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Fast particle physics on ASDEX Upgrade
Sibylle Günter G. Conway1, H.-U.
Fahrbach1, C. Forest2, S. daGraca3, M. Garcia
Muñoz1 T. Hauff1, J. Hobirk1,V. Igochine1, F.
Jenko1, K. Lackner1, P. Lauber1, P. Mc Carthy4,
M. Maraschek1, P. Martin5, E. Poli1, K.
Sassenberg4, E. Strumberger1, H. Zohm1, ASDEX
Upgrade Team

• Current profile modifications by NBI current
  drive
• Interaction of fast ions with MHD instabilities

1 Max-Planck Institut für Plasmaphysik,
Garching, Germany, EURATOM Association 2 Dept. of
Physics, University of Wisconsin, Madison,
Wisconsin, USA 3 Centro de Fusão Nuclear, Associa
cão EURATOM/IST, Instituto Superior Técnico,
Lisboa, Portugal 4 Physics Department,
University College Cork, Cork, Ireland 5
Consorzio RFX, EURATOM-ENEA per la fusione,
Padova, Italy
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NBI current drive experiments on ASDEX Upgrade
Adjustment of Te profile (ECRH)
Predicted NBI current profile
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Off-axis NBI current drive on ASDEX Upgrade
Current profile modification as predicted by
TRANSP for moderate heating power up to 5 MW for
high triangularity (? 0.4) and below for lower
triangularity
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Strongly reduced current profile modification for
larger heating power
Agreement with theory only if diffusion of fast
particles assumed (Dfast 0.5 m2/s)
no effect for on-axis current drive, but off-axis
CD strongly affected
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Radial profile of loop voltage
see P.J. McCarthy et al., TH/P3-7
on-axis phase (stationary) off-axis phase
(stationary) beginning of off-axis phase
Even in discharges with very small modification
of current profile, the loop voltage profile
changes as expected immediately after switching
from on- to off-axis beams
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Local current drive source vanishes within
milliseconds
Within 100 ms (ltlt current redistribution time)
loop voltage profile becomes flat again!
Consistent with redistribution of fast particles
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Total current drive efficiency as predicted by
theory
Fast particle redistribution - does not change
the total current drive efficiency
significantly - needed to explain the off-axis
current drive results - would not be measurable
for on-axis NBI
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Reasons for missing current profile modification?

• Fast ion redistribution by Alfvén waves?
• no Alfvén waves observed
• vb lt vA , no difference between experiments with
  full beam energy
• (vb gt vA /3) and reduced beam energy (vb lt vA
  /3)
• no dependence on q-profile, monotonic q-profile
• Current redistribution by MHD?
• only (1,1) activity observed
• no influence of qa/q1 surface (qa varied
  between 3.9 and 6.2)
• Fast ion redistribution, correlated to intensity
  of thermal transport
• Increase in heating power (independent of radial
  location and pitch angle reduces CD)

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Redistribution of fast ions by background
turbulence?

• usual argument against turbulence affecting fast
  particles
• gyro-averaging of perturbations

• but additional effect finite gyro-radii
  increase correlation length

Motion of test particles in (test) turbulent
electrostatic field
Full Lorentz dynamics and gyrokinetics
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Redistribution of fast ions by background
turbulence?
Realistic parameters for fusion plasmas K 1
3 r/lc 0.2 1

significant diffusion of fast ions in background
turbulence!

Kubo-number
so far simple geometry (drift motion
perpendicular to constant magnetic field) and
perturbation field, and tracer particles only,
but GENE calculations on the way
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New diagnostics Fast particle loss detector
energy and pitch angle resolved measurements
very high time resolution ? phase resolved
measurements possible
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Losses caused by large (2,1) magnetic islands
Passing as well as trapped particles expelled in
phase with magnetic islands
E100 keV pitch angle 35 deg
magnetics
(2,1) frequency
Modulation of NBI source
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Observed losses consistent with modeling (pitch
angle, energy, response times)
Response of fast particle losses on switch on-
and off-experiments
Response within microseconds (immdediate losses
for particles deposited on HFS, well passing)
Response within milliseconds (diffusive losses
for particles deposited on LFS)
Simulation of particle orbits in 3d equilibrium
(Orbit, Gourdon)
orbit stochastization
drift islands
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Losses of trapped particles caused by (3,2) NTMs

• Fixed phase relation for ICRH heated particles
• n2 symmetry of the particle orbits, fixed phase
  relation between island and particles possible
• ?vBr??0 responsible for outward drift

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Discrepancies between calculated and measured TAE
damping rates

• JET large discrepancies between measured and
  calculated damping rates for TAE modes (except
  for PENN model?)
• too small damping rates from all hybrid MHD-
  fast particle codes
• gyrokinetic PENN code very large radiative
  damping, strongly dependent on the plasma shape,
  stable TAE modes in ITER divertor plasmas?

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Large damping rates from theory for closed gaps
only
experimental density profile modified density
profile
open TAE gap for experimental density profile
TAE gap closes modified density profile (within
exp. error bars!)
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For comparison between theory and experiment
measurement of TAE eigenfunction beneficial

• increase of TAE eigenfunction at plasma edge in
  gyrokinetic code for closed gap only
• significant amplitude for measured eigenfunction
  at the edge
• hint for closed gap in ASDEX Upgrade

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Summary and Conclusions
NBI current drive

• total NBI current drive efficiency as expected
  from theory
• current profile modifications for moderate
  heating power/strong shaping only
• proposed reason turbulent redistribution of
  fast ions

Interaction of fast particles with MHD modes

• new diagnostics fast ion loss detector with
  high time resolution
• (lt 1MHz)
• fast ion losses in phase with magnetic
  perturbation, in agreement with modelling
• TAE damping essentially by closed TAE gaps at
  the plasma edge