Proton beams for the East Area The beams

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

What will we cover: • 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

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: Injection Ejection Qh 4. 20 4. 17 Qv 5. 29 5. 23 • Q-strips are at 0 Amp.

The Beam in the P. S. Three users : EASTA, EASTB and EASTC (combined with TOF beam) Injection (Like most other beams) • Coherent oscillations • Longitudinal blow-up (as function of shaving in P. S. Booster) Acceleration (straight forward, no splitting) • EASTA H 8 beam control • EASTB H 8 beam control for Ip > 7 1010 per bunch H 16 LI beam control for Ip < 8 1010 per bunch 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

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. What does this mean? 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 3 Q = 19

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

Sextupole (deflection (position)2) Q = 6. 25 1 st turn Q = 6. 33 2 nd turn 3 rd turn 5 th turn 4 th turn For Q = 6. 25: Oscillation is cancelled out every fourth turn, and the particle motion is stable For Q = 6. 33: Oscillation induced by the sextupole kick grows on each turn and the particle is lost (3 rd order resonance 3 Q = 19)

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

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

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 What about the ripple on the spill ? ? ? • 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

Which elements are used what for ? ? ? PE. GSBSW 57 EXTRACTOR SEPTUM MAGNET 61 D 53 D 59 FIRST SEPTUM MAGNET 57 D 61 (septum) QUADRUPOLE 29 PE. GSQSE D 27 ELECTROSTATIC SEPTUM 23 PE. GSBSW 23 QUADRUPOLE 87 D 19 SEXTUPOLE 7 PE. GSXSE D 67

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 How does some of this • increase look like on an • make dispersion small at SES 23 oscilloscope ? ? ? • make dispersion big and positive at SMH 57 • 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 (SES 23, SMH 57, SMH 61) • 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.

Magnetic preparation for slow extraction PFW F and PFW D take over Arrival at ‘flat-top’ W 8 L short circuited Sextupoles Quadrupoles Spill Bump for electrostatic septum

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

‘Optics and septa’ sources of losses Electrostatic Septum (SD 23) The electrostatic septum kicks a part of the beam and creates the space for the 1 st magnetic septum. Low momentum particle high momentum particle Cathode Anode (34 sections) 45º Septum blade Extraction Magnetic Septum (SD 57) Optimum situation obtained by changing the dispersion coefficients at SES 23 and SMH 57. This is done by the 2 quadrupoles. Dispersion at SES 23 small and positive Dispersion at SMH 57 Big and positive.

Some problems and possible solutions General shape of spill • ‘Spill shaping’ by modeling d. Qh/dt or d. B/dt (One of the study objects this year, MD’s) Low frequency ripple • Feed forward system • Feed back system • Channeling buckets (improved) (difficult, but still under study) (effective, but need optimization) 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.

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.

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) • F 61. MTV 01

Questions or ……. . ? ? ?