Magnetic Diagnostics for GLAST-III Tokamak M. A. Naveed, Aqib javeed and GLAST Team National Tokamak...
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Transcript of Magnetic Diagnostics for GLAST-III Tokamak M. A. Naveed, Aqib javeed and GLAST Team National Tokamak...
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Magnetic Diagnostics for GLAST-III Tokamak
M. A. Naveed, Aqib javeed and GLAST Team
National Tokamak Fusion Programme Islamabad Pakistan
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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Outline of the Talk 1. GLAST Tokamak2. Magnetic Diagnostics3. Rogowski Coils 4. Magnetic Probes5. Flux Loops6. Error fields7. Initial Results8. Summary
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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GLAST-III (Glass Spherical Tokamak) Its Vessel is of Pyrex Major radius =20cm Minor Radius=10 cm 12 TF Coils and Central Solenoid Capacitor Banks are used for energizing different coils Central solenoid 2.2mF , 6kV, 40kJ TF coils 484mF, 450V, 49kJ Pre-Ionization Source is 2.45 GHz microwave oven
Magnetron( 800 Watt)
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
4IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
GLAST-III
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Magnetic Diagnostics
Magnetic measurements are fundamental diagnostic for tokamak start up and operation .
GLAST with dielectric chamber facilitates us to install every pick up coil outside the vacuum. No current will be flowing in the chamber so a single Rogowski coil will be providing true plasma current.
Magnetic Probes, Flux loops and Rogowski coil are major magnetic diagnostics in GLAST-III.
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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Magnetic Probes
Measured Parameters
Winding Wire
Diameter of Probe mm
Winding Lengthcm
Total turns
DC Resistance (Ohm)
Inductance(mH)
Big Probes 36 swg 12 4 2000 56.8 27.8
Small Probes 36 swg 7.5 mm 1.34 260 4 0.160
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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Calibration of Magnetic Probes
• Helmholtz Coils• SWG 16(5A dc curret
Capacity)• Hall probe for
calibrating• 9.5 gauss per
ampere
The effective area ‘NA’ is given by
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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Pulse Behavior of Magnetic Probes
Pulse generator which is capable of generation pulses of different time durations.
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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Pulse Behavior of Magnetic Probes
For finding Magnetic field the differential signals are integrated.
Simplest are the RC Integrators.
In these studies 10ms, 22 ms and 47 ms time constant integrators are used.
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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Fabrication of Rogowski Coil
RG-11 coaxial cable is used. The central conductor serves as return path.
Uniform winding is required so groves are made with dye.
Measured Parameters
L(µH)
R(Ω) Winding wire
Turns per cm
Length(cm)
Diameter(mm)
SensitivityVs/A
Rogowski-III 81.3 24 Swg 36 10 169 7 3.35x10-8
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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Calibration of Rogowski Coil Calibration Setup
AC and pulsed sources are used for exiting a multi turn coil having number of turns up to 200 so that Rogowski coil when passed through this multi turn coil encounters a reasonable current to be measured. The LEM current monitor is used as a reference for calibration of Rogowski coils.
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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0 10 20 30 40 50 60 700
5
10
15
20
25
30
35
40
Rogow
ski c
oil
outp
ut(m
v)
Current (kA)
Rogowski coil Signal recoded with 47 ms RC integratorChanel-1: Current signal andChanel -2: Rogowski signal
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
Behavior of Rogowski coil along with passive integrator at different values of current.
Calibration of Rogowski Coil
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Flux loops on GLAST-III
In GLAST-III loop voltage is measure horizontally at the mid plane of the chamber. Three differential pairs of poloidal flux loops are installed for the poloidal flux measurement at different locations. One of these pairs as shown in Fig is installed on the mid planed with a single turn of insulated wire installed
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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Error Field corrections using flux loops
There are some error fields generated in Tokamak because of misalignments and winding inaccuracy of Toroidal field and Ohmic current drive coil systems.
These error fields create problems not only in the startup of Tokamak but also limit the pulse duration.
These fields must also be measured and compensated
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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Error field minimization
Two loops are wrapped in toroidal direction at the mid plane with radii 9.2 cm and 31.8 cm. These loops are connected to each other in such a way that average vertical field in the region where plasma is to be generated is measured. The average vertical magnetic field will be given as:Average vertical Field= Vertical Flux / π( R2
2-R12)
Where R2 = 31.8 cm
R1= 9.2 cm
0.0 1.5 3.0 4.5 6.0 7.5 9.0 10.5 12.0 13.5 15.0 16.5 18.0 19.5-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
CS and TF combine
TF
Ver
tical
Mag
netic
Fie
ld(G
auss
)
Time(mS)
CS
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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Initial Shots of GLAST-III
-2 0 2 4 6 8 10
-6
-4
-2
0
2
-10
0
10
20
30-2 0 2 4 6 8 10
Pla
sma
Curr
ent(kA
)
Time(mS)
Loop V
oltag
e(V
olts)
0 4 8
-4
-2
0
2
4
-10
0
10
200 4 8
Pla
sma
Curr
ent(kA
)
Time(mS)
Loop V
oltag
e
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
(a)Vertical field applied (b)No vertical field applied
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The magnetic diagnostics installed presently on GLAST-III tokamak worked well for the initial operation.
The Rogowski coils used with RC integrators worked well for short duration pulses of plasma current.
The pulse source developed for on bench calibration of diagnostics coils helped to evaluate the response of these coils for pulses, nearly of same time scale and shape which are to be measured on the GLAST-III tokamak.
In future magnetic diagnostics for GLAST-III will be improved so that long duration plasma operation becomes possible. For this purpose long integration time constant active integrators will be developed.
Summary
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015
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Thanks
IAEA First Technical Meeting on Fusion Data Processing, Validation and Analysis 1 – 3 June 2015