V.I. Vasiliev, Yu.A. Kostsov, K.M. Lobanov, L.P. Makarova, A.B. Mineev, D.V.Efremov Scientific Research Institute of Electrophysical Apparatus, St.-Petersburg, Russia, V.K. Gusev, R.G. Levin, Yu.V. Petrov, N.V. Sakharov A.F.Ioffe Physico-Technical Institute, St.-Petersburg, Russia Plasma Shape Reconstruction on- line Algorithm in Tokamaks JOINT MEETING OF THE 3rd IAEA TECHNICAL MEETING ON SPHERICAL TORI AND THE 11th INTERNATIONAL WORKSHOP ON SPHERICAL TORUS St. Petersburg State University, St. Petersburg, RUSSIA 3 to 6 October 2005
17
Embed
V.I. Vasiliev, Yu.A. Kostsov, K.M. Lobanov, L.P. Makarova, A.B. Mineev, D.V.Efremov Scientific Research Institute of Electrophysical Apparatus, St.-Petersburg,
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
A.F.Ioffe Physico-Technical Institute, St.-Petersburg, Russia
Plasma Shape Reconstruction on-line Algorithm in Tokamaks
JOINT MEETING OF THE 3rd IAEA TECHNICAL MEETING ON SPHERICAL TORI AND THE 11th INTERNATIONAL WORKSHOP ON SPHERICAL TORUS
St. Petersburg State University, St. Petersburg, RUSSIA 3 to 6 October 2005
Plasma Shape Reconstruction Algorithm in Tokamaks
Discussed here plasma shape reconstruction algorithm is based on using of current filaments to imitate plasma column and includes two steps.
At the first step location of the plasma current centroid is estimated roughly, using so-called plasma current density moments technique for two current filaments [1].
As results two pairs of the current filaments coordinates (r1,z1) and (r2,z2) can be calculated and they determine approximately plasma centroid location.
At the second step well known the fixed current filaments technique [2] is used to calculate plasma shape boundary.
To allocate current filaments inside the vacuum vessel (in vicinity of plasma current centroid location) two points with coordinates (r1,z1) and (r2,z2), computed at the first step, are used.
Globus-M cross-section
flux loops (21)+ two component probes (32)
U1101
U14
U5
U18
U21
PF1
PF1
PF2
PF2
PF3
PF3
HFC
HFC
HFC
HFC
VFC
VFC
CC
CC
CC
CC
CC
CC
CS
02
03
04
06
07 0809
1011
12
13
14
15
16
17
18
19
20
2122
232425
2627
28
29
U2
U3
U4
U6
U7
U8
U9
U10
U12
U13U15
U16
U17
U19
U20
U1
U1101
U14
U5
U18
U21
PF1
PF1
PF2
PF2
PF3
PF3
HFC
HFC
HFC
HFC
VFC
VFC
CC
CC
CC
CC
CC
CC
CS
02
03
04
06
07 0809
1011
12
13
14
15
16
17
18
19
20
2122
232425
2627
28
29
U2
U3
U4
U6
U7
U8
U9
U10
U12
U13U15
U16
U17
U19
U20
U1
First step algorithm
If to define as “measuring contour“ a curve l, which passes through magnetic probes coordinate points, then plasma current density moments can be written as following [1]
Here Ym is plasma current density moment of mth order. fm and gm are functions that determine order of plasma current density moment and they satisfy to equations as follows
In the case when plasma current distribution is approximated by two filament currents it is required fm and gm only up to 4th order to compute coordinates of two current filaments under condition that filament currents are equal each other.
dl)BrgfB()z,r(fIYl
mmnkkm
2
1kk0m
0r
f
r
1
r
f
z
ff
2
2
2
2*
0r
g
r
1
r
g
z
gg
2
2
2
2
First step algorithm (continue)
Here measured value of normal component of field induction in
the point of probe location with number “k”,
measured value of tangential component of field induction in the point of probe location with number “k”,
unknown current value in the jth current filament.
Formulas described fm and gm functions are presented below as following
f0 = 1; g0 = 0;
f1 = z; g1 = -ln(r);
f2 = r2; g2 = 2z;
f3 = r2z; g3 = -(1/2)r2 + z2;
f4 = -(1/4)r4 + r2z2; g4 = -r2z + 2/3 z3.
knB
kB
jI
First step algorithm (continue)
So, to compute coordinates of two current filaments it is necessary to calculate plasma current moments with using experimental data and with using current filaments approach and equate each other. Solving algebraic equation system with four unknown (r1,z1) and (r2,z2), current filaments coordinates can be found.
Points (r1,z1) and (r2,z2) serve as the reference points to set plasma current filaments in vicinity of plasma current centroid to be used at second step.
Second step algorithm
To reconstruct plasma shape boundary well known the fixed current filament technique [2] is used. In according with selected algorithm plasma is approximated by M current filaments with given coordinates (rj, zj) located inside plasma current centroid region.
In the described here procedure current filaments are uniformly placed along ellipse with focal points (r1,z1) and (r2,z2). The value of ellipse minor semi-axis is adjusted to have more acceptable results.
Unknown filament currents can be calculated by minimizing functional as follows
p l
21
N
1k
N
1m
M
1j
2J
2
mm
2kk2k
nkn IcBBBBc
Second step algorithm (continue)
computed value of normal component of field induction in the point of probe location with number “k”,
computed value of tangential component of field induction in the point of probe location with number “k”,
measured value of magnetic flux in the point of flux loop location with number “m”,
computed value of magnetic flux in the point of flux loop location with number “m”,
unknown current value in the jth filament,
adjustable parameter,
Here knB
kB
m
m
jI
c1, c2 relative weighs
Second step algorithm (continue)
, and parameters are computed with using theoretical models of poloidal field coils and vacuum vessel and experimentally measured coil currents and loops voltages.
Poloidal field coil currents are measured during plasma discharge with Rogovsky coils and they are therefore known.
Vacuum vessel current distribution is calculated with using loop voltages measured by flux loops located on the vacuum vessel shell. Interpolating experimental measured data loop voltage and current value can be computed for each finite element of vacuum vessel.
Minimizing residual functional filament currents can be calculated and then plasma column boundary can be reconstructed.
knB kB m
Application of plasma shape reconstruction technique in
Globus-M data handling
Globus-M magnetic diagnostic complex consists of:
32 two-components magnetic probes located on the vacuum vessel surface
21 full-scale flux loops located on the vacuum vessel surface
Rogovsky coils to measure PF coils currents
Rogovsky coils to measure plasma current and sum Ip+Ivv
U1101
U14
U5
U18
U21
PF1
PF1
PF2
PF2
PF3
PF3
HFC
HFC
HFC
HFC
VFC
VFC
CC
CC
CC
CC
CC
CC
CS
02
03
04
06
07 0809
1011
12
13
14
15
16
17
18
19
20
2122
232425
2627
28
29
U2
U3
U4
U6
U7
U8
U9
U10
U12
U13U15
U16
U17
U19
U20
U1
U1101
U14
U5
U18
U21
PF1
PF1
PF2
PF2
PF3
PF3
HFC
HFC
HFC
HFC
VFC
VFC
CC
CC
CC
CC
CC
CC
CS
02
03
04
06
07 0809
1011
12
13
14
15
16
17
18
19
20
2122
232425
2627
28
29
U2
U3
U4
U6
U7
U8
U9
U10
U12
U13U15
U16
U17
U19
U20
U1
flux loops (21)+ two component probes (32) Globus-M cross-section
)B,B( n
Application of plasma shape reconstruction technique
in Globus-M data handling (Continue)
Preliminary adjustment of plasma shape reconstruction procedure in numerical experiments with theoretical models.
Plasma evolution discharge scenario is simulated with using dynamic PET code with deformable plasma shape model.
Normal and tangential components of magnetic field induction ( ) relative to counter line with points of probes locations are numerically calculated.
Loop voltages that are used to estimate eddy current distribution in the vacuum vessel shell are calculated.
Test results of plasma shape reconstruction with using theoretical Globus-M model in the next picture.
kkn B,B
Application of plasma shape reconstruction technique
in Globus-M data handling (Continue)
Plasma equilibrium limiter configurationin Globus-M device;t=0.025 s, max difference = 7mm, Ip = 89.95 кА
Plasma equilibrium diverter configurationin Globus-M device;t=0.050 s, , max difference = 17mm, Ip = 165.4 кА
In total Using of 6 plasma current filaments gives acceptable results.
PF1
PF1
PF2
PF2
PF3
PF3
HFC1
HFC1
HFC2
HFC2
VFC
VFC
CC1
CC1
CC2
CC2
CC3
CC3
OH OH
PF1
PF1
PF2
PF2
PF3
PF3
HFC1
HFC1
HFC2
HFC2
VFC
VFC
CC1
CC1
CC2
CC2
CC3
CC3
OH OH
Application of plasma shape reconstruction technique
in Globus-M data handling (Continue)
Results of plasma shape reconstruction in Globus-M experiments
To demonstrate possibilities of the developed numerical plasma shape reconstruction code shot #10292 was taken as an example. To have better-fit results plasma column is simulated here with 9 currents filaments.
Reconstructed plasma shape boundary at limiter plasma discharge stage.1. case with c1=1, c2=0;2. case with c1=0, c2=1.
12
12
Reconstructed plasma shape boundary at divertor plasma discharge stage.1. case with c1=1, c2=0;2. case with c1=0, c2=1.
12
12
Conclusion
Developed here plasma shape reconstructed algorithm can be useful in time between shots to analyse output data of plasma discharges.
Proposed algorithm can be used as on-line algorithm in a feedback plasma shape control.
References
[1] Yasin I.V. PhD. Thesis, Kharkow, 1999.
[2] Ogata A., Aicawa H., Suzuki Y., “Accuracy of plasma displacement measurements in a tokamak using magnetic probes,” Jap. J. Appl. Phys., no. 16,1, pp. 185-188, 1977.