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Outline. Ex-vessel coils. MHD Saddle loops. Ex-vessel Rogowskis. High frequency coils. Divertor coils. Diamagnetic loops. In-vessel flux loops. ITER Measurement requirements Location within or outside the vessel Design features Open design issues

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Ex-vessel coils

MHD Saddle loops

Ex-vessel Rogowskis

High frequency coils

Divertor coils

Diamagnetic loops

In-vessel flux loops

  • ITER Measurement requirements

  • Location within or outside the vessel

  • Design features

  • Open design issues

  • Research activities withing EFDA TWP 2005

Anna Encheva

Slide 2

Measurement requirements

HF coils

  • Main system:

  • Low (m,n) MHD modes, sawteeth, disruption precursors

  • High frequency macro instabilities

  • Backups:

  • Plasma current

  • Plasma position and shape

Anna Encheva

Slide 3

Location within the vessel

HF coils

Located in the gap between blanket module and wall

  • their proximity to the plasma is the same as the equilibrium coils

  • measures the flux change through the area of its windings without subsequent integration

  • the measured quantities is thus the time rate of change of the magnetic field in a locally rather restricted area

  • distributed along poloidal contours

  • in 6 sectors

  • displaced by 60° toroidally

  • In order to cover up to m ~ 10, 20 high frequency coils were primary foreseen.

  • Only 18 high frequency coils are placed in each sector, due to the restriction to one/blanket module in the main chamber.

* The scaled drawing could be found on:

Anna Encheva

Slide 4

Present design features

HF coils

  • for high bandwidth a wide gap is constructed

  • coil supports are insulated to reduce eddy currents

  • for getting a high induced voltage signal – effective area of the coil has to be large

  • for avoid short-circuiting between the two layers of windings - ceramic is grooved with one layer of deep and one layer of shallow grooves which cross each other

  • for reducing the internal coil capacitance – larger winding pitch

  • for minimizing stray fields and avoiding noise in the signal - even number of layers and windings is necessary

Anna Encheva

Slide 5

Present design features

HF coils

  • usable at up to 2 MHz

measure both: equilibrium field and

fluctuation related to plasma instabilities

  • proposed implementation (minimum physics):

    • one poloidal array of ~20 coils (with non-uniform distribution) covering both low- and the high-field side on 3 machine sectors for redundancy, each coil with effective area (NA)EFF=0.1m2

    • two toroidal arrays of 20 coils (with non-uniform distribution) located at Z=ZMAG30cm, each coil with effective area (NA)EFF=0.1m2

  • heat shield – protection from the plasma,

    prevent from interfering with other circuits

    Shield - connected to the vessel ground

    the coils has to be fully isolated from the casing

  • bobbin - made of stainless steel layer and copper strips

Anna Encheva

Slide 6

Open design issues

HF coils

  • Choice of conductor

Molybdenum or Tungsten or other material, having:

  • Good winding properties

  • Withstanding high temperatures

  • Coil effective area

Now in total 0.075 sq.m. or larger?

  • Good frequency response within a wide operational range

10 kHz ÷ 1MHz

  • Withstanding electromagnetic loads by full disruption mode 200 T/sM.Roccella, ITER_D_22JQLY, May 2003

  • Withstanding high temperatures

Max. 600°C

Anna Encheva

Slide 7

Work plan 2006

HF coils

  • Transient electromagnetic analysis:

  • full disruption mode : 200T/s

  • induced voltage

  • Dynamic harmonic electromagnetic analysis:

    • induced eddy currents

    • amplitude - frequency response characteristics

  • Thermal analysis:

    • nuclear heating rate in the coil materials

    • temperature distribution in the coil structure

  • Coupled field analysis:

  • Structural analysis:

    • thermal loads

    • stress-strain distribution

Anna Encheva

Slide 8

MHD saddles

Measurement requirements

  • Main system:

  • Locked modes

  • Low (m,n) MHD modes, sawteeth, disruption precursors

  • Backups:

  • Plasma position and shape

If necessary: MHD saddles as backup measurements for the equilibrium reconstruction

Anna Encheva

Slide 9

MHD saddles

Location within the vessel

proposed implementation (general):

  • toroidal distribution: 4 sets of ~15 saddle loops with non-uniform distribution at Z=ZMAG80cm

    • 2 sets on low-field side + 2 sets on high-field side

    • toroidal positioning optimised for control of natural error field (TF ripple with/out ferrite inserts)

  • poloidal distribution: 1 set of ~20 saddle loops in >3 sectors

    • non-trivial role of *-correction (loops shrink: , lj)

    • redundancy is sufficient as saddle loops are permanent

  • where is ZMAG? need to optimise positioning of saddle loops as different magnetic equilibria are expected

  • effective area of each saddle loop (NA)EFF ~1.5m2

    • lower than previous DDD estimate (~5m2)

  • Mounted on the inner wall of vacuum vessel

  • Exist on 9 machine sector pairs (40° apart toroidally)

  • Poloidally – 8 loops mounted on each sector

  • Saddle loops are permanent

Anna Encheva

Slide 10

MHD saddles

Present design features

  • Loops of 2mm mineral insulated cable

  • attached to the vessel at frequent intervals via resistance-welded clips

  • Choice of MI cable

    Research activity, CIEMAT and SCK-CEN

  • Open design issues:

    • design changes are required to satisfy full-scope physics requirements (∆ZMAG, *-correction)

Anna Encheva

Slide 11

Divertor coils

Measurement requirements

  • measurement of separatrix-wall gaps and reconstruction of equilibria (plasma shape and position)

  • improve the reconstruction accuracy near the X-point

  • this set of coils is essential to the reconstruction of divertor configuration

  • Plasma Position and Shape:

  • Main plasma gaps with time resolution 10 ms and accuracy 1-2 cm

  • Divertor channel location (10 ms, 1-2 cm)

  • dZ/dt of current centroid for range of 5 m/s, time resolution 1 ms and accuracy 0.05 m/s (noise) + 2% (error)

  • Measured quantity:

  • Magnetic field (normal and perpendicular to diverter cassette elements) at coils locations.

Anna Encheva

Slide 12

Divertor coils

Location within the vessel

  • Position in the vessel: divertor cassette

  • Location:72 (6x6x2) coils on 6 divertor cassettes

  • ports 02, 04, 08, 10, 14, 16 (6 position)

  • System: pairs of equilibrium coils normal and tangential to the mounting surfaces of selected cassettes

  • 6 coils with an axis perpendicular to divertor cassette elements

  • 6 separate coils at equivalent positions with an axis parallel to divertor cassette elements

* The scaled drawing could be found on:

Anna Encheva

Slide 13

Divertor coils

Present design features

Nuclear heating in St.St. at coils locations

Construction of divertor coils similar to in-vessel coils

Better cooling

proposed coil effective area ~0.5m2, corresponding to ~50V

volume constraint (2x10x10x10 cm3) less severe than by in-vessel coils

for coils on pos.1,5,6  in-vessel tangential and normal coils design suitable

coils on high heat flux region pos.2,3  re-optimization of coil shape

different EM environment and screening, specially under divertor dome

0.5 W/cc

1.0 W/cc

2.1 W/cc

2.5 W/cc

1.0 W/cc

0.4 W/cc

* Reference: G.Mazzone et al., Final Report on the Revision of ITER divertor design, 2003

Anna Encheva

Slide 14

Divertor coils

Open issues

  • Design of in-vessel equilibrium coils as basis for preliminary divertor coils design

  • Choice of materials to minimize parasitic EMFs

  • Winding wire selection (MIC, bare wire, ceramic coated wire)

  • Divertor layout

    • identification of available space on divertor cassette

      • optimization of coil’s position, shape and orientation

  • Wiring and connectors

  • Estimation of mechanical errors (thermal expansion, EM forces)

  • Anna Encheva

    Slide 15

    Divertor coils

    Work plan 2006

    Identification of available space on divertor cassette (A.Martin, ITER IT)

    Re-design the present in-vessel coils for the position 2 and 3, under the divetor dome

    Dynamic harmonic electromagnetic analysis

    Thermal FE analysis

    Anna Encheva

    Slide 16

    Diamagnetic loop system

    ITER accuracy requirements

    • Main system:

    • Plasma energy

    • Toroidal magnetic flux

    • Range βp = 0.01÷3

    • Accuracy 5% at βp = 1

    • accuracy is highly demanding

    • estimation of mechanical errors is needed

    • definition of compensation methods

    Anna Encheva

    Slide 17

    Diamagnetic loop system

    ITER frequency requirements

    • f = 1 kHz

    • flux is attenuated by vessel eddy currents by a factor of:

    • poloidal time constant

    • Achieved in present device ~ 300 (TCV, time const. 5.3ms,10kHz)

    • Bandwidth is highly demanding

    • Importance of vessel eddy current compensation

      • Are the compensation coils adequate ?

      • Advantage of a double loop set-up ?

    Anna Encheva

    Slide 18

    Diamagnetic loop system

    Location and design

    3 sets mounted on the inner vessel wall, separated by 120°:

    • 2 diamagnetic loop, wired in parallel (to circumvent obstacles)

    • Attached to the wall by spot welded clips

    • 2 compensation coils

    • additional poloidal field compensation loops

    Diamagnetic loop contour

    Compensation coil


    Anna Encheva

    Slide 19

    Diamagnetic loop system

    Method for performance analysis

    Identify and describe sources of mechanical errors (2005)

    • construction misalignements and assembly errors in sensors

    • construction misalignements in PF and TF coils, VV

    • deformation under EM forces in PF and TF coils

    • deformation after thermal expansion of VV

    Quantifying mechanical errors requires:

    • magnetic field mapping (2006)

    • thermal expansion modelling of VV (2006)

    • modelling of VV deformation under EM forces

    • modelling of eddy currents in VV (2006)

    Anna Encheva

    Slide 20

    Diamagnetic loop system

    Diamagnetic loop status in short

    • Assessment of ITER measurement requirements:

    • very demanding

    • Methodology to perform comprehensive performance analysis

    • (requires modelling tool for various ITER components)

    • Feasibility of alternative set-up to be studied (double loop)

    Anna Encheva

    Slide 21


    Ex-vessel tangential and normal coils:

    specifications overview

    Ex-vessel tangential and normal coils is a backup set measuring plasma current, plasma equilibrium and plasma low frequency MHD activity.

    Location:On the outer VV skin in a poloidal cross-section

    Temperature: 200°C

    Effective area: 2.0 m2

    Issues: Available space 7x57x250mm3

    Radial dimension is small  coil sizing difficult



    Slide 22














    Progress made in TWP2004 task

    • Technical review EFDA TWP 2004 task

    • Number of coils defined : 60 Bnorm + 60 Btang

    • Choice of conductor : insulated copper wire (f0.25mm)

    • Coil design

    Bnorm cross section

    Btang cross section

    • Electrical parameters have been defined (resistance,inductance, capacitance, cut-off frequency, etc.)

    • Sources of errors have been identified

    • Future work : EFDA TWP 2005 task

    • Investigate winding issues

    • Error assessment using VV EM and movement models

    • Performance analysis of ex-vessel Bnorm and Btang coils (EFIT)


    Slide 23


    Ex-vessel continuous Rogowski:

    specifications overview

    Ex-Vessel continuous Rogowski is a separate backup measuring the plasma current and giving relevant information on current flowing through the vessel.

    Location:In 14.5mm diameter groove cut inTFC casing, coil OD is 12mm

    Temperature: 4.0K

    Sensitivity: typ. 800 mV s / MA

    Issues: Available space, joints

    Requirements :


    Slide 24


    Rogowski : Stainless steel former model

    Progress made in TWP2004 task

    • Technical review EFDA TWP 2004 task

    • Rogowski routing in TFC is defined

    • Number of joints as low as possible: One joint at the top ofTFC, another one at the bottom of TFC

    • Stress analysis during cool-down / warm-up cycles andplasma operation  Selection of material (former and cable)

    • Rogowski design and model have been done

    • Former having a double screw groove – regular winding

    two layers:

    1st layer diameter 11 mm

    2st layer diameter 9 mm

    Routing constrains: 100m radius of curvature

    • Electrical parameters have been defined (resistance,inductance, capacitance, cut-off frequency, etc.)


    Slide 25


    Ex-vessel continuous Rogowski:

    specifications overview

    • Future work : EFDA TWP 2005 task

    • Refine the design and former selection (easy bending)

    • Rogowskis in two parts

      Define the joints

    • Assess Rogowski’s accuracy and source of error


    Slide 26


    Inner vessel partial and continuous flux loops: specifications overview

    Continuous and partial flux loops contribute as the main set-up to plasma equilibrium calculation (with in-vessel Bnorm and Btang).

    The continuous loops supply loop voltage and are supplementary set to get plasma current.

    Partial flux loops are also a supplementary set measuring plasma MHD activity.

    Location:Inner surface of the VV

    Number:4 continuous flux loops + 6 sets of 20 saddle loops

    Design: 2mm MIC

    Mechanic:Attached to the VV byspot welded joints

    Temperature: 300°C

    Issues: Subjected to plasma and nuclear heatingContinuous flux loops interrupted by 9 welded joints


    Slide 27


    Section for removal

    Contact plate

    Flux loop

    Support plate

    Joint soldered to

    support plate


    Progress made in TWP2004 task

    • Technical review EFDA TWP 2004 task

    • 9 special welded joints allowing 3 replacements by remote handling

    • Electrical parameters have been defined (resistance,inductance, capacitance, cut-off frequency, etc.)

    • Source of errors have been investigated

    • Open issues

    • Define the thermal gradient along the cable (TIEMF effect)

    • Measurement errors assessment using VV EM and movement models


    Slide 28

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