Production of negative hydrogen and deuterium ions in microwave-driven ion sources. Page: 1 of 5
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PRODUCTION OF NEGATIVE HYDROGEN AND DEUTERIUM IONS IN
MICROWAVE-DRIVEN ION SOURCES*
David Spence, Keith R. Lykke **
Argonne National Laboratory, Argonne, Illinois 60439 USA
We report progress we have made in the production of
negative hydrogen and deuterium atomic ions in
magnetically-confined microwave-driven (2.45 GHz) ion
sources. The influence of source surface material,
microwave power, source gas pressure and magnetic field
configuration on the resulting ion current is discussed.
Results strongly suggest that, at least in our source,
vibrationally excited molecular hydrogen, the precursor to
atomic negative ion production, is produced via a surface
mechanism suggested by Hall et al.  rather than via a
gas phase reaction as is generally believed to be the case
in most ion sources.
In order to accumulate (store) or accelerate large
currents of protons (H') in circular machines, it is
necessary, from phase-space considerations, that the ions
be injected into the circular storage/acceleration ring in
the form of negative ions, H', with the H being stripped of
its electron to form H' at the point of injection. Linac
accelerator' performance can also be significantly
improved through simultaneous acceleration of positive
and negative ion beams. Suitable positive ion sources are
available now, but negative ion source development has
All advanced high current H' sources currently
available, including surface sources and RF driven
(2MHz) volume sources require the addition of cesium in
order to achieve high H' current. This is undesirable for
several reasons, not the least being the technical problems
associated with introduction of cesium into the source in a
controllable manner over a long period of time.
Moreover, all high current RF H' and D' sources
developed to date consume tens of kilowatts of power and
can only produce beams of a few mA per square
centimeter of extraction aperture when operating cw (i.e.,
100% duty factor).
Our novel approach to high current cw H and D'
formation involves modification of an extremely simple
low power consumption (100's of watts vs. 10,000's for
other type) microwave-driven source.
'Work supported by US DOE via Laboratory Directed
Research and Development Funds.
Previous attempts elsewhere  at negate n t action
from this type of source have been singularly
unsuccessful. Our approach involves application of
pioneering studies by Hall et al.  which demonstrated
the effectiveness of freshly evaporated tantalum surfaces
in producing copious quantities of vibrationally excited
molecular hydrogen (a required precursor to H'
formation). The observations of Hall et al. appear to
never have been deliberately, or successfully, applied to
the production of high-current cw H' or D' beams.
2 APPARATUS AND SOURCE
Figure 1: Schematic of apparatus.
The major components of our apparatus shown in Fig. 1
include a magnetically-confined microwave-driven (ECR)
source purchased from Atomic Energy of Canada, Ltd.
which is powered by a 2.45 GHz microwave generator (2
>W). The microwave generator is coupled to the source
via a circulatory and a four-stub autotuner. The ion source
is attached to a large high-vacuum oil-free diagnostic
chamber with a base pressure of 1x104 Torr.
Ion beams extracted at few hundred volts from the 5
mm source aperture by an accel-decel arrangement are
primarily collected on the decel electrode that is in the
configuration of a faraday cup. A 0.5 mm aperture in the
decel electrode allows a small portion of the beam to be
transported to a quadruple mass spectrometer (QMS) via
an electrostatic zoom lens for quantitative beam
composition measurement. Light from the ion source is
monitored by an optical monochromator by a clear line-
of-sight through the QMS (sapphire window). 'he
monochromator continuously monitors the atomic
'hydrogen Balmer o, radiation (656 nm) to give a measure
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Spence, D. Production of negative hydrogen and deuterium ions in microwave-driven ion sources., article, September 11, 1998; Illinois. (digital.library.unt.edu/ark:/67531/metadc625152/m1/1/: accessed June 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.