Negative Ion Optimization – NIO1

The Negative Ion Optimization experiment, NIO1, aims to enhance the knowledge of NEGATIVE ION SOURCES, focused on the production of powerful ion beams to be used for plasma heating in nuclear fusion devices.

NIO1 is operating since 2014, with the goal of achieving NOMINAL PARAMETERS: the production of a current of hydrogen ions of 130 mA distributed in 9 beamlets accelerated to 60 KeV.

Experimentation with the Cesium vaporizer is underway since 2020, to increase the current of negative ions and bring it to nominal performance.

How does NIO1 work?

The plasma source is a 7cm long cylindrical chamber with an internal radius of 10 cm.
A radio frequency coil winds around this chamber which is used for the formation of the plasma, or “ionized gas”.
To increase the number of negative ions which will form the beam, 3 power supplies with low voltage and high current have been installed.

The extraction and acceleration of particle beamlets

The extraction and acceleration of the PARTICLE BEAMLETS takes place through copper grids.
Negative ions are EXTRACTED FROM AN INTENSE ELECTRIC FIELD, generated by the application of a potential of a few kilovolts to the Extraction Grid which contains the magnets necessary to deflect the electrons (negatively charged particles), which are inevitably extracted from the source together to negative ions.

Data extraction and recovery system

Also present in the experiment is the acquisition, data recovery, interlocking and control system, built specifically for NIO1 and completely automated.

Diagnostics system

In the terminal part of the vacuum chamber, a diagnostic system is placed to determine the characteristics of the beam consisting of a graphite tile that is hit by the beam on its front facing. On the back of the tile there is a thermal imaging camera that reads the thermal imprint of the beam.

Another very important diagnostic tool is the Beam Emission Spectroscope which provides the beam optics parameters, i.e. measures performance.

… NIO1 is needed also for

In recent years NIO1 has also been used to train personnel to operate sources of negative ion beams.

Experimental campaigns

The 2019 experimental campaign focused on maximizing the extracted ion current, improving vacuum tightness and suppressing plasma fluctuations.

  • The setup of the magnetic filter field configuration has been completed.
  • Successfully verified that experimental sessions with plasmas in mixture of Oxygen and Argon help to improve the stability of the plasma, the extracted current and the high voltage.
  • To improve the high voltage resistance, some probes positioned in front of the negative ion acceleration system have been removed.
  • Other gases were tested to evaluate the replacement of oxygen in operations in anticipation of the use of the Cesium oven.

The 2020 experimental campaign focused on improving the vacuum seal and experimenting with the Cesium furnace which will allow a large increase in the production of negative ions in the NIO1 source.

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