MgB 2. Technology Institute of. Antti Stenvall h t t p : / / w w w. t u t. f i / s m g

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t p : / / w w w . t u t . f i / s m g

MgB

2

research

at

Tampere University of

Technology Institute of

Electromagnetics

Antti Stenvall

antti@stenvall.fi

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t p : / / w w w . t u t . f i / s m g Outline • Earlier activity Coil modelling Test coil Conductor modelling • Current activity

Conductor modelling and measurements ALUHEAT project

• Future activity

Conductor modelling and measurements

• Other than MgB2 activities • Conclusions

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t p : / / w w w . t u t . f i / s m g Coil modelling

• Considerations of modelling MgB2 coils with

ferromagnetic matrix

Stenvall, Korpela, Mikkonen and Kováč SUST 19 (2006) 32-38

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t p : / / w w w . t u t . f i / s m g

Coil modelling cont.

• Computation of engineering permeability takes considerably much time as well as other non-linear modelling

• Rather accurate results can also be achieved with ”traditional” method (Boom-Livingstone and shape factor or linear FEM modelling)

• Does the proposed method or inaccuracy of initial data cause more uncertainty than

”traditional” method?

Stenvall, Korpela, Mikkonen and Kováč ASC06 IEEE Trans. Appl. Supercond. In Press

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t p : / / w w w . t u t . f i / s m g

Coil modelling – more questions

• Is the n-value of MgB2 low or high?

• What kind of modelling is really required?

Left: Kitaguchi et al Physica C 401 (2004) 246-250

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t p : / / w w w . t u t . f i / s m g Test coil • 46 m of Columbus Superconductors MgB2/Ni/Fe/Cu tape

Stenvall, Hiltunen, Korpela,

Lehtonen, Mikkonen, Viljamaa and Grasso SUST 20 (2007) 386-391

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t p : / / w w w . t u t . f i / s m g

Conductor stability computations

• Analytical formulations for normal zone propagation velocities and MQE

• Analysis of effective material properties

Stenvall, Korpela, Mikkonen and Grasso SUST 19 (2006) 184-189

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t p : / / w w w . t u t . f i / s m g

Current transfer length model

• 1D analytical and 2D numerical

model for current diffusion from matrix to superconducting region through highly resistive barrier layer/contact resistance

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t p : / / w w w . t u t . f i / s m g ALUHEAT project

• Project is for constructing DC induction heater which utilizes MgB2 as a coil material

Responsibilities of TUT:

Cryostat design Quench analysis

Force computations

(attractive force between the coils)

Construction begins in

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t p : / / w w w . t u t . f i / s m g

measurement in poorly cooled (adiabatic) measurement station

• Numerical (FEM) and semi-analytical model of

adiabatic V-I measurement for study of temperature rise during measurement and errors in measured n

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Adiabatic V-I measurement

• A model will be constructed to convert constant temperature measurement from variable

temperature measurement with real

measurement data by this way real n-value can be determined... perhaps...

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t p : / / w w w . t u t . f i / s m g Future activity - CTL

• Adaptation of metric in interface layer in FEM model of CTL to reduce the amount of elements

• Current diffusion past hairline crack (heat generation is the main motivation)

• CTL model for round conductors (axial symmetry in 2D)

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t p : / / w w w . t u t . f i / s m g

Future activity – other stability related issues

• To construct a FEM model for normal zone propagation velocity and minimum quench energy

• To construct a thorough model in which the stability of two conductors can be compared from the perspective of particular application and then better conductor for the application can be chosen

• Stability is a trade off between amount of stabilizer and engineering current density

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t p : / / w w w . t u t . f i / s m g

Future activity - M.Sc. Thesis

• Conductors from Columbus Superconductors

• CTL measurements

• MQE measurements

• Normal zone propagation velocity measurements

• Related to ALUHEAT project

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t p : / / w w w . t u t . f i / s m g

Other superconductivity related activities

• Super3C project (Lauri Rostila)

• Appeal for national cable project (Lauri Rostila+one graduate student)

If accepted researcher exchange needed!

• Appeal for Nordic YBCO research

(FIN+SWE+NOR+DEN one graduate student each)

Our contribution will be linked with possible cable

project

• Maria Ahoranta's thesis about conductor mechanical behaviour

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Other superconductivity related activities cont.

• Detailed FEM modelling of the effect of the quench origin to hot spot temperature and other quench characteristic

Size

Location (it can be quite arbitrary)

Current with respect to critical (e.g. can

self-protective magnet be non-self-self-protective during possible training?)

Team: Antti Stenvall, Aki Korpela, Jorma

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t p : / / w w w . t u t . f i / s m g Conclusions

• MgB2 research at TUT was presented • Modelling

Coil critical current

Current transfer length

Basic stability characteristics

• Experiment

Coil

Figure

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References

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