introduction cern ps booster (psb) overview motivation for linac4 and psb beam dynamics studies
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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
Status and Plans and open Questions
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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)
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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
PSB Booster - limitations, plans for Linac4 ...13th May 2011
Active longitudinal Painting
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 …”
PSB Booster - limitations, plans for Linac4 ...13th May 2011
Active longitudinal Painting
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
Injection Chicane and Lattice Perturbations
“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
Injection Chicane and Lattice Perturbations
“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)
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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
PSB Booster - limitations, plans for Linac4 ...13th May 2011
ORBIT simulations done so far Comparison of compensation schemes (M. Scholz, M.
Martini …)
PSB Booster - limitations, plans for Linac4 ...13th May 2011
0 2000 4000 6000 8000 10 0002 .2 5
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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.)
PSB Booster - limitations, plans for Linac4 ...13th May 2011
Plo
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Status and Plans and open Questions
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)
PSB Booster - limitations, plans for Linac4 ...13th May 2011
Status and Plans and open Questions
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
PSB Booster - limitations, plans for Linac4 ...13th May 2011
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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?
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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)
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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
PSB Booster - limitations, plans for Linac4 ...13th May 2011
Emittance evolution comparison
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0 20 40 60 80 100 120 140 160 180 200Time [ms]
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rms_H ORBIT (200000 mp)
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
Simulations of Beam Dynamics with strong direct Space Charge Forces
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
PSB Booster - limitations, plans for Linac4 ...13th May 2011
Evolution of rms emittances after injection - blow-up (extrapolation ?) may be too large(slightly larger relative blow-up for 99% and 100% emittances)
Simulations of Beam Dynamics with strong direct Space Charge Forces
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)
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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
. r.m
.s. e
mitt
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(m
m-m
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)turn
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
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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
PSB Booster - limitations, plans for Linac4 ...13th May 2011
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