Design and comparison of the Cs ovens for the test facilities ELISE and SPIDER

Cristofaro, S.; Fröschle, M.; Mimo, A.; Rizzolo, A.; Muri, M. De; Barbisan, M.; Fantz, U.

doi:10.1063/1.5128620

Cited by 15 publications

(8 citation statements)

References 14 publications

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“…The background pressure is monitored with a cold cathode gauge and the composition of the residual gas can be measured with a differentially pumped residual gas analyser (RGA, not calibrated for absolute partial pressures). As the residual gas is clearly dominated by water vapour, the background pressure can be approximated by the partial pressure of H 2 O. Cs is evaporated into the experiment by means of a Cs oven [7] attached to the bottom plate of the vacuum vessel. The nozzle of the oven is directed towards a sample holder, which is mounted with a ceramic block on the bottom plate to ensure electrical and thermal insulation.…”

Section: Methodsmentioning

confidence: 99%

Ultra-low work function of caesiated surfaces and impact of selected gas species

Heiler,

Friedl,

Fantz

2024

J. Inst.

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Modern high-power negative hydrogen ion sources rely predominantly on the surface production of negative hydrogen ions. Hence, low work function converter surfaces are mandatory, for which the alkali metal Cs is commonly evaporated into the ion source to lower the work function of refractory metals by surface adsorption. To study the work function behaviour upon caesiation under the typically given non-ultra-high vacuum conditions, investigations are performed at a dedicated laboratory experiment. In a vacuum environment dominated by water vapour, the work function evolution is found to be dependent on the flux ratio of Cs to H2O onto the surface. For sufficiently high flux ratios, ultra-low work functions in the range of 1.25±0.10 eV are generated with excellent reproducibility. In the absence of Cs evaporation, the work function gradually increases under the influence of the residual gases, and re-caesiation processes lead to lower quantum efficiencies and higher work functions of typically 1.9–2.1 eV. While the addition of hydrogen and deuterium gas at several Pa as well as the leakage of inert gases (argon and nitrogen) into the vacuum system have a negligible influence on the caesiation process, small amounts of oxygen with partial pressures of ∼10-2–10-1 Pa lead to an instant reduction of the Cs density in the gas phase by several orders of magnitude and to an increase in the work function of the order of 1 eV. After the oxygen exposure is terminated, however, the Cs density and work function fully recover within several minutes.

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Section: Methodsmentioning

confidence: 99%

Ultra-low work function of caesiated surfaces and impact of selected gas species

Heiler,

Friedl,

Fantz

2024

J. Inst.

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“…A milestone towards caesium operation is the commissioning and testing of all and each of the three caesium ovens. Caesium evaporation from each caesium oven is being demonstrated and characterised 30 in the dedicated facility CATS 11 . In the next phase, a functional test of the ovens installed in SPIDER is planned, to demonstrate the reliability of the mechanical and electrical design, despite high voltage and RF environment.…”

Section: Iic Future Experimental Plan (End Of 2019-2020)mentioning

confidence: 99%

First operation in SPIDER and the path to complete MITICA

Serianni

Toigo

Bigi

et al. 2020

Review of Scientific Instruments

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The requirements of ITER neutral beam injectors (1 MeV, 40 A negative deuterium ion current for 1 h) have never been simultaneously attained; therefore, a dedicated Neutral Beam Test Facility (NBTF) was set up at Consorzio RFX (Padova, Italy). The NBTF includes two experiments: SPIDER (Source for the Production of Ions of Deuterium Extracted from Rf plasma), the full-scale prototype of the source of ITER injectors, with a 100 keV accelerator, to investigate and optimize the properties of the ion source; and MITICA, the full-scale prototype of the entire injector, devoted to the issues related to the accelerator, including voltage holding at low gas pressure. The present paper gives an account of the status of the procurements, of the timeline, and of the voltage holding tests and experiments for MITICA. As for SPIDER, the first year of operation is described, regarding the solution of some issues connected with the radiofrequency power, the source operation, and the characterization of the first negative ion beam.

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“…The negative ions are mainly produced by surface conversion of neutrals on a low work function caesiated surface [7]. Caesium is evaporated in the source by two ovens [8].…”

Section: The Elise Test Facility Towards the Iter Nbimentioning

confidence: 99%