Post on 23-Dec-2015
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Luminosity Optimisation Overview
Philip Burrows (QMUL)
• Introduction• Tools• Active component stabilisation• Beam-based feedback• Beam parameter diagnostics• Summary
Philip Burrows MDI Workshop, SLAC 6-8/01/05
1. Introduction
Relative component displacement -> emittance blowup (linac, BDS) mis-steering (FF), esp. final quads
• ‘static’ effects: misalignments …• diffusive effects: settling, hydrology …• ‘seismic’ motion: earthquakes, ocean waves …• cultural/facilities noise: traffic, pumps, water flow…• slow drifts: temperature, pressure …
IP
Luminosity
vs. beam offset
50nm: ~ 80% lost
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Available solutions
• Optimise site choice + civil/mech. engineering:
minimise (relative) component motion• Active component stabilisation:
compensate via (inertial/optical) feedback• Beam-based feedback/scans:
move beam(s) position/angle via feedback• Integrated system:
some/all of the above working in harmony
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Issues for machine-detector Interface
• Stabilisation of final doublets• Intra-train and pulse-pulse beam feedback• Beam parameter diagnostics
Terse summary/overview: hopefully raise issues for discussion
Philip Burrows MDI Workshop, SLAC 6-8/01/05
2. Tools
• Ground motion data/models• Facilities noise models • Linac -> IP beam transport
PLACET+MERLINDIMAD+LIARintegrated Matlab environment: MatMERLIN,
MatLIAR• Beam-beam interaction: luminosity, backgrounds
CAINGUINEAPIG
• Materials/detector simulations: shower tracking GEANT3 -> GEANT4
EGS
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Site studies + ground motion
CDR/TDR: more studies to bound problem?
studies of specific sites?
(Seryi)
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Facilities Noise
Example:
noise at SLD
Not difficult
to find noisy
environments!
TDR: need to model
for real engineered
MDI design?
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Engineering approach (Asiri)
Far-Field Excitation(Ambient Ground Motion
Measurement)
Acceptance Criteria
Select a Location(Representative Site)
Good Geology and Quiet
Estimate Near-Field Excitation
(At Their Footings)
Geotechnical Studies(Soil/Rock
Classification)
Attenuation Characteristics of
Soil/Rock
Adopt as a Concept Design Requirement
Estimate Vibration @ Invert of Beam Housing( Response to Near and
Far Fields Sources)
Select and LocateNear-Field
(Cryo/compressors, pumps)
NoYes
Done O(1) for few sites
Revisit for cold ILC
Reestablish for cold ILC
Philip Burrows MDI Workshop, SLAC 6-8/01/05
2. Tools
• Ground motion data/models• Facilities noise models • Linac -> IP beam transport
PLACET+MERLINDIMAD+LIARintegrated Matlab environment: MatMERLIN,
MatLIAR• Beam-beam interaction: luminosity, backgrounds
CAINGUINEAPIG
• Materials/detector simulations: shower tracking GEANT3 -> GEANT4
EGS
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Codes Database Pagehttp://hepwww.ph.qmul.ac.uk/~white/accodes/codedeb.htm
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Example: GUINEA PIG Pagehttp://hepwww.ph.qmul.ac.uk/~white/accodes/guinea.htm
Philip Burrows MDI Workshop, SLAC 6-8/01/05
QMUL High Throughput Cluster (HTC)
• 174 x 2 GHz cpus
• 40 TB attached storage
• GBit ethernet
• Peak capacity:
50k cpu-hours/week
• 400k cpu-hours used for
LC simulations (9 mos.)
• Another 2-300 ‘boxes’
by Spring 06
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Linac to IP Simulation Results Repositoryhttp://hepwww.ph.qmul.ac.uk/lcdata/
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Output files
Philip Burrows MDI Workshop, SLAC 6-8/01/05
3. Final quadrupole stabilisation
Passive:‘cushioned’ magnet supportssupport tube connecting opposite sides of IR
Active:inertial stabilisationoptical anchoring schemes
NB: details linked to final doublet technology (Parker et al), crossing angle …
IP
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Final doublet stabilisation: inertial(SLAC, CERN/CLIC …)
Sub-nm achieved > few Hz
SLAC: mockup of final quad girder: Non-magnetic inertial sensor
CERN: stabilisation of CLIC quad:
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Final doublet stabilisation: optical(UBC, SLAC, CERN, KEK …)
UBC prototype 10kg mass:
90 -> 5 nm (ground)
4.5 -> 1.5 nm (isolated)
Optical anchor system in
development:
NanoBPM project (ATF)
Optical anchor concept
Philip Burrows MDI Workshop, SLAC 6-8/01/05
‘Nano’ Project at KEK ATF
System test: aim for optical-anchor stabilisation of pair of
BPM triplets at nm level, with intra-train beam FB/FF
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Possible ATF optical anchor scheme (Oxford):simulations in progress
Urner
Philip Burrows MDI Workshop, SLAC 6-8/01/05
4. Beam-based feedback
• ‘slow’ upstream orbit feedbacks• IP pulse-pulse feedback (5 Hz)• IP intra-train (bunch-bunch) feedback: 3 MHz
Position and angle corrections:
most critical in vertical dimension
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Beam-beam deflection
GUINEAPIG simulations (White)
Deflection curve depends on: Q, sigma-x, sigma-y, sigma-z …
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Intra-train Beam-based Feedback Concept(same hardware for pulse-pulse FB)
Intra-train beam feedback is last line of defence against relative beam misalignment
Key components:
Beam position monitor (BPM)
Signal processor
Fast driver amplifier
E.M. kicker
Fast FB circuitTESLA TDR: principal IR
beam-misalignment correction
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Zero-degree crossing angle (TESLA TDR)
FB BPM
Upstream
kicker(s)
Philip Burrows MDI Workshop, SLAC 6-8/01/05
‘Large’ crossing angle (NLC)
FB BPMkicker
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Angle feedback: upstream in BDS
300 400 500 600 700 800 900 1000
5
10
15
20
25
30
BPM 2
KickerR
~450 m
BPM 1
~158 m
Distance from IP (m)
y ( m
)
Place kicker at point with IP phase.
BPM at phase 90 degree downstream from kicker.
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Angle feedback: locally near IP – crab cavity(IR with crossing angle)
Fast phase adjust using a second klystron and fast phase difference.
Diagram by J. Frisch
Needs
careful
integration
into MDI
design!
Philip Burrows MDI Workshop, SLAC 6-8/01/05
IP Feedback modelIP Feedback model
Linearise Beam-Beam Kick Curve Response
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Feedback AlgorithmFeedback Algorithm
1
0( ) ( ) ( ) ( ) ( )
k
PI P I P Ij
u k u k u k K e k K e j
•Subtract uPI(k-1) to get recursive algorithm:
( ) ( 1) ( ) ( 1) ( 1)PI PI P Iu k u k K e k e k K e k
•2 free parameters: gains KP and KI :
•KP provides fast response to error signal.
•KI cancels steady-state error.
•Iterate simulation to obtain optimum parameters to give fast correction and maintain collisions at 0.1y level.
•Proportional-Integral (PI) Controller:
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Illustration of Intra-train feedback performance (White/QMUL) (TESLA TDR)
0 100 200 300 400 500 6000
1
2
3x 10
34
Bunch #
Lu
min
os
ity
/ c
m-2s
-1
y position FB:
restore collisions
within 100 bunches1 seed:
post-BBA
+ GM
+ wakes
y position scan:
optimise signal
in pair monitor (+4%)
y angle scan
OPTIMAL
LUMINOSITY
Excellent
starting point:
need to add
further
‘reality’ …
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Intra-train beam feedback prototypes and beam tests (QMUL, Oxford, DL, SLAC, KEK …)
FONT1 and FONT2 prototype intra-train FB systems tested with beam at SLAC/NLCTA.
Latency 53ns
Full delay-loop feedback on:
FONT3/FEATHER
beam tests at KEK/ATF
summer 2005:
micron-level stability
of 1.3 GeV ATF beam
(model of nm- level
stability of ILC beam)
Cold ILC:
robustness,
algorithmic control
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Continuing feedback hardware development
Short-term: FONT3 at ATF: aim for micron-level stability of 1 GeV beam
Long-term:
demonstrate robust intra-train FB system for ILC, based on digital signal processing, and ideally test with beam:
requires long bunchtrain with 337 ns bunch spacing
2005-6: 3 (or 4) bunches x 100 ns at ATF would allow first tests:
stabilise last bunch at 100 nm level as part of Nano project
also feed-forward studies ring -> extraction line?
> 2006: 20 bunches x 337ns at ATF/ATF2 would allow FB algorithm
development
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Backgrounds (QMUL)
Need to ensure: FB system performance OK,
FB material does not cause additional backgrounds in detector.
Considering experimental background tests at SLAC/ESA
Feedback system incorporated into GEANT IR model
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Pulse-pulse IP beam deflection feedback(Hendricksen)
Input GM models
A, B, C:
Linac->IP tracking
+ 5 Hz FB (TESLA)
<Luminosity>
Need for
intra-train FB
Need to integrate simulation of FBs:
upstream slow, active stabilisation, 5Hz, intra-train …
Philip Burrows MDI Workshop, SLAC 6-8/01/05
SLC optimised ‘dither’ feedback at IP(Phinney)
Deflection scans: 5 knobs/beam : x/y waist, x/y dispersion, coupling
Old method: scan of
beam size vs. single knob:
Poor resolution, lumi loss
New method: optimise lumi
w. dither FB on each knob
Increased lumi, eased ops.
Philip Burrows MDI Workshop, SLAC 6-8/01/05
5. IP beam parameter diagnostics
Sigma xSigma ySigma z
Sigma x'Sigma y'
x offset y offset
x' offset y' offset
x-waist shift y-waist shift
Bunch rotation N particles/bunch Banana shape … …
Luminosity
What do you want to know?!
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Available diagnostics
• Transverse emittance: sigma x, sigma y, sigma x’, sigma y’
laserwire etc. beam size monitors (probably upstream) • Bunch length: sigma z
electro-optic, ODR, Smith-Purcell etc. monitors• Bunch charge:
toroids• Beam position/angle offsets:
beam-beam deflections • Luminosity
Pair/beamstrahlung monitors
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Beam diagnostics possibilities in IR limited
Lumi mon.
(Bhabhas)
IP BPM (beam
deflections)
Forward
BSR mon.
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Beam parameters from beamstrahlung?(Stahl, White)
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Observables/Beam Params List
E_totr moment 1/r moment Thrust DirectionThrust ValueAngular SpreadE_out/E_inL-R AsymmetryT-B AsymmetryDiagonal Asymmetry N/E_tot
Forward + backwardcalorimeters
•Sigma x
•Sigma y
•Sigma z
•Sigma x'
•Sigma y'
•E
•E spread
•x Offset •x' offset•y offset •y'' offset •x-waist shift •y-waist shift • Bunch rotation• N particles/bunch• Amount of y+y’ type-1 banana• Amount of y+y’ type-2 banana• Amount of y+y’ type-3 banana
Each variable where appropriate exists for the mean of e- + e+ bunch and difference in obs/par between them.
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Parameter Reconstruction
•Compute Taylor matrices through multiple GP runs varying beam params-> use Grid computing at QM to do in finite time (have to stick to 2nd order calculations realistically).
•For parameter reconstruction: Solve x for given f(x) using multi-parameter fit. Prob. no unique solution- choice of fit technique likely to be important.
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Single-parameter analysis: sanity check
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Initial results (Gaussian beams) (Stahl)
Seems to be promising; MUCH more study needed …
Philip Burrows MDI Workshop, SLAC 6-8/01/05
Summary of collision optimisation/MDI issues
• Active position stabilisation of final quads?
-> properly engineered design incl. laser tubes etc.
(through detector)• IP beam deflection feedback essential: intra-train and 5Hz
-> FB BPM, kicker, cables … need integrating into MDI design
-> understand background environment better• Crab cavity could be used for angle feedback?
-> needs integrating into real MDI design• Fast bunch-by-bunch lumi measurement vital input to FB
-> develop realistic prototypes of fast BSR/pair monitor• BSR/pair monitor offers potential for beam parameter determination
-> more simulation work needed• Need to develop integrated FB + scanning strategy:
-> intra-train + 5 Hz + dither + upstream slow + feedforward …