Formation of negative ions by charge transfer: He/sup -/ to Cl/sup -/ Page: 2 of 13
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FORMATIOM Of NEGATIVE IONS BY CHARGE
TRANSFER: He" to Cl*
Alfred S. Schlachter
Lawrence Berkeley Laboratory
University of California
Berkeley, CA 94720
formation of energetic beams of negative ions of elements
with atomic numbers 2-17 (helium to chlorine) by charge transfer
in metal vapors is discussed.
Negative ions are useful for atomic physics, for injection
into accelerators, and for plasma physics. Energetic negative
ions can be efficiently converted into neutral atoms, for which
many uses are known or proposed relating to magnetically confined
plasmas of fusion interest, fast beams of HO and D° produced
by electron detachment from H* or 0" are presently being
developed for heating of plasmas for fusion. Grisham and
co-workersl have proposed using multi-MeV neutral beams of
heavier atoms for plasma heating, made by neutralization of
negative ions. The energy per atom is greater than that for H or
D at the same velocity, so that less current would be needed to
achieve a desired level of heating power. They also suggest that
the injected beam could be used to drive current in a tokamak or
for tandem-mirror-reactor end plugs.? Post and coworkers have
discussed the use sf a fast light-atom beam, e.g., multi-MeV
Lio, as a diagnostic for fast confined alpha particles
resulting from deuterium-tritium reactions in a magnetically
contained plasma: 2-electron transfer would neutralize alpha
particles, allowing them to escape from the plasma. Afrosimov4
has discussed neutral-particle diagnostics of plasmas.
Negative ions can be formed by several methods: a) direct
formation by volume processes in a discharge; b) sputtering,
backscattering, or desorption from a surface; and c) charge
transfer of fast positive ions in an appropriate gas or vapor
target. Method b) is used for high-current H- and D*
sources,5 in “universal" sources of heavy ions,*> and is often
used with tandem accelerators. Method c) has been used for pro-
duction of intense beams?**! of H*, 0”, and He*, as well
as heavier ions, and is the subject of this review, in which
results of formation of negative ions heavier than H* or D*
by charge transfer are summarized. The Aarhus group has made
many of the measurements on heavy negative ion formation.9
Tykesson has previously presented considerable data on this
subject, and much of the data presented here is from that review
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Schlachter, A.S. Formation of negative ions by charge transfer: He/sup -/ to Cl/sup -/, article, December 1, 1983; [Berkeley,] California. (digital.library.unt.edu/ark:/67531/metadc1074466/m1/2/: accessed November 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.