Calculations of Ion Beam Emittance for Hot Cavity Ion Source

Abstract

Emittance of short-lived nuclide beams produced in hot cavity ion sources is calculated. Inuence of halflife period as well as the average sticking time on beam emittance is under investigation. Two dierent shapes of ionizer cavity are considered: almost fully spherical and hemispherical ones. Changes of beam emittance due to the extraction channel geometry (its diameter and length) are studied. A new concept of scaled eciency (ion source brightness analogon) is introduced in order to compare the two-ion source congurations. Phase space portraits of the extracted beams are presented.

Ion Beam Emittance for an Ion Source with a Conical Hot Cavity

“…Moreover, the longer is the cavity, the higher is the beam quality. In the case of short cavities the particles reach the extraction region with a larger transversal momentum component as it was observed in the case of hemispherical cavities [32]. This results in larger emittance values exceeding 50 mm mrad in the case of h = 30 mm.…”

“…In the case (C) one observes lowering of ε rms (β ) with the decreasing τ 1/2 (improving the beam quality) while the reverse trend could be seen for the configuration (E). It should be noticed that the ε rms (β) curves are much flatter (particularly for β < 0.1) compared to the case of (hemi)spherical cavities [32]. Influence of average sticking time τ s on the beam emittance was also investigated (Fig.…”

“…In analogy to the beam brightness, another frequently applied figure of merits for the ion source, a scaled efficiency, was introduced in the previous paper [32]:…”

“…the extraction opening radius and the length of the extraction channel (329) is studied. A previously introduced [32] concept of scaled efficiency is used in order to compare beam quality for different extraction opening configurations as well as isotope half-lives.…”

Ionization in Hot Cavity Ion Sources

“…Some of them focused on thermal ionization in the hot cavity [11,22,23], describing the crucial effect of multiple collisions with the walls of the hot cavity, while other papers presented issues such as vapour transport from the bombarded target to the ionizer [24,25] or the release of nuclides from the walls of the ionizer [26,27]. Various shapes of ionizers were considered in the literature; the most popular being tubular [23,[28][29][30], rarely employed spherical or hemispherical [31][32][33], but also conical [34][35][36], and even the most exotic, resembling a kind of mace with spikes [22]. Recently, a cavity having the shape of a flat disc was considered [37], being a case of tubular ionizer characterized by a very small length compared to its diameter, which results in a large number of particle-wall collisions during the particle's travel to the extraction aperture.…”