348 research outputs found
Vibrationally resolved ionization cross sections for the ground state and electronically excited states of the hydrogen molecule and its isotopomeres
Influence of the magnetic filter field topology on the beam divergence at the ELISE test facility
The ELISE test facility hosts a RF negative ion source, equipped with an
extraction system which should deliver half the current foreseen for the ITER
Neutral Beam Injector, keeping the ratio of co-extracted electrons to ions
below 1. An important tool for the suppression of the co-extracted electrons is
the magnetic filter field, produced by a current flowing in the plasma grid,
the first grid of the 3 stage extraction system. To boost the source
performances new concepts for the production of the magnetic filter field have
been tested, combining the existing system with permanent magnets attached on
the source walls. The topologies of these new magnetic configurations influence
the beam particles trajectories in the extraction region, with consequences for
the overall beam optics. These effects will be characterized in this article by
studying the angular distribution of the beam particles, as measured by the
Beam Emission Spectroscopy (BES) diagnostic. The behavior of the beam will be
studied also through the measurements of the currents flowing on the grounded
grid (the third grid) and on the grid holder box surrounding its exit. The main
finding is that the broader component of the beam increases when the magnetic
field is strengthened by permanent magnets, i.e. in the cases in which most of
the co-extracted electrons are suppressed.Comment: 7 pages, 4 figures. Contributed paper for the NIBS 2016 conference.
Accepted manuscrip
Beam characterization by means of emission spectroscopy in the ELISE test facility
The ELISE test facility at IPP Garching hosts a RF H-/D- ion source and an
acceleration system. Its target is to demonstrate the performance foreseen for
the ITER NBI system in terms of extracted current density (H/D), fraction of
co-extracted electrons and pulse duration. The size of the ELISE extraction
area is half that foreseen for the ITER NBI. This paper presents a detailed
study of the ELISE beam divergence and uniformity. In particular, it was
possible to describe the beam as the sum of two components at very different
divergence: about 2{\deg} vs. 5{\deg}{\div}7{\deg}. As test cases, the beam
properties have been measured as function of two source parameters. The first
one is the current flowing through the grid facing the plasma, the Plasma Grid,
in order to generate the magnetic filter field. The second one is the bias
current flowing between the Plasma Grid and the source walls. Both the filter
field and the bias current influence the fraction of co-extracted electrons,
but also the properties of the plasma just in front of the extraction system
and the beam properties. The divergence and the uniformity of the beam have
been measured by a Beam Emission Spectroscopy (BES) diagnostic; the detailed
analysis of the raw spectra collected by BES led to describing the beam with
two components of different divergence. This concept has been supported by the
information given by thermal imaging of the diagnostic calorimeter. Further
support to the proposed beam model has been found in the behavior of the
currents flowing in the acceleration system and beamline components; these
currents are given by the most divergent (charged) particles of the beam.Comment: 15 pages, 8 figures. Accepted manuscript (embargo expired
Review of particle-in-cell modeling for the extraction region of large negative hydrogen ion sources for fusion
On the proton flux towards the plasma grid in a RF-driven negative hydrogen ion source for ITER NBI
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