proton beams for the east area the beams and their slow extraction by : rende steerenberg ps/op
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Proton beams for the East Area
The beams and their slow extraction
By : Rende Steerenberg PS/OP
• 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:
The Beam in the P.S. BoosterTwo 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.
Injection Ejection
Qh
Qv 5.23
4.20 4.17
5.29
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 1010 per bunch
H16LI beam control for Ip < 8 1010 per bunch
Three users : EASTA, EASTB and EASTC (combined with TOF beam)
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 phaseadvance of the betatron oscillation is such that the oscillationrepeats itself.
E.g. If the phase advance per turn is 120 degrees then thebetatron oscillation will repeat itself after 3 turns
E.g. This corresponds to Q = 6.333 or 3Q = 19
What does this mean?
x’
x
1st turn
2nd turn
3rd turn
2q = 2/3
q = fractional part of Q
Third order resonance on a normalized phase space plot
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
-10 -7.5 -5 -2.5 2.5 5 7.5 10
-6
-4
-2
2
4
6
Septum
A more realistic view on a 3rd order resonant extraction
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
- 45
0 m
s
p0
p0
%1.0p
p
%3.0p
p
P0 = Average momentum, 24GeV/cExtracted beam
Q
p
Which variable influences which parameter ???
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 3rd 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 ???
FIRST
EXTRACTOR SEPTUMMAGNET 61
SEPTUMMAGNET 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
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 thislook like on an oscilloscope ???
Magnetic preparation for slow extraction
Arrival at ‘flat-top’
W8L short circuited
PFW F and PFW D take over
Bump for electrostatic septum
Sextupoles Quadrupoles
Spill
R.F. preparation for slow extraction
Schematically:
Detected pick-up
R.F. voltage
Real life:
‘Optics and septa’ sources of losses
Extraction Magnetic Septum(SD57)
(34 sections) 45º
Electrostatic Septum (SD23)
Cathode Anode
Low momentum particle
high momentum particle
Sep
tum
bla
de
The electrostatic septum kicks a part ofthe beam and creates the space for the 1st magnetic septum.
Optimum situation obtained by changing the dispersion coefficients at SES23 andSMH57. This is done by the 2 quadrupoles.
Dispersion at SES23 small and positiveDispersion at SMH57 Big and positive.
Some problems and possible solutionsGeneral shape of spill
• ‘Spill shaping’ by modeling dQh/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)
Channeling buckets
Amplitude
PHASE
Resonanceregion
Resonance linefor low betatronamplitudes
Resonance linefor high betatronamplitudes
Sense of stackacceleration
E
The basic idea is that the particles cross the resonance more quickly. This leaves less time for the perturbations to influence the resonatingparticles, which in the end will reduce the ripple on the extracted spill.
DiagnosticsWe 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
Questions or ……..
???
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