Machine Background Status & issues in BaBar/PEP-II

W. Kozanecki BBBTF meeting, 27 (27) May 04

Background sourcesBackground sources

Characterization experimentsCharacterization experiments

Long-term projections & vulnerabilitiesLong-term projections & vulnerabilities

Machine Background Status & issues Machine Background Status & issues in BaBar/PEP-IIin BaBar/PEP-II

W. Kozanecki, CEA-Saclay


Background sources in PBackground sources in PEEP-IIP-II

Synchrotron radiation Synchrotron radiation (this bkg negligible in PEP-II)

Beam-gas (bremsstrahlung + Coulomb)Beam-gas (bremsstrahlung + Coulomb)

HEB only: BHbg ~ IH * (pH0 + PH

Dyn * IH) Note: p0 = f(T) !

LEB only: BLbg ~ IL * (pL0 + PL

Dyn * IL) Note: p0 = f(T) !

beam-gas x- term: BLHbg ~ cLH * IL * IH (LEB+HEB, out of collision) (?)

Luminosity (radiative-Bhabha debris) – Luminosity (radiative-Bhabha debris) – major concern as L major concern as L BP ~ dP * L (strictly linear with L)

Beam-beam tailsBeam-beam tails

from LER tails: BL, bb ~ IL * fL(L,H +/-)

from HER tails: BH, bb ~ IH * fH(L,H +/-)

Trickle background: BTrickle background: BLi Li ,, BBHiHi (injected-beam quality/orbit + beam-beam)

Touschek: BTouschek: BLTLT (signature somewhat similar to bremsstrahlung; so far small)


Background characterization measurementsBackground characterization measurements

Step 1: Step 1: Beam-current scansBeam-current scans single-beam termssingle-beam terms

Data: Jan 04 (bef. therrmal outgassing crisis)


SVT occupancy (FL1 M01-)

EMC cluster multiplicity

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

Step 2: L & beam-beam termsStep 2: L & beam-beam terms

Total occupancy

- HER single beam

- LER single beam


Step 3: Background ParametrizationsStep 3: Background Parametrizations

DCH example: total current & occupancies

Step 4: Background ExtrapolationsStep 4: Background Extrapolations

IDCH =

HER LER LuminosityNOW 1.2 A 1.9 A2004 1.6 A 2.7 A2005 1.8 A 3.6 A2006 2.0 A 3.6 A2007 2.2 A 4.5 A

7.2x1033 cm-2s-1

12.1x1033 cm-2s-1

18.2x1033 cm-2s-1

23.0x1033 cm-2s-1

33.0x1033 cm-2s-1

PEP-II parameter projections

Tracking efficiency drops by roughly 1% per 3% occupancy

DCHDCH

LER contribution very small

60 L


EMCEMC

# of crystals used in cluster finding

Looked at number of crystals with any/significant energy & clusters

Small quadratic term from single beam data

Currently physics events have ~110 digis and 8 clustersLong term impact on physics analysis not clear yet


32.5

2 1.51

0.5

LER Radiative Bhabhas

-7.5 -5 -2.5 0 2.5 5 7.5

0

10

20

30

-10

-20

-30

m

cm

M. SullivanFeb. 8, 2004API88k3_R5_RADBHA_TOT_7_5M

3.1 G

eV

3.1 G

eV

9 GeV

9 GeV

Luminosity background Luminosity background ee+ + ee-- e e++ ee--

• elm shower debris

• neutrons!

• no contribution from coasting HEB or LEB

• may dominate DCH, DIRC rate


Neutron BackgroundNeutron Background

Effort underway to measure neutron background in BaBar

BF3 counter installed on fwd Q4

Sees large rate (>10 kHz) during colliding beams, not single beam

Rate only seen with polyethylene moderator ~1 MeV neutrons

Neutrons thought to be from radiative Bhabhas hitting

Q2 septum maskand inside support tube

- Shielding of BaBar is being investigated


32.5

2 1.51

0.5

LER Radiative Bhabhas

-7.5 -5 -2.5 0 2.5 5 7.5

0

10

20

30

-10

-20

-30

m

cm

M. SullivanFeb. 8, 2004API88k3_R5_RADBHA_TOT_7_5M

3.1 G

eV

3.1 G

eV

9 GeV

9 GeV

EMC default digi map: luminosity

background (N. Barlow)

W

Fwd Bkwdindex

EE

in

dex


DCH + TRGDCH + TRG

When combined with higher trigger rates, long read-out time leads to

unacceptable deadtime.A major DCH elx upgrade

is now in progress.


It has recently 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-LERLER beam-gas X-term (but: similar extrap’ltn).

the HER single-beam background in Jan 04 is about 2x what it was in 2002 improve?

SVTSVT Yearly dose will be more than 1 Mrad/year by 2007

Backward:

Forward:

TopEast West Bottom

TopEast West BottomN

OW

2004

2005

2006

2007

Background now is ~75% HEB

[LEB negligible (!)]

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

Background strongly - dependent

By 2007 predict 80% occupancy right in

MID-plane

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


HEB current scanHEB current scan

LER X spot size

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

0 0.2 0.4 0.6 0.8 1

HER bunch current (mA/b)

Sp

ot

size

(m

m)

LEB only = 1.23

LER Y spot size

0.30

0.35

0.40

0.45

0 0.2 0.4 0.6 0.8 1

HER bunch current (mA/b)

Sp

ot

size

(m

m)

LEB only = .337

LEB scan: beam currents

0

500

1000

1500

2000

2500

40000 42000 44000 46000 48000 50000 52000

Time (sec)

Bea

m c

urr

ent

(mA

)

I_LER

I_HER

Luminosity/bunch

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Bunch current product (mA 2/B^2)

L/b

un

ch (

10^

30)

Data: 27 Jan 04


HEB scan: evidence for Touschek & beam-beam backgroundHEB scan: evidence for Touschek & beam-beam background

LER Betatron collimators (x)

0

1000

2000

3000

4000

5000

6000

0 200 400 600 800 1000 1200 1400

HER current (mA)

BL

M c

ou

nts

L_XCOL1

HER Betatron collimators (x)

0

50

100

150

200

250

300

350

400

0 200 400 600 800 1000 1200 1400

HER current (mA)

BL

M c

ou

nts

H_XCOL1

HER Betatron collimators (y)

0

100

200

300

400

500

600

700

800

900

1000

0 200 400 600 800 1000 1200 1400

HER current (mA)

BL

M c

ou

nts

H_YCOL1

LER Betatron collimators (y)

0

10000

20000

30000

40000

50000

60000

70000

0 200 400 600 800 1000 1200 1400

HER current (mA)

BL

M c

ou

nts

L_YCOL2


New (?) major background source:New (?) major background source: thermally thermally-enhanced -enhanced beam-gasbeam-gas

in incoming LER straight (exacerbated by NEG activation; now limits Ib)

sensitive to LER current; several time constants in a time-dependent mix

suspect: NEGs, ion pumps, collimator jaws, misc. vac. pipe secs

SVT dose + occupancy (E-MID); minor impact on dead time

in incoming HER straight (triggered the NEG activation; now limits Ib)

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 (now limits Ib )

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 mechanismHOM 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

Many “??” Many “??” (minor, inocuous changes large effects, good or bad) detailed analysis by GW

Outgassing storms (April 04)Outgassing storms (April 04)


Thermal time constantsThermal time constants

VGCC2187 (HER sensitive)

BW diamond [+ BBR dead time] (HEB sensitive)

VGCC3027 (incoming

LEB)

BE diamond (LEB sensitive)

LER current

12 hours

A potential limitation A potential limitation for run 5!for run 5!


HOM interference in IRHOM interference in IR

VGCC3027 (incoming

LEB)

VGCC2187 (HER sensitive)

BE diamond (LEB sensitive)

BW diamond (HEB

sensitive)

Collision phase = [t(e-) - t(e+)]IP

<ZIP> (BaBar)

Data: 13 Apr 04


Thermal outgasssing now limits the beam currentThermal outgasssing now limits the beam current

VGCC3027 (nT, incoming LEB)

VGCC2187 (nT, HEB side)

HER current

LER current

BE diamond (mR/s)

Babar dead time (%)


Summary (I)Summary (I)

TrickleTrickle injection injection is a major success in terms of improving

machine stability + abort frequency integrated L

overall injection quality

accumulated SVT dose

The associated detector backgrounds appear largely negligible (most – but not all – of the time)

Improved understandingImproved understanding of background & abort sources of background & abort sources genuine radiation aborts down to < 1 /day

clear & reproducible correlations between diamond dose rates, on-line SVT occupancies, dead time, and pressure measurements in incoming HER & LER straights

“lumi [background] is [really due to] lumi”! (except in the SVT – maybe)

Stored-beam backgroundsStored-beam backgrounds (dose rate, data quality, dead time) (dose rate, data quality, dead time) OK most of the time (& better w/ trickle) until recently

thermal outgassing now limits beam currents (primarily in the HER)


Summary (II)Summary (II)

Background Background characterization experiments characterization experiments were highly valuable in identifying the origin, magnitude & impact of

single- & two-beam backgrounds.

On the long term, the dominant backgrounds are expected to be, in order of decreasing importance:

radiative-Bhabha debris (all subdetectors), incl. a significant neutron flux

HER beam-gas (SVT, TRG), especially that due to thermal outgassing

beam-beam tails & their fluctuations (DCH, EMC, TRG, IFR wall!)

In the medium term (In the medium term (2005-072005-07), the ), the main vulnerabilitiesmain vulnerabilities are are beam-gas backgrounds from HOM-related thermal outgassing as I+,- high dead time associated with growing data volume & trigger rates

[Mainly HER beam-gas (TRG, SVT) & radiative-Bhabha debris (DCH)]

high occupancy and radiation ageing in the mid-plane of the SVT local loss of tracking coverage (?)

closely monitor the HER single-beam background & keep it similar to 2002 levels

high n flux (~ 1 MeV) correlates with L, some spikes is it an issue?


Spare slidesSpare slides


Run-4 radiation-abort historyRun-4 radiation-abort historyB. Petersen L.Piemontese

• ~ 60% of stable-beam radiation aborts “sympathetic”

• 2/19 – 4/29: < 0.9 (genuine) rad. aborts/day (out of ~7 total avrg)


Stored-beam background historyStored-beam background history

SVT ocp’cy @ = (HEB-sensitive)

SVT ocp’cy @ = (LEB-sensitive)

20% 20%

DCH current normalized to Jan 04 background data

I DC

H, m

srd

/pre

d

10%

04


Evolution of HER single-beam background, 2002-04Evolution of HER single-beam background, 2002-04B Petersen N. Barlow

M. Cristinziani/T. Glanzman J. Malcles

Jan 2004

Feb 2002

Apr 2004

DC

H c

urr

ent

(A

)

HER current (A)

Jan 2004

Apr 2004

Feb 2002Feb 2002

SVT occupancy

DCH current

Jan 2004EMC clusters

Apr 2004


SVTSVT: projected integrated dose: projected integrated dose

Dose projections assume negligible injection background

Implies replacement of mid-plane modules during 2005 shutdown


DCH current vs. Luminosity DCH current vs. Luminosity during a X scan (all currents during a X scan (all currents

constant)constant)

DC

H c

urr

ent

(mic

roA

)

Luminosity (1E33)


DCH/TRG background extrapolationsDCH/TRG background extrapolations

• HER single-beam & lumi lumi ((bkgbkg + + physicsphysics)) terms dominate

• Trickle: only average shown. Must be able to accomodate large fluctuations.

• Beam-beam: only best case shown. Data taken since then show beam-beam can easily be 2 x larger – not counting short-term fluctuations.

• LER single beamLER single beam: small (mostly beam-gas), no fluctuations expected


Time evolution of the thermal outgassing backgroundTime evolution of the thermal outgassing background

The The different time dependenciesdifferent time dependencies of the of the pressure readings allow to fit the pressure readings allow to fit the measured background level (BE measured background level (BE diamond) as a linear combination of 4 diamond) as a linear combination of 4 LER Pumps, on a LER Pumps, on a fill by fill basisfill by fill basis

The 4 pumps are located in the The 4 pumps are located in the incoming LER straight and all exhibit incoming LER straight and all exhibit HOM-induced thermal outgassing (e.g. HOM-induced thermal outgassing (e.g. change of pressure associated with change of pressure associated with change of bunch length)change of bunch length)

A very satisfactory A very satisfactory description of the description of the background was obtained in all casesbackground was obtained in all cases

The The sensitivity coefficientssensitivity coefficients for each for each pump were then extracted. They pump were then extracted. They represent the Nrepresent the N22-equivalent pressure -equivalent pressure integral with the same time integral with the same time dependence as the pump reading.dependence as the pump reading.

Fill March 28, 12pm-3 pm

0 3 h1 2

Data points

VP3044

VGCC3027

Fit

VP3147

End of injection

mR

ad/s


Evolution of the sensitivity coefficients (Apr 04 outgassing storms)Evolution of the sensitivity coefficients (Apr 04 outgassing storms)

The coefficients are The coefficients are normalizednormalized to to their pre-NEG activation values , their pre-NEG activation values , indicated by the red line (1 point per indicated by the red line (1 point per long fill)long fill)

The The backgroundbackground problem was problem was notnot related to an related to an increaseincrease in in locallocal pressure reading (at the pump) but pressure reading (at the pump) but to a to a huge increasehuge increase in background in background sensitivitysensitivity

The problem was solved The problem was solved (serendipitously) by:(serendipitously) by:

continued processing

opening collimator jaw(s)

changing in bunch pattern

These changes had different actions on the various background drivers

VP3044 VGCC3027

Days in March (April 1 = day 32)

10

200


Mismatch (x 10-100) betw. time evolution of Mismatch (x 10-100) betw. time evolution of msrd pmsrd p and of and of bkgdbkgd

BE diamond (LEB

sensitive)

NE

G

actv

td

VGCC3027 (incoming

LEB)

NE

G

actv

td

BW diamond (HEB sensitive)

NE

G

actv

td

VGCC2187 (HER

sensitive)

NE

G

actv

td

demonstrated by detailed analysis of local pressure contributions to background signals


NE

G a

ctvt

d

NE

G a

ctvt

d

NE

G a

ctvt

d

NE

G a

ctvt

d

Large variety of processing times, mechanisms, & bkg sensitivitiesLarge variety of processing times, mechanisms, & bkg sensitivities


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


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

Machine Background Status & issues in BaBar/PEP-II

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