“When most people hear the term ‘particle accelerator’, the one machine they think about is the Large Hadron Collider (LHC) at Cern, because it is the biggest atom smasher in the world,” says Professor Carsten Welsch. Yet what is far less well known “is just how many particle accelerators there are in the world and what applications they’re used for”. Welsch estimates that globally there are probably somewhere in the region of 50,000 accelerators in operation, of which only a “tiny fraction” are at all comparable in size to the LHC, the biggest machine in the world.

Most of them are used for materials science, medical and security applications. “We’re surrounded by accelerators today,” says the German scientist, before explaining that “this was even more the case in the past before flat-screen TVs, when people had big electron tubes. They were essentially accelerators: an electron source in the centre and an electric field that brings the beam to high energy, and some steering elements that can scan it across the screen to create the image on the television. So, everybody had an accelerator at home.”

Welsch thinks the public in general seem to have got the wrong end of the stick about accelerator technology, which he prefers to regard as bringing tangible benefits to society, rather than a vast one-off multi-billion euro machine in Switzerland that few outside the physics community can see the point of. For Welsch, it opens up the world of “medical imaging techniques or direct treatment, be that with electron or ion beams for cancer applications”. In the world of security “when you go on your summer holiday to Spain, you’ll pass through airport security scanners, which have at their core particle accelerators generating X-rays and creating images of the passenger’s body”.

Welsch describes his main research interests as being in the field of “the design and optimisation of particle accelerators and light sources – machines that bring charged particles to very high velocities, which are then used for fundamental science purposes, experiments or a range of applications both in research and daily life”. He’s a great believer that, where possible, fundamental science should be for the benefit of society. Yet it’s more than simply a case of justifying to the tax-paying public what their money is being spent on.

“The one thing that fundamental science drives is innovation. For new experiments, we very often have to enter a territory where nobody has been able to go before. At this point we sometimes must develop the tools, techniques and infrastructure to do these experiments.” The unintended consequence is that once all these conditions are in place, there “are always benefits that go beyond the ones we aimed for at the start. That’s a really important aspect when it comes to the debate about science-funding in general. Scientists these days are asked to provide a ‘pathway to impact’ and to think about knowledge transfer. But you can’t foresee all the applications that will come from technologies that are developed.”

History has shown this a lot, says Welsch, who cites the invention of the world-wide web: “Nobody had any idea of the impact this would eventually have on our daily lives. It is the same for detector technologies. If I today want to characterise a particle beam more fully, or quicker, or with higher resolution, then I know the kind of technology limits that I have to overcome. I know what kind of sensor I’d like to have. But I can’t foresee what will be the benefits in terms of imaging applications.” On the other hand, “I do know that if I have a better sensor that will help me with my experiment, it will also help a clinical doctor using similar sensors for imaging a patient”. Welsch admits you can “maybe kind of guess” what sort of new technologies will come out of the developments in fundamental science, “but the biggest surprises always came from serendipitous discoveries”.

For Welsch, studying physics in his youth was “not only a dream. It was a plan that I had from a very young age. I love mathematics. I love physics. It was obvious to me that I’d go on to study this at university.” However, the scientist is also an economist, a discipline he studied in order to keep the door open for working in industry and research management, with the combination of an academic grounding in both physics and economics “ideal for that purpose”. Yet the career strategy was derailed when, two years into his post-doc, consulting in industry and running his own company, Welsch was offered a fellowship at Cern, “which I decided to take up”. He spent “probably the best three years of my life” in Switzerland. For Welsch, this wasn’t just because his career was on a successful trajectory, but “because of what Cern stands for in terms of physics research”.

What he found at Cern was that “the big goal – namely to do experiments that nobody else was working on or had worked on before – was being achieved with the best scientists in the world, from all over the world. Forget about nationalities and cultures, let’s all do this together. That way of thinking, that way of working, that way of solving a problem together was something I found to be absolutely fantastic. And that motivated me to go into the academic career path because, as an academic, so long as someone funds your research, you have unlimited freedom. Of course, you have to have an idea, and you have to be able to convince people that the idea is good.

“In my case, in the field of accelerators, there are many areas where we need to do things better and over different timescales: one to five years, where we know exactly what we need to do, and others are perhaps over 30 years where there is less of a picture of the future.”

Welsch says he was also motivated to investigate how researcher training could be improved: “We need this in science in general and in post-graduate physics in particular. I’ve always taken the view that you can complain about things, or you can try to do things better yourself. I have been in the area of post-graduate training since 2007, setting up international networks in collaboration with industry and my target is to train these early-career researchers in the best way possible. I want them to have many career options and I really don’t want them to focus only on academic, or only industry career paths. I want to give them a skillset that is absolutely unique.”

‘As an academic, so long as someone funds your research, you have unlimited freedom’.

To understand where we are today in the field of particle accelerators, Welsch says it’s helpful to go back to the early 20th century when “atom clashers were basically trying to build better microscopes in order to better understand what was going on in the world around us. Ernest Rutherford split the atom, but we knew that with the natural radiation sources available, there was only ever going to be that maximum energy where you can use a particle beam to basically scan your material to find out what’s inside it.”

Scientists at that time, he says, knew that if they wanted to look deeper into the inner structure of atoms and the sub-particles that make up the atom, “they would have to go to higher energies. Which is when accelerators came along. But the options are limited: you can’t use neutral particles because you can’t accelerate them to high energies. But charged particles allow you to do that. You then use electric fields that bring these particles to higher and higher energies. And the higher the energy, the deeper you can look into matter, particularly when you do collision experiments. In terms of timescale, we’ve been trying to get closer to the origin of the universe. The hotter you make that collision, the higher the energy of your particle beam, the closer you get to the Big Bang and the more you reveal the particles that were there at the beginning of time and have not been seen free ever since.”

Welsch then goes into a long description of how and why this happens, the technology required to get the results, the science and the maths behind decades of analysis, exploration and discovery in the field. All of which brings us to what’s going on at the LHC currently. “Of course,” he says, “ideally we’d like to have a machine that goes to even higher energy because then we could look into a mass range of particles that no-one’s looked into.” But for the moment: “We can’t do it because of the limitations of the magnetic field strength. If your end goal is to have higher energy, you not only need to develop the magnet, but you need to have the cable technology too.”

If one of the biggest challenges today is to get to higher energy levels, a corresponding challenge is to come up with different concepts of particle accelerators, “by shrinking the technology by a factor of a thousand to bring the particles to the same energy a thousand times quicker”. They are called ‘novel accelerators’ as they don’t employ the conventional century-old radio frequency cavity technologies, but use plasmas instead, “where the electric gradients are not limited by the same breakdown principles that you’d find in cavity technology. For some time, we have been trying to drive a plasma by firing a laser beam into it, and more recently a proton beam, and then to modulate it. You have a cloud of charged particles. You fire a beam into it and rearrange the particles. In that rearranged plasma you have extremely high gradients, which you can use to accelerate a particle beam.” The bottom line is that current developments in the field are to shrink the accelerators by using plasma technology while “ending up with the same beam quality”.

Welsch says that the University of Liverpool is working on “all of this. We are working on the conventional accelerator technology – based on RF technology and magnets – which we are trying to make better. We are also working on plasma-based technology – the next generation of particle accelerators, if you want – that take a different approach.” What this could mean is that, in the case of the laser‑based accelerator, “if that was possible you could have a research facility like Cern not just in one place, but at a number of universities”, leading to massive amplification of innovation potential, while providing opportunities for researchers who don’t have access to Cern due to geographical practicalities.

If the technology can be significantly reduced in size, the potential for ion beam therapy to treat cancer can be taken into different territories. Currently ion beam therapy facilities require their own “very large” building. While the patient treatment room resembles a standard magnetic resonance imaging (MRI) scanning environment, “what’s behind the wall – what you don’t see as a patient – is a building that has the ion source, then the accelerator that brings the beam to a high energy, followed by a beam transfer system that guides the beam precisely to the patient. That’s a building in itself. For heavy ions, it’s a very large building.” All of which carries “a major cost element for a hospital that has to decide whether it is prepared to first create the mechanical infrastructure, before putting in the accelerator. But if we can shrink the technology, pretty much any hospital could have such a facility.”

The example of ion beam cancer therapy becoming something that could fall into the everyday reach of hospitals worldwide shows what Welsch calls a bridge between fundamental science and its application for the benefit of society. “Only last year, the first centre for high-energy proton beam treatment opened in the UK and there are many more to come. We have one opening in Liverpool soon, basically just down the road. So, patients will benefit here in the UK, and this is exactly the message of particle accelerators being used for societal benefit, in this case personal health.”

Looking into the future, Welsch predicts that accelerators will simply become “more accessible and more abundant in number”. This is because the technologies that are being developed, along with the associated infrastructures, will create lower entry costs for users in medical imaging, cancer treatment, security and materials science. “But we need to put much more effort into communicating this.”

“When most people hear the term ‘particle accelerator’, the one machine they think about is the Large Hadron Collider (LHC) at Cern, because it is the biggest atom smasher in the world,” says Professor Carsten Welsch. Yet what is far less well known “is just how many particle accelerators there are in the world and what applications they’re used for”. Welsch estimates that globally there are probably somewhere in the region of 50,000 accelerators in operation, of which only a “tiny fraction” are at all comparable in size to the LHC, the biggest machine in the world.

Most of them are used for materials science, medical and security applications. “We’re surrounded by accelerators today,” says the German scientist, before explaining that “this was even more the case in the past before flat-screen TVs, when people had big electron tubes. They were essentially accelerators: an electron source in the centre and an electric field that brings the beam to high energy, and some steering elements that can scan it across the screen to create the image on the television. So, everybody had an accelerator at home.”

Welsch thinks the public in general seem to have got the wrong end of the stick about accelerator technology, which he prefers to regard as bringing tangible benefits to society, rather than a vast one-off multi-billion euro machine in Switzerland that few outside the physics community can see the point of. For Welsch, it opens up the world of “medical imaging techniques or direct treatment, be that with electron or ion beams for cancer applications”. In the world of security “when you go on your summer holiday to Spain, you’ll pass through airport security scanners, which have at their core particle accelerators generating X-rays and creating images of the passenger’s body”.

Welsch describes his main research interests as being in the field of “the design and optimisation of particle accelerators and light sources – machines that bring charged particles to very high velocities, which are then used for fundamental science purposes, experiments or a range of applications both in research and daily life”. He’s a great believer that, where possible, fundamental science should be for the benefit of society. Yet it’s more than simply a case of justifying to the tax-paying public what their money is being spent on.

“The one thing that fundamental science drives is innovation. For new experiments, we very often have to enter a territory where nobody has been able to go before. At this point we sometimes must develop the tools, techniques and infrastructure to do these experiments.” The unintended consequence is that once all these conditions are in place, there “are always benefits that go beyond the ones we aimed for at the start. That’s a really important aspect when it comes to the debate about science-funding in general. Scientists these days are asked to provide a ‘pathway to impact’ and to think about knowledge transfer. But you can’t foresee all the applications that will come from technologies that are developed.”

History has shown this a lot, says Welsch, who cites the invention of the world-wide web: “Nobody had any idea of the impact this would eventually have on our daily lives. It is the same for detector technologies. If I today want to characterise a particle beam more fully, or quicker, or with higher resolution, then I know the kind of technology limits that I have to overcome. I know what kind of sensor I’d like to have. But I can’t foresee what will be the benefits in terms of imaging applications.” On the other hand, “I do know that if I have a better sensor that will help me with my experiment, it will also help a clinical doctor using similar sensors for imaging a patient”. Welsch admits you can “maybe kind of guess” what sort of new technologies will come out of the developments in fundamental science, “but the biggest surprises always came from serendipitous discoveries”.

For Welsch, studying physics in his youth was “not only a dream. It was a plan that I had from a very young age. I love mathematics. I love physics. It was obvious to me that I’d go on to study this at university.” However, the scientist is also an economist, a discipline he studied in order to keep the door open for working in industry and research management, with the combination of an academic grounding in both physics and economics “ideal for that purpose”. Yet the career strategy was derailed when, two years into his post-doc, consulting in industry and running his own company, Welsch was offered a fellowship at Cern, “which I decided to take up”. He spent “probably the best three years of my life” in Switzerland. For Welsch, this wasn’t just because his career was on a successful trajectory, but “because of what Cern stands for in terms of physics research”.

What he found at Cern was that “the big goal – namely to do experiments that nobody else was working on or had worked on before – was being achieved with the best scientists in the world, from all over the world. Forget about nationalities and cultures, let’s all do this together. That way of thinking, that way of working, that way of solving a problem together was something I found to be absolutely fantastic. And that motivated me to go into the academic career path because, as an academic, so long as someone funds your research, you have unlimited freedom. Of course, you have to have an idea, and you have to be able to convince people that the idea is good.

“In my case, in the field of accelerators, there are many areas where we need to do things better and over different timescales: one to five years, where we know exactly what we need to do, and others are perhaps over 30 years where there is less of a picture of the future.”

Welsch says he was also motivated to investigate how researcher training could be improved: “We need this in science in general and in post-graduate physics in particular. I’ve always taken the view that you can complain about things, or you can try to do things better yourself. I have been in the area of post-graduate training since 2007, setting up international networks in collaboration with industry and my target is to train these early-career researchers in the best way possible. I want them to have many career options and I really don’t want them to focus only on academic, or only industry career paths. I want to give them a skillset that is absolutely unique.”

‘As an academic, so long as someone funds your research, you have unlimited freedom’.

To understand where we are today in the field of particle accelerators, Welsch says it’s helpful to go back to the early 20th century when “atom clashers were basically trying to build better microscopes in order to better understand what was going on in the world around us. Ernest Rutherford split the atom, but we knew that with the natural radiation sources available, there was only ever going to be that maximum energy where you can use a particle beam to basically scan your material to find out what’s inside it.”

Scientists at that time, he says, knew that if they wanted to look deeper into the inner structure of atoms and the sub-particles that make up the atom, “they would have to go to higher energies. Which is when accelerators came along. But the options are limited: you can’t use neutral particles because you can’t accelerate them to high energies. But charged particles allow you to do that. You then use electric fields that bring these particles to higher and higher energies. And the higher the energy, the deeper you can look into matter, particularly when you do collision experiments. In terms of timescale, we’ve been trying to get closer to the origin of the universe. The hotter you make that collision, the higher the energy of your particle beam, the closer you get to the Big Bang and the more you reveal the particles that were there at the beginning of time and have not been seen free ever since.”

Welsch then goes into a long description of how and why this happens, the technology required to get the results, the science and the maths behind decades of analysis, exploration and discovery in the field. All of which brings us to what’s going on at the LHC currently. “Of course,” he says, “ideally we’d like to have a machine that goes to even higher energy because then we could look into a mass range of particles that no-one’s looked into.” But for the moment: “We can’t do it because of the limitations of the magnetic field strength. If your end goal is to have higher energy, you not only need to develop the magnet, but you need to have the cable technology too.”

If one of the biggest challenges today is to get to higher energy levels, a corresponding challenge is to come up with different concepts of particle accelerators, “by shrinking the technology by a factor of a thousand to bring the particles to the same energy a thousand times quicker”. They are called ‘novel accelerators’ as they don’t employ the conventional century-old radio frequency cavity technologies, but use plasmas instead, “where the electric gradients are not limited by the same breakdown principles that you’d find in cavity technology. For some time, we have been trying to drive a plasma by firing a laser beam into it, and more recently a proton beam, and then to modulate it. You have a cloud of charged particles. You fire a beam into it and rearrange the particles. In that rearranged plasma you have extremely high gradients, which you can use to accelerate a particle beam.” The bottom line is that current developments in the field are to shrink the accelerators by using plasma technology while “ending up with the same beam quality”.

Welsch says that the University of Liverpool is working on “all of this. We are working on the conventional accelerator technology – based on RF technology and magnets – which we are trying to make better. We are also working on plasma-based technology – the next generation of particle accelerators, if you want – that take a different approach.” What this could mean is that, in the case of the laser‑based accelerator, “if that was possible you could have a research facility like Cern not just in one place, but at a number of universities”, leading to massive amplification of innovation potential, while providing opportunities for researchers who don’t have access to Cern due to geographical practicalities.

If the technology can be significantly reduced in size, the potential for ion beam therapy to treat cancer can be taken into different territories. Currently ion beam therapy facilities require their own “very large” building. While the patient treatment room resembles a standard magnetic resonance imaging (MRI) scanning environment, “what’s behind the wall – what you don’t see as a patient – is a building that has the ion source, then the accelerator that brings the beam to a high energy, followed by a beam transfer system that guides the beam precisely to the patient. That’s a building in itself. For heavy ions, it’s a very large building.” All of which carries “a major cost element for a hospital that has to decide whether it is prepared to first create the mechanical infrastructure, before putting in the accelerator. But if we can shrink the technology, pretty much any hospital could have such a facility.”

The example of ion beam cancer therapy becoming something that could fall into the everyday reach of hospitals worldwide shows what Welsch calls a bridge between fundamental science and its application for the benefit of society. “Only last year, the first centre for high-energy proton beam treatment opened in the UK and there are many more to come. We have one opening in Liverpool soon, basically just down the road. So, patients will benefit here in the UK, and this is exactly the message of particle accelerators being used for societal benefit, in this case personal health.”

Looking into the future, Welsch predicts that accelerators will simply become “more accessible and more abundant in number”. This is because the technologies that are being developed, along with the associated infrastructures, will create lower entry costs for users in medical imaging, cancer treatment, security and materials science. “But we need to put much more effort into communicating this.”