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Proton beams for the East Area The beams and their slow extraction By : Rende Steerenberg PS/OP

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The beam in the P.S. Booster The beam in the P.S. The slow extraction process –An intuitive approach –How does it work in our P.S. machine –Some problems and possible solutions Diagnostics What will we cover:

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The Beam in the P.S. Booster Two users : EASTA and EASTB (in future a third one TOF) EASTA is 1 bunch ring 3 on H=1 EASTB is depending on the required intensity: 1 bunch ring 3 on H=1 2 bunches ring 3 on H=2 Intensity for both is adjusted by means of transverse shaving. Low intensity Q-settings: Q-strips are at 0 Amp. InjectionEjection Qh Qv 5.23 4.20 4.17 5.29

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The Beam in the P.S. Injection (Like most other beams) Coherent oscillations Longitudinal blow-up (as function of shaving in P.S. Booster) Preparation for slow extraction (later in more detail) Prepare machine magnetically R.F. gymnastic for bunch rotation Slow extraction (later in more detail) Length and instantaneous intensity of spill Shape of spill Position of extracted beam in East Area beam lines Acceleration (straight forward, no splitting) EASTA H8 beam control EASTB H8 beam control for Ip > 7 10 10 per bunch H16LI beam control for Ip < 8 10 10 per bunch Three users : EASTA, EASTB and EASTC (combined with TOF beam)

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The slow extraction process ‘intuitively’ The slow extraction in the P.S. machine is no ‘hocus pocus’, but is based on the third order resonance. After a certain number of turns around the machine the phase advance of the betatron oscillation is such that the oscillation repeats itself. E.g. If the phase advance per turn is 120 degrees then the betatron oscillation will repeat itself after 3 turns E.g. This corresponds to Q = 6.333 or 3Q = 19 What does this mean?

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x’ x 1st turn 2nd turn 3rd turn 2 q = 2 /3 q = fractional part of Q Third order resonance on a normalized phase space plot

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Sextupole (deflection (position) 2 ) For Q = 6.33: Oscillation induced by the sextupole kick grows on each turn and the particle is lost (3rd order resonance 3Q = 19) For Q = 6.25: Oscillation is cancelled out every fourth turn, and the particle motion is stable 1st turn 2nd turn 3rd turn 4th turn Q = 6.25 5th turn Q = 6.33

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Septum A more realistic view on a 3 rd order resonant extraction

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The slow extraction process in the P.S. P.S. Main field Resonance area Resonance area R R time T start T + t T end 350 - 450 ms p0p0 p0p0 P 0 = Average momentum, 24GeV/c Extracted beam Which variable influences which parameter ???

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Variables to change, parameters concerned. Radial position or average momentum different start of spill Momentum spread or magnetic ramp length and start of spill will change Horizontal emittance instantaneous momentum spread will be different Horizontal tune Qh if change is big then no 3 rd order resonance if change is small then different start of spill Horizontal chromaticity h can create more or less losses on extraction septa (we will see later why) Sextupole strength resonance area will have a different size and thus the instantaneous momentum spread will be different What about the ripple on the spill ???

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FIRST EXTRACTOR SEPTUM MAGNET 61 SEPTUM MAGNET 57 QUADRUPOLE 29 ELECTROSTATIC SEPTUM 23 SEXTUPOLE 19 SEXTUPOLE 7 QUADRUPOLE 87 D53 D59 D61 (septum) D67 D27 D19 Which elements are used what for ??? PE.GSQSE PE.GSXSE PE.GSBSW57 PE.GSBSW23

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Preparation for slow extraction ‘boucle en huit’ goes to 0 Amp (short circuited), PFW D and F generate: the correct tune Qh = 6.2 the correct chromaticity h = -0.9 Switch on the slow extraction elements (bumps, quadrupoles, sextupoles and septa) Quadrupoles: add a Qh of 0.13 which gives Qh = 6.33 increase make dispersion small at SES23 make dispersion big and positive at SMH57 Sextupoles: add a h of 0.4 which gives h = -0.5 control the ‘stability triangle’ size and the ‘spiral pitch’ (phase space kick) Bumps: approach beam to the different septa Septa (SES23, SMH57, SMH61) Put the beam on the right orbit (with perturbation) Perform bunch rotation, jump to and from the unstable phase Switch off the R.F. voltage when the bunch is upright in the bucket De-bunch the beam The slope on the flat top of the magnetic field will now move the beam into the resonance. How does some of this look like on an oscilloscope ???

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Magnetic preparation for slow extraction Arrival at ‘flat-top’ W8L short circuited PFW F and PFW D take over Bump for electrostatic septum SextupolesQuadrupoles Spill

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R.F. preparation for slow extraction Schematically: Detected pick-up R.F. voltage Real life:

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‘Optics and septa’ sources of losses Extraction Magnetic Septum (SD57) (34 sections) 45º Electrostatic Septum (SD23) Cathode Anode Low momentum particle high momentum particle Septum blade The electrostatic septum kicks a part of the beam and creates the space for the 1st magnetic septum. Optimum situation obtained by changing the dispersion coefficients at SES23 and SMH57. This is done by the 2 quadrupoles. Dispersion at SES23 small and positive Dispersion at SMH57 Big and positive.

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Some problems and possible solutions General shape of spill ‘ Spill shaping’ by modeling dQ h /dt or dB/dt (One of the study objects this year, MD’s) Stability and reproducibility In case of drift, how to determine what has drifted, why and how to correct it. Setting-up, measurement and debugging procedures. Low frequency ripple Feed forward system (improved) Feed back system (difficult, but still under study) Channeling buckets (effective, but need optimization)

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Channeling buckets The basic idea is that the particles cross the resonance more quickly. This leaves less time for the perturbations to influence the resonating particles, which in the end will reduce the ripple on the extracted spill.

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Diagnostics We can distinguish again two different parts: 1. Beam between slow extraction preparation and extraction Tune measurement Chromaticity measurement Bunch shape measurement Transverse emittance measurement (flying wire scanner) 2. Beam during extraction Beam losses at 23, 57, 61, 63. (analog signals) Mini Toposcope 57 Spill measurement LSD Spill analyzer (extended and improved) F61.MTV01

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Questions or …….. ???

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