Two approaches for H− ion production with 2.45 GHz ion sources

Over the last few years, the accelerator community requested the development of improved negative hydrogen ion sources. For spallation sources, like SNS or ESS, pulsed high intensity H− ion beams of a few tens of milliamperes, with a duty cycle close to 10%, are required. New facilities like CERN also ask for high performance negative ion beams. Since CEA undertook an electron cyclotron resonance (ECR)-based ion source programme, a European network devoted to high performance negative ion source development has been created.In this group, several laboratories developing 2.45 GHz ECR sources follow different approaches to increase the extracted ion current. At Saclay, with a solenoidal magnetic structure based on coils, close to 3 mA H− ion beam is now extracted in pulsed mode (2 ms/100 ms). A metallic biased grid separates the plasma bulk from the H− ion production zone and significantly improves the H− extracted current. At Ecole Polytechnique, the source Camembert III operates in continuous wave and pulsed modes. Photodetachment measurements in continuous wave mode show considerable H− ion density (109–1010 cm−3), whether the primary electrons are provided by filaments or small ECR modules inserted into the plasma chamber. Similarities and differences between the ECR-driven and the filamented source are discussed. Representative experimental results from the sources of the two laboratories as well as future plans are reported here.