Kinetic Control - Nucleus

Kinetic Control

F. Janky, E. Fable, O. Kudlacek, W. Treutterer, H. Zohm

Max-Planck Institute for Plasma Physics

5th IAEA DEMO Programme Workshop

7th – 10th May, 2018, Daejeon

Outline

• Introduction

What is kinetic control

Previous works

Comparison between DEMO and ITER diagnostics and actuators

• DEMO kinetic control: What and how do we control

Tools

• Results

Tungsten impurity in separatrix

Pellet success rate

Pellet size

Pump speed

NTM control

• Conclusion

5th IAEA DEMO Programme WorkshopF. Janky 2

Kinetic control


• Pfus

= n2× Ti0÷2

• Core

DT pellet mixture

Heating with P⍺, NBI, ECRH

⅘ energy from DT reaction goes to neutrons

and ⅕ to alpha particles. P𝜶 and Pheat has to be

radiated in the core and SOL/div region before

it reaches the divertor tiles.

Xe impurity puff to radiate energy

• Psep

> 1.2 × PLH

(130 MW) – H-mode

• SOL/div

DT gas mixture to the midplane

Ar, Kr impurity

Divertor temperature Tdiv

< 5 eV (erosion

should be minimised)

→ Fully detached plasma

AUG cross-section

Motivation


• Model DEMO (physics, technology and controllability of

scenario)

• Design and develop control of DEMO

• Test and validate different physical models

• Test different control approaches

How to control Pfus

, Psep

, Tdiv

• Answer technical questions using model of DEMO

Precision and noise in diagnostics

Error and delay in actuators

How much NBI or ECRH power

Previous works

• D. Moreau and I. Voitsekhovitch, 1999, NF, advanced steady state control – requires high diagnostic precision to deduce radial profile of the internal plasma flux – unlikely for DEMO

• M. D. Boyer and E. Schuster, 2014, PPCF, 0-D model, isotopic fuelling, sophisticated non-linear control

• M. D. Boyer and E. Schuster, 2015, PPCF, 0-D model, 1-D model used to test robustness

• C. E. Kessel et al., 2014, different 1-D models, however, no perturbations and no delays and realistic actuators and diagnostics

• Our work – 1-D model, external disturbances, delays, realistic actuators

• Experiment: T. T. C. Jones et al., 2001, EPS, ICRH as a simulation of P⍺ with RT

control


Diagnostics and actuators


Control quantity Operational

limits

DEMO Diagnostics ITER Diagnostics Actuators +

interactions

Plasma (edge) density

density limit ReflectometryIR polarimetry/interferometryPlasma radiation

interferometer/polarimeter pellet injection (fuel)gas injectionpumping system

Plasma radiation, impurity mixture, Zeff

radiation limitLH threshold

Spectroscopy+radiation meas.Uloop

bolometry: radiated power, Ha, vis. spectroscopy, VUV, X-ray(core + divertor), CXRS, BES

impurity gas injectionauxiliary heating

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

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

diamagmetic loop: plasma energy,neutron flux monitors and cameras,neutron spectrometer: fuel ratio,

neutral particle analyzer: fuel ratio,D/T influx: Ha, vis. spectroscopy

pellet injection (fuel)impurity gas injectionauxiliary heating

Divertor detachment and heat flux control

divertor wall loads LH threshold

Spectroscopy+radiation meas.ThermographyDivertor thermo-currents

Reflectometry, ECE

IR thermography, VIS/IR imaging, pressure gauges, residual gas analysers, Langmuir probes

gas injection (impurities + fuel)pellet injection (fuel)

PF coils, pumps

ELMs Target overheat Ha, vis. spectroscopy ELM pellet inj,ITER: ELM ctr. coils

Gas pressure in main chamber

pressure gauges gas injection, pumps

Te, ne profiles Thomson scattering, ECE, reflectometry

EC

Ti profile X-ray

Current profile MSE, polarimetry EC, NBI

Plasma rotation X-ray, CXRS NBI

Legend:

• Usable/foreseen for DEMO

• Big issues/not feasible in DEMO

• Applicable with restrictions

(e.g. resolution, sacrificial)

EU DEMO1


R 9.1 [m]

a 2.935 [m]

Bt 5.7 [T]

κ 1.7013

𝛅 0.383

Ip 20 [MA]

V 2500 [m3]

Ti0 35 - 40 [keV]

ne0 1e20 [m-3]

Pfus 2 [GW]

PLH 130 [MW] R. Wenninger, et al., 2015, Nucl. Fusion, 55, 063003

8

Control - DEMO

• Currently use ideal diagnostics

• Realistic pellet actuators according to AUG technology

Different pellet size, success rate and launch frequencies

• Delays on every actuator based on realistic assumptions

• Transport coefficient 𝛘 with random noise 5%

• Controllers with FF and FB PI components

• Fusion power Pfus

Target: 2 GW

Actuators: NBI, pellet D/T ratio, pellet frequency

Diagnostics: Pfus

= 5 × P

~ nneutron

• Pedestal top electron density Greenwald fraction, ne/n

GW

Target: 0.8 – 0.95 (given by density limit – operational limit)

Actuators: pellet frequency

Diagnostics: electron density at r/a = 0.94

9

Control - DEMO

• Divertor temperature

Target: < 5 eV

Actuators: Ar or Kr gas puff to divertor

Diagnostics: divertor temperature

• Separatrix power Psep

Target: Psep

> 170 : 200 MW ( about 1.2 PLH

)

Actuator: Xe gas puff to midplane

Diagnostics: Psep

= Pa

+ PNBI

+ PECRH

- Prad

• NTM control

Target: small or no island

Actuator: ECCD at rational surface

Diagnostics: electron temperature profile

10

Tools

• ASTRA [*]

• 1-D transport code with 2-D MHD equilibrium solver (SPIDER)

• Serves as a plasma model

[*] G. V. Pereverzev and

Yu. P. Zushmanov, IPP

5/98 2002

[*] E. Fable, et al.,

2013, Plasma Phys.

Control. Fusion, 55

124028

11

Physics: core

• 1-D transport code

• SPIDER for 2-D MHD equilibrium (in this study fixed boundary)

• Core transport model: semi-empirical model fitted to the present

experiment (ASDEX Upgrade - AUG)

• L-H and H-L model with low hysteresis based on Psep

> PLH

• Sawtooth model - complete reconnection if magnetic shear s > scrit

• Pedestal model – ion neoclassical transport for Ti,e, ni,e; pedestal top

pressure saturates according to EPED scaling ~ 𝛽N0.43 [*] ”no ELMs”

[*] E. Fable et al., FED, 2018

12

Physics: edge

• SOL/div 0-D particle balance model

Enrichment factor 𝜖j – Ar 20, Xe 6, He 1.2, W 6;

Dj – SOL/div time scale = 1 [s-1]

• SOL/div analytical exhaust model “c” fit to 1-D model [*] – in practice

W flux model:

fr – redeposition factor; j - species

[*] M. Siccinio, et al., 2016, Plasma Phys. Control. Fusion, 58, 125011

13

Tools

• Simulink

• Commercial tool for simulation purposes

• Provides environment to simulate different physics and control

oriented tasks with a graphical user interface

• Serves as a control system

14

Coupling ASTRA and Simulink

• ASTRA

• Serves as the plasma model

• Simulink

• Serves as the control system

• Plasma Control System Simulation Platform - (PCSSP)

• Framework developed within Simulink for ITER tokamak

• Waveforms and events generators

• Easily adaptable for different machines (currently ITER, DEMO,

AUG)

15

Coupling ASTRA and Simulink

Pa, n

e

Flow

Xe, Ar, Kr

D, T

Tdiv

, Psep,

nsep

PNBI

, PECRH

Pa, T

e

fpellet

Choose operation point


• ne(GW) reference step

• Ideal pellet actuator

• Big influence at fusion

power

• 100 MW NBI power is

not sufficient enough to

compensate the drop

(NBI saturated)

• Operational points

must satisfy both

physics limits and

actuator margins

Tungsten flake (simulation)


• 3 mg of a tungsten falling into

separatrix

FF vs. FB

FB on Pfus (PNBI), Psep (Xe)

„Old“ electric field shear LH

model with high hysteresis

• No HL transition occurred

„New” Psep/PLH model without

hysteresis

• radiation collapse

• Realistic physics models are

extremely important to answer

DEMO questions

Open loop simulation

• Realistic pellet success rate 90% (plasma lost within 20 s)


Closed loop

• Feedback loop – with 90% success


Success rate variation

Success rates: 95%, 90%, 80% for 3e21 p/pellet


Success

rate

Pfus

std dev

95% 49 MW

90% 73 MW

80 114 MW

Pellet size variation

Success rate: 90%; Pellet size [p/pellet]: 6e21*, 3e21, 1e21

Mean ne(GW): 0.83, 0.79, 0.79; Mean fpellet [Hz]: 1.8, 4.1, 12.8


pellet

size

[p/pellet]

Pfus

variance

6e21 89 MW

3e21 73 MW

1e21 60 MW

[*] P. Lang et al., FED,

2015

Smaller pellets have

lower success rate

to reach the plasma!

Pump speed change


NBI saturated

Simulation of NTM stabilisation


• EC beam half width 3 cm

• Power deposited at island location

and applied 0.5 s after the island

appears

• Initial Wseed = 0.01 ρtor (3 cm)

• 3/2 stabilization: 11 MW

• 2/1 stabilization: 9.5 MW

• More power needed to stabilize 3/2

due to higher jbs at q=1.5 flux surface

• Power deposition error is critical

• modified Rutherford equation taking into account neoclassical, classical,

curvature and CD effects [Sauter 1999, 2002, 2004]

• current drive: proportional to EC power, η=5.3 from TORBEAM simulation:

𝐈𝐞𝐜𝐜𝐝 =𝛈𝑻𝒆𝐏𝐄𝐂

𝟐𝛑𝐑 𝟓+𝒁𝒆𝒇𝒇 𝒏𝒆

Analysis of deposition error effect


• Effect of off-island EC power

deposition

Analyse the relation between

o power needed to stabilize the

mode

o deposition error

EC power available: 30 MW

o Error must stay below 3 cm

Sweeping deposition across

the expected NTM position will

be mandatory

• Future plans:

Include mode position identification using ECE diagnostics with realistic

noise levels (Consiglio Nazionale delle Ricerche - collaboration)

Study the effect of the sweep amplitude

Conclusions

• This kinetic modelling and control work is important to

Physical models – test, compare and validate in present experiments

Actuators – estimate required power, efficiency, maximum delays

Diagnostics – estimate tolerable noise and required resolution

Control – investigate control strategies and controllability of scenario

• Caveat - explorative work

More physical realistic models are necessary

• Detected issues

Actuator saturation:

o not be able to stay above PLH in case of impurity event

o Pedestal density Greenwald fraction too low

o Pumping speed is too low – plasma dilution by He

Actuator reliability

o Fusion power oscillations due to missing pellets

Diagnostic issues – Future work


Future work

• Physics

New LH model based on electric field shear

Validate models at operating devices

Implement to ASTRA heating and current drive models

• Diagnostics

Model realistic diagnostics in Simulink

• Control

Test different control strategies (MIMO)


Thank you for your attention


Extras


Reactivity


30

Coupling

• ASTRA

• 1-D transport code with 2-D MHD equilibrium solver (SPIDER)

• Serves as the power plant

• Simulink

• Synchronisation and data exchange is done using semaphores and

shared memory – Read/write access for ASTRA is blocked by Simulink

semaphore until Simulink finishes writing and vice versa

DEMO D/T ratio control


D-T reaction


http://www.crossfirefusion.com/

nuclear-fusion-reactor/crossfire-

fusion-reactor.html

Sun reaction


Kinetic Control - Nucleus

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