Heavy-ion-induced desorption yields of cryogenic surfaces bombarded with $1.4\mathrm{MeV}/\mathrm{u}$ xenon ions

Heavy-ion-induced desorption of two different cryogenic targets was studied with a new experimental setup installed at the GSI High Charge State Injector. One gold-coated and one amorphous-carbon-coated copper target, bombarded under perpendicular impact with $1.4\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Xe}}^{18+}$ ions, were tested. Partial pressure rises of ${\mathrm{H}}_2$, CO, ${\mathrm{CO}}_2$, and ${\mathrm{CH}}_4$ and effective desorption yields were measured at 300, 77, and 8 K using continuous heavy-ion bombardment. We found that the desorption yields decrease with decreasing target temperature and measured the yield rises as a function of CO gas cryosorbed at 8 K. In this paper we describe the experimental system comprising a new cryogenic target assembly, the preparation of the targets, the test procedure, and the evaluation of the effective pumping speed of the setup. Pressure rise and gas adsorption experiments are described; the obtained results are discussed and compared with literature data.

Figure 1

Schematic view of the experimental setup, which has been attached at the GSI HLI for heavy-ion-induced desorption measurements at $1.4\mathrm{MeV}/\mathrm{u}$.

Figure 2

Top: schematic view of the cold-head assembly used for heavy-ion-induced desorption measurements at cryogenic temperatures. Bottom left: frontal view of the cold head with installed gold-coated target and inner thermal radiation shield, thermally anchored at the first stage of the cold head. Bottom right: installed target and outer thermal radiation shield anchored at ambient temperature.

Figure 3

Schematic display of the gas flux, pumping speeds, and geometry relevant for the heavy-ion-induced desorption of a cryogenic target installed in the experimental vacuum chamber.

Figure 4

Product of pumping speed $S$ and reduction factor $\alpha$ as a function of sticking probability $\sigma$ for the used experimental setup calculated; the shown curves were calculated for CO.

Figure 5

Heavy-ion-induced pressure rises at 300 K target temperature. Partial pressure rises ($\Delta P$) of ${\mathrm{H}}_2$, CO, ${\mathrm{CO}}_2$, ${\mathrm{CH}}_4$, and total pressure rises measured for the $\mathrm{Au}/\mathrm{Cu}$ and $\mathrm{aC}/\mathrm{Cu}$ samples continuously bombarded under $\theta =0°$ with $1.4\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Xe}}^{18+}$ ions are shown.

Figure 6

Heavy-ion-induced pressure rises at 77 K target temperature. Partial pressure rises ($\Delta P$) of ${\mathrm{H}}_2$, CO, ${\mathrm{CO}}_2$, ${\mathrm{CH}}_4$, and total pressure rises measured for the $\mathrm{Au}/\mathrm{Cu}$ and $\mathrm{aC}/\mathrm{Cu}$ samples continuously bombarded under $\theta =0°$ with $1.4\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Xe}}^{18+}$ ions are shown.

Figure 7

Heavy-ion-induced pressure rises at 8 K target temperature. Partial pressure rises ($\Delta P$) of ${\mathrm{H}}_2$, CO, ${\mathrm{CO}}_2$, ${\mathrm{CH}}_4$, and total pressure rises measured for the $\mathrm{Au}/\mathrm{Cu}$ and $\mathrm{aC}/\mathrm{Cu}$ samples continuously bombarded under $\theta =0°$ with $1.4\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Xe}}^{18+}$ ions are shown.

Figure 8

Left: temperature dependence of the heavy-ion-induced desorption yield of gold-coated and amorphous-carbon-coated copper surfaces bombarded under $\theta =0°$ with $1.4\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Xe}}^{18+}$ ions. Right: comparison of LINAC 3 desorption data obtained for $4.2\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Pb}}^{54+}$ ions bombarding bare and gold-coated copper targets under $\theta =0°$ [5].

Figure 9

Left: Heavy-ion-induced desorption yields as a function of adsorbed CO monolayers on gold-coated and amorphous-carbon-coated copper surfaces bombarded at 8 K with $1.4\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Xe}}^{18+}$ ions under $\theta =0°$. Right: comparison with LINAC 3 desorption data obtained for $4.2\mathrm{MeV}/\mathrm{u}$ ${\mathrm{Pb}}^{54+}$ ions bombarding under $\theta =0°$ bare and gold-coated copper targets at 6.3 K [5].