A new MKE concept for SPS?

A new MKE concept for SPS? B.Goddard Acknowledgements to M.Barnes, J.Bauche, V.Mertens, J.Borburgh, M.Gyr

Overview • Present kickers are ferrite c-core, but closed by conductor – therefore full aperture needed for injected beam • Impedance: kicker heating, instabilities • Kick strength limited by vertical gap • Could conceive of an open C-core kicker, where the beam is bumped into the aperture just before extraction • Smaller gap means larger kick strength possible • Beam only in kicker aperture at high energy • Beam only in kicker aperture for short time

Constraints / assumptions • Total extraction angle from kicker should be about 0.5 mrad. • Aperture for extracting CNGS beam at 300 GeV • Aperture for the injected beam should not be less than at present. • Flat-top ripple maximum ±1% (field quality similar). • Rise- and fall-time ≤1 us for the CNGS (can be longer for LHC, ~6 us) • The pulse-length enough for CNGS, i.e. 10.8 us. • One design for LSS6 and LSS4 • Optics and beam size at kicker locations • Maximum beta functions assumed are 100 m X, 35 m Y. • 12/8 pi.mm.mrad normalised emittance for CNGS beam • Dispersion – assume to be 0.5 m, Dp/p 0.1% • Orbit allowance +/-4mm, Alignment tolerance +/-1mm, Acceptance +/-5 sigma • H half-aperture is 14.9 mm, V is 9.5 mm • Full aperture for 300 GeV beam is 30 mm h, 20 mm v (same in v as downstream MS septa)

Kicker system • Assume 10 mm needed to edge of kicker for poor field region (may be 20 mm – to check – shimming of poles possible) • Keeping present H aperture at TPSG/MSE and scaling to MKE location with  gives required H aperture for injected beam of ~48 mm at MKE entrance • Bump height at kicker entrance is then about 73 mm • Kicker strength per magnet assumed to scale with 1/h, so maximum ~0.2 mrad per magnet. 3 magnets only needed per extraction (for present magnet length) • Return conductor can either be split on end of ferrite legs, or as back leg (easier for coil and injected beam aperture)

Kicker and bump (mm)

Kicker impedance and rise time • For transmission line system have • U = L I/dt, I=U/2Z, L = mu0(w/h) lm, B = mu0 I/h • Present system impedance is 10  – assume this is kept • Present voltage of 50 kV gives 2.5 kA, so new B gap is 0.16 T • With same magnetic length lm of 1.674 m, 3 magnets give 0.804 Tm, or 0.53 mrad at 480 Tm rigidity for 450 GeV • Present (w/h) is 147/35, so L = 9 H, and fill-time is ~1 s. For same magnetic length, ((w+h/2)/h) of 60/20 gives 6.4 H, or 0.75 s fill time – significantly faster than at present (~1 s ). 40 mm width is even faster. • Could keep this margin or (probably better) build 2 longer magnets to give same deflection but with cheaper installation, and increase slightly rise time. Magnets of 2.5 m long at 0.16 T gap field would have L = 9.5 H, or 1.1 s fill time

Extraction bump • Extraction bump should provide an offset of 73 mm at MKE. Bump must also bring circulating beam close to TPSG/MSE for extraction. • A long extraction bump with 5 magnets is needed. • HB1.412 (weak, -0.05) to adjust angle at the extraction kicker • HB2.414 (strong, 0.79) to produce offset at extraction kicker • HB3.416 (strong, 0.23) to keep beam close to the TPSG/MSE • HB4.417 (strong, 0.72) to keep beam close to the TPSG/MSE • HB5.420 (strong, 0.95) to close the bump • Existing MPLH magnets can reach 1.2 mrad, MPSH 0.6 mrad. • Possible HB3 and HB 4 could be combined into one stronger magnet (as used for slow extraction in past). • Bump rise time to be fast enough that the time spent by circulating beam in kicker is short compared to the rise-time of the detrimental processes (vacuum, instabilities). • A rise time of ~200 ms, comparable to existing MPSH/MPLH would mean maybe 50 ms during which the beam is inside the kicker aperture. • CNGS beam will be an additional 50 ms inside the kicker for the 2nd batch

Bump

Extraction trajectory and apertures • Assuming 3 magnets extraction kicker strength needed is about 0.18 mrad per magnet: similar maximum current to the present MKE operating at 52 kV (32/20 * 0.112 = 0.179), and corresponds to 0.16 T in the gap. • The maximum excursion in QFA418 is 90 mm for the 3 sigma edge of the beam. • Because of the larger negative angle from the bump than for the present extraction this pushes the extraction septum inwards by about 2.5 mm, which reduces slightly the aperture available for the injected beam. • The aperture at the TPSG for the injected 14 GeV FT beam decreases from 5.49 to 5.21 sigma.

Extraction trajectory

Other systems affected • Additional enlarged quadrupoles QFA and QDA will be needed at 416 and 415 respectively. • Four enlarged quadrupoles in total would be needed. There are only 4 spare magnets of this type – and one needs rebuilding (no tooling exists). • Apertures of other elements (correctors, pickups etc.) in the LSS between Q15 and Q17 will need to be large enough horizontally – similar to already used in the extraction and injection regions of the SPS near the enlarged quadrupoles.

Unknowns and possible issues • Quantify gap width/shim height requirement from field quality calculations, and produce magnet cross-section • Define maximum allowable field in ferrite/gap and required magnetic length • Investigation of bumper rise-times and powering • Potential impedance/stability issues for 50/100 ms of beam inside kicker gap • Costing?? (will be several MCHF – maybe 4-6?) • Resources – needs study, design, prototyping, measurement, production, exchange, … • Other risks/issues/oublies?

A new MKE concept for SPS?