Influence of High Energy Electrons on ECRH in LHD
S. Kubo, H. Takahashi, T. Shimozuma, Y. Yoshimura, M. Nishiura, H. Igami, S. Ogasawara, R. Makino 17th Joint Workshop on ECRH and ECE 2012.05.07-­‐11 Durne, Nerderland Motivation: High energy electrons affects
the heating efficiency of bulk electrons"
At ne>3x1018m-3"
effective bulk
heating and kept
Te0> 10 keV,"
but"
at ne<3x1018m-3"
bulk electron
temperature
decreased under
the same heating
condition."
High energy
electrons can
absorb injected
power at
relativistic down
shifted O-mode"
Contents
•  History •  Presence of High Energy Electrons –  Energy range, high energy raPo •  Effects on ECRH absorpPon •  Power DistribuPon to the bulk and high energy components –  Response of stored energy, ECE •  Summary Creation of high energy electrons "
in low density regime"
250
200
150
100
50
0
#100604
#100625
#100637
15
10
5
3.5
4
time (s)
4.5
-3
20
#100604
#100625
#100637
3
19
2
1.5
1
0.5
0
#100604
#100625
#100637
ne(x10 m )
3
2
1
0
Slow rise
5
0
Te,0(keV)
wp(kJ)
PECH(MW)
LHD Shot 100604,100625,100637
Creation of high energy electrons screen
central power deposition"
Power deposiPon to the core bulk plasma might be screened by the presence of high energy electrons. Trad,ECE (keV)
ECE spectra show highly non-thermal
feature in the low density case"
Trad, ECE (keV)
Bulk Te
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
#100603 t= 3.7-3.8
#100625 t= 3.7-3.8
#100637 t= 3.7- 3.8
#100603 t= 3.8-3.9
#100625 t= 3.8-3.9
#100637 t= 3.8-3.9
t=3.7-3.8
2nd harmonic"
X mode
#100603 t= 4.0-4.1
#100625 t= 4.0-4.1
#100637 t= 4.0-4.1
0
0.2
0.4
3nrd harmonic"
X mode
#100603 t= 4.2-4.3
#100625 t= 4.2-4.3
#100637 t= 4.2-4.3
t=4.0-4.1
0.6
reff/a
0.8
t=3.8-3.9
1 0
0.2
0.4
t=4.2-4.3
0.6
reff/a
0.8
1
ECE Spectra calculation with high energy
electrons (100 keV variable density)"
Spectrum calculated "
for bi-Maxwellian"
Total density 2x10^18m^-3"
fixed"
re-absorption"
bulk Te0 15 keV "
high energy "
Th 100 keV fixed"
neh = 1%-99% of total"
Cold second harmonic peak
relativistic down shift effect of 2nd harmonic"
relativistically down shifted 3rd harmonic"
Comparison of power deposition profile from raytracing calculation and experiments "
•  ray tracing
calculation and
deduced
deposition well
coincides each
other"
•  "
Modulation ECH"
8 Ray-trace calculation with and without high
energy components (Rfoc scan)"
Perpendicular Injection "
Deposition
profile
Integrated
absorption
Without high
energy
With high
energy 20 % of the
injected power
is absorbed by
high energy
electrons
Ray-trace calculation with high energy components"
Absorption by high energy electrons dominated by
relativistic down-shifted second harmonic absorption"
Without "
high energy
1-st"
O-mode
With "
high energy
power deposiPon profile
2-nd"
O-mode
integrated power deposiPon profile
2-nd"
O-mode
Responses of the stored energy to
modulated ECH"
Response of the stored
energy to fast and slow
ECRH modulation
indicates the mechanism
of acceleration and
confinement of high
energy electrons."
Deviation of the averages
for fast and slow
modulation indicates nonlinear response of the
stored energy to ECRH
power. "
Confinement time of high energy electrons is the order of 200-300 ms"
Responses of wp to slow modulation"
• Response of High
energy electrons"
• Slower "
• than bulk"
• Fast and
strong"
• as off-axis"
• as oblique"
Perpendicularly Injected beam couples
more at high field side
ne 0.1,
ne 0.1,
ne 0.3,
ne 0.3,
on axis"
off axis"
on axis"
off axis"
off-axis
qualitatively
explained by"
the drift surface is
off-axis"
and down-shifted
resonance"
at high field side ne=0.1x1019 m-­‐3 Perp off-­‐axis Mod. Oblique InjecPon added
Cold resonance position
Dopler down shiZed 3rd-­‐harmonice X
Dopler down shiZed 2nd-­‐harmonice X
time (s)
19 -­‐3
ne=0.1x10 m Oblique Mod, Cold resonance position
Perp on-­‐axis injecPon added
time (s)
19 -­‐3
ne=0.1x10 m Perp Mod at on-­‐axis Cold resonance position
Oblique injecPon added
time (s)
Cold resonance position
ne=0.1x1019 m-­‐3 Oblique ModulaPon Perp on-­‐axis added
time (s)
Summary"
• Power deposition is much affected by the presence of high
energy electrons. Careful control of high energy electron is
necessary to achieve high electron temperature in the
collision-less regime. "
• ECE spectra, HX PHA analysis show high ratio of high
energy electrons in low density plasmas in LHD."
• Injected power can be absorbed by relativistically down
shifted O2 region."
• Inevitable in the "
• O1 heating or X2 for low field side injection scenario."
• The response of the stored energy shows non-linearlity. "
• Creation and relaxation process of high energy electrons
will be investigated by the response of stored energy and
ECE spectra"