Summary of the annual meeting of the sewg transient heat loads on 1/2 september 2010 in jülich

Summary of the annual meeting of the SEWG Transient Heat Loads on 1/2 September
2010 in Jülich

This SEWG addresses the heat loads arising during transient events like ELMs and
disruptions and the development of techniques to mitigate these heat loads. In 2010, the scope
of this group was extended to also include the assessment of inter-ELM heat flux with respect
to far-SOL transport, fast particle loss and loss of detachment. All these studies are
accompanied by heat load simulations which assess the material properties and degradation
under high repetitive heat pulses. The status of these work packages as well as related JET
work has been reported in this meeting.
Disruptions
Work has started to quantify heat fluxes during mitigated disruptions and new data from Tore
Supra, TEXTOR and JET has been presented. Runaway electrons are an important issue to be
solved for ITER. The generation process has been analysed using JET data and first attempts
of the heat load quantification have been done at JET with accompanying modelling with the
codes MEMOS and ENDEP run at KIT. Disruption mitigation by massive gas injection
(MGI) has been further analysed at Tore Supra and JET with respect to timescales and
mitigation of runaways, heat loads and forces. First results from MGI have been reported
from MAST. Modelling of MGI with the 2d fluid code TOKES has started.

ELMs
The work on ELMs focused on heat flux quantification for different ELM scenarios, on the
impact of resonant magnetic perturbations (RMP) and on the understanding of the underlying
transport processes during ELMs. AUG reports on the impact of boronisation on the ELM
strength. The dynamics of ELMs have been further studied using AUG data obtained from a
probe combining Langmuir tips and coils to measure the current carried by the ELM
filaments. The work on RMP concentrated on the penetration process of the perturbation field
and the impact on the heat flux distribution. The latter has been addressed in TEXTOR
experiments where the heat flux redistribution on a test limiter and the related material
erosion has been recorded during RMP.

Inter-ELM loads
Two issues have been addressed in 2010: loss of fast ions and SOL heat flux profiles. Fast ion
losses have been observed in AUG and JET. At AUG scintillator probes (FILD) have been
used to measure the energy and the pitch angle of fast ions lost during core MHD instabilities
and ELMs. Modelling with the code ASCOT is in preparation, which will be benchmarked
with FILD and IR measurements. At JET, the fast ion loss has been analysed with respect to
the release of metal impurities during impact. A clear relation between impurity release and
number of lost ions can be shown during MHD activities like sawteeth, fishbones, etc. Limiter
heat flux profiles have been measured in Tore Supra showing a scaling of the heat flux e-
folding length which deviates from the present scaling of the ITER database based on divertor
profiles.

Test facilities
Impact of transient heat loads on material properties are investigated in the JUDITH facilities
as well as at the linear plasma device PILOT. The latter device has been recently equipped
with an AC power supply (capacitor bank) to allow in addition to the steady state load a
transient increase of the heat flux at the target. Biasing allows in addition to control the ion
energy. First results from experiments with tungsten target have been reported. Experiments
at JUDITH focused on the assessment of tungsten layer on CFC during transient heat load at
different heat flux levels and bulk temperatures. The beam guidance in JUDITH-II has been
optimised to allow precise heat load exposure with high cycle numbers. In addition to the
reports from plasma simulators, tungsten melting experiments in TEXTOR have been
presented.

General
The common aspects of the issues addressed in this SEWG and those relevant for inertial
fusion have been discussed. A talk on the expected loads in the inertial fusion experiment
HiPER and the related material requirements has been given by Dr. Álvarez from the
polytechnical university of Madrid.

Source: http://www.efda-taskforce-pwi.org/efda/___files/File/summary.pdf