Introduction CERN PS Booster (PSB) Overview Motivation for Linac4 and PSB Beam Dynamics Studies

PS Booster - Limitations, Plans for Linac4, Simulations ….

Christian Carli 13th May 2011On behalf of many people contributing(M. Aiba, M. Scholz, M.Martini, J.-B. Lallement, C. Bracco, R. Garoby, B. Goddard and W. Weterings and team, M. Martini, M. Chanel, S. Cousinau and her colleagues at SNS, F. Ostiguy, A. Findlay, S. Hancock, K. Hanke, B. Mikulec, F. Gerigk ….. )

Introduction CERN PS Booster (PSB) Overview Motivation for Linac4 and PSB Beam Dynamics

StudiesActive longitudinal PaintingLattice Perturbations by the Injection ChicaneORBIT simulations done so far

Principle to implement time dependence Some Results

Status and Plans and open Questions

PSB Booster - limitations, plans for Linac4 ...13th May 2011

Overview of the presentation

Introduction CERN PS Booster (PSB) Overview Motivation for Linac4 and PSB Beam Dynamics Studies

Active longitudinal Painting Issues Related to the new H- Charge Exchange

Injection Lattice Perturbations by the Injection Chicane Conceptual Aspects for the Injection Layout Scenario proposed (Layout, Machine Acceptance)

Recent Simulations of Beam Dynamics with strong direct Space Charge Forces Principle to implement time dependence Some Results



Introduction – CERN PS Booster (PSB) Overview

Recapitulation of the present Booster with Linac2: Constructed in the 70ies to improve the performance (intensity) of the

PS Four superimposed rings (chosen instead of fast cycling synchrotron

or 200 MeV Linac) 16 cells with triplet focusing, phase advance >90o per period Large acceptances: 180 m and 120 m in the horizontal and

vertical plane, respectively Multiturn injection with betatron stacking and septum at 50 MeV Acceleration to 1400 MeV (was 800 MeV at the beginning)

Sketch of the PS Booster with: - Distribution of Linac beam into 4 rings - Recombination prior to transfer


Introduction – CERN PS Booster (PSB) Overview Mandatory for high Intensity and Brightness

Double harmonic RF (now: h=1 and h=2),

Resonance compensation, Dynamic working point … Maximum direct space charge tune

shifts larger than 0.5 in the vertical plane Intensities above 1013 protons per ring

(more then four times design) obtained Versatile machine - many different beams

with different characteristics

PSB to PS Transfer Energy: Increased (in two steps) from

800 MeV to 1400 MeV to reduce direct space charge effects in the PS

Direct Space Charge at PSB Injection a Bottleneck

Dynamic Working point with lower vertical tune – no syst. 3rd order resonance (taken from a presentation by M. Chanel)


Introduction – Motivation for Linac4 and PSB Beam Dynamics Studies

Rationale for Linac4: PS Booster limited by direct space charge effects, quantified by direct

space charge tune shift ∆Q, at injection energy Increase injection energy such that the brightness can doubled (double

intensity within unchanged normalized emittances) without changing ∆Q Raise injection energy from 50 MeV with Linac2 to 160 MeV with Linac4

Convert to H- charge exchange injection Reach the Phase Space Density expected in the PSB Allows - with a Linac4 Beam chopper - for longitudinal Painting New injection hardware for increased injection energy and charge

exchange injection Aim of PSB Beam Dynamics with Linac4 studies

Answer the question: Is above argument the whole story?(e.g. the Beam will stay a bit longer with large ∆Q in the PSB)

Thorough understanding of the implications of Linac4 on the PSB Make sure that PSB performance expected with Linac4 is reached fast:

Anticipate possible additional limitations & difficulties and devise for cures

Ensure integration of PSB with Linac4 into the complex (versatility ….)

Next bottleneck around the corner: PS and SPS at low energy


Active longitudinal Painting

With Linac4: similar RF system than at present Double harmonic

fundamental h=1 and h=2 systems to flatten bunches

reduces maximum tune shifts

Injection with d(B)/dt = 10 Tm/s (no need for injection with small ramp rate with painting any more)

Little (but not negligible) motion in longitudinal phase space.

No way for painting from synchrotron motion (large harmonic numbers and RF voltages ruled out)

Need for active painting (aim: fill bucket homogeneously) and energy modulation



Principle: Triangular energy modulation (slow, ~20 turns for LHC) Beam on/off if mean energy inside a contur ~80% of acceptance Nominal LHC: intensity with 41mA (!!!) after 20 turns High intensity: several and/or longer modulation periods

Potential limitations: Linac4 jitter, debunching of Linac4 structure in Booster Note that D ~ 1.4 m at the PSB injection Ideas on implementation: see talk on “RF Aspects …”



Simulation with ESME for nominal LHC beam: Energy modulation 1.1 MeV, plus rms spread 120 keV About 98 % of particles at the and buching factor ~0.60.

High intensity (reduced bucket hight due to direct space charge): Similar results with reduced E modulation

After 10 turns after 20 turns (completed injection) after~3000 turns

Injection Chicane and Lattice Perturbations

Injection chicane required to merge incoming H- beam with circulating protons No use of main bend field (as done e.g. at BNL) Little space available in injection section (existing machine) to install chicane

“BS” magnets

Perturbation of lattice due to BS magnets adding focusing Strong beta-beating in vertical plane due to tune close to (and even above) half-

integer(mandatory for good performance with high intensity/brightness beams)

Make BS magnets as long as possible to reduce additional focusing Compensate lattice perturbations (as much as possible) by additional

quadrupolar fieldsPSB Booster - limitations, plans for Linac4 ...

Incoming H-

Reference trajectory without bumps

Closed orbitwith chicane andpainting 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

13th May 2011


“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 -functions (small horizontal perturbation

small hor. ‘s)

Slow chicane fall (say 5 ms) to make sure that quad trim PSs 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 Fast chicane fall possible without compensation currents (if Eddy currents are nor a

problem) PSB Booster - limitations, plans for Linac4 ...

Injection straight section

QDE03 and QDE14appropriate for

Compensating 2QV = 9

13th May 2011


“Active” compensation with trims on appropriate QDE quads: Proposal (M. Aiba, B. Goddard ..) for additional quads ruled out initially:

complicated scheme with similar -function in both planes for quads in straights

Trims on QDE quadrupoles are appropriate (chicane made of rectangular bends):

Large (-function and) compensation in vertical plane with little (-function and) perturbation in the horizontal plane

In practice: trims on appropriate “Q-strips” (additional windings of PSB quads) Appropriate quads for “lower vertical tune: QDE03 and QDE14

Compensation during (no compromise) whole chicane fall Preliminary discussion on Power Converters: feasible provided chicane fall

time is not too short (at least a few ms)


β-beating with (dashed) and without (solid) compensation

Blue: vertical; red: horizontal

ORBIT simulations done so far Time dependent lattice implemented following a

procedure proposed by M. Aiba (found by looking into the code!!) Chicane magnets modeled as bends with time-varying

properties during chicane fall For “active” compensation, variation of quadrupole

components as well. Lattice regularly (every turn during chicane fall) read

from file, properties of some magnets redefined

Emittance evaluations: Dispersion (from file) used for emittance evaluations not any

more the one of the lattice in the simulation (magnet properties redefined)

Emittances and lattice functions from analysis of dumped macro-particle distributions


ORBIT simulations done so far Comparison of compensation schemes (M. Scholz, M.

Martini …)


0 2000 4000 6000 8000 10 0002 .2 5

2 .3 0

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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 V (m

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ORBIT simulations done so far Study on painting with slower energy modulation

(M.Martini, J.-B. Lallement) Injection painting bump optimization (C.Bracco et al.)


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Simulations with original ORBIT version concentrated on Injection Studies Shorter duration, blow-up due to injection hardware “easier” to assess Choice of “active” compensation of chicane

Motivation: simpler for hardware For performance, both a fast “passive” and a slow “active”

compensation seem feasible Perturbation from chicane modeled as (time-dependent bending

magnets) Time dependence implemented by regular lattice redefinitions

More recently (still with original ORBIT version) First studies on longer energy modulation period (J.-B. Lallement and

M. Martini) Studies on transverse painting (C. Bracco)



Plans and open questions (optimistic wish-list? … resources needed) Feasibility to study “long term” (~100 ms) blow-up?

Comparison (Benchmark) with exp’s Machine imperfections (misalignements, multipoles from mech. tolerances ..) Working point optimizations ??

Injection of 50 MeV protons from Linac2 and Linac4 with conventional multiturn injection

Recent question: to which extent Linac4 can “replace” Linac2 in case of failure (>2014 when Linac4 may be ready but not yet connected to the Booster)

Injection with a magnetic septum (PTC ORBIT suitable?) to be studied Imperfections of the chicane magnets (multipoles …. with time dependence) Completion studies on injection with constraints on (slower) energy modulation Completion of injection painting optimizations RCS studies (proposed/studied as new PS injector):

Asses performance to be expected (Laslett tune shifts > 0.5 to be expected) Space charge limit with low periodicity and, possibly,£ large variations of beta

functions Losses … and activation Any

Emittance and lattice function estimates only based on analysis of macro-particle distributions



Issues Related to the new H- Injection – Conceptual Aspects for the Injection

Dynamic working point and vertical tune at injection: At present: highest intensity with vertical tune at injection above half-

integer resonance (but below for LHC type beams) With Linac4 always below half-integer resonance:

Double brightness for LHC, Less than twice the intensity for high intensity (less losses, limited by machines

further downstream as well) Dispersion matching:

Large energy modulation for longitudinal painting and dispersion of PSB If beam arrives from Linac4 with D=0 m (dispersion mismatch): correlation of

transverse emittance and position in longitudinal phase space Should beam arrive with D matched to the PSB lattice (see chapter on

simulations) Acceptance with Linac4

At present: Large beams close to limit of ejection channel acceptance (losses)

With Linac4: aim for same maximum emittances at ejection Smaller physical emittances at injection -> reduce machine acceptance For acceptances: AH=130 m, AV=60 m and Ap/p=±2.2 10-3: Half-apertures in long straights: horizontal ±33 mm and vertical ±18 mm Can one take profit of a localized aperture to concentrate losses?


Issues Related to the new H- Injection – Conceptual Aspects for the Injection

Layout of the injection region (mainly by TE/BT team working on hardware) Superposition of two closed orbit bumps:

Chicane to merge incoming H- beam with circulating protons Injection painting bump: horizontal painting and removes beam

from foil Options (with different conceptual approaches)

Small injection bump and “high” chicane (baseline): No problems with apertures Chicane is used as well to remove circulating beam from foil

Large injection bump and small height of chicane (ABP proposal):

Foil outside of machine acceptance after fall of chicane Aperture in bends within injection painting bump critical

Plans for the near future: Evaluation of the two options by simulation with failures (e.g.

painting triggered bump too early and injection with large betatron amplitudes)

Fix layout (and specify maximum chicane fall time)


Issues Related to the new H- Injection – Scenario proposed (foil outside acceptance without painting bump)

Limiting aperture (“BeamScope” like) in straight ~2 from foil (5L1) Aperture displaced towards inside of PSB -23 mm to +43 mm to save aperture for

the injected beam -> “average” momentum (for large beams) pav/p = -10mm/D Height of painting bump:

Distance chicane to inner edge of foil: 33 mm + 7mm = 40 mm Distance edge of foil to incoming beam (pav/p) : 3*(2rms)1/2 + D ppaint/p ~ 15 mm Height of the injection painting bump: 55 mm (instead of 35 mm proposed by BT) Problem: tight for aperture (taken by painting bump)

Make use of acceptance reduction to implement rough collimation Thin aperture defining acceptance (at beginning) in straight section Thicker absorber behind in same straight section and/or in straights further

downstream First step: look into feasibility


Simulations of Beam Dynamics with strong direct Space Charge Forces

Assessment of slow blow-up by Simulations feasible?: Benchmark comparing measurements (by M. Chanel) with

simulations (by M. Aiba and M. Martini) and between ACCSIM and ORBIT (M. Aiba and M. Martini)

For the moment, no satisfactory agreement (yet?)

Example: 2nd harmonic RF to

shorten bunches toincrease tune shift

ACCSIM largelyoverestimates blow-up

ORBIT overestimatesblow-up as well

Dependance on numberof macro-part’s

Numerical artefacts?

Successful benchmark is prerequisite to apply simulations for blow-up and loss estimates


Emittance evolution comparison

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rms_V ORBIT (200000 mp)

rms_H MEAS

rms_V MEAS

rms_H ACCSIM (100000 mp)

rms_V ACCSIM (100000 mp)

nH=19.2m

nV=7.1m

nH=20.4m

nV=7.3mACCSIM

ORBIT


Impact of injection matching and painting on PSB performance Filamentation of structure due to injection dispersion mismatch? Investigated by M. Aiba with input from B. Goddard – longitudinal and

transverse painting of an LHC type injected over 20 turns

No significant difference with and without dispersion mismatch To do: Impact (minor ?) of transverse matching and painting on performance?

Simulation on impact on and of the injection foil by BT team and M. Aiba


Evolution of rms emittances after injection - blow-up (extrapolation ?) may be too large(slightly larger relative blow-up for 99% and 100% emittances)


Evolution of beam parameters during fall of chicane with lattice perturbations and passive compensations and different fall times (simulations by M. Aiba) “Passive” compensation (see above) by pole-face rotation of chicane magnets yield Simulations with ORBIT and additional routine for time dependant focusing of

chicane, but no synchrotron oscillations Simulations indicate significant reduction of blow-up

Chicane: LBS = 0.25 m and sector bends Chicane: LBS = 0.25 m and “tapered” bends

Lattice perturbation and “active” (by trims on QDE’s) compensation Injection painting, “static chicane and compensation” and with synchrotron motion Similar results (compensation reduces blow-up)


0 500 1000 1500 2000 2500 3000

2.422.432.442.452.462.472.482.492.502.512.522.532.54

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Hor, w/o edge, =1ms Ver, w/o edge, =1ms Hor, SBEND, =1ms Ver, SBEND, =1ms Hor, SBEND, =10ms Ver, SBEND, =10ms

0 500 1000 1500 2000 2500 3000

2.422.432.442.452.462.472.482.492.502.512.522.532.54

norm

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Hor, w/o edge, =1ms Ver, w/o edge, =1ms Hor, T BEND, =1ms Ver, T BEND, =1ms Hor, T BEND, =10ms Ver, T BEND, =10ms


Activities and Plans for the working Group on “PSB Beam Dynamics with Linac4”

Proposed longitudinal painting proposed and follow-up (implementation, see talk on “RF aspects and possible limitations”)

Beam dynamics with strong direct space charge forces Benchmark to which extent simulation are appropriate tools Apply simulations: filamentation of structure from injection, losses slow blow-

up … ?) Beam dynamics issues related to the new H- charge exchange injection

(with BT team) Integration into the CERN Complex (see talk on “Operational Scenarios

…”): Generation of all (also low intensity without painting) beams to be provided,

minimization of losses and activation Transfer of LHC type beams between PSB and PS

Check limitations of present Booster hardware: Instabilities (existing damper with higher intensities) (Beam loading problems of h=2 cavities for h=1 beams … limitations ISOLDE

beams ?) Beam Losses, Activation (“normal” losses, failure scenarios …):

Losses at Injection (Line and Ring) in collaboration with or by injection hardware team ?

Feasibility of rough Collimation System (if feasible, resources need to be requested and allocated)

Summary, Status and Questions

Linac4 aims at increasing the brilliance out of the PSB by about a factor 2.

Beam dynamics studies aim: Thorough understanding of implications of Linac4 on PSB Anticipating problems to implement measures ensuring fast and

efficient (i) restart of the PSB with Linac4 (ii) performance increase to expected levels

Status Progress on many topics during the last year, but work on some

topics still in starting phase Present priority on studies with possible impact on hardware (e.g.

finalization of injection) Questions to the review board:

Validation of proposed longitudinal painting Advice on finalization of injection layout Validation of proposed reduction of the machine acceptance Advice on simulations with strong direct space charge effects


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Introduction CERN PS Booster (PSB) Overview Motivation for Linac4 and PSB Beam Dynamics Studies

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