase adv/cell) 1-pass 2-pass 3-pass ISS Workshop, UC Irvine, August 21, 2006.

  10. Straight-Arc - Periodic transition Triplet FODO ISS Workshop, UC Irvine, August 21, 2006.

  11. Summary • ‘Dogbone’ RLA – preferred configuration (compared to the ‘Racetrack’) • better orbir separation for higher passes • more efficient use of the rf (extra half-pass) • offers symmetric solution for simultaneous acceleration of m+ and m- • FODO lattice more favorable (compared to the triplet) to accommodate large number of passes • uniform phase advance decrease in both planes • smaller variation of Twiss function – easier match to the Arcs • allows to maintain 900 phase advance per cell for lowest passes • Proposed 10 GeV two-step-dogboneRLA (30 mm rad acceptance) • 3.0-10GeV ‘dogbone’ with 400MHz SRF? • Needed: front-to-end simulation, magnet error/misalignment sensitivities etc. ISS Workshop, UC Irvine, August 21, 2006.

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