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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

    Iter frequency requirements

    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

    Method for performance analysis

    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 status in short

    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 in TFC 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 of TFC, another one at the bottom of TFC

    • Stress analysis during cool-down / warm-up cycles and plasma 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 by spot 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