Spectroscopic Study of Interaction of High Power
Plasma Stream with Lithium-Carbon Composites
at Multimirror Trap GOL-3
A.A. Shoshin, A.V. Burdakov, I.A. Ivanov, K.N. Kuklin,
S.V. Polosatkin, V.V. Postupaev
Budker Institute of Nuclear Physics SB RAS
Novosibirsk State University
Li in Tokamaks
FTU limiter (J. Nucl. Materials 390–391 (2009) 876–885)
T11M limiter
2002 Plasma Phys. Control. Fusion 44 955
Li Capillary-Pore System
Journal of Nuclear Materials 390–391 (2009) 876–885
CDX-U “Try limiter” (Journal of Nuclear Materials 390–391 (2009) 876–885)
Li pellets in NSTX (Journal of Nuclear Materials 363–365 (2007) 791–796)
LiD pellets in GOL-3
Li vacuum evaporation in stellarator TJ-II
(Journal of Nuclear Materials 390–391 (2009) 852–857)
Multimirror trap GOL-3
Electron beam generator U-2
Electron beam
• 0.8-1 MeV
• 30 kA
• 8-12 s
• up to 300 kJ
Plasma
• length ~12 m
• 1020- 1022 m-3
• temperature ~1-4 keV
• 1 ms
Ribbon beam diode with
beam compression
system
Solenoid with corrugated magnetic field
Plasma exhaust,
materials test station
Plasma stream parameters
2
pow er density, M W /cm /keV
100
10
1
Plasma
Suprathermal
electrons
0 .1
Beam
electrons
0 .0 1
0 .1
1
10
energy, keV
100
1000
Energy density in the plasma stream 2 MJ/m2
Main power contained in the energetic (1-10 keV) electrons
Specific energy release is below volumetric destruction threshold (10 MJ/m2 )
1200
J /g
1000
800
600
M e ltin g p o in t (1 8 1 C )
400
200
0
0
1
2
z ,m m
3
4
5
Calculated energy deposition over depth of lithium under action of
electron stream in GOL-3 facility (power density 2 MJ/m2, target
inclined at 30º). Horizontal solid and dashed lines correspond to
start and end of phase transition, correspondingly. Initially target
was at room temperature.
Li-graphite phase diagram
Physical Rev.B. 2010, v.82, n.12, p.125416
Physical Rev.B. 1984, v.30, n.12, p.7092
Known different binary compounds Li4C, Li6C2, Li8C3, Li6C3, Li4C3, Li4C5 …
They are mainly thermodynamically metastable and after heating dissociate to
metallic Li and Li2C2
SIBUNIT - SYNTHETIC CARBON MATERIAL
Sibunit is a new class of porous carbon-carbon
composite materials combining advantages of
graphite (chemical stability and electric conductivity)
and active coals (high specific surface area and
adsorption capacity).
Compared to active coals, Sibunit has the
following advantages:
• high mechanical strength;
• chemical and thermal stability;
• high purity.
Boreskov Institute of Catalysis SB RAS, Novosibirsk
Patents were granted in the Russian Federation (1990)
and the United States (1992).
Sibunit synthesis
Li-Sibunit
Several lithium-carbon composite samples
was made by different methods:
1. Lithium together with graphite or sibunit
was heated in argon atmosphere to the
temperature 700 ºС. In the experiments
these samples were held in special
graphite box.
2. Lithium was heated on graphite sample
at temperature about 250-300ºС and
after melting lithium was smearing for
producing homogeneous layer of 0.5 –
1 mm depth.
Li film on graphite
Layout of target irradiation experiments in the GOL-3 exit unit
Target
holder
Target
Diaphragm
Plasma stream
Vacuum chamber
Magnetic coils
Optical diagnostics of target plasma
Target
CCD
Plasma
Beam
Survey
spectrometer
resolution 0.3 nm
range 100 nm
High-resolution
spectrometer
MDR-12 or DFS-24
resolution 0.08 nm
0.005 nm
exposure 7-300 microseconds
CCD
2D imaging
system
Plasma radiation in narrow spectral band
of graphite target (top) and sibunit-lithium
composite in 4cm graphite box (bottom)
under action of hot plasma stream moving
from the right.
1500
Spectrum of surface
plasma produced near
lithium-graphite target
under action by power
plasma stream.
In te n s ity , a .u .
Li I
1000
H
500
C II
Li I
C II
0
580
600
620
640
660
680
W a v e le n g h ts , n m
One can determine the plasma electron temperature by relation of intensities of lines Li I
610,36 и 670,78 nm. In different shots temperatures varied within 0.7 - 1.2 eV. Temperature
of lithium plasma is less than temperature of surface plasma near graphite targets (was
measured by ratio of C II lines). It corresponds to smaller first ionization potential and higher
transmissibility of lithium with respect to carbon.
2D Spectral selective optical system
Object
objective
lenses
CCD
камера
1.2
Вт/см2* нм
1
0.8
Narrow
band filter
Filter transition coefficient
Spectrum С2
0.6
0.4
0.2
0
508
510
512
514
wavelength,
длина
волны, нм
nm
516
518
520
Consider a flux of atoms ФA, along a line-of-sight r from surface into a fully ionized plasma. If we
assume all the incoming atoms are ionized by electron collisions, between r1 and r2
r2
ФA 
n
A
( r ) n e ( r )   ionization v e  dr
(1)
r1
where nA(r) and ne(r) are the density of atoms and electrons. Ionization rate coefficient <ionization> is
a function of the electron temperature Te(r). Electron impact excitation of the atom leads to photon
emission with the intensity IA
IA 
hB
4
r2
n
A
(2)
( r ) n e ( r )   excitation v e  dr
r1
where <excitation> is the electron impact excitation coefficient for the excitation of the upper level of
the radiating state, and B is the branching ratio for the radiative decay which leads to appearance of
the observed photons. Equations (1) and (2) give a relation between the particle fluxes and
intensities. Provided the rates do not vary much over the observation volume we may write
ФA 
4
hB
IA
  ionization v e  dr
  excitation v e  dr

4
h
IA
S
(3)
XB
Equation (3) enables conversion of the photon flux ФA (photons/сm2s) into the particle flux. The
inverse photon efficiency S/XB is the ratio between ioniSation rate and the product of eXcitation rate
and Branching ratio for the observed electronic transition. For 670.8 nm Li I lines S/XB = 1/8.6 was
calculated with data from Aladdin database. Estimated atomic lithium flux from the surface was
11020 atoms/(cm2s), it is 3 times smaller with respect to atomic carbon fluxes from graphite targets.
Li-Sibunit (carbon)
before and after irradiation 5 shots per 2MJ/m2
Li on graphite surface before and after 6 shots per 2 MJ/m2
View of carbon target with lithium films under action of cold plasma
in exit unit of GOL-3 facility.
Conclusion
Several lithium-carbon targets (including Li-Sibunit) were designed,
produced and tested under action of plasma stream.
Set of diagnostics was developed and used for investigation
parameters of surface plasma near targets.
It was shown that lithium erosion depth corresponds to melting
depth.
Temperature of surface plasma about 1 eV was measured.
Atomic lithium flux from surface was determined. The flux 1020
atoms/(cm2s) cannot explain the erosion value.