Transcript 3D effects on energetic ions (particles)

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
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 TBMs
1,1%
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...
Fully 3D
ASCOT
– 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
M. Schaffer & al, Nucl. Fusion 51 (2011) 103028
Experimental neutron flux in
the TBM mock-up exp’t
Fraction of confined tritium in the
plasma as calculated by ASCOT
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-4
Ip = 9MA ’only’
 Confined fast ions vulnerable
Axisymmetry vs ripple vs FI
2-limiter case
Axisymmetric B-field
With ’nude’
Ripple
w/ FI’s
ripple
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 year
Tritium 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.