JOINT RESEARCH DOCTORATE AND EUROPEAN DOCTORAL NETWORK ON FUSION SCIENCE AND
ENGINEERING
Thesis proposal for the 2015-2017 Ph.D. cycle
1) Program where the main part of activity will be realized
‘NBI Project’
2) Thesis title:
Modelling and exploitation of instrumentation for protection and operation of neutral beam injectors
3) Thesis supervisor
Mauro Dalla Palma
4) Group/s that will be involved in the program
RFX Plasma Engineering Group (IP)
5) Thesis abstract (max 600 characters)
Thermal, mechanical, and electrical instrumentation is foreseen for the protection of MITICA, the
prototype of the ITER neutral beam injector. Particle currents have to be simulated to evaluate the
interaction of the beam with surface properties of the surrounding components. The applied beam
conditions will be correlated with the measurements simulated on the injector components.
The numerical results will be verified and validated by comparing the simulated conditions with the
measurements acquired during operations of SPIDER experiment.
6) External collaborations (existing or to be started), which might involve the Ph.D. student (if any)
The framework of the collaboration can be extended to LHD NIFS (Toki, Japan) and IPP (Garching,
Germany) to verify the instrumentation installed on experimental beamlines.
7) Preliminary list of milestones for each of the three years
YEAR 1
The milestones are fixed considering the released technical specification for the procurement of
MITICA instrumentation and the status of the manufacturing of SPIDER experiment:
1) Development of numerical models simulating measurements acquired by the instrumentation
to be installed on the MITICA and SPIDER experiments; the models will simulate
measurements corresponding to different heating scenarios produced by expected beam
optics.
2) Verification of the MITICA technical specification for the procurement of the beamline
instrumentation.
3) Follow up of the procurement of SPIDER thermal sensors.
YEAR 2
The activities carried out during the first year are completed considering the opportunity to attend to
experimental measurements:
1) Further development of the models to simulate heating conditions corresponding to beam
non-ideal and off-normal scenarios.
2) Verification of the instrumentation installed on experiments at IPP and NIFS.
3) Follow up of the procurement of MITICA instrumentation.
YEAR 3
The validation extends the use of the developed models to the beam line of SPIDER and MITICA:
1) Verification of the numerical models and validation by comparison with measurements
acquired during operations of SPIDER experiment.
2) Prediction of instrumentation measurements expected during MITICA operation simulating
beam non-ideal and off-normal scenarios.
3) Proposal of the instrumentation layout and simulations of machine protection for the DEMO
beamline.
8) Description of the research project (max 8000 characters)
In a neutral beam injector for heating the plasma of fusion machines, the monitoring and protection of
components against over-temperatures are realised using thermal measurements.
Actually, thermal, mechanical, and electrical instrumentation will be installed on the new experiments
under construction at Consorzio RFX, Padova.
Thermocouples and accelerometers are foreseen in the ITER size beam source with 100kV accelerator,
SPIDER. Thermal control and protection are performed in the ITER NBI prototype with one megavolt
accelerator, named MITICA, by monitoring temperatures, boiling conditions, and thermal
deformations on components that could experience overheating.
Different sensor technologies will be tested in MITICA in-vacuum components: (a) thermocouples as
temperature measurement sensors extensively distributed and embedded in the in-vessel
components, (b) accelerometers as boiling detectors mounted on tubes of cooling channels subjected
to high heat fluxes (more than few MW/m2), (c) fibre Bragg gratings as temperature measurement
sensors on high voltage biased panels, (d) strain gauges as strain sensors on panels heated on one side
only.
Mainly, the MITICA test facility will be thermally monitored and protected by using thermocouples,
complemented by few piezoelectric accelerometers detecting vibrations of boiling heat transfer:
vapour bubbles, nucleated at the channel wall, collapse in the subcooled coolant bulk and vibration
transmitted in the solid material can be correlated to the exchanged heat flux in order to detect
incipient critical conditions.
The instrumentation proposed for the new experiments under construction at Consorzio RFX can be
verified considering installations tested at IPP and NIFS for beam line components.
Numerical simulations have to be developed in order to correlate the measurements simulated on the
injector components with the heating conditions produced by the expected beam optics.
Transient events can be simulated considering the characteristic time constants of the heat transfer
and thermo-mechanical phenomena.
The physics of particles with charge exchange could be integrated in the numerical code to simulate
the interaction of the particle beam with surface properties of the surrounding components. Currents
of positive and negative particles collected on components can be used to recognise the fraction of
particle species, to reconstruct the beam optics, and to quantify the efficiency of neutralisation and
residual ion dumping. So, the test facility monitoring and protection using thermal and mechanical
measurements can be complemented with currents produced by positive and negative particles by
processing very fast signals decreasing the time constant for the machine protection.
The numerical code can be verified and validated by comparing the simulated conditions with the
measurements acquired during operations of the SPIDER experiment. After validation, a suitable set of
sensors can be proposed and simulations can be undertaken for the protection of the neutral beam of
the DEMO reactor.