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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MgB

2

research

at

Tampere University of

Technology Institute of

Electromagnetics

Antti Stenvall

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

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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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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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

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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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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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

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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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...

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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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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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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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

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