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Accumulator & Compressor Rings with Flexible Momentum Compaction arccells MAP 2014 Spring Meeting, Fermilab, May 27-31, 2014 Y. Alexahin (FNAL APC)

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Motivation 2 A & C Rings Design - Y. Alexahin, MAP14 meeting, FNAL 05/28/2014 D. Neuffer proposed a two-ring scenario: one for accumulation with sufficiently large slippage factor to increase the microwave instability threshold, the other for bunch compression with small | | to reduce the required RF voltage ParametersARCR Circumference, m308.23 Momentum compaction-0.0520.001 Slippage factor-0.063-0.01 RF frequency, MHz3.87 RF voltage, kV10240 Synchrotron tune 2.1 10 -4 4.2 10 -4 Peak current, A1001040 Final r.m.s. bunch length, ns29.23.2 Final r.m.s. energy spread 5.2 10 -4 6.9 10 -3 Threshold impedance, Ohm20 3 53 R.m.s. emittance, m 55 Space charge tuneshift, h/v0.02/0.020.14/0.16 Betatron tunes, h/v7.94/6.916.76/8.44 Two major problems with Accumulator/Compressor rings - space-charge and microwave instability - can be mitigated with the Flexible Momentum Compaction (FMC) lattice design: Large (and negative) momentum compaction factor c increases the microwave instability threshold Large dispersion (characteristic to FMC lattices) reduces the space-charge tuneshift Micro-structure of “pre-chopped” injected beam for 4 bunches : 129 ns 1.034 s 129 ns

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Regular Arc Cell 3 A & C Rings Design - Y. Alexahin, MAP14 meeting, FNAL 05/28/2014 Sector Dipoles 1.94T @ Ekin=8GeV, length 5.1m and 0.9m Quadrupoles ~10T/m, aperture 0.5m long Sextupoles +9.5T/m 2, -6.2T/m 2 0.4m gaps between all magnets Phase advances 3 /2 per cell, 4 cells per arc tunes ~7 Momentum compaction factor from -0.135 to +? By changing the strength of the central quadrupole it is possible to vary D x and c in wide range using other quadrupoles for tune correction. There is almost no effect on -functions.

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Accumulator Ring v1 4 A & C Rings Design - Y. Alexahin, MAP14 meeting, FNAL 05/28/2014 Accumulator Ring layout with identical straight sections (v1). Doublets can be moved farther apart to increase space (now 14m) for painting arrangement. This will also increase -functions at the symmetry point. Injection with this design was considered by Milorad Popovic (next two slides) Optics functions in the last arc cell and half of straight section. y (max) =75m, at the symmetry point (on the right) x =2m, y =6m Beam size @ QD (5 )=10cm

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Main magnet 500 Gauss magnet Stripping foil ORBUM’s ORBUM’s are strong, B=1.8T, L=1m and can be DC. There is 1m separation between first two, bend angle 3.5 degree. At exit from the second ORBUM orbit is 0.12m away from central orbit Distance between second and third ORBUMP is 7 m. ORBUMs can be tilted to have vertical displacement, painting?? H- Beam There is 14 m straight section in Yuri design 500 Gauss magnet, L=2m, at distance of 4m from second ORBUMP. Incoming/ outgoing beam is under 0.1 degree angle. Beam is displaced for additional 7mm Stripping foil 500 Gauss magnet ORBUM’s HORIZONTAL VERTICAL, different set of ORBUM magnets, or tilted? M. Popovic 12.7cm 15cm 5

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M. Popovic coil field-free pipe for H - Quad gradient = 6.1 T/m 6

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7 A & C Rings Design - Y. Alexahin, MAP14 meeting, FNAL 05/28/2014 Accumulator Ring v2 Purpose of the upgrade: Provide permanent orbit bump to direct H 0 away from quadrupoles Move doublets farther apart to increase space for painting bump Move tunes to below half-integer to reduce sensitivity to misalighnments Layout and optics functions in injection insertion and adjacent arc half-cells 0.5T magnet for H - separation C-magnet with outlet for H 0 fast magnets for painting bump, 0.4T for x=5.3cm septum magnet Beam size @ QD increased to 5 =12cm

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8 A & C Rings Design - Y. Alexahin, MAP14 meeting, FNAL 05/28/2014 Orbits @ Injection Insertion (V. Kapin)

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Orbits @ H - Separation Magnet (V. Kapin) 9 A & C Rings Design - Y. Alexahin, MAP14 meeting, FNAL 05/28/2014 Is 1.8T DC field achievable in BEI2 septum magnet?

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10 A & C Rings Design - Y. Alexahin, MAP14 meeting, FNAL 05/28/2014 Accumulator Ring v2 Layout kicker for vertical extraction H - beam 3.87 MHz RF V=11 kV Extraction kick 1mrad/m (5mrad total) will provide y=5.9cm (8 ) at the straight center, y=9.5cm (12 ) at QF entrance. – Lambertson septum or QF with extraction channel?

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Compressor Ring 11 A & C Rings Design - Y. Alexahin, MAP14 meeting, FNAL 05/28/2014 The main differences with Accumulator ring: Small (and positive) momentum compaction factor c smaller dispersion Dispersion-free straights where a lot of RF cavities can be placed Relocated defocusing sextupoles Optics functions in the last arc cell and half of straight section

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