The quest for fusion energy demands lots of theoretical science and practical engineering. To ensure that even young people can participate in this race, the EUROfusion Engineering Grants support early-career engineers. In our series, we introduce some of the 21 exceptional heads which were awarded grants in 2024. This time, we present Bence Longauer from Hungary who works on those machines responsible for providing proper fusion fuel: extruders.
Hi, you are one of the EUROfusion Engineering grantees. Please, introduce yourself and let us know what your role is!
My name is Bence Longauer, and I work at the HUN-REN Centre for Energy Research (CER in short) as a development engineer. My tasks include the mechanical design, simulation, assembly and testing of devices related to fusion research.
What made you interested in fusion in the first place?
I thought it was a challenging field, with lots of headroom for professional development. As a young engineer, that was an attractive aspect. During my day-to-day work, I can always learn something new here.
What are you currently working on?
The most challenging project that I am working on is the development and testing of a cryogenic hydrogen batch extruder. Such extruders are important to fuel the fusion reaction in current and future fusion devices. They produce a solid rod composed of frozen hydrogen (deuterium or tritium). We have built a pellet puncher prototype for DEMO and also a batch extruder that is necessary for its thorough testing.
A pellet puncher is supposed to cut a continuously flowing solid hydrogen rod (typically frozen deuterium or tritium) into fuelling pellets ofpredefined length. These pellets are later injected into a fusion plasma — at high speed, with precision timing and trajectory. They must be injected in a controlled and repeatable way to maintain the complex fusion reaction. Extruders, pellet punchers and accelerators (collectively known as pellet injectors) are therefore crucial for a future fusion power plant.
How would you explain the challenges of constructing a pellet injector so that everyone can understand the importance of it?
In a fusion reactor, light hydrogen isotopes (deuterium and tritium) go through a fusion reaction that releases energy. At the same time, these isotopes are consumed, thus a continuous resupply must be provided.
Without going into too much detail about the benefits and drawbacks of different approaches, pellet injection is considered the leading solution nowadays. This solution utilises small pellets (for instance, solid hydrogen pieces) that are shot into the plasma. The injector itself consists of three major components: a solid hydrogen source with continuous operation, a puncher device and an accelerator. A solid hydrogen source is generally an extruder, which provides a solid hydrogen rod with a constant flow rate. The puncher is placed after the extruder die, and its purpose is to cut the solid hydrogen rod into pellets of predefined length. The accelerator then accelerates the pellet and forwards it to a guide tube.
What makes it so difficult?
Knowledge and experience in this field is a scarce resource especially within the EU. In terms of operation, the extrusion process is very sensitive to changes in process parameters, and these parameters are interdependent as well. Infrastructure-wise, the required equipment is very special and expensive (high-vacuum environment, cryogenic refrigerators, liquid helium cooling, etc.)
How has this grant helped you collaborate with others in the EUROfusion community, and what have you learned through these partnerships?
My engineering grant has just started, but I am sure it will enable valuable collaboration with the EUROfusion community, fostering joint research. Nonetheless, I already worked with colleagues from various research units, and our discussions were essential for advancing research on all sides.
What knowledge in particular are you looking for?
I am looking for colleagues with extensive knowledge and experience in the design and operation of hydrogen extruders. This includes cryogenics, vacuum technology, and rheology of solid hydrogen isotopes.
Looking ahead, what are you most excited about in fusion research or engineering, and how do you see your role evolving?
I am somewhat biased. Of course, I would like to see a substantial advancement in European fuelling pellet injection systems. In recent years, the development of such devices has primarily taken place in the USA and Russia.
CER is well-positioned, in terms of infrastructure, to support these developments— and we have already begun. In a few years, I would like to be a specialist in cryogenic extruder development.
Do you have a favourite place in Europe where you want to work in five years?
I have favourite places in the EU; however, I do not intend to change workplaces as of now. We have adequate resources in CER, and many research activities were shifted towards cryogenic experiments and pellet injector developments (both fuelling and SPI).
Finally, any advice for future applicants to the EEG/ERG grants?
Engineering grants are a great opportunity to grow professionally, collaborate internationally, and gain unique research experience. I would definitely encourage young engineers to apply if they find a field that aligns with their interests!