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 ……..

???