Introduction and overview of plasma control

Introduction and overview of plasma control(with emphasis on boundary conditions arising from diagnostic limitations)

5th IAEA DEMO Programme Workshop

Daejeon, South Korea, 7 - 10 May 2018

Wolfgang Biel1,2 and contributors to EUROfusion WPDC1Institute of Energy- and Climate Research, Forschungszentrum Jülich GmbH, Germany2Department of Applied Physics, Ghent University, Belgium

[email protected]

W. Biel | Introduction to plasma control, 5th IAEA DPW, Daejeon, Korea, 07th May 2018 |

W. Biel1,2, R. Albanese3, R. Ambrosino3, M. Ariola4, M. v. Berkel17, I. Bolshakova18, K.-J. Brunner16 , R. Cavazzana8,

M. Cecconello5, S. Conroy5, A. Dinklage16, I. Duran6, R. Dux7, T. Eade20, S. Entler6, G. Ericsson5, E. Fable7,

D. Farina15, Th. Franke7,9, L. Giacomelli15, L. Giannone7, W. Gonzalez1, A. Hjalmarsson5, M. Hron6, F. Janky7,

A. Kallenbach7, J. Kogoj13, R. König16, O. Kudlacek7, R. Luis11, A. Malaquias11, O. Marchuk1, G. Marchiori8,

M. Mattei19, F. Maviglia3,9, G. De Masi8, D. Mazon12, H. Meister7, K. Meyer13, A. Mlynek7, S. Nowak15, Ch. Piron8,

A. Pironti3, H. Policarpo11, N. Rispoli15, V. Rohde7, G. Sergienko1, S. El Shawish14, M. Siccinio7,9, A. Silva11,

F. da Silva11, C. Sozzi15, M. Tardocchi15, M. Tokar1, W. Treutterer7, A. Vale11, H. Zohm7

1Institut für Energie und Klimaforschung, Forschungszentrum Jülich GmbH, Germany2Department of Applied Physics, Ghent University, Belgium3Università degli Studi di Napoli Federico II, Consorzio CREATE, Italy4Universita’ di Napoli “Parthenope”, Consorzio CREATE, Italy5Department of Physics and Astronomy, Uppsala University, Sweden6Institute of Plasma Physics, Czech Academy of Science, Praha, Czech Republic7Max-Planck-Institut für Plasmaphysik, Garching, Germany8Consorzio RFX (CNR, ENEA, INFN, Università di Padova), Padova, Italy9EUROfusion Power Plant Physics and Technology (PPPT) department, Garching, Germany10Department of Physics, Universita ‘degli Studi di Milano-Bicocca, Milano, Italy11Instituto de Plasmas e Fusão Nuclear, IST, Universidade de Lisboa, Portugal12CEA, IRFM F-13108 Saint Paul-lez-Durance, France13Cosylab, Ljubljana, Slovenia14Jožef Stefan Institute, Ljubljana, Slovenia15IFP-CNR, Istituto di Fisica del Plasma, Milano, Italy16Max-Planck-Institut für Plasmaphysik, Greifswald, Germany17DIFFER institute, Eindhoven, The Netherlands 18Magnetic sensor laboratory, Lviv, Ukraine19Universita’ della Campania “Luigi Vanvitelli”, Consorzio CREATE, Italy20CCFE, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, United Kingdom

Contributors to EUROfusion WPDC


1. Cover all DEMO control needs - diagnostics are only for control

2. Provide high reliability, availability (and accuracy) of plasma operation

over long time

• optimise fusion performance (go near to operational limits)

• avoid disruptions (machine damage)

(keep distance from operational limits, install redundant systems)

• caveat: strong adverse effects acting on diagnostic components

while possibilities for maintenance are limited

3. Minimum impact on the tritium breeding rate (TBR) and shielding

• only limited space available for diagnostic integration (TBR < 0.04) prefer

diagnostic systems with low space consumption

4. Minimise efforts

• Prefer proven methods and technologies (reduce risks and development effort)

• Standardisation / modularization of components and integration approach

Requirements and challenges for theDEMO diagnostic and control system

impact on definitionof plasma scenario(controllability)

impact on machinedesign


Radiation issues for plasma diagnostic front end components on EU DEMO

Typical irradiation levels behind the blanket:

ITER: 1 GGy1020 n/cm2

DEMO: 1.2 GGy (gamma + n, OB)12 GGy (gamma + n, IB)

> 1021 n/cm2 (OB)1022 n/cm2 (IB)

DEMO neutron flux map

Neutron fluences behind the EU DEMO blanket are 10 .. 100 times larger than on ITER

(T. Eade, CCFE)

(G. Vayakis,

ITER_D_26ZGC3)

(T. Eade, CCFE)

Radiation effects on diagnostic components:• radiation-induced conductivity (RIC)• radiation-induced thermoelectric sensitivity (RITES)• radiation-induced absorption (RIA)• radio-luminescence• thermal conductivity decrease• volume changes (swelling)• …..

Active cooling required for all front-end components.


1019

1020

1021

1022

1023

4.0

1022

n·m-2

9·1019

n·m-2

2.0

1.0

0

3.0

ITER lifetime fluences

for ex-vessel sensors

Se

nsitiv

ity,

S x

10

4 (

mV

·A-1·T

-1)

Fluence, F (n·m-2)

1

2

1019

1020

1021

1022

1023

1024

2.0

2.5

1.5

1.0

0

Sen

sitiv

ity, S

(m

V·A

-1·T

-1)

Fluence, F (n·m-2)

1

2

0.5

Hall sensors based on the InAs nanofilms Hall sensors based on the Au nanofilms

no degradation up to 0.1 dpa

Hall sensors for the ITER and DEMO lifetimes neutron fluences

On-line testing at the pulsed fast reactor IBR-2 (JINR)

Irradiation testing in IBR-2 reactor: neutron flux 1.5×1017 n∙m-2∙s-1 ; temperature 130 °C

• Semiconductor (InAs) Hall sensors: stable up to fluence of 1022 n∙m-2 (ITER ex vessel)

• Gold Hall sensors: stable up to fluence of 1024 n∙m-2 (DEMO behind blanket)

InAs sensors parameters

Carrier concentration (1) 2.4·1018 cm-3

(2) 6.0·1018 cm-3

Active element sizes 0.2×0.2 mm2

Film thickness 100 nm

Substrate material GaAs

Resistance 80 Ohm

Au sensors parameters

Manufacturing method (1) vacuum thermal deposition

(2) electron-beam evaporationActive element sizes 0.2×0.2 mm2

Film thickness 50 nm

Substrate material Al2O3

Resistance 2 Ohm

(I. Bolshakova et al., Nucl. Fusion 2015) (I. Bolshakova et al., Nucl. Fusion 2017)

B = 1 mT U ~ 100 nV


First mirror lifetime investigations for DEMO: erosion(modelling for deposition ongoing)

M. Z. Tokar, submitted to: Plasma Science and

Technology, Ed. Haikel Jelassi, InTechOpen

Geometry investigated: Mirror surface erosion per full power year:

Duct geometry required for 1st mirror protection against erosion (vacuum conditions):• h/ρ0 > 80 for IR diagnostics (interferometry, thermography)• h/ρ0 > 100 for VIS spectroscopy• h/ρ0 > 200 for VUV spectroscopy

kinetic

calculation

diffusion

approximation


Improvement of first mirror erosion lifetimeby a gas target in the duct

Mirror surface erosion per full power year:

M. Z. Tokar, submitted to: Plasma Science and

Technology, Ed. Haikel Jelassi, InTechOpen

Duct geometry required for 1st mirror protection against erosion• h/ρ0 > 40 for IR diagnostics (interferometry, thermography)• h/ρ0 > 50 for VIS spectroscopy• h/ρ0 > 80 for VUV spectroscopy

(dashed – double dotted line corresponding to gas target in duct with density nH = 3e19 m-3, mean free path ~ 10 cm)


EU DEMO concept for implementation of diagnostic front-

end: durable components; retracted mounting positions

• In front of blanket and divertor:

• No diagnostic components

• Within blanket area:

• Microwave antennae+waveguides (metallic)

• tube-like penetrations for spectroscopy, interferometry/polarimetry, neutron+gamma

• Behind blanket:

• Optical mirrors (metallic) and beam paths

• magnetic sensors (metal+ceramic) & cablingt.b.d. (depending on durability)

• Port plugs:

• signal routing, mirror labyrinths

• penetrations (cables, tubes) and windows

• Within/behind divertor target:

• Implementation of sheath voltage or thermo-current measurement

• [narrow sightlines using gaps betweencassettes or tube-like access in low power region, t.b.d.]

equatorialports

vertical ports


EU DEMO main diagnostic methods (1): magnetic sensors

(A. Pironti et al.)

Estimation of vertical plasma position

Zp using magnetic diagnostics

Conclusion:• Fast changes (~ 10 ms) of plasma

position cannot be followed by ex-

vessel sensors only (eddy current

shielding by the vacuum vessel)

Simulation results:Coil based sensors:• time integration of low signals over long pulses

Hall sensors: • very low signals, temperature dependent

Open issue: irradiation hardness of in-

vessel magnetic sensors on DEMO


Simulation of equilibrium control based on in-vesselmagnetics: loss of confinement event

M. Ariola et al, SOFT 2018 (submitted)

change of plasma

position up to 25 cm

control power to PF

coils up to 700 MW

Equilibrium control is marginal even under optimistic assumptions

This simulation is

assuming ideal

in-vessel magnetic

sensors

Adding small noise

to the magnetic

measurements leads

to loss of control

voltages at PF coils

go to saturation


EU DEMO main diagnostic methods (2):Microwave diagnostics

Diagn. methods: ➢ reflectometry➢ ECE

Control tasks tobe covered:

➢ ne profile in gradient region➢ Te profile➢ plasma position and shape➢ plasma instabilities

Implementation: ➢ > 100 antennae distributed toroidally and poloidally (LFS, HFS, upper, x-point)➢ integration of antennae + waveguides in slim poloidal diagnostic cassettes➢ routing of waveguides to upper port (attached to „blanket bananas“)➢ Microwave feedthroughs or ceramic windows near upper port

A. Silva,

A. Malaquias,

C. Sozzi,

G. de Masi, et al.

Integration study of MW antennae

Predicted gap accuracy:

green: high (few cm)

red: low (~ 10 cm)

G. Marchiori et al., SOFE 2017R. Luis et al., SOFE 2017

A. Malaquias et al., SOFE 2017

In case of 2 full poloidal sectors (< 25 cm each)the effect on TBR would be TBR < 0.01


EU DEMO main diagnostic methods (3):IR polarimetry/interferometry

Diagn. methods: ➢ IR interferometry (combined with polarimetry), ~ 10 µm wavelength

Control tasks tobe covered:

➢ ne in core plasma (r/a < 0.7)➢ plasma position and shape (startup phase!)➢ plasma instabilities (contribute)

Implementation: ➢ Laser beams entering at eq. ports; IR windows at port plate or bioshield t.b.d.➢ first mirror and retro-reflectors behind blanket (inboard or outboard, tbd)

Sightline arrangement for DEMO system to be based on theITER layout:

poloidal beams or toroidal beams

(A. Mlynek, K.-J. Brunner, et al., IPP)

Option for vertical position control!

Protection of retro-reflectors?

First mirrors can be well protected!

Mid-plane allows only 3 different beam paths?


• Two contradicting requirements for power exhaust control are driving the requirements:

• qdiv < divertor wall limit – margin

• Psep > PLH + margin

• Actuators for divertor control: impurity injection for plasma core (Xe) and for divertor radiation (Ar)

Diagnostic contributions planned for power exhaust control:

1) Measurement of core radiation (H mode control)

• Psep = Pheat – Prad,core

2) Measurement of divertor thermo-current

• based on sheath voltage due to plasma-wall contact

3) Spectroscopic detection of divertor detachment

• T, v, location of ionisation front, fluxes(?)

• check for X-point MARFE (upper limit of detachment)

• assuming that full detachment is sufficient for divertor protection

4) Spectroscopic measurement of W erosion flux at divertor strike-point

• control (limitation) of W erosion of the divertor target needed

• assuming that vanishing W flux is sufficient for divertor protection (non-monotonic relation?)

5) Thermography on divertor target

• needs lines of sight with angle > 30 degrees against divertor target

Approaches for DEMO power exhaust control

small differences of big numbers to be measured

strong background radiation in detached plasma

requires isolated mounting of divertor, low signal only

spatial resolution?

spatial resolution?


Main diagnostic methods in DEMO (4):Divertor thermo-current measurement for detachment control

Principle:

▪ sheath voltage at divertor target depends

on plasma temperature

A. Kallenbach et al., J. Nucl. Mat. 2001 Study on implementation on DEMO:

▪ isolate divertor targets against vacuum vessel

▪ use coolant tubes as shunt resistor

▪ implementation in each divertor target

L. Giannone, IPPS. El-Shawish, JSI/cosylab

Feasibility depends on durability of insulators

against neutron irradiation and on limiting

current generated in cooling pipes by a disruption.

Low signal levels (10…100 mV) are expected.

Shunt resistor (100 µ)


• Diagnostics methods:

• spectroscopy from X-ray to IR

• plasma radiation (power) measurement

• thermography

• Control tasks to be covered:

• radiation control (core, edge, x-point, divertor)

• divertor detachment control

• wall surface temperature control (div. and FW)

• spectroscopic and radiationmeasurements are essential for power exhaust control

• Integration issues:

• first mirrors in protected locations (long ducts)

• secondary mirrors in vessel to guide light toports (1-2 mirrors per channel)

• spatial coverage <150 narrow lines ofsight, space occupation under investigation

• certain sightlines may not be feasible foradvanced divertors

EU DEMO main diagnostic methods (5):spectroscopic and radiation measurements


EU DEMO main diagnostic methods (6)

Diagn. methods: ➢ Neutron and gamma flux measurements + spectroscopy

Measurements: ➢ Fusion power density profile➢ Ion temperature profile in core (from neutron/gamma spectra)➢ ne and Ti profile in core from neutron flux (contribute during burn phase)➢ plasma position and shape (contribute during burn phase)

Implementation: ➢ 2 equatorial system(s) and 2 vertical port system(s) at different toroidal locations, each with ~ 12 beams

➢ straight tubes leaving the ports, ex-bioshield detectors

M. Cecconello,

L. Giacomelli, et al.

Integrated calibra-tion tracking of fluxmonitors (fissionchambers), activation foils andthermal power measurements


Control quantity Operational limits Diagnostics Actuators + interactions

Plasma current safety factor limit (q95) magnetic diagnostics(in-vessel and ex-vessel)

CS coilsauxiliary heating

Plasma position and shape, incl. vertical stability

wall loads (FW and div.)max. z / VDE disruption

magnetic diagnosticsMW reflectometry, ECEneutron/gamma diagnosticsIR polarimetry/interferometry

PF + CS coils(in-vessel coils?)auxiliary heatinggas injection

Plasma density density limit MW reflectometry (edge)IR polarimetry/interferometry

pellet injection (fuel)gas injectionpumping system

Plasma radiation, impurity mixture, Zeff

radiation limitLH threshold

Spectroscopy+radiation meas.Uloop

impurity gas injectionauxiliary heating

Fusion power wall loads (FW and div.)LH threshold

Neutron diagnosticsFW/blanket and div. power (for calibration only)

pellet injection (fuel)impurity gas injectionauxiliary heating

Divertor detachment and heat flux control

divertor wall loads LH threshold

Spectroscopy+radiation meas.ThermographyDivertor thermo-currentsMW reflectometry, ECE

gas injection (impurities + fuel)pellet injection (fuel)PF coilspumping system

(MHD) plasma instabilities various ( disruptions) MW reflectometry, ECEIR polarimetry/interferometrymagnetic diagnosticsneutron/gamma diagnostics

auxiliary heatingECCDPF coils

Plasma pressure beta limit magnetic diagnosticsdensity and temperature meas.

auxiliary heatingfuel and impurity injection

Unforeseen events (impurityingress, component failure)

various ( disruptions) all all

EU DEMO: summary of the diagnostic&control concepte

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• Diagnostic implementation and performance on DEMO are limited by:

• degradation of front-end components by ionising radiation, erosion and deposition

retracted mounting of front-end components lower spatial resolution, lower accuracy

selection of robust diagnostic methods and components only

• low space available for diagnostics, remote maintenance and integration issues

• Actuator properties are limited as well:

• only limited amount of auxiliary power can be afforded

• ex-vessel PF coils act slowly, eddy current shielding by blanket and vacuum vessel

• Most critical issues and risks:

• feasibility/durability of in-vessel magnetic measurements; fast equilibrium control

• feasibility of power exhaust (divertor detachment) control

• unforeseen events not captured by plasma models disruptions

• large number of measurement channels to be integrated

• Feasibility of control system will have impact on:

• plasma scenario (operational space for reliable control)

• machine design / size and architecture

Some conclusions

Loss of plasma control typically ends up in a disruption.

A disruption in a fusion reactor will release an energy of 1..2 GJ within a

short time of a few ms to the first wall.

Reliable plasma control in a reactor means:

• Aiming for less than one (full energy) disruption in 10…100 full

power years of operation.

Reliable plasma control


Introduction and overview of plasma control

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