linac4 beam commissioning committee psb beam optics and painting schemes 9 th december 2010 beam...

Linac4 Beam Commissioning Committee PSB Beam Optics and Painting Schemes 9 th December 2010

Beam Optics and Painting Schemes

C. Bracco, C. Carli, B. Goddard, J.-B. Lallement, M.Martini, W. Weterings

• Motivation for a H- Charge Exchange Injection

• Lattice Perturbations and their Compensation

• Injection Painting

• Apertures

• Typical Simulation Results

• Conclusions, Outlook, Questions


Motivation for a H- Charge Exchange Injection

Injected and circulating beam merged with a dipole BS2 No septum separating space into region for injected beam and beam circulating in the PSB

No losses on the injection septum (~50% now for LHC beams) Injection painting bump can decrease slowly allowing injecting a larger number of turns High brightness beams possible in the Booster with a beam current lower than the one

from Linac2 New injection hardware required perturbing the lattice Emittance increase due to Scattering of protons traversing the injection foil

Incoming H-

Reference trajectory without bumps

Closed orbit with chicane and maximum painting bump

BS1 BS2 BS3 BS4

Injection straight at the beginning of the injection (trajectory of incoming H - coincides with closed orbit)Stripping foil

Bending magnet


Lattice Perturbations and their Compensation

Source of the problem: Injection chicane and other hardware to be implemented within available straight section (with

“fixed” geometry of incoming beam) Short “strong” (for dipoles generating an orbit bump) BS magnets to create the chicane Additional focusing created by BS magnets perturbs lattice

With rectangular magnets focusing in the vertical plane With vertical tune close to half integer QV ~ 4.5 (even above half-integer resonance for highest

brightness and intensity) strong beta-beating in the vertical plane

As long BS magnets as possible to reduce the additional focusing and compensation schemes (next slides)


Lattice Perturbations and their Compensation

“Active” compensation Look for appropriate locations to add (time-varying) quadrupolar fields Trims on QDE magnets (on additional windings …) in period 03 and 14 with appropriate phases Effective compensation with large vertical b-functions (small horizontal perturbation small hor. b‘s)

Slow chicane fall (say 5 ms) to make sure that quad trim PCs can follow programmed currents “Passive” compensation

Do not use R-Bends, but add pole-face rotations to bring part of perturbation in (less sensitive) horizontal plane

No perfect compensation during chicane fall, more difficult for magnets and power converters Fast chicane fall possible and necessary without compensation currents (if Eddy currents are nor a problem)

04/02/2010

Injection straight section

QDE03 and QDE14appropriate for Compensating 2QV = 9


Injection Painting Longitudinal painting

with energy modulation(just a brief recapitulation)

Transverse (horizontal) painting Most simulations up to now assumed linear decrease of the painting bump➠ Transverse distribution with dense core and tails Study started (by Chiara, see presentation by Luc Sermeus on KSWs in this BCC) on optimized painting

bump with fast decrease at the beginning to reduce density at the center Slow decrease at the end of the injection to reduce tails Fast decrease to move the beam away from the foil

Vertical emittances (beam sizes) with vert. offset and betatron mismatch (of injected beam)


Apertures (with zero dispersion of the incoming beam)

Conductor of septum-like BS2 magnet

Injected beam

Black: maximum beam extension after painting bump decreasedRed: positive energy offset part’sBlue: negative energy offset part’s

Solid lines: beginning of injectionDashed: end of injection

Incoming beam: 10 mm offset, zero dispersion; circulating beam centered (“BeamScope” window with reduced aperture centered in say 4L1) and 35 mm painting bump, (compare with B.Goddards L4BCC presentation on 8th September 2009)

“BeamScope” windowreduces acceptance

(in 2L1 for sketch)


Apertures (with matched dispersion of the incoming beam)

Black: maximum beam extension after painting bump decreasedRed: positive energy offset part’sBlue: negative energy offset part’s

Solid lines: beginning of injectionDashed: end of injection

Incoming beam: 5 mm offset, zero dispersion; circulating beam off-centered (“BeamScope” window in 2L1 with reduced aperture and shifted by 10mm towards the inside) and 50 mm painting bump,


Typical simulation results(phase space plots with active compensation taken from M. Martini)

turn 19

turn 1

turn 250

turn 500

turn 750

turn 1000

turn 1000

turn 3000

turn 4000

turn 5000

turn 1000

turn 1000

turn 3000

turn 4000

turn 5000

turn 250

turn 500

turn 750

turn 20

turn 1

turn 1000

166 mp


Typical simulation results(emittance evolutions taken from M. Martini)

Fast emittance blow-up during injection and decrease of the injection chicane (500 turns for passive compensation and 5000 turns for active compensation)

Probably feasible to estimate beam properties with available programs Slow blow-up afterwards

Difficult (impossible?) to estimate, depends on simulation parameter like number of macro-particles

Are machine imperfections (not taken into account at present) relevant?

0 2000 4000 6000 8000 10 0002 .2 5

2 .3 0

2 .3 5

2 .4 0

2 .4 5

2 .5 0

Tu rn s

xmrad

P assive com p en sa t io n 1 E 6 pP assive com p en sa t io n 5 E 5 pA ctive com p en sa t io n 1E 6 pA ctive com p en sa t io n 5E 5 p

0 2000 4000 6000 8000 10 0002 .2 5

2 .3 0

2 .3 5

2 .4 0

2 .4 5

2 .5 0

Tu rn s

x y2mr

ad

P assive com p en sa t io n 1 E 6 pP assive com p en sa t io n 5 E 5 pA ctive com p en sa t io n 1 E 6 pA ctive com p en sa t io n 5 E 5 p

Evolution of the horizontal (left image) and vertical (right image) emittances during about 10ms from the start of the injection


Summary, Outlook, open Questions …… activities to be discussed and redefined with the new LIU structure

Compensation of lattice perturbations Simulations indicate that both active and passive compensation give acceptable results (tendency: less

losses with active compensation) Additional power converters required for active compensation feasible Very likely that active compensation will be the choice … simpler for BS magnets (and their power

converters)

Aperture restriction (“BeamScope” like window) Proposal to reduce the acceptance of the machine to have the foil out side the acceptance after the

painting bum decrease … and possibly to install a rough collimation system Are there still plans to study/install such a restriction … and activation in general?

Transverse painting optimization to be continued to to define matching parameters at the injection point (by Chiara …)

Effect on beam dynamics with direct space charge?!

Follow-up of longitudinal painting PSB injection timings, definition of an application …

How to deal with longer energy modulation periods? Investigations started … impact on scattering in foil?

Injection steering … not to forget: Install and construct BI.DVT/DHZ50 & 70 Required strengths estimated

linac4 beam commissioning committee psb beam optics and painting schemes 9 th december 2010 beam...

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