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Hall A Tungsten Calorimeter

Preliminary Mechanical Designand

Thermal Analysis

May 14, 2004

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Contents

• Objective & Requirements• Location• Mechanical Design• Thermal Analysis• Silver/Tungsten Comparisons• Assembly, Test & Installation• Cost Estimate• Schedule• Open Questions

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Objective & Requirements

• OBJECTIVE:– Produce a calorimeter for beam current

measurements in Hall A that meets or exceeds design specifications on schedule and within budget

• REQUIREMENTS:– Design must

• minimize heat leaks• support thermometry• contain heater(s) for calibration• have method of cooling for repeat measurements• be insertable due to invasive nature of calorimetric

measurement• fit in available Hall A beamline real estate• survive in high radiation environment

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257.22”

BCM

• Hall A Layout

• Super Harp Girder

- Locate Calorimeter between BCMs on girder

Location

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15”12.75”

• Real Estate Constraints– Plenty of room above the

girder– Primarily constrained by

distance from beamline to girder

Super harp girder cross-section

Hall A Beamline 1.5” Dia

Mechanical Design

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• The Slug

Volume = 3131.32 cm^3

BEAM

Mechanical Design

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– Desire a fully dense, machinable part with good thermal properties

– Pure tungsten shapes typically produced by powder met process (pressing and sintering followed by a extrusion or swaging operation to reduce porosity). Subsequent operations to reduce porosity are not practical for a part a large as ours.

– Density and machinability can be improved by adding small amounts of Ni and Cu (W,Ni,Cu 95:3.5:1.5) but thermal properties are less desirable.

– OSRAM/Sylvania produces a W,Cu 95:5 powder that will produce a very dense(~99%), homogenous, machinable part that has higher thermal conductivity than the above materials and still retains a high density. This is a unique process for making W:Cu composites that does not require infiltrating the Cu into a tungsten framework. Infiltrating would not be an option for a part as large as ours. This is the material of choice and has been used for the thermal analyses presented here.

* Thermal properties detailed later in the thermal analysis section

• The Slug (Con’t)

Mechanical Design

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• Three Position Actuation Scheme– Advances in compliant thermal interfaces that

improve contact conductance in vacuum at low contact pressures offer an opportunity to cool the slug by conduction rather than convection. The scheme proposed eliminates the need to embed or otherwise attach cooling tubes that could increase the heat loss from the slug and would complicate the thermal response due to non-homogeneous diffusion properties.

The three positions:• 1. Charging• 2. Equilibrating• 3. Cooling

Mechanical Design

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Mechanical Design

22.1”

40.2” Ø16.5”

11.8”

BEAM

Approximate Weight

450 Lbs

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• Mechanism

Mechanical Design

3 Position Pneumatic Cylinder

Guided Support & Feedthru Cross

Welded Bellows

Support & Guide Rod

Ball Bushing

Instrumentation & Power

Feedthrus

Turnbuckle

Slug Vertical Support Tube

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• Slug Support & Cooling Plate

Mechanical Design

Oversized ebeam/ horizontal support tube allows beam ops to continue when slug is equilibrating or cooling (i.e., position 2 or 3)

Socket set screws to support & align slug (contains ceramic insert to provide thermal and electrical isolation)

3 point mount to base of vessel to align cooling plate to slug flat

Cu Cooling plate covered with compliant thermal interface material

Cooling plate alignment base

Cooling plate thermal isolation

Slug support arms

Coupling to attach to vertical support tube

Opening in base of tube to route wires to slug

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• Compliant Thermal Interface– Consists of an array of aligned

7µm diameter carbon fibers– Each fiber spans the gap

between mating surfaces resulting in improved thermal performance over conventional particle filled pads

– High aspect ratio provides mechanical compliance (~.006” displacement at 15psi for .020” thk pad)

– Fibers can be directly attached to cooling plate using a thermally conductive epoxy or encapsulated in a polymeric base.

Mechanical Design

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• Vacuum Vessel

Mechanical Design

3 point mount to super harp girder

Ø 8” CF access port

Ø 10” CF port provides access to cooling plate

Ø 2.75” CF Chill water feedthru (jacketed to minimize heat transfer to vessel)

Ø 2.75” CF beamline port

Ø 16.5” CF

Ø 4.5” CF port for instrumentation feedthru

Vessel baseplate

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• Calorimeter on super harp girder looking downbeam

Mechanical Design

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Beam

Mechanical Design

• Calorimeter on super harp girder

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Thermal Analysis

• Design Considerations– Heat Loads

• Power I*E <= 5kW

– Need to understand…• Thermal Response Time • Heat Leaks

– Conductive through mounts and wires (TC’s, Faraday, and heater(s))

– Radiation exchange with surroundings• Cooldown Time

– Require ability to repeat measurements in ~ 30 minutes• Effect of heater(s) on the thermal response of the device

– Correlate calibration vs. ebeam run

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Thermal Analysis

• Thermal Modeling– For initial modeling, a 2d transient axis-symmetric implicit

finite difference (FD) model was written using Visual Basic for Applications in Excel

– Lumped mass model used for initial cooldown estimates – IDEAS TMG transient solver now available at Jlab was

used to check results from FD code and conduct more detailed analyses that more accurately capture the transient heat flow out of (and into) the slug. Future refinements will include radiation exchange and a heater model for comparisons between simulated calibration and ebeam runs. Analyses presented here use the FD code to capture the radiation losses.

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Thermal Analysis

• Material Properties

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• Finite Difference Thermal Model

– Decreased radius to match volume of actual slug to account for flat and entrance hole

– Conduction losses calculated at each time step. Heat flow based on assumption that T is linear thru the mounts.

– Radiation losses assume a two surface enclosure for each face of the slug (e.g., slug upbeam face only views Area1 of idealized chamber)

Thermal Analysis

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• Finite Difference Thermal Model Input Panel

*

* Kmount very small here to capture only rad losses

Thermal Analysis

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Upbeam Mounting Pins

(spaced 90° apart)

Downbeam Mounting Pins

(spaced 90° apart)

Faraday Wire

Downbeam TC Wires

(spaced 120° apart)

Upbeam TC Wires

(spaced 120° apart)

• IDEAS/TMG Model

– Took advantage of symmetry and modeled only half of the slug

– Mounting pins and wires modeled using beam elements

– Slug modeled using solid elements

– Wires are 8”Lg, mounts are 1”Lg

Thermal Analysis

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Thermal Analysis

• Initial and boundary conditions used for the simulations presented in the next several slides– Uniform initial temperature distribution of 0°C– The ends of the wires and mounts are fixed at 0°C– From time t=0s to t=48s 5kW of beam power is deposited

uniformly in a cylindrical volume 5mm in diameter that begins one radiation length into the slug at the base of the entrance hole and extends five radiation lengths into the slug

– At t=350s the slug is brought in contact with the cooling plate. Overall contact conductance of 1250W/m^2/K to a fixed -15°C (corresponds to a chill water temp of ~12°C)

– At t=1050s the slug is lifted from the cooling plate

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RTD Temperatures

-10.000

0.000

10.000

20.000

30.000

40.000

50.000

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600

Time [s]

Tem

p [K

]

Up Beam Upper RTD Up Beam Lower RTD Down Beam Lower RTD Down Beam Upper RTD

• IDEAS/TMG Thermal Model Results

Thermal Analysis

Beam off (t=48s)

Lift off cooling plate (t=1050s)

Measurement over/ begin cooldown (t=350s)

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• IDEAS/TMG Thermal Model Results

Thermal Analysis

Estimated Conductive Loss from RTD & Faraday Wires

-0.050

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Time [s]

Hea

t L

oss

[W

]

Up Beam Down Beam Faraday Total

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• IDEAS/TMG Thermal Model Results

Estimated Conductive Heat Loss from Mounts

-0.250

-0.150

-0.050

0.050

0.150

0.250

0.350

0.450

0.550

0.650

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Time [s]

Hea

t L

oss

[W

]

Up Beam Down Beam Total

Thermal Analysis

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• IDEAS/TMG Thermal Model Results

Estimated Conductive Heat Loss from Wires & Mounts

-0.400

-0.200

0.000

0.200

0.400

0.600

0.800

1.000

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600

Time [s]

Hea

t Lo

ss [W

]

Thermal Analysis

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• IDEAS/TMG Thermal Model Results

Estimated Integrated Heat Loss from Wires & Mounts

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0

25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

400

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Time [s]

Hea

t Lo

ss [J

]

Thermal Analysis

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• Finite Difference Thermal Model Results

Estimated Radiation Heat Loss

0.000

0.200

0.400

0.600

0.800

1.000

1.200

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375

Time [s]

Hea

t Lo

ss [W

]

Up Beam Face Down Beam Face Outer Face Total

Thermal Analysis

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• IDEAS/TMG & Finite Difference Thermal Model Results

Estimated TOTAL Heat Loss

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

1.600

1.800

2.000

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375

Time [s]

Hea

t Lo

ss [W

]

Thermal Analysis

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• IDEAS/TMG & Finite Difference Thermal Model Results

Estimated TOTAL Integrated Heat Loss

0

50

100

150

200

250

300

350

400

450

500

550

600

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350

Time [s]

Hea

t Lo

ss [J

]

Thermal Analysis

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• IDEAS/TMG Thermal Model Results Summary

Thermal Analysis

– Total energy deposited 48sec*5kW=240kJ– Total energy lost before taking measurement

=531J– This represents a loss of only ~.2%

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Silver/Tungsten Comparisons

• Time constants (using FD model):– Silver ~ 35sec (for 14cm diameter x 24cm Lg slug)– Tungsten ~ 39sec

Temperature Response Comparisons

0

5

10

15

20

25

30

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0 25 50 75 100 125 150 175 200 225 250 275 300 325 350

Time [s]

Do

wn

bea

m R

TD

Tem

p [K

]

Silver Tungsten

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Assembly, Test & Installation

• Plan to obtain samples of thermal

interface candidates and conduct outgassing, particulate, and thermal testing ASAP

• Will assemble and test the device outside of the Hall

• Expect minimal modifications to super harp girder to accommodate device

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Cost Estimate

• MECHANICAL Portion of Device– Mechanism………………………..$10k– Slug……..…………………………..$9.5k– Cooling Plate……………………..$5.6k– Vacuum Vessel…..................$11.3k

TOTAL = $36.4k

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Schedule

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Open Questions

• Will the thermal interface material perform as modeled?

• What effect does the heater(s) have on the thermal response and losses?

• What can be done to increase the heat transfer from the heater cartridge to the slug?