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Machine-Detector Interface (MDI) report Presented by M. Weaver, SLAC Operational issues radiation aborts radiation-dose and background monitoring Background characterization characterization experiments long-term projections & vulnerabilities Simulations G4 development status

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machine detector interface mdi report
Machine-Detector Interface (MDI) report

Presented by M. Weaver, SLAC

  • Operational issues
    • radiation aborts
    • radiation-dose and background monitoring
  • Background characterization
    • characterization experiments
    • long-term projections & vulnerabilities
  • Simulations
    • G4 development status
    • collimation studies
  • Other background developments
run 4 radiation abort history

B. Petersen

Run-4 radiation-abort history

<stable-beam trips> ~ 1.7/day (Sep 03-Jul 04)

<injection trips> ~ 0.6/day, 1-31 Jul 04

run 4 radiation abort history cont d

B. Petersen L. Piemontese / S. Foulkes

Run-4 radiation-abort history (cont’d)

Since 1 March 04

  • 172/332 = 52% sympathetic aborts
  • <rad. signature-only aborts> ~ 1/day ...but ~ ½ of these are probably sympathetic!
run 4 radiation dose history

B. Petersen

Run-4 radiation-dose history

HER trickle starts

HER trickle starts

increase probably instrumental

Vacuum valve ROD

Outgassing storms

slide5

LER injection-quality monitor

HER injection-quality monitor

Monitor using injection-gated triggers (1 ms x 15 ms)

Injection- & trickle- background history

EMC trigs (always on) LER trickle

DCH trigs LER trickle

EMC trigs (always on) HER trickle

DCH trigs HER trickle

slide6

Stored-beam background history

IDCH, msrd/pred

DCH current normalized to Jan 04 background data

04

HEB sensitive

20%

SVT ocp’cy @ f = 0 (LEB-sensitive)

DCH ocp’cy

10%

DCH L1 rate

Dead time

background sources in p e p ii
Background sources in PEP-II
  • Synchrotron radiation (this bkg negligible in PEP-II, but not in KEKB)
  • Beam-gas (bremsstrahlung + Coulomb)
    • HEB only: BHbg ~ IH * (pH0 + PHDyn * IH) Note: p0 = f(T) !
    • LEB only: BLbg ~ IL * (pL0 + PLDyn * IL) Note: p0 = f(T) !
    • beam-gas x- term: BLHbg ~ cLH * IL * IH (LEB+HEB, out of collision) (?)
  • Luminosity (radiative-Bhabha debris) – major concern as L 
    • BP ~ dP * L (strictly linear with L)
  • Beam-beam tails
    • from LER tails: BL, bb ~ IL * fL(xL,H+/-)
    • from HER tails: BH, bb ~ IH * fH(xL,H+/-)
  • Trickle background: BLi ,BHi(injected-beam quality/orbit + beam-beam)
  • Touschek: BLT(signature somewhat similar to bremstrahlung; so far small)
background characterization measurements

Data: Jan 04 (bef. therrmal outgassing crisis)

Background characterization measurements

Step 1: Beam-current scans

 single-beam terms

slide9

Total occupancy

  • HER single beam
  • LER single beam
  • Beam-beam term
  • present in all subdetectors
  • fluctuations, short - & long-term
  •  parametrization optimistic ?

Step 2: L & beam-beam terms

EMC cluster multiplicity

SVT occupancy (FL1 M01-f)

slide10

IDCH =

DCH

Step 3: Background Parametrizations

  • DCH example: total current & occupancies

Step 4: Background Extrapolations

60 L

Tracking efficiency drops by roughly 1% per 3% occupancy

PEP-II parameter projections

LER contribution very small

dch trg
DCH + TRG

When combined, higher trigger rates and long read-out time leads to unacceptable deadtime, driven by the DCH

3-step strategy

  • DCZ trigger (ready)
  • Waveform decimation (was implemented Summer ’04)
  • DCH DAQ upgrade (Summer 05)

+DCZ

slide12

Backward:

East

Top

West

Bottom

Background strongly - dependent

By 2007 predict 80% chip occupancy right in MID-plane

In layer 1, 10% will be above 20% occupancy

NOW

2004

2005

2006

2007

Forward:

East

Top

West

Bottom

Integrated dose will be more than 1 Mrad/year by 2007

SVT

Background now is ~75% HEB [LEB negligible (!)]

In 2007, it will be 50% HER, 50% L

  • It has been realized that in the SVT (but not in other subdetectors), a large fraction of the “Luminosity”background is most likely due to a HER-LER beam-gas X-term (but: similar extrap’ltn).
slide13
Given that future backgrounds have serious implications for detector performance, can anything be done to mitigate them?
  • Beam-gas backgrounds : manage residual gas pressure
  • Luminosity backgrounds : learn how to shield
  • Beam-beam backgrounds : learn how to collimate
  • How will the IR upgrade affect each of these?
  • Need to turn to simulation to improve our understanding and test mitigation strategies.
slide14

B Petersen N. Barlow M. Cristinziani/T. Glanzman J. Malcles

Jan 2004

Apr 2004

Feb 2002

SVT occupancy

Evolution of HER single-beam background, 2002-04

Jan 2004

EMC clusters

Apr 2004

Regularly activating NEGs & TSPs does help !

We should continue to take advantage of single beam opportunities to monitor the background.

slide15

109 GeV/s @ L = 1034

P. Roudeau, A. Stocchi, W.K. (preliminary)

Turtle Simulation :

e+ e- e+e-g Background

M. Sullivan

- z (m)

slide16

E

E

Fwd

q index

Bkwd

Electromagnetic shower debris or…

EMC default digi map: luminosity background (N. Barlow)

f index

W

slide17

Neutrons

Measurements appear consistent with Turtle radiative Bhabha simulation + GDR cross sections. Projected neutron rates may affect detector electronics – depends upon neutron energy spectrum.

J. Va’vra

slide18

Turtle Level Simulations

Beam-gas background from the HER (and LER)

R. Barlow

Where do scattered e-come from ?

Where do scattered e-hit?

slide19

B1

Q1

Q2

Q4

Q5

Geant4 Simulations

  • Determining detector response requires Geant level simulation
  • Beam line up to Q5 implemented in Geant4 simulation of BaBar detector
    • Considering re-implementation for robustness but carrying on w/o
  • Added e-N, g-N and neutron transport to physics processes
  • Detector background analyses integrated for data and simulation alike
  • First full G4 simulation output of 2004 geometry recently available
    • Single beam background comparisons look good (normalization?)
  • Post-2005 configuration (IR upgrade) Turtle not ready
large x emittance phase space plot

Beam-Beam Collimation Study

Large X-Emittance: Phase Space Plot

Starting x, x’ coordinates of particles lost along the beamline.

x’/x;

x/x

Z location where particles are lost. Colors correspond to upper plot.

Z [m]

IP

IP

slide21

+25.2 m from IP

LER

-25.2 m from IP

X [mm]

Results are based on an older LER deck (’98) with a tune of 0.57 (in x).

X [mm]

beam beam collimation study summary
Large-amplitude, horizontal b-tron tails originating at the IP can be effectively curtailed at + 25 m

...at least in the simulation

basically because of the phase-advance relationships reduce this to a one-turn problem, and assuming the impact on LEB lifetime remains manageable.

This study should be redone with the new LER deck & current x-tune of 0.51.

Vertical tails are not an issue (in the LER)

Pre-trickle collimator-scan data remain to be analyzed.

However, the +25 m collimator

can’t replace existing PR04 collimators in some corners of phase space

provides no protection against Coulomb scatters between PR04 and PR02

Both horizontal and vertical b-tron tails will be studied for the HER

Beam-beam collimation study: summary
slide23

Outgassing storms

  • Major background source: thermally-enhanced beam-gas
    • in incoming LER straight
      • Sensitive to LER current; several time constants in a time-dependent mix
      • Action: removed several NEGs and collimator jaws
      • Pressure at low currents may be worse now, but less susceptible to heating
      •  SVT dose + occupancy (E-MID); minor impact on dead time
    • in incoming HER straight
      • sensitive to HER current, very long time constants
      •  BaBar dead time + SVT occupancy (W-MID)
    • in (or very close to) the shared IR vacuum system
      • sensitive to both beam currents; at least 2 time constants
      • suspect: NEG + complicated IR ‘cavity’ (Q2L  Q2R) + HOM interference
      •  BaBar dead time + SVT occupancy (W-MID + E-MID)
  • HOM dominant heating mechanism
    • mostly long to very long time constants (30’-3 h): suggests low power
    • sensitive to: bunch pattern, VRF, collimator settings, Z(IP), hidden var’s
slide24

Continued BaBar involvement in Accelerator Performance Improvements (I)

  • Background analysis & mitigation [BP, MC/TG, NB, JM/JV, RM, LP, WK/GW]
  • Background simulations [RB, MB, GC, WL, SM, PR/AS, WK + SLAC (TF/GB)]
  • Fast monitoring of machine backgrounds  available online in PEP-II CS [MW, C’OG, AP, GDF,...]
    • injection & trickle quality variables: SVT, DCH, EMC
    • subdetector occupancies: SVT, DCH, EMC, DIRC
    • BaBar dead time
    • more operator-friendly displays (& controls) of radiation inhibits/aborts
  • BaBar-based machine diagnostics
    • time distribution of injection triggers [LP, BP, ...]
    • Online centroids & sizes of luminous region using BaBar mm,ee [C’OG, BV, AP, IN, MB,...]
slide25

BaBar involvement in Accelerator Performance Improvements (II)

  • Beam dynamics
    • beam-beam simulations [IN (Caltech), YC (Slac ARD), WK]
    • beam-beam experiments, monitoring of beam-beam performance [WK]
    • e, b*, sz measurements using mm, ee
  • Instrumentation
    • Gated camera: now operational in both in LER & HER [DD, Slac Exptl Grp C]
    • LER interferometer software [AO, Orsay]
    • Installation of an X-ray beam-size monitor for the LER [Caltech + LBL + SLAC]
    • SVTRAD sensor & electronics upgrade [BP et. al. (Stanford); MB/DK et. al. (Irvine) (initiated & funded by BaBar)]
    • CsI background sensors , n detectors & shielding [JV, Slac Exptl Grp B]
    • Forward end Fe shielding wall (may allow better collimation elsewhere)
summary i
Summary (I)
  • Stable-beam (genuine) radiation aborts are down to ~ 1/day
  • Injection backgrounds under control, expect even better in Run5
  • Stored-beam bgds (dose rate, data quality, dead time)
    • OK most of the time –watch for thermal outgassing, esp. HER
  • Background characterization experiments
    • Highly valuable in identifying the origin, magnitude & impact of single- & two-beam backgrounds – be opportunistic
    • Maintain a measure on the projected backgrounds – impacts detector remediation/upgrades with long lead times
  • G4 Simulation progressing; anticipate better understanding and correlation of sources with detector response
  • Collimation simulations can direct future background improvements
summary ii
Summary (II)
  • In the medium term (2005-07), the main vulnerabilities are
    • beam-gas backgrounds from HOM-related thermal outgassing as I+,-
    • high dead time associated with DCH data volume & trigger rates (addressed by DCH elx upgrade)
    • high occupancy and radiation ageing in the mid-plane of the SVT,
      • possibly leading to a local loss of tracking coverage.
      •  reduce the HER single-beam background back to 2002 levels (/1.5-2) ?
    • a high flux of ~ 1 MeV neutrons in the DCH (wire aging from large pulses, possibly also contributions to occupancy)
  • Background simulations
    • large investment in reviving/updating tools + rebuilding the group
    • ‘almost’ ready to evaluate backgrounds in IR upgrade
    • manpower limited
  • BaBar-based accelerator performance enhancement
    • common BaBar-PEPII diagnostics greatly improved, starting to pay off
    • very significant involvement of BaBarians in beam instrumentation & simulation
mdi abstracts submitted to pac05
MDI abstracts submitted to PAC05
  • Predicting PEP-II Accelerator-Induced Backgrounds Using TURTLE
    • R. Barlow, W. Dunwoodie, W. Kozanecki, S. Majewski, P. Roudeau, A. Stocchi , T. Fieguth & J. Va’vra
  • Modelling Lost-Particle Accelerator Backgrounds in PEP-II Using LPTURTLE
    • T. Fieguth, et al.
  • GEANT4-based Simulation Study of PEP-II Beam Backgrounds in the BaBar Detector at the SLAC B-Factory
    • W. Lockman, D. Aston, N. Barlow, N. Blount, M. Bondioli, G. Bower, G. Calderini, B. Campbell, M. Cristinziani, C. Edgar, W. Kozanecki, B. Petersen, S. Robertson, D. Strom, G. Wormser, D. Wright
  • Beam-induced Neutron Fluence in the PEP-II Interaction Region
    • G. Bower, W. Lockman, J. Va'vra, D. Wright
  • Measurement of the Vertical Emittance and beta Function at the PEP-II Interaction Point Using the BaBar Detector
    • J. M. Thompson & A. Roodman
  • Measurement of the Luminous-Region Profile at the PEP-II IP, and Application to e+/- Bunch-Length Determination
    • B.Viaud, W. Kozanecki, C. O’Grady, M. Weaver
  • Experimental Study of Crossing-Angle and Parasitic-Crossing Effects at the PEP-II e+e- Collider
    • W. Kozanecki, Y. Cai. I. Narsky, M. Sullivan & J. Seeman
slide29
Measurement of the Vertical Emittance and beta Function at the PEP-II Interaction Point Using the BaBar Detector
    • J. M. Thompson & A. Roodman
  • Measurement of the Luminous-Region Profile at the PEP-II IP, and Application to e+/- Bunch-Length Determination
    • B.Viaud, W. Kozanecki, C. O’Grady, M. Weaver
  • Experimental Study of Crossing-Angle and Parasitic-Crossing Effects at the PEP-II e+e- Collider
    • W. Kozanecki, Y. Cai. I. Narsky, M. Sullivan & J. Seeman