study on fluctuations during the rf current ramp-up phase in the cpd spherical tokamak
DESCRIPTION
4 th IAEA TCM on Spherical tori and 14 th International workshop on Spherical Torus ENEA Frascati, October 7-10, 2008. Study on Fluctuations during the RF Current Ramp-up Phase in the CPD Spherical Tokamak. - PowerPoint PPT PresentationTRANSCRIPT
Study on Fluctuations during the RF Current Ramp-up Phase in the
CPD Spherical Tokamak
H. Zushi1), T. Ryoukai2), K. Kikukawa2), T. Morisaki3), R. Bhattacharyay2), T. Yoshinaga1,3), K. Hanada1), T.Sakimura2), H. Idei1), K. Dono 2), N. Nishino4), H. Honma2), S. Tashima2), T. Mutoh3), S.
Kubo3), K. Nagasaki5), M. Sakamoto1), Y. Nakashima6), Y. Higashizono1), K. N. Sato1), K. Nakamura1), M. Hasegawa1), S. Kawasaki1) H. Nakashima1), A. Higashijima1)
1)RIAM, Kyushu University, Kasuga, Fukuoka, Japan, 816-8580, 2) IGSES, Kyushu University,
Kasuga, Fukuoka, Japan, 816-8580, 3) National Institute for Fusion Science, 4) Hiroshima University, 5) Kyoto University, 6) University of Tsukuba,
4th IAEA TCM on Spherical tori and 14th International workshop on Spherical TorusENEA Frascati, October 7-10, 2008
1
MotivationWhy steady Bz is required forThe initial condition ?
Forrest PRL 1992
1. Confine the trapped electrons => toroidal precession current
2. Pressure driven/ Uni-directional PS current => seed toroidal current
Motivation (Role of Bz)Slab-Annulus plasma is unstable because of bad curvature
QUEST CPD
Fast camera image shows vertically moving modes
Slab plasma in simple torus
Fluctuations & Conversion efficiency
1.00.80.60.40.20.0Tr
ansim
issio
n
0.200.150.100.050.00Ln(m)
pol=2cm
40% 20% 10% 1%
f=8.2GHz, fce=4.92GHz
TOX v.s. Ln at f=8.2 GHz. Fluctuation level= 1% (solid-circle), 10% (dot-dashed), and 20% (dotted), and 40 % (solid-square). lpol =20 mm, and parallel refractive index N||=0.7.
According to Laqua PRL 1997
Open to Closed flux surfaces during the current ramp
#507034 External Bv Field Closed Flux Surfaceon the Flattop
Ip increases slowly with the slow increase of Pinj (~60kW for Ip ~ 1.7kA).Less effective than current jump(Pinj ~ 30kW for Ip ~ 2kA).
Cen
ter Po
st
Vertical shift is suppressed
under Bv field with higherdecay index.
t = 0.146 sYoshinaga ICPP2008
OUTLINE
1. Diagnostics of fluctuations
2. Results during the current ramp-up 2-1) fluctuations in slab-annulus plasma role of Bz
2-2) fluctuations during the current jump
3. Summary
7
MM14MM13
赤道面ポート配置
(MH3 )180゜
270゜90゜
425 .81
(MM12 )
(MH2 )
346 .40
(MM15 )
(MM16 )
(MH4 )
402 .86
(MM11 )306 .41
(MM17 )
(MM18 )
(MH1 )
590.00
525.00
590.00
525.00
RF antennaHX(CdTe-PHA)
VUV spectrometer
SX array
Visible monitor
Li-CCD
Fast camera(10s)
RotatingPumplimiter
Pump(TMP,Cryo)
Probe
Ha filter
Li-BES(50 PMTs)
Rogowskii coil
Medium speed camera(1ms)
AM-reflectometer
Stray rf power
Stray rf power
IR-TV camera
IR spectroscopy
Visible spectroscopy
(Hyougo Univ)
CT injector
(NIFS)
(NIFS)(NIFS)
(NIFS)
(Hirosima Univ.)
(Tsukuba Univ.)
CS
I.
45 Flux loop coils
8
Ex.1 Ex.2
2fcefce fceOpen Closed+Open
Bt=0.29T, Bv=40G, Ip~3kARf 8.2GHz, 60kW
I. CPD Li-imaging (CCD & LBFS)4 TFcoils
CS
TF
CCD
R
Z
10x10 fiber+50PMTs
50x50mm
Li injector
-600mm
Typical discharge0.220.200.180.160.14
Rre
s(m
) (a)
5040302010
0
Bz(
G)
R=0.25 m
(b)
2.01.51.00.50.0
Ip (
kA
) (c)
60
40
20
0
Prf (
kW
)
0.400.300.20
(d)
-0.2-0.10.00.1
Vlo
op
(V
)
R=0.106Z=0.325
(e)
50004000300020001000
0Pst
ray(
a.u
.) Z=0.225(f)
43210
LiI
(a.u
.) R=0.182Z=0.04
(g)
0.60.40.20.0
H(a
.u.)
0.400.300.20
(h)
Fluctuations in Annulus Plasma w/o Bz3.0x10
17
2.0
1.0
0.0
ne(
m-3
)
240220200180R (mm)
507795 z=-80mm
0.1
2
4
1
2
4
10
<S>x
x (a
.u.)
6
103
2 4 6
104
2
f (Hz)
507795 t=0.18-0.2s
R=0.2m,z=-0.08m
1.0
0.8
0.6
0.4
0.2
0.0
2
6
103
2 4 6
104
2
f(Hz)
2R(z=-0.08m) 2
z(R=0.2m)
0.250.200.150.100.050.00
0.220.200.180.16
507795
1 kW
Rres=164 mm
LF mode with Long correlation length
1.0
0.8
0.6
0.4
0.2
0.0
2
0.240.220.200.180.16R(m)
f=1.1kHz
(a) 1.0
0.8
0.6
0.4
0.2
0.0
2
-0.10 -0.06Z(m)
507795_1_1.1kHz_175_200ms
-0.100
-0.090
-0.080
-0.070Z
(m)
0.220.200.18R (m)
f=1.1kHz (507795_1_175_25_1.1_CS)
1.00.80.60.40.20.0
(a)
R~ 5 cmz> 2.5 cm
Bz suppresses density fluctuations
600
400
200
LiI
(a.u
.)
300250200150R(mm)
'1fr_Bz=50G' '2fr_Bz=40G' '3fr_Bz=32G' '4fr_Bz=24G' '5fr_Bz=15G'
507918Z=-50mm
0.40
0.35
0.30
0.25
0.20
IL
i/<I L
i>
-50 -40 -30 -20 -10 0Bz(G)
Bz=0G 507803(11/ 14)others 507918(11/ 14)
Density profile is not significantly affected by Bz (< 50G)However, the fluctuation level is much reduced.
Bt=0.29T Bz< 50 G Liee
e nnIII
nn *,
~~
Power spectrum and coherency are much reduced
68
1
2
4
68
10
2
Sxx
ch1 (a
.u.)
6
103
2 3 4 5 6
104
frequency[Hz]
Bz=50G (t=100-110ms) Bz=8G (t=310-320ms) Bz= 0G (t=100-110ms)
507903-918(a)
-30x10-3
-20
-10
0
Z(m
)0.200.180.16
R (m)
cohrz_507918_1_90_30_2.05_CS
1.00.80.60.40.20.0
(b)Square coherency at 2kHz
Low frequency components are reduced as Bz increases.Correlation length is drastically reduced.
Better conversion
Bz is desirable to reduce fluctuationsSteady Bz is required for the initial condition !
Forrest PRL 1992
1. Confine the trapped electrons => toroidal precession current
2. Pressure driven/ Uni-directional PS current => seed toroidal current
Ryoukai, ICPP 20083. Reduced Fluctuations => more efficient conversion
1.00.80.60.40.20.0T
rans
imis
sion
0.200.150.100.050.00Ln(m)
pol=2cm
40% 20% 10% 1%
f=8.2GHz, fce=4.92GHz
2 Fluctuations during Current Jump0.220.200.180.160.14
Rre
s(m
) (a)
5040302010
0
Bz(
G)
R=0.25 m
(b)
2.01.51.00.50.0
Ip (
kA
) (c)
60
40
20
0
Prf (
kW
)
0.400.300.20
(d)
-0.2-0.10.00.1
Vlo
op
(V
)
R=0.106Z=0.325
(e)
50004000300020001000
0Pst
ray(
a.u
.) Z=0.225(f)
43210
LiI
(a.u
.) R=0.182Z=0.04
(g)
0.60.40.20.0
H(a
.u.)
0.400.300.20
(h)
Burst in LiI and during Ip Jump
2.01.51.00.50.0
Ip (
kA
) (a)
43210
LiI
(a.u
.) R=0.182Z=0.04
(b)
-0.15-0.10-0.050.000.05
Vlo
op (
V)
R=0.106Z=0.325
(c)
4 msBlue: t=218msGreen:t=220 msRed: t=221ms
4
3
2
1
0
LiI
(a.u
.)
0.2230.2220.2210.2200.2190.218
R=0.182Z=0.04
Contour of LiI(R,Z) during Jump
Li_508279_0.218_0.2181_CS(a)
Li_508279_0.219_0.2191_CS
0.50.40.30.20.1
(b)
Li_508279_0.2195_0.2196_CS(c)
Li_508279_0.221_0.2211_CS(e) Li_508279_0.2215_0.2216_CS(g)
Li_508279_0.2218_0.2219_CS(h)
Li_508279_0.222_0.2221_CS(i)
Li_508279_0.2209_0.221_CS(d) Li_508279_0.2212_0.2213_CS(f)
Vertically aligned contour => horizontally aligned contourOpen field => Closed field lines
159 <R<215 mm 27<Z< 52 mm
Rres=194mm
4
3
2
1
0
LiI
(a.u
.)
0.2230.2220.2210.2200.2190.218
R=0.182Z=0.04
0.6
0.5
0.4
0.3
0.2L
i (R
)0.210.200.190.180.170.16
R (m)
'0.2206_0.2207' '0.2210_0.2211' '0.2212_0.2213' '0.2215_0.2216'
t=0.1ms
Profile flattening occurs 1ms before the burst
Coherency of 1kHz during Jump
cohrz_508279_1_211_2_1.17_CS (a) cohrz_508279_1_213_2_1.17_CS
1.00.80.60.40.20.0
(b) cohrz_508279_1_217_2_1.17_CS (c)
cohrz_508279_1_219_2_1.17_CS (d) cohrz_508279_1_221_2_1.17_CS (e) cohrz_508279_1_223_2_1.17_CS (f)
4
3
2
1
0
LiI
(a.u
.)
0.2240.2200.2160.212
R=0.182Z=0.04
Highly coherent mode at f~1 kHz dominates the viewing area
Summary
1. Initial Bz suppresses the density fluctuations, suggesting that the injected ECW can be converted efficiently to EBW
2. 2D structure of the density fluctuations shows that highly coherent mode at low freq. with very long correlation length grows just before the burst of LiI only during the current jump.
2 Current Jump in CPDNormal X-mode injectionCo-directional O-mode injection
ThresholdP ~ 20 kW
ThresholdP ~ 25 kW
Co-directional O-mode injection seems more efficient for achieving current jump than normal X-mode.
The critical parameter for current jump phenomenon should be the value of Ip, since Ip just before and just after current jump are almost identical.
The difference of the threshold power on the incident mode may be due to the heating efficiency in each mode. Ip itself may be determined from some equilibrium conditions.
Yoshinaga IAEA (2008)
for X-mode injection (X-B scenario) (Normal to B-field)
for O-mode injection (O-X-B scenario) (injection angle is adjustable)
Midplane
Reflector Shaft
Reflecting mirror
Microwave (8.2GHz) Launching System in CPD
Incident wave must be converted into Electron Bernstein Wave (EBW) mode to heat the core plasma region in overdense plasmas.
Microwave launchers from 8 klystrons are separated into normal X-mode injectors and co-directional O-mode injectors to study injection mode dependencies.
Current Jump discharge in CPD
Current Jump
3ms
EC
R
2nd
EC
R
EC
R
2nd
EC
R
External Bv FieldClosed Flux ConfigurationAfter Current Jump
Cen
ter Po
st
Cen
ter Po
stt = 0.153 s t = 0.157 s
#506967
Vertical Shift is observed both in magnetic flux and H image.
Non-Inductive Current Generation by ECH via Current Jump
Current Jump occurs under relatively high Bv (≥ 30 G).
In this range of Bv, Ip saturates at ~ 1.8 kA without current jump.This suggests that the current jump is necessary to obtain higher Ip under higher Bv.
Under Bv ≤ 30 G, Ip increases slowly and there is no clear current jump.
Finally achieved Ip with and without current jump increases roughly proportional to Bv.
Pinj < 60 kW
Summary of ECH current start-up experiments in CPDCurrent jump discharges have been observed in CPD.
This suggests that the current jump occurs commonly in ST devices.
Current jump is necessary to achieve higher Ip under higher Bv.
-2
0
2
ph
ase
(ra
d)
6
103
2 4 6
104
2
f(Hz)
R(z=-0.08m) z(R=0.2m)
(a)
10
8
6
4
2
0
S xx(a
.u.)
0.240.220.200.180.16R(m)
'f=1.2kHz' 'f=4.1kHz'
z=-84mm
外部垂直磁場Ip = 0 kA
電流ジャンプにおけるポロイダル磁場構造の時間発展Flat top1.5 kA
電流ジャンプ
60
400 2
0R(cm)
EC
R
2nd
EC
R
0.8 kA
0
20
40
60
-20
-40
-60
Z(cm)
1.5 kA1.4 kA1.2 kA1.0 kA
R=35.8cm
Ip = 0.8 kA 1.2 kA1.0 kA 1.4 kA
磁場構造の変化にあわせて tip B の浮遊電位が低下
tip A
tip B
-100V -1000V
-30V