SPIDER Cs Ovens functional tests

Muri, M. De; Rizzolo, A.; Sartori, E.; Cristofaro, S.; Barbisan, M.; Fadone, M.; Ravarotto, D.; Rizzieri, R.; Capobianco, R.; Cinetto, P.; Laterza, B.; Rossetto, F.; Rancan, Marzio; Armelao, Lidia; Taliercio, C.; Serianni, G.; Marcuzzi, D.

doi:10.1016/j.fusengdes.2021.112331

Cited by 10 publications

(15 citation statements)

References 13 publications

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“…The preparation of the caesium operation also included a thorough testing and qualification of the caesium ovens [37][38][39], necessary to validate the design and to quantify the evaporation rates, and also to define adequate loading procedures. Each of the three caesium ovens, fully contained inside the SPIDER vacuum vessel, was loaded with 10 g of caesium.…”

Section: Experimental Configuration Of Spider and Operation With Caesiummentioning

confidence: 99%

First operations with caesium of the negative ion source SPIDER

Sartori¹,

Agostini²,

Barbisan³

et al. 2022

Nucl. Fusion

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The negative-ion based neutral beam injector for heating and current drive of the ITER plasma (ITER HNB) is under development, at present focusing on the optimization of the full-scale plasma source in the SPIDER test stand. The production of H- or D- ions in the ion source is based on the low work function surfaces obtained by caesium evaporation. This paper describes the caesium conditioning procedure and the corresponding beam performances during the first operation of SPIDER with caesium. Technical solutions to overcome present limitations of the test stand are described. The influence of source parameters on the caesium effectiveness was investigated in short beam pulse operation; with total RF power of 400 kW and filling pressure below 0.4 Pa, and a limited number of extraction apertures, a negative ion current density of about 200 A/m2 was extracted in hydrogen, with beam energy lower than 60 keV. Beam optics and beam uniformity were assessed thanks to the acceleration of isolated ion beamlets. A possible procedure to accelerate a uniform beam was demonstrated at low RF power. The results obtained in this first investigation provided key indications on the operation of one of the largest existing sources of accelerated negative hydrogen-like ions.

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Section: Experimental Configuration Of Spider and Operation With Caesiummentioning

confidence: 99%

First operations with caesium of the negative ion source SPIDER

Sartori¹,

Agostini²,

Barbisan³

et al. 2022

Nucl. Fusion

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“…The latter results from the Hershkowitz approximation [22] for floating condition, which is only an indicative estimation, so that a large margin was taken with respect to the axial extent of the nozzle. The alternative solution of operating the oven at higher temperatures, so that transients during plasma on would have a minor impact, is not compatible with the present design [23]; oven operation during long pulses will have to be assessed in the future.…”

Section: Control Of Caesium Evaporation and Improvement Of The Emissi...mentioning

confidence: 99%

Highlights of recent SPIDER results and improvements

Sartori,

Agnello,

Agostini

et al. 2023

J. Inst.

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Three years of experiments on SPIDER allowed characterization of the main features of the source plasma and of the negative ion beam, in the original design configuration. For the large dimensions of the source chamber, and of the extraction area, the investigation of the single-beamlet currents and of the source plasma uniformity had to be carried out to extend the knowledge gained in smaller prototype sources. The configuration of the multiple RF drivers and filter field topologies were found to cause a peculiar behavior in the plasma confinement in the drivers, creating left-right asymmetries which were also visible in the extracted negative ion currents, even after the early implementation of a new scheme of plasma-grid current send and return busbars that greatly improved performance at high filter fields. The plasma properties in the driver and expansion region as well as the positive ion energy at the extraction region were studied in different experimental conditions, and interpreted also with the support of numerical models, suggesting that an improved plasma confinement could contribute to the increase of the plasma density, and to a certain extent to a lowering of the plasma potential profile; both effects shall contribute to increase the presence of cold negative ions for the formation of low-divergence beamlets. Early results related to unwanted RF discharges on the back of the plasma source and the gas conductance of the beam source suggested the reduction of the vessel pressure as mitigation, leading to the definition of a new pumping system. The difficulties related to the simultaneous operation, stable control and high-power operation of multiple RF self-oscillating vacuum tube based RF generators were an unambiguous obstruction to the experimentation, calling for the implementation of RF solid-state amplifiers. The initial tests related to caesium management, the non-uniform plasma properties at different locations across the plasma grid, and the challenges in the measurement of the current and divergence of the accelerated beamlet, unambiguously resulted in the need of new diagnostic systems to investigate with better resolution the spatial uniformities. This contribution summarises how the main experimental findings in the previous experimental campaigns are driving modifications to the SPIDER experiment, during the present shut down, in view of future operations.

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“…The source was mostly operated at 50 kW/driver; the features exhibited at low RF power were amplified or even exaggerated in this case, and so did the nonhomogeneity both in the beam and in the plasma properties at the extraction region. For instance, during the operation with standard filter field, the average ion beam current at the bottom half of the bottom segment was regularly lower than in the rest of the source; the line-averaged density of neutral cesium measured at the same location in front of PG and BP also showed a lower value, although the three cesium ovens, uniformly distributed along the vertical direction of the source, were operated with identical parameters [33], and their emission rates were confirmed to be very similar from Langmuir-Taylor detector estimations [34]. As already mentioned, visual inspection of the plasma source at the end of the operation confirmed that the bottom half of the bottom segment of both PG and BP was substantially cleaner than the other segments.…”

Section: Uniformity Inside the Ion Source And In The Beammentioning

confidence: 99%