A1258150666yONKP

1
Prospects of increasing the radiation resistance
in the bulk and at the surface of dielectric
materials for fusion reactors Prof. Aleksandr
Lushchik (luch_at_fi.tartu.ee)
Institute of Physics University of Tartu (IPUT),
Estonia
Laboratory of Physics of Ionic Crystals and
Laboratory of X-Ray Spectroscopy Estonian
Target-financed project Fundamental Phenomena in
Wide-Gap Materials and Their Prospects of
Application, PI A.Lushchik, permanent
scientific staff 16 (PhD and DSc)
2

• ITER,
• DEMO, PROTO
• For industrial powerful high-temperature
  thermonuclear reactors it is necessary
• to increase the radiation resistance of
  construction materials (including dielectric
  ones),
• to elaborate new thermo-stable blanket ceramic
  materials for tritium reproduction and heat
  removal by a flow of helium.

3
Formation mechanisms of radiation defects
1. Impact (knock-out) mechanisms
2. Non-impact mechanisms Ionisation energy losses
- decay of electronic excitations
Radiative decay Non-radiative decay
Non-radiative decay
Creation of Frenkel pairs and groups of defects
Heat release (phonon package)
Emission of light (luminescence)
4

• Our General Goals
• ? Search for the prospects of the suppression of
  the non-impact defect creation processes
  connected with the decay of electronic
  excitations (EEs) formed by 4-2000 eV-photons or
  fast particles in pure and doped with luminescent
  impurities MgO, Al2O3, SiO2, LiF etc.
• ? Investigation of the peculiarities of defect
  creation in the tracks of swift ions (core and
  peripheral regions).
• ? Investigation of the peculiarities of EEs and
  radiation processes in lithium-containing
  materials for breeding blanket (e.g., Li4SiO4).
• ? Spectroscopic and thermoactivation diagnostics
  of materials.

5

• Experimental approach
• ? Complex study of electronic excitations and
  defects by means of low-temperature (down to 2 K)
  VUV-XUV spectroscopy methods.
• ? Complex study of the origin and annealing
  processes of defects by means of absorption,
  luminescence and EPR spectroscopy methods.

Methods of irradiation ? Selective VUV
radiation (IPUT) and synchrotron facilities at
MAX-lab, Lund and HASYLAB at DESY, Hamburg
4-2000 eV ? Single electron pulses (3 ns, 300
keV, 10-120 A/cm2) and an electron beam (1-30
keV, T 6-500 K), IPUT. ? Heavy and light
swift ions 238U, 198Au, 82Pb, 78Kr, 58Ni -
Gesellschaft fьr Schwerionenforschung (GSI,
Darmstadt, Germany).
6
Tracks of swift ions in LiF
7
Investigation of the structure of swift ion
tracks in single crystals using VUV and
thermoactivation spectroscopy methods
8
Mechanisms of defect creation in the crystals
with Eg lt EFD
Recombination of non-relaxed (hot) electrons and
holes
Recombination of relaxed (cold) electrons and
holes
9
Dielectric materials with high radiation
resistance (Eg lt EFD) BeO
SiO2 ZrO2 Y2O3 MgO
Al2O3 MgAl2O4 YAlO3
CaO Sc2O3 CaAl2O4
Y3Al5O12
Spectra of hole intraband luminescence (IBL)
Novel experimental method of the study of the
width and structure of a valence band
A simplified energy-band diagram of a crystal
with EFD Ed gt Eg
10
Luminescent defence against defect creation at
the hot recombination of carriers in the
materials with Ed gt Eg.
Crystal doping with some impurity ions causes the
direct energy transfer by hot carriers to
impurity centres, resulting in the excitation of
impurity luminescence and the drastic decrease
of the probability of hot recombination of
electrons and holes.
Direct energy transfer by hot holes to Cr3 and
Ge2 centres takes place in MgO. This process
causes essential difference of the excitation
spectra of Cr3 emission with respect to that for
purely recombination emission of Al3vc centres.
Excitation spectra of Cr3 and Al3vc emissions
11
Function mechanisms of high-melting Li4SiO4
ceramics promising blanket materials for fusion
reactors

• ? Synthesis of pure and doped Li4SiO4.
• ? Investigation of the electron-hole and
  interstitial-vacancy processes at 6-750 K.
• ? Experimental modelling of the tritium release
  from Li4SiO4 via the investigation of the
  release of deuterium and hydrogen from the
  irradiated Li4SiO4(D) and Li4SiO4(H) ceramics.

Pre-irradiation and radiation traps for electrons
and holes bind tritium, formed in irradiated
Li4SiO4. Ceramics heating above 500 K causes the
release of the tritium.
Novel method of the investigation of e-h
processes in Li4SiO4 (Eg ? 9 eV).
TSL is observed after the irradiation by
electrons (1-30 keV), X-rays (50 keV) and 9-30
eV photons
Thermally stimulated luminescence after ceramic
irradiation by 20-keV electrons at 6 K (a, ?? 10
K/min) or X-irradiation at 295 K (b ?? 2.9 K/s).
Creation spectrum of the centres of
photostimulated luminescence at 10 K
12
Thank you for your attention