Beam Induced Backgrounds and Radiation at CDF

R.J. TesarekFermilab1/28/04

Initial Operational Problems

Low voltage power supply failures• 12 power supplies lost in single day (St. Catherine’s Day)

• catastrophic component failure

Physics backgrounds• Missing ET distributions

• High calorimeter occupancy

Radiation• Detector damage/lifetime

Silicon detector “incidents”/concerns• Beam related failures

> Work still in progress

CDF-II Detector (G-rated)

L.V. Power Supply Failures• Power Factor

Corrector Circuit

• Most failures were associated with high beam losses or misaligned beam pipe

> Power MOSFET SEB (radiation induced)

silicon in MOSFET sublimatedduring discharge through single

component

epoxy coveringfractured

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Single Event Burnout (SEB)

SEB Features• beam related

• damage at low doses

• depends on bias voltage

SEB cross section measurement

Solution (lower Vbias)• Factor of 50 reduction in radiation

sensitivity

• No failures in > 1 year operation

What about radiation? 10-12

10-11

10-10

10-9

10-8

10-7

10-6

400 600 800 1000 1200Vsd(V)

!S

EB (

cm

2 )

Vicor (CMS)

ASTEC (CDF/booster eval)

ASTEC (Indiana)

IRFPG50 (ASTEC replacement)

IRG4PH5OU (IGBT)

IRFBG20 (CAEN original)

BUH2M20AP (Bipolar)

designedmodified

operating voltage

} failed component

Test beam data, 20 MeV protons

Radiation Source?• Counter measurements show low beta quadrupoles form a

line source of charged particles.

• Power supply failure analysis shows largest problem on the west (proton) side of the collision hall.

antiprotonsprotons

CDF Detector (R-rated)

Collision Hall RadiationMeasure radiation in the collision hall using thermal luminescent dosimeters (TLDs).

• Ionizing radiation

• Low energy neutrons (thermal)

Measurements at 755 < Z < 775 cm

Radius (cm)D

os

e/L

um

ino

sit

y (

rad

/pb

-1)

0.03

0.04

0.05

0.06

0.07

0.08

0.090.1

0.2

0.3

0.4

200 300 400 500 600

D = Ar−α

r measured transverse to beam

K. Kordas, et al.Neutron energy measurements and simulations of radiation in progress.

W. Schmitt, L. Nicolas

Collision Hall Radiation Field

10-1

1

Z(cm)

X(cm)

Rdose2 (rad/pb

-1)

-1000

-800

-600

-400

-200

0

200

400

600

800

1000

-2000 -1500 -1000 -500 0 500 1000 1500 20000.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

Z(cm)

X(cm)

Rdose3/Rdose

2

-1000

-800

-600

-400

-200

0

200

400

600

800

1000

-2000 -1500 -1000 -500 0 500 1000 1500 2000

Radiation Field in the CDF collision hallRatio = Rshielding/Rno shieldingRi = Dose/

∫Ldt

Physics Backgrounds

• Jet triggers show peak at phi=0

• Missing ET triggers show peak at phi=pi

• Very energetic events

K. Maeshima, M. Albrow, J. Spalding, K. Terashi

Hot spots

MET > 35 GeV MET > 50 GeV

“Jet” Background EventsEvents show “track” in calorimeter

• High energy muon

• Beam “halo” hitting Roman pot detectors

Protons

Central Wall

PlugPlug

Wall

Calorimeter Schematic

Particle “tracks”

protons antiprotons

W Backgrounds

• W trigger requires Energy imbalance in calorimeters.

Trigger: Missing Et > 25 GeVmuon bremsstrahlung

peak/background ~ beam current

proton side

antiproton side

φ = π :

φ =nπ

2:

Plug BackgroundsGaps in shielding aligned with backgrounds

between torroid halfs"Fin" to plug 2" gap

Plug Calorimeter

Wall Calorimeter

2” gap

torroid steel

Run I Shielding

• Detector configuration different in Run II

• Run I detector “self shielded”

• Additional shielding abandoned (forward muon system de-scoped).

• Shielding installed surrounding beam line.

• Evaluation of shielding continues

Tevatron Losses and CDF Shield Configuration In Run I

~ 0 Track Chamber. Calorimeter.. Steel. Concrete Shield In Tevatron tunnel

RunllCDF Shielding Design for Run II

~ 0 Track Chamber. Calorimeter. Steel. Concrete Shield In Tevatron tunnel

"Snout" on Toroidshelps . M~on Systems

/Shield between

beamplpe' andMuon Systems

Steel betweentorolds shieldsIMU from beam pipe

Run I Shielding

Tevatron Losses and CDF Shield Configuration In Run I

~ 0 Track Chamber. Calorimeter.. Steel. Concrete Shield In Tevatron tunnel

RunllCDF Shielding Design for Run II

~ 0 Track Chamber. Calorimeter. Steel. Concrete Shield In Tevatron tunnel

"Snout" on Toroidshelps . M~on Systems

/Shield between

beamplpe' andMuon Systems

Steel betweentorolds shieldsIMU from beam pipe

Run II Shielding (beginning of run)

concretesteelcalorimeter

concretesteel

Measuring Losses/HaloBeam Losses all calculated in the same fashion• Detector signal in coincidence with beam passing the

detector plane.

• ACNET variables differ by detector/gating method.

• Gate on bunches and abort gaps.

"Lost Particle"

Proton Bunches

Gate

Detector

CDF

“Halo Particle”

Definitions:lost particles: close to beamhalo particles: far from beam

Beam Monitors!"#$#%&'(")*$(#%

IP

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CENTRAL

DETECTO

R

IMU

IMU

Beam Shower Counters (BSC)

Halo counters Halo counters

BSC counters: monitor beam losses and abort gap Halo counters: monitor beam halo and abort gap

After 11/03 After 11/03

Detectors

PMT

Lig

htp

ipe

fron

t fa

ce

2-3

/4"

BEAM PIPE 6

"

PMT

K.G

. 12

/98

9-3/4"

9-3/4"

3"

3"

scintillator

1"

2-1

/2"

lightpipe

FLANGE

2-5/16"

(at back)

066

040

054014

West Alcove floor

23.1 cm

59.1 cm

284 cm

Q3Quadrupole!Low

48.6 cm

45.7 cm

North

48 cm

PQ3

Halo Counters Beam Shower Counters

B0PHSM: beam haloB0PBSM: abort gap lossesB0PAGC: 2/4 coincidence abort gap losses

B0PLOS: proton losses (digital)LOSTP: proton losses (analog)B0MSC3: abort gap losses (E*W coincidence)

ACNET variables:

active area = 0.9 m2 active area = 77 cm2

Beam Halo Counters

CDF

ProtonsAntiprotons

quadrupole

separator

dipole

Roman pots

collimatorCDF

Typical Store

QuantityRate(kHz)

Limit(kHz) comment

P Losses 2 - 15 25 chambers trip on over currentPbar Losses 0.1 - 2.0 25 chambers trip on over currentP Halo 200 - 1000 -Pbar Halo 2 - 50 -

Abort Gap Losses 2 - 12 15 avoid dirty abort (silicon damage)

L1 Trigger 0.1-0.5 two track trigger (~1 mbarn)

Losses and Halo:

Beam Parameters:Protons: 5000 - 9000 109 particlesAntiprotons: 100-1500 109 particlesLuminosity: 10 - 50 10

30cm

−2s−1

Note: All number are taken after scraping and HEP is declared.

Monitor Experience“Typical good store”

proton halo

proton losses

proton abort gap

proton beam current

Beam CollimationBackground reduction at work

proton haloproton losses

E0 collimator

proton beam current

Halo Reduction

• Vacuum problems identified in 2m long straight section of Tevatron (F sector)

• Improved vacuum (TeV wide)

• Commissioning of collimators to reduce halo

> Physics backgrounds reduced by ~40% C:B0PHSM

T:F1IP1A

PRESSURE

STORE 1207

PROTON HALO

175 mins

R. Moore, V. Shiltsev,N.Mokhov, A. Drozhdin

Radiation Measurements• TLDs installed in tracking volume

• 3 exposure periods

• 0.06 pbarn (p-loss dominated)

• 12.3 pbarn

• 167 pbarn 0

0.05

0.1

0.15

D

ose (

Gy) Feb 25,2001 - May 02,2001

SVX spacetube (r = 18cm)

ISL spacetube (r = 35cm)

0

2

4

D

ose (

Gy) May 02,2001 - Oct 18,2001

SVX spacetube (r = 18cm)

ISL spacetube (r = 35cm)

0

20

40

60

-200 -150 -100 -50 0 50 100 150 200Z(cm)

D

ose (

Gy) Oct 18,2001 - Jan 13,2003

SVX spacetube (r = 18cm)

ISL spacetube (r = 35cm)

Fig. 2. Ionizing radiation dose as a function of ; protons travel in thedirection. The top, middle and bottom plots correspond to the three exposureperiods (see Table I). Curves on the plots serve only to guide the eye betweenmeasurements at the same radius from the beam.

the closed points in Figure 4. The shaded band in the figure

represents the systematic uncertainty on the loss measurement.

Good agreement is seen between the collision dose rate sep-

arated from the first two periods and the dose rate (raw dose

normalized by the luminosity) in the third period as indicated by

the open points. One may estimate the fraction of the ionizing

radiation from collisions by dividing the raw dose observed in

a given period by the product of the collision dose rate and the

luminosity. Using this prescription, we find collisions account

for 20%, 82% and 91% of the ionizing radiation for the first,

second and third exposure periods, respectively. Qualitatively,

the increase in the fraction of radiation from collisions improves

with the beam conditions. We note here that a substantial period

of accelerator studies and beam tuning occurred before the

installation of the silicon detectors and radiation monitors.

V. MODELING

In order to predict the radiation seen by various detector

components, one needs a model to extrapolate the above

measurements to device locations. We use a model based on

previous experience from silicon damage profiles measured in

the CDF detector [2]. This model assumes that the radiation

field surrounding the interaction region is cylindrically sym-

0

0.02

0.04

0.06

0.08

0.1

0.12

Ne

utr

on

do

se

(G

y)

Feb - May 2001 Exposure

r = 35 cm (ISL space tube)

r = 18 cm (SVX space tube)

0

0.5

1

1.5

2

2.5

3

-200 -150 -100 -50 0 50 100 150 200Z (cm)

Ne

utr

on

dose

(G

y)

May - Oct 2001 Exposure

r = 35 cm (ISL space tube)

r = 18 cm (SVX space tube)

Fig. 3. Neutron radiation dose as a function of ; protons travel in thedirection. The top and bottom plots correspond to the first two exposure

periods (see Table I). Curves on the plots serve only to guide the eye betweenmeasurements at the same radius from the beam.

metric and follows a power law in , where is the distance

from the beam axis. We fit the data at each location to the

functional form:

(1)

where is an absolute normalization, is the power law

and is the beam-detector relative offset. The normal-

ization and power law results are summarized as a function

of in Figures 5 and 6 for the collision and proton loss

components of the ionizing radiation field, respectively. We

see good agreement between the collision component separated

from the first two periods and the data of the third period

for the region of the tracking volume occupied by the silicon

detectors ( cm). We find the value of for the

collision component ranges 1.5 – 1.6 in this region while the

loss component in the same region ranges 1.7 – 2.0.

Ultimately, one wishes to compare the radiation field mea-

surements with the damage observed in the detectors. The

radiation field predicted by the TLD measurements can be

tested by comparing particle fluxes calculated from leakage

current measurements in the low radius silicon detectors. The

particle flux is calculated by measuring the slope in the silicon

leakage current as a function of accelerator delivered luminos-

ity. The rate of increase in the current is corrected from C

to C and a damage factor of . The

dose rate in the TLDs is converted to a particle flux using the

conversion factor of minimum ionizing particles

(MIP)/rad and dividing the result by the luminosity for the

antiprotonsprotons

0.06 pbarn−1

12.3 pbarn−1

167 pbarn−1

-400

-300

-200

-100

0

100

200

300

400

-400 -300 -200 -100 0 100 200 300 400

Z (cm)

X (

cm

)

CCALCCAL

PCALPCAL

WCAL WCAL

COT

CLCBeamPipe

Silicon Support

Silicon

-1

-1

-1

Summary

• Halo/Losses contribute to operational problems• High chamber currents• Damage to rad-soft equipment•

• Accelerator problems contribute to backgrounds• Good vacuum important• Good collimation system essential•

• Monitor beam conditions• Dedicated monitors of accelerator operation

References (Incomplete List)• General:

• http://ncdf67.fnal.gov/~tesarek

• http://www-cdfonline.fnal.gov/acnet/ACNET_beamquality.html

• CDF Instrumentation:

• M.K. Karagoz-Unel, R.J. Tesarek, Nucl. Instr. and Meth., A506 (2003) 7-19.

• A.Bhatti, et al., CDF internal note, CDF 5247.

• D. Acosta, et al., Nucl. Instr. and Meth., A494 (2002) 57-62.

• Beam Halo and Collimation:

• A. Drozhdin, et al., Proceedings: Particle Accelerator Conference(PAC03), Portland, OR, 12-16 May 2003.

• L.Y. Nicolas, N.V. Mokhov, Fermilab Technical Memo: FERMILAB-TM-2214 June (2003).

• Radiation:

• D. Amidei, et al., Nucl. Instr. and Meth., A320 (1994) 73.

• S. d’Auria, et al., Nucl. Instr. and Meth., A513 (2003) 89-93.

• K. Kordas, et al., Proceedings: IEEE-NSS/MIC Conference, Portland, OR, November 19-25 (2003).

• R.J. Tesarek, et al., Proceedings: IEEE-NSS/MIC Conference, Portland, OR, November 19-25 (2003).