GIST Develops Inverse Design Technology for Ion Beam Energy Distribution

Achieving Solar-Level Temperatures While Maintaining Solid State
Designing Ion Beam Parameters After Setting Heating Conditions

On May 13, the Gwangju Institute of Science and Technology (GIST) announced that Professor Woo Seok Bang's research team from the Department of Physics and Optical Science has proposed an inverse design method for ion beam energy distribution that enables optimal heating of materials while maintaining the high density characteristic of solid states.

High-energy ion beams are streams of charged ions rapidly accelerated, allowing direct energy delivery into materials. Utilizing this, one can achieve extremely high temperatures (on the order of tens of thousands of kelvin), far exceeding the melting point of solids, within an extremely short time frame of less than a nanosecond, all while maintaining the high density of a solid state.

This extreme state is known as Warm Dense Matter (WDM), which represents a material phase between solid and plasma. This phase is an important research subject for understanding planetary interiors and the state of nuclear fusion fuel.

However, conventional ion beam heating methods have difficulty achieving uniform heating of samples because the depth at which ions stop within a material varies depending on ion energy. Due to the Bragg peak phenomenon, energy is concentrated at specific depths, resulting in non-uniform temperature distributions within the sample. Conversely, significantly increasing the ion energy can improve heating uniformity, but many ions then pass through the sample without depositing energy, reducing energy transfer efficiency. Therefore, the key challenge has been designing an ion energy distribution that simultaneously satisfies both heating uniformity and energy efficiency.

To overcome these limitations, the research team proposed an 'inverse design' method, where the desired heating conditions are set first, and the corresponding ion energy distribution is then calculated in reverse to achieve those conditions. To do so, they used Monte Carlo simulations to compute how energy is delivered and absorbed at different depths as carbon ions with varying energies pass through a 1 cm thick solid-density aluminum sample.

Monte Carlo simulation is a method that calculates complex physical phenomena by repeatedly performing random sampling. In this study, it was used to determine how much energy ions deposit at various depths as they travel through the material.

The team applied this computational method to carbon ion beams and derived the conditions necessary to achieve uniform heating of a 1 cm thick solid-density aluminum sample. As a result, a super-exponential energy distribution was identified, in which most of the energy is concentrated around 1 giga-electron volt (GeV), maximizing energy transfer efficiency. Computer simulation verified that under this distribution, the ion beam achieved an energy transfer efficiency of 99.1% and a heating non-uniformity of only 0.55%, demonstrating that both uniformity and efficiency can be simultaneously maximized.

Professor Woo Seok Bang stated, "This study demonstrates that it is possible to computationally design the optimal ion energy distribution to achieve a predetermined heating profile," and added, "By presenting ion beam conditions that meet both uniformity and efficiency requirements, we expect this approach to contribute broadly to research and applications that require precise heating of extreme-state materials while maintaining solid density."

This research, supervised by Professor Woo Seok Bang and with Seongmin Lee and Suji Cho as co-first authors, both Integrated Master's and PhD Course Students, was supported by the Mid-career Researcher Program of the Ministry of Science and ICT and the National Research Foundation of Korea. The results were published online on April 19 in 'International Communications in Heat and Mass Transfer,' an international journal ranked in the top 6.1% in the field of mechanics according to the Journal Citation Reports (JCR).