Solid Target Studies for NFSolid Target Studies for NF

Rob EdgecockRob Edgecock

On behalf of:On behalf of:

J.Back, R.Bennett, S.Gray, J.Back, R.Bennett, S.Gray, A.McFarland, P.Loveridge & A.McFarland, P.Loveridge &

G.SkoroG.Skoro

Tungsten wire Tungsten wire at 2000Kat 2000K

ReminderReminder

• Solid means

tungsten bars, each ~2x20cm

150-200 bars

changed between beam pulses

cooled radiatively or possibly by helium/water

• Why?

lots of experience world-wide & safer

already have a license at RAL

• Issues for solids:

shock – original show-stopper

radiation damage

target change

• Focus has been on shock - but now moving on

ShockShock

• Was solid show-stopper: one of main reasons for liquids

• Impossible to lifetime test with proton beam, so

60kV, 8kA PSU, 100ns rise time

Aims: measure lifetimevalidate LSDyna modelunderstand W behaviour

Lifetime/fatigue tests resultsLifetime/fatigue tests results I, II, III –> ‘chronology’.I, II, III –> ‘chronology’.We have got better with We have got better with the tests over time the tests over time (better clamping of the (better clamping of the wire; better wire; better understanding of ‘violin understanding of ‘violin modes’ –> better modes’ –> better alignment of the wire)alignment of the wire)

SEM imagingSEM imagingBegbrokeNano, Oxford MaterialsBegbrokeNano, Oxford Materials

Characterisation ServicesCharacterisation Services

The aim to observe any surface The aim to observe any surface damage which might indicate the damage which might indicate the presence of thermal fatiguepresence of thermal fatigue

Results: inconclusiveResults: inconclusive

More than sufficient lifetime More than sufficient lifetime demonstrated:demonstrated:

> 10 years for 2cm diameter > 10 years for 2cm diameter targettarget

> 20 years for 3cm diameter > 20 years for 3cm diameter targettarget

Focus now:Focus now:

Measure stress;Measure stress;

Confirm modelling.Confirm modelling.

Better at lower temperature!Better at lower temperature!

200 200 targetstargets

Laser Doppler VibrometerLaser Doppler Vibrometer

• VISAR

Mis-informed that VISAR required at high temp

Large irreducible noise in our frequency range

Took a long time to get any (poor) results

• LDV

Much, much, much, ................. better than VISAR

Works to >2300K

Used to measure wire surface velocity

Frequency analysis used to extract results

Compared with LSDynaother measurements

Laser Doppler VibrometerLaser Doppler Vibrometer

• Longitudinal

Bigger oscillations: ~μm; lower frequency: ~20kHz

But.....temperature variation along wire

Wire fixed at one end, constrained at other

Oscillations more difficult to understand

• Radial

Smaller oscillations: 50-100nm; higher frequency: ~12MHz

But......fixed temperature

Easier to model

WireLaser beam

Laser beam

Longitudinal and radial

mesurements possible

Longitudinal oscillationsLongitudinal oscillations

Longitudinal oscillations vs LSDyna

Frequency analysis

Radial oscillationsRadial oscillations

Radial oscillations: frequency analysis vs

LSDyna

Radial oscillations vs LSDyna

Comparison with LSDynaComparison with LSDyna

• Oscillations are complicated

wire partially fixed to frame

frame also moves

violin modes, etc

Have pretty good agreement but studies continuing

• Level of stress is correct

correct velocity is reproduced

wire is being stressed at above NF levels

• Lifetime results are valid

‘Fit’ – will be used later for

comparison

Comparison with MeasurementsComparison with Measurements

J.W. Davis, ITER Material Properties Handbook, 1997, Volume AM01-2111, Number 2, Page 1-7, Figure 2

Concern: low

strength from static

measuremts at

high temp

Measurement in Wire TestsMeasurement in Wire Tests

If we know the Poisson’s ratio , density , root of corresponding Bessel function , wire radius r and measure

the frequency f as a function of temperature then:

1

21112 2

2

22 rfE

CT 5100893.1279.0

Wire

Laser beam

Illustration

Tungsten Young’s ModulusTungsten Young’s Modulus

Young’s Modulus of TungstenYoung’s Modulus of Tungsten

• Results are very encouraging

• But……

E is not tensile strength

Tensile strength is what really matters

• Expectation is E would fall rapidly once plastic

• Can we check this?

• Difficult with tungsten....having a go with Ta (see GS talk)

Young’s Modulus ConclusionsYoung’s Modulus Conclusions

• Measurements ~ comparable with existing

• Details largely understood, but more work required

• Bottom line:

Strength remains high at high temperature and at high stress!

• Reason why measured lifetime higher than some expected

• Plans:

Continue detailed studies

Repeat lifetime tests, but measure with LDV over time

Use beams and measure with LDV to cf LSDyna - request made to ISIS- use Ilias’s facility at CERN

Radiation DamageRadiation Damage

• ISIS:

used tantalum for > 10 years, tungsten ~5 years

targets changed after ~12dpa

~2-5 years at NF, depending on # of targets

no signs of swelling or embrittlement

Ta examined in detail; W still to be done

• Still to be done

tensile strength after irradiation

hope to form consortium to measure 12dpa ISIS target

but……..

Radiation DamageRadiation Damage

NB Static measurements.

Target ChangeTarget Change

• Current option: a wheel – being investigated now

• Several already used, but most relevant: design study

Horizontal for compatibility with baseline target station

Target ChangeTarget Change

• For us, major issue is capture solenoid

• Helmholtz coil looks difficult due to forces

• Placing wheel up-stream of solenoids:~60% of Study II muon capture rate

Target ChangeTarget Change

• Arranging visit to discuss collaboration with ESS

• But.....problem being studied by ISIS TS2 engineers

• Given free reign, uninhibited by physicists

• Studying an idea with minimal impact on solenoids

• More if it works out

ConclusionsConclusions

• Shock:

We’ve done this to death!

Don’t believe it is a problem

Tests with beams to come

• Radiation damage:

Lots of local experience exists

Needs to be applied to our case

But existing data are encouraging

• Target change:

Wheel looks feasible – detailed study underway

Alternatives being investigated