review vacuum final

8/14/2019 Review Vacuum Final

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BTEV PIXEL DETECTOR INTERNAL REVIEW 20-NOV-01 1

THE BTEV VACUUM SYSTEMCHALLENGE

Requirements for dynamic aperture andminimal mass leads to pixel elements in

vacuum Large Gas Loads

Confined and Congested Space

Operating in Dipole Magnetic Field

Pressure requirements: minimize background toexperiment from beam-gas interactions

Tolerant to Pressure Upsets


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RESOURCES

EngineeringVacuum System Mayling WongVacuum Vessel Alex Toukhtarov

Testing and PrototypingPAB Cary KendzioraLab 7

Technical Guidance from Mauro Marinelli

INFN Genova


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BTEV VACUUM SYSTEM

The BTeV Vacuum System, includingbeam pipes and pixel detectorvacuum, has been modeled to betterunderstand the pressure distribution System specifications

Layout

Model Input Results

Measured Gas Load

10% Mock-Up


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SYSTEM SPECIFICATIONS

< 1e-7 torr in system betweenRICH detectors

Determine the gas load in systemand the composition of the gas

Determine pumping requirements


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VACUUM SYSTEM LAYOUT

Ion Pump80 L/sec

RICH beamPipe 1.92 ID

Forward beamPipe 1.0 ID

Clean side:Pump 100-1000 L/sec

Dirty side:

Cryopumps 800 L/secWater Pumps 10,000+ L/sec


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DETAILS OF PIXEL DETECTOR

VACUUM Thin metal

membrane isolatingpixels from beam

line

Thin membrane = RFshield

RF shield will

probably not be aperfect seal


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MODEL INPUTS

Geometry of vacuum systemBeam pipesClean side of RF shield beam lineDirty side of RF shield pixel detector

Pumpingspeeds

Total gas load in beam pipes due to

outgassing1e-10 torr-L/cm^2/sec (clean,unbaked aluminum pipe)


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MODEL INPUTS (CONTD)

Total gas load in pixel detector due tooutgassing Initial estimate 1.4 e-2 torr-L/sec (caution

from Mauro: It may require lowering the

temperature of 90% of the detector tocryogenic temperatures to get the gas loadthis low)

Based on current measurements 1.5 e-3

torr-L/sec (Caution from Mauro: smallsample size may effect accuracy)

Apertures in RF shield


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RESULTS

Pressure Distribution in BTeV Vaccum System

1.00E-09

1.00E-08

1.00E-07

1.00E-06

-10 -5 0 5 10

Distance from C0 (m)

Pressure(torr)

Pixel gas load 1.5e-3 torr-L/s

Pixel gas load 1.4e-2 torr-L/s

Pumps:

- Beam pipe ion pump 80 L/sec

- "Clean volume" pump 50 L/sec

- "Dirty volume" pump 800 L/sec

Aperture in RF shield: 0.5 cm dia.

Inside RF shield, max. pressure:

- Gas load 1.5e-3 torr-L/sec:

1.56e-5 torr

- Gas load 1.4e-2 torr-L/sec

1.45e-4 torr


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GAS LOAD MEASUREMENTPROCEDURE

Treat sample by bakingand/or cleaning w/ alcohol

Bake empty stainless steelvacuum chamber for 3 days

After cooled, place sample

into chamber

Pump for 3-10 days

Measure rate-of-rise eachday

Record RGA readingperiodically to determinegas composition


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1.00E-11

1.00E-10

1.00E-09

1.00E-08

1.00E-07

1.00E-06

0.0 50.0 100.0 150.0 200.0 250.0 300.0

Time (hr)

O

utgassingRate(tor

r-L/s/cm^2)

Glassy c.f. tubes- 1stGlassy c.f. tubes- 2ndHDI

Circuit boards

SS chamber

Carbon fiberpanel

Total surface area for each sample:

- Vacuum chamber: 1731 cm 2

- Glassy c. f. tubes: 84 cm^2

- HDI: 756 cm^2

- Circuit boards: 773 cm 2

- Carbon fiber panels: 380 cm^2

MEASURED OUTGASSING RATES


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MEASURED GAS LOADS

1.00E-08

1.00E-07

1.00E-06

1.00E-05

0.0 50.0 100.0 150.0 200.0 250.0 300.0

Time (hr)

Gasload(torr-L

/sec)

Fuzzy carbon - 1st run

Fuzzy carbon - 2nd run

Bump bonded chips

Bump bonded chips - solder

Overall dimensions:

Fuzzy carbon:

5.25"x0.31"x0.75"

Bump bonded chip:

0.5"x0.32"

Total number of chips:

6 indium bonded chips

6 soldered chips


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PIXEL VACUUM (DIRTY SIDE)GAS LOADS

Component Material

Est. Outgassing

Rate (torr-L-

sec^-1-cm^-2)

Est. Gas

Load (torr-

L-sec^-1)

Meas.Outgassing Rate

(torr-L-sec^-1-

cm^-2)

gas load

(torr-L-

sec^-1)

pixel vessel inner wall aluminum 1.00E-10 4.08E-06 4.08E-06

silicon sensor / ROC

ass'y

indium or lead-tin

bump bond 4.00E-09 7.02E-05 3.50E-05

plane (coupon) fuzzy carbon 1.08E-04

plane support structure carbon fiber 7.50E-08 6.29E-03 1.19E-09 9.98E-05

cooling manifold glassy c.f. 7.50E-08 4.62E-04 1.03E-08 6.35E-05

coupon to main cooling plastic 2.90E-07 9.54E-04 9.54E-04

wire bonds aluminum 1.00E-10

HDI kapton 7.50E-08 5.57E-03 8.85E-10 6.57E-05

Circuit boards G-10+elec cmpts 1.00E-08 2.12E-04 5.30E-09 1.12E-04

Beryllium coupon beryllium 1.58E-13 3.45E-09 3.45E-09

RF shielding aluminum 1.00E-10 1.77E-07 1.77E-07adhesive bonding Hysol epoxy 7.99E-09

Caution from Mauro: It may require lowering the temperature of 90% of the detectorto cryogenic temperatures to get the gas load this low


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MEASURE GAS LOAD FROM

MOCK-UP OF PIXEL DETECTOR Assembly that comprises

10% of the total pixeldetector

Includes assemblyfeatures (virtual leaks,adhesives)

Will include cryopanels

Good test of temperature

effects on gas load


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CURRENT DESIGN DIRECTION

Lower the gas load by cooling as much of thepixel detector assembly as possible tocryogenic temperatures

Add in-situ water pumps (cryo panels) insidevacuum vessel.

Develop a seal at the ends of RF shield thathas a conductance less than 1/10 of thepumping speed on the clean side of the RFshield


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FUTURE PLANS

Measure gas loads and compositionContinue long-term gas load measurements

Continue setting up 10% mock-up

Investigate effect of lowering the entire Pixel

Detector to cryogenic temperatures

Investigate pump characteristics (speed andcapacity)

Conduct RF shield mechanical tests

Work with Mauro on developing and verifyingdesign of BTeV vacuum system

review vacuum final

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