FY2010 - Oak Ridge National Laboratory

Director’s R&D Fund—
General
05570
Development of a High Magnetic Field Helicon Plasma Source
for Fusion Energy Materials and Component Tests
Richard H. Goulding, Frederic W. Baity, and John B. Caughman
Project Description
The need for additional facilities to investigate critical issues related to the plasma-material interface
(PMI) in fusion devices was a specific conclusion of a DOE strategic review meeting held earlier this
year. A facility using a helicon-based plasma source offers significant advantages over more conventional
sources, since there are no internal electrodes and a large fraction of the injected gas is ionized. An
important question, and the focus of this work, is whether the present highly efficient hydrogen helicon
performance can be extended to the magnetic field strength (≥1 T) and particle flow (>10 21 s -1 ) needed for
such a facility. We will resolve these questions through experiments with a new source equipped with
suitable diagnostics. The tasks include (1) modeling and design of a helicon source operating at the
required parameters; (2) construction of the source and installation in existing facilities modified for
higher magnetic fields, radio frequency (rf) power, and particle throughput; (3) measurement and
optimization of performance characteristics during high power tests; (4) study of the effect of magnetic
field geometry on performance; and (5) determination of power deposition profiles on critical components
to enable the design of a steady-state source.
Mission Relevance
The construction of new PMI research facilities was recommended as an outcome of the DOE Office of
Fusion Energy Sciences strategic planning Research Needs Workshop (ReNeW). The ultimate goal of
these facilities, as expressed in the “Greenwald Report” to the Fusion Energy Sciences Advisory
Committee, is to obtain sufficient knowledge to “design and build, with high confidence, robust material
components that interface the hot plasma in the presence of very high neutron fluence.” Physical
phenomena of interest include surface sputtering, erosion, redeposition, and tritium retention and
migration. This project will develop a robust, large-diameter particle source for a linear PMI facility that
will ultimately deliver a power flux of 20 MW/m 2 and an ITER divertor-like particle flux >10 23 m -3 s, over
an area of ~100 cm 2 . The ultimate facility will allow near-term, cost-effective studies of plasma
interactions with fusion materials, including neutron damaged ones, and plasma facing components, over
a wide range of parameters.
Results and Accomplishments
Construction of the High Magnetic Field Helicon Plasma Source has been completed, and the device itself
has been commissioned (goal 2). Experiments are under way, but device power has been limited due to
the fact that our 100 kW rf amplifier is not yet operational. However, experiments utilizing a low-power
(3 kW) rf amplifier have achieved helium plasma densities up to 10 19 m -3 for pulse lengths up to 2 s, as
confirmed both through Langmuir probe and microwave interferometer measurements, at a forward
power level of only 1.6 kW. This is a higher-than-expected density for this power level. The magnetic
field strength in the helicon region for optimum plasma production was observed to be 0.14 T and is
approximately the expected value for this plasma density and species. Hydrogen operation has also begun.
Based on initial operating experience, it should be possible to quickly optimize high power, long pulse
performance (goal 3) with hydrogen once the 100 kW amplifier becomes available.
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