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ESS End-to-End Optics and Layout Integration Håkan Danared European Spallation Source Catania, 6 July 2011

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E22 Odarslövsvägen

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Energy2.5 GeV Current50 mA Average power5 MW Pulse length2.86 ms (new value since April 2011, equal to 2×20/14) Rep rate14 Hz (new value since April 2011) Length392 m, plus HEBT Max cavity field40 MV/m Longer than previously because of ”hybrid design”, smoother longitudinal phase advance, lower field gradients,... Present Geometry and Top-Level Parameters

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Optimization of Linac Length Length of superconducting linac is 363 m in the HS_2011_06_22 layout, which is the currently favoured “smooth hybrid”. Total length from ion source to vertical bend, i.e. including HEBT/upgrade, is 492 m. All calculations for superconducting linac made by Mamad Eshraqi. Hybrid between fully segmented and cryo-string gives high serviceability, low cryo load, is good for instrumentation... HS_2011_06_22

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Beam Envelope and Emittance Growth in Superconducting Linac (HS_2011_06_22) Envelope horizontal Envelope vertical Envelope long. (Δφ at 352 MHz) Emittance growth horizontal Emittance growth vertical Emittance growth longitudinal

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Beam Density, Hofmann Plot (HS_2011_06_22) RFQ (A. Ponton)Spokes, Ellipticals

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Accelerating Gradients (HS_2011_06_22) Ratio of peak surface field to accelerating field taken from fit to experimental data [P. Pierini], peak surface field chosen to be 40 MV/m. Is this the optimal value? Accelerating gradient (MV/m) in superconducting linac, for smooth and stepwise longitudinal phase advance. Cavity power (kW) in superconducting linac, for smooth and stepwise longitudinal phase advance (specification for power couplers now 900 kW).

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Tolerance against Cavity Failure (HS_2011_06_22) Failure of one cavity, or klystron, in the spokes section (most sensitive section) can be handled with maximum about 25% transverse and 12% longitudinal emittance growth. Failure of two adjacent cavities cannot be compensated without large emittance growth and beam loss. Transverse emittance increase due to a failed cavity where energy gain is largest (green bar above) is approximately 12%. It is expected that the elliptical sections are less sensitive to cavity failure than the spokes section.

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Effects of RF amplitude and phase errors (HS_2011_06_22) First study of tolerance to RF amplitude and phase errors. Results of 100 sets of ”random” coupled amplitude and phase offsets up to 3% and 3°. Effects start to be seen on emittances and energy and phase deviations at errors between 0.5 and 1.0 %,°. More statistics is needed and more kinds of errors must be included, like alignment errors, magnetic-field variations, multipole fields, current and emittance variations. Essential figures of merit include beam trans- mission (absence of particle losses) and beam stability on target.

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Energy2.5 GeV Current50 mA Average power5 MW Pulse length2.86 ms Rep rate14 Hz Length392 m, plus HEBT Max surface field ellipticals40 MV/m Frequencies352.21, 704.42 MHz Current/Optimal Linac Parameters Ion source output75 keV RFQ output3 MeV DTL output50 MeV Spokes output188 MeV Low-beta output606 MeV High-beta output2500 MeV Gaps per spoke cavity3 Cells per low-beta cavity5 Cells per high-beta cavity5 Cavities per spoke module2 Cavities per low-beta module4 Cavities per high-beta module8 No. of spoke modules14 No. of low-beta modules16 No. of high-beta modules15 Geometric beta spokes0.57 Geometric beta low-beta0.70 Geometric beta high-beta0.90 Accelerating field spokes8 MV/m Max surface field ellipticals40 MV/m Max power per coupler900 kW Optimization criterionlinac length “Phase laws”... Mechanical dimensions... Chopper(s)/time structure... Collimators... Upgradability...

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Energy2.5 GeV Current50 mA Average power5 MW Pulse length2.86 ms Rep rate14 Hz Length392 m, plus HEBT Max surface field ellipticals40 MV/m Frequencies352.21, 704.42 MHz Current/Optimal Linac Parameters Ion source output75 keV RFQ output3 MeV DTL output50 MeV Spokes output188 (202) [245] MeV Low-beta output606 (524) [589] MeV High-beta output2500 MeV Gaps per spoke cavity3 Cells per low-beta cavity5 Cells per high-beta cavity5 Cavities per spoke module2 (3) [3] Cavities per low-beta module4 (3) [4] Cavities per high-beta module8 (6) [8] No. of spoke modules14 (13) [15] No. of low-beta modules16 (11) [10] No. of high-beta modules15 (19) [14] Geometric beta spokes0.57 (0.53) [0.54] Geometric beta low-beta0.70 (0.65) [0.67] Geometric beta high-beta0.90 (0.86) [0.84] Accelerating field spokes8 (8.3) [8.3] MV/m Max surface field ellipticals40 (50) [50] MV/m Max power per coupler900 kW Optimization criterionlinac length “Phase laws”... Mechanical dimensions... Chopper(s)/time structure... Collimators... Upgradability...

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Parameter Tables www.esss.se/linac

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Lattice and Accelerator Science

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Integration MEBT meeting, 4 May, Bilbao Warm-linac meeting, 6 July, Catania End-to-end beam-dynamics workshop, 31 Oct – 1 Nov, Lund Integration of entire linac lattice end of 2011, gives emittance table, aperture requirements,... FODO DTL, M. Comunian Source emittance, R. Miracoli ESS RFQ, A. Ponton SC Linac, M. Eshraqi HEBT, A. Holm / H. Thomsen Target footprint, H.D.

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