w. kozaneckipep-ii mac review, 9-11 oct 03 machine-detector interface issues machine backgrounds,...
Post on 20-Dec-2015
217 views
TRANSCRIPT
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Machine-Detector InterfaceMachine-Detector Interface
IssuesIssues
Machine Backgrounds, Present & FutureMachine Backgrounds, Present & Future
BaBar involvement in Accelerator Performance ImprovementsBaBar involvement in Accelerator Performance Improvements
SummarySummary
W. Kozanecki, CEA-Saclay
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
The IssuesThe Issues
Backgrounds operational efficiency (this coming run)
long-term projections (2005 & beyond)
New IR design background simulations: can BaBar live with predicted levels?
make it all fit (unavoidable hardware changes!) [this topic likely to grow in importance]
Accelerator Performance Improvements background remediation
beam dynamics
instrumentation
IR geometry, orbits & optics
BaBar-based accelerator diagnostics
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Backgrounds: what has happened so farBackgrounds: what has happened so far
Try & revive the ‘Try & revive the ‘Background GroupBackground Group’’ Strong (and largely successful) effort at
awareness-raising in BaBar (“work on backgrounds? why?”)
recruiting help
Identified subdetector background contact persons (SBC)
Regular MDI meetings (~ every other week)
Background WorkshopBackground Workshop: 22-24 Sep 03: 22-24 Sep 03http://www.slac.stanford.edu/BFROOT/www/Public/Physics/bgd2003_workshop/agenda_items/agenda.html
In-depth review of radiation-abort policies: “make BaBar & PEP-II transparent to each other”
Run-4 backgrounds: operational issues, vulnerabilities, long-term projections
Launch the background-simulation effort
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Background Sources I Background Sources I (())
Synchrotron-radiation X-raysSynchrotron-radiation X-rays Power: mostly separation dipoles
Background: mostly HER IP quadrupoles
Duck it if you can! else mask it, but watch out for multiple bounces
Masking very effective: SR backgrounds not a problem in BaBar so far
Cool it well - or else!
Lost-particle backgroundsLost-particle backgrounds Bremsstrahlung: e + gas -> e’ + (E’ < E)
By now, almost exclusively from the last few (tens of) m ==> vacuum!
Coulomb scattering: e + gas -> e’ (E’ = E, but )Potentially from the whole ring, depending on limiting apertures and on pressure profile. In practice no longer an issue
Touschek : similar to bremsstrahlung BaBar: neglected so far. Should be checked for very-high current operation.
Luminosity (e+ e- => e+’ e-’ )
Elm shower debris (radiation + occupancy) + beam-wall p’s (trigger)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
# Xtls
> 10 MeV
Single-beam backgroundsSingle-beam backgrounds
EMC
vs. I+, I-
IDCH vs. I+
Two-beam backgroundsTwo-beam backgrounds
% occpcy (> 1 MeV)
EMC vs. I
(I+ = 1100)-
L1 trigger rate vs. I- (I+ = 1100)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Background ProjectionsBackground Projections (based on bgds measured in 2000, then 2002)
High-Luminosity Model (JS, PEP-II AP Note 130) combined with ( - I- + - I-2 ) + (+ I+ + + I+
2 ) + L
Drift Chamber Bakground Projection (July 2000 characterization)
Beam-current timeline model
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
2000 2001 2002 2003 2004 2005?Calendar year
Avera
ge c
urr
ent
(A)
HER
LER
Luminosity timeline model
0
5
10
15
20
25
30
2000 2001 2002 2003 2004 2005?Calendar year
Avera
ge L
(10
33
)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
SVT SVT Bakground Bakground ProjectionProjection
Pain threshold: ∫dose ~ 2 MRad
Horiz. plane: ~ 2 MRad by 2003-4, then 0.5 - 1 MRd/y
Other : ~ 0.25 MRad by 2004, then ~ 0.1 MRad/y
DIRC DIRC Bakground Bakground ProjectionProjection
Pain threshold: PM rate ~ 200 kHz Pain threshold: PM rate ~ 200 kHz
(dead time ~ % @ 300 kHz, 20% @ 500 kHz)
Note how different the relative contributions are between subdetectors
July 2000 characterization
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Recent background history: DCHRecent background history: DCH
Compare measured DCH background to that expected
at the same LER currentLER current, HER current & LuminosityLuminosity,
based on the Feb. 2002 characterization
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Background Sources IIBackground Sources II (())
Lost-particle backgrounds Lost-particle backgrounds (continued)
Beam-beam (?) tails ~ Coulomb-like signature ==> collimation ? ( LER !)
elm shower debris in incoming detector straight (esp. LER?)
‘‘steady state’ : DCH, IFR – but also SVT (dose + occupancy)steady state’ : DCH, IFR – but also SVT (dose + occupancy)
Spikes & fluctuations DCH, TRG
Radiation burstsRadiation bursts spikes (“fast aborts”)
trapped events
Injection backgroundsInjection backgrounds 30-90% of SVT dose
45% of EMC dose (CsI calorimeter)
~ 50% radiation aborts
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Recent background history: SVT, IFRRecent background history: SVT, IFR
SVT IFR endcap
predicted (2002)
measured
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
DCH current
steady-state level
HER lifetime
400 sec
Manual abort
Radiation burstsRadiation bursts
Fast (auto) abort
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Injection BackgroundsInjection Backgrounds
FW FE BW BETOP 81 (14%) 52 (41%) 100 (9%)MID 374 (63%) 333 (67%) 488 (66%) 215 (65%)BTM 90 (30%) 59 (38%) 82 (20%) 58 (45%)
25 (55%)
(Numbers are in krad, (%) is of dose in stable beams)
SVT Radiation dose from January to June 2003
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
SR + beam gas + “Lumi” (eSR + beam gas + “Lumi” (e++ee-- e e++ e e-- ) (“traditional”)) (“traditional”) not an issue ’05 w/ present IR geometry (& * !) however beam-gas in the LER may become a major contributor to the SVT
integrated dose occupancy
once the LER current is raised significantly
Beam-beam tails (SVT occupancy, DCH spikes, dead-time Beam-beam tails (SVT occupancy, DCH spikes, dead-time burstsbursts, IFR , IFR currents) a currents) a growinggrowing limitation (including for BaBar data quality) limitation (including for BaBar data quality)
Interplay between BaBar radiation-abort strategy, and (primarily)Interplay between BaBar radiation-abort strategy, and (primarily) radiation bursts (spikes/trapped evts) ==> significant source of beam aborts difficult injection (poor injection efficiency, high backgrounds, repeated aborts)
==> major inefficiencies
Backgrounds Backgrounds operational efficiency (’03-’04) operational efficiency (’03-’04)
Radiation-abort strategy
Radiation burstsInjection backgrounds
Beam-beam tails
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Backgrounds: long-term projections IBackgrounds: long-term projections I
Experimental background extrapolations
2005 (2009)
Currently based on 2002 bkgd data. An updated characterization will be carried out once PEP-II stabilizes.
BaBar hardware/performance limitations?
2005 (2009)
(see W. Wisniewski’s talk)
extrapolation of ‘traditional’ backgrounds (in present geometry) valid 200x ? * ==> Coulomb still OK? can one extrapolate beam-beam backgrounds – at all? how to take into account evolution of injection losses
any limitations/vulnerabilities in Babar hardware or physics performance? radiation damage? operational limitations (power supplies, trigger/dataflow bandwidth,...) physics performance (tracker occupancy/efficiency/resolution, calorimeter resolution)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
SVT elx SVT elx threshold threshold problem problem
??
Projected integrated dose in SVT midplane Projected integrated dose in SVT midplane (Basis: 2002 characterization, no beam-beam tails, no injection improvements)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Extrapolated dose rates in the SVT mid-plane (stable beams)
50 mR/s ~ 10% chip occupancy
Projected SVT data quality Projected SVT data quality (Basis: 2002 characterization, no beam-beam tails)
“BaBar needs to better understand the implications of high beam occupancies”
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Projected DCH currents & data-flow dead time Projected DCH currents & data-flow dead time (Basis: 2002 characterization, no beam-beam tails)
remedy under active study
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Backgrounds: long-term projections IIBackgrounds: long-term projections II
Beam-beam ?
Lattice mods ? (dynamic aperture)
Beam-gas simulations
• ring: Turtle
• IR Geant4
SR simulations
(an intrinsic part of the new-IR design)
2 themes...2 themes... validate IR upgrade design
make sure that what we install in ’05 does not suffer from built-in flaws...
...at least for those processes we can calculate (SR, beam-gas)
understand / improve backgrounds in present machine
...that are intimately intertwined...that are intimately intertwined validation requires credibility
update “old” simulations to incorporate what we learnt
simulations of present machine/detector configuration better get the ‘right’ answer (when confronted with measurements)...
...if we want to believe predictions for the upgraded IR
improve those backgrounds we canNOT calculate both for today’s and for tomorrow’s sake!
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Background analysis & mitigation [BP, LP, TG: some just starting, but too few...]
Background simulations [RB, MB, GC, SM + SLAC (TF/GB)]
Fast monitoring of machine backgrounds PEP-II [MW, C’OG, AP, GDF,...]
injection quality (SVT, EMC: dDose /dIb )
time distribution of injection triggers
data quality: occupancies, dead time,... for the stored beams
in the ‘trickle’ window
more operator-friendly displays (& controls) of radiation inhibits/aborts
BaBar involvement in Accelerator Performance Improvements (I)BaBar involvement in Accelerator Performance Improvements (I)
EMC
L1 trigger rate
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Beam dynamics beam-beam simulations [IN (Caltech), YC (Slac ARD)]
beam-beam experiments, monitoring of beam-beam performance
Instrumentation gated camera in LER & HER [D. D., Slac Exptl Grp C + A. Fisher +...]
beam-beam effects (flip-flop, ‘raining buckets’, parasitic crossings)
electron-cloud effects
development of an X-ray beam-size monitor for the LER: SLAC + zone-plate approach: J A (Caltech)
pin hole approach: JK (LBL), HDS
SVTRAD sensor & electronics upgrade [B P et. al. (Stanford); MB/DK et. al. (Irvine) (initiated & funded by BaBar)]
CsI background sensors [JV, Slac Exptl Grp B]
IR geometry, orbit & optics IR orbit monitoring & stability, IP & ring orbit feedbacks
on-line monitoring of IP position PEP-II control system [RB, Slac; GDF, Caltech; ..]
on-line monitoring of luminous spot sizes PEP-II control system
[MW (Slac); GDF (Caltech); MB/GR (Nikhef);...]
BaBar involvement in Accelerator Performance Improvements (II)BaBar involvement in Accelerator Performance Improvements (II)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
SummarySummary
BaBarians...BaBarians... ...have (re-started) contributing significantly to the machine
“BaBar-based machine diagnostics “ a growing & important effort
But more help is needed, esp. on medium- & long-term issues
BaBar vulnerabilities BaBar vulnerabilities betterbetter understood understood short term: SVT elx chip, DCH data flow, IFR aging
medium term: SVT (& EMC ?) integrated dose, tracker occupancies, physics systematics
?? implications of lattice mods ( dyn. aperture) for backgrounds?
Most urgent short-term gainsMost urgent short-term gains injection (lack of reproducibility, abort cascades, ++dose, fatigue)
beam-beam tails (more agressive and/or upgraded collimation)
radiation bursts (“dust events”)
Most significant long-term gain potentialMost significant long-term gain potential LER vacuum in last 20 m (?) [tbc by updated bgd characterization]
injection (30-90% of integrated dose in SVT & EMC)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Appendix: radiation bursts (aka ‘dust’ events)Appendix: radiation bursts (aka ‘dust’ events)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Statistical study of trapped event properties (T. Schietinger, 1999)Statistical study of trapped event properties (T. Schietinger, 1999)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
SVT diode pattern during trapped eventsSVT diode pattern during trapped events typical, but not universal
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
An odd sequence of slow radiation bursts (2003)An odd sequence of slow radiation bursts (2003)Diamonds
0
50
100
150
200
250
19400 19600 19800 20000 20200 20400 20600 20800 21000Time (sec)
mR
/s
DIAM_E
DIAM_W
Backward-top diodes (W/E)
0
5
10
15
20
25
30
35
40
19400 19600 19800 20000 20200 20400 20600 20800 21000Time (sec)
mR
/s
SIG7
SIG5
HER Betatron collimators (y)
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
19400 19600 19800 20000 20200 20400 20600 20800 21000Time (sec)
BL
M c
ou
nts
PR12_BLHC8072
Inverse HEB lifetime
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
0.0045
19400 19600 19800 20000 20200 20400 20600 20800 21000Time (sec)
Inv
ers
e li
feti
me
(m
in^
-1)
1/tau_H
?
?
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
An odd sequence of slow radiation bursts (c’td)An odd sequence of slow radiation bursts (c’td)HER Betatron collimators (y)
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
19400 19600 19800 20000 20200 20400 20600 20800 21000Time (sec)
BL
M c
ou
nts
PR12_BLHC8072
Inverse HEB lifetime
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
0.0045
19400 19600 19800 20000 20200 20400 20600 20800 21000Time (sec)
Inv
ers
e li
feti
me
(m
in^
-1)
1/tau_H
?
HER momentum collimator
0
5000
10000
15000
20000
25000
30000
19400 19600 19800 20000 20200 20400 20600 20800 21000Time (sec)
BL
M c
ou
nts
PR12_BLHC9082
HER BLMs (incoming S2A)
0
5000
10000
15000
20000
25000
30000
35000
40000
19400 19600 19800 20000 20200 20400 20600 20800 21000Time (sec)
BL
M c
ou
nts
BLSC7017
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
A collection of fast radiation spikes (stored beams)A collection of fast radiation spikes (stored beams)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Geometry of some detectors useful for such studiesGeometry of some detectors useful for such studies
Q1Q2
Q4
Q5
171
192
Amp.20,VSAM 29{outboard Q4)
Amp.19,VSAM 28(inboard Q4)
Amp.18,VSAM 27(next to Q2)
Amp.17,VSAM 26(downstream of Q1)
20
Amp.22,VSAM 31, 3043(Downstream collimator)
Amp.21,VSAM 30(outboard Q5)
IP3
LER
HER
14 4
Amp.23,2-nd VSAM 0, 3054(downstream of a bend)
Amp.24,2-nd VSAM 1, 3075(Upstream collimator)
HER
LER
LER
HER
Q1 Q2
Q4
Q5
10
96 7
Amp.6,VSAM 15(near Q2)
Amp.7,VSAM 16(inboard Q4)
Amp.9,VSAM 18(inboard Q4)
Amp.10,VSAM 19(between Q4&Q5), 7045
8
Amp.8,VSAM 17(inboard Q4)
Amp.5,VSAM 14(upsream of bellows)
IP
51211
Amp.11,VSAM 20(outboard Q5), 7044
Amp.12,VSAM 21(Luminosity chamberdownstream), 7043
13 14
Amp.13,VSAM 22(HER collimatordownstream), 7042
Amp.14,VSAM 23(HER collimatorupstream), 7042
(East)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Radiation bursts: “summary”Radiation bursts: “summary”
Statistical study of trapped event properties (T. Schietinger, 1999)Statistical study of trapped event properties (T. Schietinger, 1999)http://www.slac.stanford.edu/~schieti/background/trapped
SVT diode pattern during trapped eventsSVT diode pattern during trapped eventshttp://www.slac.stanford.edu/~schieti/background/trapped/svt_response.html
A collection of recent slow & fast radiation burstsA collection of recent slow & fast radiation bursts
Some guesses...Some guesses... NEG dust from near IR pumps?
gas ‘bubbles’? (would explain correlation with current increases)
possibly some incorrectly latched fast beam instabilities (RF, TFB ?)
...but certainly no coherent picture nor robust interpretation...but certainly no coherent picture nor robust interpretation
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
PEP-II Mid-Project EvaluationPEP-II Mid-Project Evaluation
ResourcesEwan Paterson, TDPersis Drell, RDBill Wisniewski, Babar
ResourcesEwan Paterson, TDPersis Drell, RDBill Wisniewski, Babar
Parameters, Parameters, LLdtdt John Seeman, Stan Ecklund
Jonathan Dorfan, Co-ordinator
Lattice/ModelLattice/ModelTor RaubenheimerUli Wienands
Vacuum SystemsVacuum SystemsNadine KuritaScott DeBarger
RF SystemRF SystemRon AkreRay Larsen
Feedback SystemsFeedback SystemsEric ColbyDmitry Teytelman
Reliability/UptimeReliability/UptimeRoger EricksonName #2
Machine/Detector InterfaceMachine/Detector InterfaceWitold KozaneckiGuy Wormser
New IR DesignNew IR DesignMike SullivanName #2
DiagnosticsDiagnosticsMark RossSteve Smith
InjectionInjectionFranz-Josef DeckerName #2
ControlsControlsTom HimelRusty Humphrey
stricly speaking
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Fast Abort ChangesFast Abort Changes
Will leave abort settings during stable beams unchangedWill leave abort settings during stable beams unchanged Forgiveness (2 Rad) cannot be increased as that endangers the SVT
Increasing threshold (~1 R/s) could result in running at >1R/s for 10 minutes, which we do not want to try
We can try to change settings during injectionWe can try to change settings during injection There is no immediate danger to the SVT as it is not biased
The increase in dose (a few krad/year) would be regained if we can get rid of 10-20% of the aborts
Suggested change:Suggested change:
Increase forgiveness by factor 3 over stable beams (e.g. 6-8 rads)Increase forgiveness by factor 3 over stable beams (e.g. 6-8 rads)
Set threshold at 2 times stable beams (~2rad/s) instead of 5 timesSet threshold at 2 times stable beams (~2rad/s) instead of 5 times
Would like to have causes of aborts, which still occur be Would like to have causes of aborts, which still occur be identified and logged by operatorsidentified and logged by operators
Brian Petersen, 3
Oct 03
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Slow Abort ChangesSlow Abort Changes
We will enable “extend” button for 10-minute timer, but We will enable “extend” button for 10-minute timer, but restrict it to 10 additional minutesrestrict it to 10 additional minutes
We will monitor it for abuse (of course)
Activate 10 minute timer for the diamonds Activate 10 minute timer for the diamonds Suggest to replace BW:MID diode with BW diamond
Use threshold of 75 mrad/s?
Changes can be implemented by next week
Brian Petersen, 3
Oct 03
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Possible Longer Term ChangesPossible Longer Term Changes
Should separate “forgiveness” from protection against very Should separate “forgiveness” from protection against very fast spikesfast spikes
Very quickly abort beams on dose rates of 0.1 to 1krad/s
Allow rates of 1-100 Rad/s for a little longer (x2-4?) than today
Requires the SVTRAD1.5
Abort only one beam?Abort only one beam? Not clear that HER and LER always clearly separated during aborts
Gain in integrated dose will be minimal as most aborts would be of the HER
Would require new electronics in IR-2 alcove (previous electronics were done by Mark Petree)
Brian Petersen, 3
Oct 03
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
MID Radiation Doses Until NowMID Radiation Doses Until Now
Budget is set to reach 4 Mrad by 7/1-2005 (to be lowered?)
FW:MID is consistently overestimated in Run 3
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
TOP Module Doses until 2009TOP Module Doses until 2009
TOP modules look OK, except if FE:TOP becomes MID module
BW:TOP and FW:TOP doses are probably overestimated
85-90% of the dose is supposed to come from injection
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
BABAR scorecard todayBABAR scorecard today
TODAYRadiation damage Operation Data Quality
SVT x xDCHDRC fixedEMC - ?IFR x x xTRGDAQSVTRAD x x
X: visible effect with non-zero impact - : visible effect with no impact
? : yet unknown fixed: det upgrade to fix a significant issue
G. Wormser, Bgd Workshop
summary, 24 Sep 03
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
BABAR scorecard July 2004BABAR scorecard July 2004
July 2004Radiation damage Operation Data Quality
SVT X? xDCH XDRC fixedEMC - ??IFR x X XTRGDAQSVTRAD x improved
G. Wormser, Bgd Workshop
summary, 24 Sep 03
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
BABAR scorecard July 2006BABAR scorecard July 2006
July 2006Radiation damage Operation Data Quality
SVT fixed xxDCH TO BE FIXEDDRC fixedEMC - ???IFR fixed fixed fixedTRGDAQSVTRAD fixed fixed
G. Wormser, Bgd Workshop
summary, 24 Sep 03
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
BABAR scorecard 2009BABAR scorecard 2009
2009Radiation damage Operation Data Quality
SVT X xxxDCH fixedDRC fixedEMC X ????IFR X X XTRG XDAQ XSVTRAD fixed fixed
G. Wormser, Bgd Workshop
summary, 24 Sep 03
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Architecture of background simulations (1)Architecture of background simulations (1)
Synchrotron RadiationSynchrotron Radiation MAGBENDS / QSRAD: stand-alone programs
SR background calculations: an intrinsic component of IR re-design
shouldn’t these be interfaced to GEANT?
Beam-gasBeam-gas step 1: LP-TURTLE transports particles around 1 ring turn
full model of ring optics (treated as transport line)
start with ‘nominal’ beam at IP
beam-gas scattering randomly around ring (bremsstrahlung or Coulomb scattering) transport ‘secondaries’ (e’, )
simplified model of IR apertures (simple geometry, no showering!)
those particles lost ‘near’ the IP are saved @ scoring plane
input to step 2
step 2: full GEANT simulation of detector + near-IR (+- 8.5 m) see Mario Bondioli’s talk
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Architecture of background simulations (2)Architecture of background simulations (2)
Beam-beamBeam-beam full simulation of beam-beam tails impractical
focus on collimation studies optimize collimator placement/relocation (SM)
understand main characteristics of collimator secondaries (HB)
provide guidance for machine experiments
use Turtle machinery
Strategy considerationsStrategy considerations improve/update description of magnetic fields & apertures (TF, GC)
many fundamental features easier to understand at Turtle level first round of IR-upgrade design validation will be done this way (RB)
GEANT-level simulation essential (MB, GB, GC) to benchmark computations against data
to make sure there are no “alligators” hiding in new design
absolute background predictions always suspect even when benchmarked against experiments. However...
...ratios (new design /present machine) much more reliable.
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Lost-particle backgroundsLost-particle backgrounds
IP
Normalized to:- uniform pressure profile of 1 nT- 1 A beam current
IP
Coulomb scattering
in Arcs (y-plane)
e- Brems-strahlung
in last 26 m
(x-plane)
Vacuum pipe / mask apertures
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
The The “Background Zones” “Background Zones” reflect the reflect the combined effectcombined effect of.... of.... beam-line geometry (e.g. bends)
optics at the source and at the detector
aperture restrictions, both distantdistant (good!)(good!) & close-by (bad!)
X (
mm
) Zone 1
X (
mm
)
Zone 2
Zone 3
X (
mm
)
IP
Zone 4
Coulomb scattering
in Arcs
Bremmsstrahlung in field-free region
Bremmsstrahlung
Bremmsstrahlung
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Benchmarking of simulations: Benchmarking of simulations: comparing “comparing “predictedpredicted” and ” and measuredmeasured background levels background levels
Radiation patternsRadiation patterns for a given sensor type: independent of absolute calibration
among different sensors: compare fractional derivatives
Absolute background levelsAbsolute background levels sensor calibration!
absolute pressure profile !
Global consistency/sanity checksGlobal consistency/sanity checks operational experience in MCC
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Pressure-bump experiment: NEGPressure-bump experiment: NEG heating in BaBar straight heating in BaBar straight
Vacuum gauge reading (nT)
• Create localized P-bumps• NEG heating• DIPS on/off
• Measure response of background monitors
• Compare relative measured & simulated monitor response to validate Monte Carlo
Heated NEG at -8 m
0
5
10
15
20
FE-T
OP
FE-M
ID
FE-B
TM
FW
-TO
P
FW
-MID
FW
-BTM
BE-T
OP
BE-M
ID
BE-B
TM
BW
-TO
P
BW
-MID
BW
-BTM
Dose r
ate
in
pin
dio
de (
mR
/s)
MCVP7043, scaledDifferent
regions
==>
• diff. patterns• diff. abs. levels
Heated NEG at -60 m
0
0.1
0.2
0.3
0.4
0.5
FE-T
OP
FE-M
ID
FE-B
TM
FW
-TO
P
FW
-MID
FW
-BTM
BE-T
OP
BE-M
ID
BE-B
TM
BW
-TO
P
BW
-MID
BW
-BTM
Dose r
ate
in
pin
dio
de (
mR
/s)
MC
VP7011,scaled
Abort diode signal (mR/s)
W. Kozanecki PEP-II MAC Review, 9-11 Oct 03
Compare measured & predicted dose rates in HER:
• Monte Carlo lost-particle simulation (Turtle + BBSIM) validated by p-bump experiments
• Computed pressure profile in detector straight section (N2-equivalent, not vac.-gauge units!)
• Average ring pressure (from lifetime) for arcs & distant straights
UnderstandingUnderstanding the absolute level of the absolute level of HER backgrounds HER backgrounds (Sep 99)(Sep 99)
BW diode: measured vs. predicted background
0
5
10
15
20
0 0.1 0.2 0.3 0.4 0.5
HEB current (A)
Dose
rate
(m
R/s
)
MC pred
Msrd
Abort diodes: msrd/predictedHER background ratio (400 mA)
0.0
0.5
1.0
1.5
2.0
FE-T
OP
FE-M
ID
FE-B
TM
FW-T
OP
FW-M
ID
FW-B
TM
BE
-TO
P
BE
-MID
BE
-BTM
BW
-TO
P
BW
-MID
BW
-BTM
Msr
d/p
red r
ati
o
HER pressure model
Zone 1 2 3 4Range (m) 4 to 26 26 to 42 42 to 66 66-2200
P_base (nT) 0.5 0.5 0.5 1.43P_dyn (nT) 2.8 1.2 6.8 3.4