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Consorzio RFX and INFN-LNL have designed, built and operated the compactradiofrequency negative ion source NIO1 (Negative Ion Optimization phase 1)with the aim of studying the production and acceleration of H- ions. Inparticular, NIO1 was designed to keep plasma generation and beam extractioncontinuously active for several hours. Since 2020 the production of negativeions at the plasma grid (the first grid of the acceleration system) has beenenhanced by a Cs layer, deposited though active Cs evaporation in the sourcevolume. For the negative ion sources applied to fusion neutral beam injectors,it is essential to keep the beam current and the fraction of co-extractedelectrons stable for at least 1 h, against the consequences of Cs sputteringand redistribution operated by the plasma. The paper presents the latestresults of the NIO1 source, in terms of caesiation process and beamperformances during continuous (6{\div}7 h) plasma pulses. Due to the smalldimensions of the NIO1 source (20 x (diam.)10 cm), the Cs density in the volumeis high (10^15 \div 10^16 m^-3) and dominated by plasma-wall interaction. Themaximum beam current density and minimum fraction of co-extracted electronswere respectively about 30 A/m^2 and 2. Similarly to what done in othernegative ion sources, the plasma grid temperature in NIO1 was raised for thefirst time, up to 80 {\deg}C, although this led to a minimal improvement of thebeam current and to an increase of the co-extracted electron current.

Continuous pulse advances in the negative ion source NIO1