ELISE achieves target values for ±¬×ߺÚÁÏ
Researchers at the Max Planck Institute for Plasma Physics in Garching, Germany, have generated the ion current densities required for ±¬×ߺÚÁÏ neutral beam injection on the ELISE testbed—a negative ion source prototype that is half the size of ±¬×ߺÚÁÏ's. This experimental first is good news for the development of reliable, high-performance heating neutral beam injectors for ±¬×ߺÚÁÏ.
The ±¬×ߺÚÁÏ heating neutral beams will play an essential role in providing power and current drive to the ±¬×ߺÚÁÏ plasma, allowing access to burning plasmas with high fusion power amplification factors. ±¬×ߺÚÁÏ will be equipped with two heating neutral beam injectors (with a provision of a third injector) and a neutral beam line for diagnostic purposes.
Research is ongoing at the ±¬×ߺÚÁÏ Neutral Beam Test Facility (NBTF) to develop the beam source and achieve the required parameters. One of the key parameters is the current density extracted through the multi-aperture, multi-grid accelerator system, with targets of 329 A/m2 when operating in hydrogen, and 286 A/m2 when operating in deuterium. This also needs to be stable throughout the ±¬×ߺÚÁÏ pulse.
The Max Planck Institute for Plasma Physics, in Garching, Germany, is the location of the ELISE (Extraction from a Large Ion Source Experiment) test stand, a key experiment in the development of the ±¬×ߺÚÁÏ neutral beam source, supporting the research of NBTF. ELISE has operated a half-size ±¬×ߺÚÁÏ beam source since 2013, allowing modifications and experience to be passed to the NBTF and finally to the ±¬×ߺÚÁÏ heating neutral beams.
Recent experiments at ELISE have focused on extending the pulse length for hydrogen beams, looking for a high but steady H- current, and stable and low co-extracted electron current. Caesium evaporation, the key technique, is used both to enhance the negative ion production and to reduce the co-extracted electron current to acceptable levels (< 0.5 x jH- with H, or < 1 x jD- with D). How to achieve the optimum caesiation distribution has been a topic of research for some time.
The experiments at ELISE have now produced the of achieving the required current density in hydrogen for the first time (330 A/m2) over short pulses (<10 s), with nearly 90% of the target reached over a 600 s pulse.
Negative ion current density is proportional to the radiofrequency power used to drive the source. However ELISE is only capable of delivering 75% of the value that will be available at ±¬×ߺÚÁÏ, making this achievement more impressive, and providing good confidence going forward for the NBTF and ±¬×ߺÚÁÏ heating neutral beams to deliver the required heating power needed for early deuterium-tritium operation and beyond.
See the press release issued by the Max Planck Institute for Plasma Physics in or .