Speaker
Description
The test facilities BATMAN Upgrade with a $1/8$ ITER-size ion source ($0.3\times0.6\,\mathrm{m}^2$) and ELISE with a half ITER-size ($1\times1\,\mathrm{m}^2$) source are essential parts of the European Roadmap towards the ITER NBI system (size of the ion source $1\times2\,\mathrm{m}^2$). These sources rely on the production of negative ions on caesiated low-work function surfaces. The ion source for ITER NBI should deliver a high current density of extracted negative ions ($329\,\mathrm{A}/\mathrm{m}^2$ in hydrogen, $286\,\mathrm{A}/\mathrm{m}^2$ in deuterium) for up to one hour at an electron-ion ratio below one and highly homogeneous ($>90\,\%$) over the extraction area.
Refined caesium conditioning techniques, a modified magnetic filter field topology and/or modified electrostatic potentials in the plasma enabled for the very first time long pulses with $90\,\%$ of the ITER target for the extracted negative ion current density both in deuterium (at BATMAN Upgrade) and in hydrogen (at ELISE). The achievable performance typically is limited by the amount, asymmetry and temporal increase of the co-extracted electrons.
Presented and discussed are investigations on the interplay between electrostatic potentials close to the plasma grid and the co-extracted electrons. The impact of additional biased surfaces like the potential rods influencing at ELISE the electron flux towards the plasma grid is investigated both in hydrogen and deuterium. The ELISE bias plate was set to different potentials, including the plasma grid potential. The latter is a test for completely removing the bias plate which is planned for the second half of 2026 on request by ITER IO.
| Email address | dirk.wuenderlich@ipp.mpg.de |
|---|---|
| Visitor's Visa | no |
| Classification | H- and D- sources for fusion, accelerators and other applications |