Best C⁴⁺ and C⁵⁺ Beams of the Kei2 ECR Ion Source

Abstract：

With the prototype ECR ion source for the next carbon therapy facility in Japan a new series of measurements has been performed in order (a) to find the highest beam currents of C⁴⁺ ions, and (b) to study the effect of "special" gas- mixing by using a chemical compound as a feed gas. An isotopic effect has been found in a previous experiment: with deuterated methane (CD₄ gas) the C⁵⁺ beam currents are about 10% higher than with regular methane (CH₄ gas). For butane gases (C₄D₁₀ and C₄H₁₀ respectively) the isotopic effect for C⁵⁺ production is even stronger (>15%). For production of C⁴⁺ ions the isotopic effect appears to be absent. It turns out that the relative amount of carbon is much more important: acetylene gives 15% higher C⁴⁺ current than butane, which in turn gives about 10% higher C⁴⁺ ion currents than methane.