ESS End-to-End Optics andLayout Integration

Håkan DanaredEuropean Spallation Source

Catania, 6 July 2011

2

E22

Odarslövsvägen

Energy 2.5 GeVCurrent 50 mAAverage power 5 MWPulse length 2.86 ms (new value since April 2011, equal to 2×20/14)Rep rate 14 Hz (new value since April 2011)Length 392 m, plus HEBTMax cavity field 40 MV/m

Longer than previously because of ”hybrid design”, smoother longitudinal phase advance, lower field gradients, ...

Present Geometry and Top-Level Parameters

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

Beam Envelope and Emittance Growth in Superconducting Linac

(HS_2011_06_22)

Envelope horizontal

Envelope vertical

Envelope long. (Δφ at 352 MHz)

Emittance growth horizontalEmittance growth vertical

Emittance growth longitudinal

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).

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.

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.

Energy 2.5 GeVCurrent 50 mAAverage power 5 MWPulse length 2.86 msRep rate 14 HzLength 392 m, plus HEBTMax surface field ellipticals 40 MV/mFrequencies 352.21, 704.42 MHz

Current/Optimal Linac Parameters

Ion source output 75 keVRFQ output 3 MeVDTL output 50 MeVSpokes output 188 MeVLow-beta output 606 MeVHigh-beta output 2500 MeV

Gaps per spoke cavity 3Cells per low-beta cavity 5Cells per high-beta cavity 5

Cavities per spoke module 2Cavities per low-beta module 4Cavities per high-beta module 8

No. of spoke modules 14No. of low-beta modules 16No. of high-beta modules 15

Geometric beta spokes 0.57Geometric beta low-beta 0.70Geometric beta high-beta 0.90

Accelerating field spokes 8 MV/mMax surface field ellipticals 40 MV/mMax power per coupler 900 kW

Optimization criterion linac length“Phase laws” ...

Mechanical dimensions ...Chopper(s)/time structure ...Collimators ...Upgradability ...

Parameter Tables

www.esss.se/linac

Lattice and Accelerator Science

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.