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 RASNovosibirsk State University
Li in Tokamaks
FTU limiter (J. Nucl. Materials 390–391 (2009) 876–885)
T11M limiter2002 Plasma Phys. Control. Fusion 44 955
Li Capillary-Pore SystemJournal 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)
Electron beam generator U-2
Ribbon beam diode with beam compression system
Solenoid with corrugated magnetic field
Plasma exhaust, materials test station
Multimirror trap GOL-3
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
Plasma stream parameters
2
0.1 1 10 100 1000energy, keV
0.01
0.1
1
10
100po
wer
den
sity
, M
W/c
m
/keV
Plasma
Suprathermalelectrons Beam
electrons
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 )
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.
0 1 2 3 4 5
0
200
400
600
800
1000
1200
z,mm
J/g
Melting point (181 C)
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).
Patents were granted in the Russian Federation (1990) and the United States (1992).
Boreskov Institute of Catalysis SB RAS, Novosibirsk
Compared to active coals, Sibunit has the following advantages:
• high mechanical strength; • chemical and thermal stability; • high purity.
Sibunit synthesis
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-Sibunit
Li film on graphite
Plasma stream
Magnetic coils
Target
Diaphragm
Target holder
Vacuum chamber
Layout of target irradiation experiments in the GOL-3 exit unit
Beam
Plasma
Surveyspectrometerresolution 0.3 nmrange 100 nm
High-resolutionspectrometer
2D imagingsystemTarget
Optical diagnostics of target plasma
CCD
CCD
MDR-12 or DFS-24resolution 0.08 nm 0.005 nmexposure 7-300 microseconds
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.
Spectrum of surface
plasma produced near
lithium-graphite target
under action by power
plasma stream.
580 600 620 640 660 680
0
500
1000
1500
Li I
H
C II
C II
Li I
Intensity, a.u.
W avelenghts, nmOne 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.
508 510 512 514 516 518 5200
0.2
0.4
0.6
0.8
1
1.2
Вт/см2*нм
длина волны, нм
Filter transition coefficientSpectrum С2
2D Spectral selective optical system
objectivelenses
Object
Narrow band filter
CCD камера
wavelength, nm
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
(1)
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
(2)
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
(3)
Equation (3) enables conversion of the photon flux ФA (photons/сm2s) 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 11020 atoms/(cm2s), it is 3 times smaller with respect to atomic carbon fluxes from graphite targets.
XB
SI
hdrv
drvI
BhФ A
eexcitation
eionizationAA
44
2
1
)()(4
r
r
eexcitationeAA drvrnrnBh
I
2
1
)()(
r
r
eionizationeAA drvrnrnФ
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.
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/(cm2s) cannot explain the erosion value.
Conclusion