1. 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. Miettunen
S. Sipilä, A. Snicker and S. Äkäslompolo

2. 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

3. 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

4. But life is never so simple...
Fast ions can have large gyro radii and ENORMOUS banana widths

5. 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

6. 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)

7. Example: BT (φ) at the edge of ITER
Toroidal ripple 0.25%,
Field bump due
to NBI ports
0.57%
Field bump due
to TBMs
1,1%

8. 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...

9. ASCOT Fully 3D Realistic orbit tracing Comprehensive interactions
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

10. 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

11. The effect of ferritic structures
Case Study:
TBM mock-up DIII-D

12. NBI-generated deuterons in DIII-D discharges w/ TBM mock-up
limiters
TBM mock-up coils

13. DD  DT  14 MeV n Experimental neutron flux in the TBM mock-up exp’t
M. Schaffer & al, Nucl. Fusion 51 (2011)
Experimental neutron flux in the TBM mock-up exp’t
Fraction of confined tritium in the plasma as calculated by ASCOT

14. The effect of ELM-mitigation Coils
Case study:
B-coils in ASDEX Upgrade

15. Losses of 60keV NBI deuterons
Direct ripple well losses
Additional spot next to the coil

16. Advanced Scenario-4 Ip = 9MA ’only’  Confined fast ions vulnerable
Fusion alphas in ITER
Advanced Scenario-4
Ip = 9MA ’only’
 Confined fast ions vulnerable

17. Axisymmetry vs ripple vs FI 2-limiter case
Axisymmetric B-field
Ripple w/ FI’s
With ’nude’ ripple

18. Also wall shape matters...
Original wall w/ 2 limiters
Present wall design w/ poloidally extended ’continuous’ limiters

19. 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 year
Tritium experiments at JET (2015?)

20. Thank you for your attention!

21. 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 and No
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.