Moving fast in fusion reactors: ASCOT – race track for fast ions

T. Kurki-Suonio, Aalto University

for the ASCOT team

O. Asunta, E. Hirvijoki, T. Koskela, J. MiettunenS. Sipilä, A. Snicker and S. Äkäslompolo

MeV–range ions in reactors MW/m2 on the wall?

Today’s tokamaks– only mock-fuel: pure D ”no” fusion reactions

Tomorrow’s reactors:– Fusion reactions 3.5 MeV alphas– Neutral beams 1 MeV deuterons and/or

tritons– ICRH heating ions with several MeV

How to confine hot ions so that ― they heat the plasma ― they do not destroy the wall?

In principle, charged particles are glued to the magnetic field lines

But life is never so simple...

Fast ions can have large gyro radii and ENORMOUS banana widths

Engineering reality: no axisymmetry

An almost ideal situation:JET w/ 32 coils

Reactor reality: ITER w/ 18 coils

Only finite # of TF coils B-field becomes a ”toroidal sausage” = Toroidal Field Ripple

ITER reality: There is more to life than the TF ripple...

Even the harmonic ripple structure is destroyed by things like

Presence of ferritic material in the walls* Ferritic inserts (FI) reduce the TF ripple* Ferritic structures can introduce strong local

perturbations. Prime example: TBMs in ITER* Also by lack of FIs (around NBI ports)

External coils can generate their own ’ripples’ at their will. * Prime example: ELM-mitigation coils in ITER

(and, today, at AUG, DIII-D, JET)

Example: BT (φ) at the edge of ITER

Toroidal ripple 0.25%,

Field bump due to NBI ports 0.57%

Field bump due to TBMs1,1%

How to study fast ions today:

DT-experiments to produce 3.5MeV alphas?– few and far apart:

~TFTR (1993): Pfus = 10.6 MW~JET (1997): Pfus = 16.1 MW (Q ~ 0.7)

Externally produced fast ions?– Neutral beam injection: only up to about 100keV– ICRH: MeV range ions but only few

We are left at the mercy of simulations– Multitude of codes, but one appears quite far

ahead of the others...

ASCOTFully 3D

– 3D magnetic field– 3D Wall

Realistic orbit tracing– Guiding center (fast)– gyro orbit (accurate)

Comprehensive interactions– Coulomb collisions– Turbulent transport– Models for relevant MHD:

• NTM-type magnetic islands• Alfven Eigenmodes

Some examples: 3D effects on fast ions a la ASCOT

TBM mock-up experiments at DIII-D– Effect on NBI-ions– Effect on neutrons from DD -> DT -fusion reactions

The effect of ELM-mitigation coils on wall loads:– NBI-ions in ASDEX Upgrade

ITER wall power loads due to fusion alphas:– The effect of ripple & Co– The effect of wall structure

The effect of ferritic structures

Case Study: TBM mock-up experiments @ DIII-

D

NBI-generated deuterons in DIII-D discharges w/ TBM mock-up

limiters

TBM mock-up coils

DD DT 14 MeV n

Experimental neutron flux in the TBM mock-up exp’t

Fraction of confined tritium in the plasma as calculated by ASCOT

M. Schaffer & al, Nucl. Fusion 51 (2011) 103028

The effect of ELM-mitigation Coils

Case study: B-coils in ASDEX Upgrade

Losses of 60keV NBI deuterons

Direct ripple well losses

Additional spot next to the coil

Fusion alphas in ITER

Advanced Scenario-4Ip = 9MA ’only’

Confined fast ions vulnerable

Axisymmetry vs ripple vs FI2-limiter case

Axisymmetric B-field With ’nude’ rippleRipple w/ FI’s

Also wall shape matters...

Original wall w/ 2 limiters Present wall design w/ poloidally extended ’continuous’ limiters

Future of fast stuff: full of work!

F4E task approved: – GRT-379: “Calculation of the TBM-induced

ripple in ITER, wall loads, impact on plasma and optimization”, 2012 – 2014; 777 500 €

ITPA-EP activity: expert group twice a yearTritium experiments at JET (2015?)

Thank you for your attention!

Acknowledgements

For input data:• ITER Organization, IPP Garching, General Atomics

For computing resources:• The supercomputing resources of CSC – IT center for science• HPC-FF

For funding:• This work was partially funded by the Academy of Finland Projects No. 121371 and No. 134924• This work, supported by the European Communities under the contract of Association between Euratom/Tekes, was carried out within the framework of the European Fusion Development Agreement. The views and opinions expressed herein do not necessarily reflect those of the European Commission.