Miniature Ion Gun to Explore Tungsten Nanofuzz Formation

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Nanofuzz is a very fine network of nanoscale whiskers created on the surface of tungsten in the extreme environment it will face as the lining of a magnetic-confinement nuclear fusion reactor. Whilst this has been an intense area of research in recent years, the processes by which this nanofuzz is formed are still not well understood. Transmission electron microscopy (TEM) can observe materials on the nanoscale and when combined with in-situ heating and ion irradiation can create conditions similar to those under which tungsten nanofuzz forms and therefore has excellent potential to elucidate the fundamental mechanisms which drive this intriguing phenomenon.However, so far it has not been possible to ion irradiate with the required helium ions at the very low energies (< 500 eV) needed to properly simulate this environment and thus use in-situ TEM to directly observe the formation of tungsten nanofuzz. The primary reason for this is that these slow-moving light ions are significantly deflected by the strong magnetic fields inside a TEM as they travel to the sample position.The first stage of this project will be to design and build a miniature helium-ion gun which can be integrated into a customised sample holder or otherwise inserted inside a TEM. By placing this very close to the sample position, the ions will have only a short distance to reach the surface of the sample and will thus avoid being heavily deflected.Next, TEM with in-situ high-temperature low-energy helium-ion irradiations will be performed to study the formation of tungsten nanofuzz exploring the effects of temperature, ion energy, ion fluence and the characteristics of the tungsten itself (for example, by varying the grain size of the starting material). This will provide invaluable new experimental evidence giving novel insights into the atomistics which lead to the creation of these fascinating and scientifically-important structures.The University of Huddersfield is home to the Microscopes and Ion Accelerators for Materials Investigations (MIAMI) facility which is a world-leading centre of excellence in the field of TEM with in-situ ion irradiation. Our extensive links to international laboratories across Europe, the United States and Japan will be used to support this PhD project at the forefront of nuclear fusion research.