In the past, when people would ask me what I do for a living, I would answer with ‘I’m a laser plasma research physicist’. It would often result in a blank stare and the conversation would then lead in the direction of ‘but what does that mean?’ and ‘oh it must be too complicated for me to understand’. I found that describing myself as a physicist was too daunting for most people. This is one of the reasons that I am so active in science communication, for I’d really like there to be a day that introducing myself as a research physicist is as normal or accepted as saying I am a lawyer, a nurse or a teacher. Until then, I’m dedicated to taking a different approach, one that is inviting and not intimidating.
I now say that I work with the most powerful lasers in the world to design new technology that helps to solve really important challenges that we face, such as where we’ll get our energy sources from in the future and how we can use technology to beat the trickiest and most widespread of diseases, such as cancer. My job is to bring research to reality and figure out the physics needed for tomorrow’s technology.
My tool of choice for this endeavour is super intense, high power lasers. I work for the Central Laser Facility (CLF), which is at the centre of the Rutherford Appleton Laboratory in Oxfordshire. The CLF is paid for by UK taxpayers via the Government’s Science & Technology Facilities Council, whose mantra is Impact, Inspiration and Innovation, and one to which I am perfectly aligned. For I now know that I am an application driven, solution focussed physicist, but it took me a while to figure that out. By the end of my undergraduate physics degree I was pretty jaded about the idea of studying the subject any further and was instead going to use it to get me a big shot job in the city. But then I discovered high power lasers, by doing a summer placement at the CLF. I learned that they were generating some of the most extreme conditions one could imagine, millions of degrees in temperature compressing metals into flowing lavas of charged particles that are as dense as lead, using only light from a laser pulse that lasts for a trillionth of a second. How extraordinary! I was hooked.
And then when I learned that they were using these extreme laser-solid interactions to deliver fusion reactions on earth so that we can do away with burning coal and nuclear fission in power stations, or for building miniature accelerators that sit neatly in hospitals to deliver beams of ions for zapping away cancers tumours. Well, I turned my back on the city and I signed up for a PhD in this field pretty much straight away and thought: this is how I was going to use my physics training to contribute to our future and leave a legacy behind in the form of new knowledge that will last longer than I ever will.
Here comes the science bit………….
Plasma, the 4th state of matter, is generated when the building blocks of matter, atoms, are shaken or heated so violently that they rip apart, leaving their charged insides, electrons and ions, exposed and interacting with one another in a flurry of fluid dynamics meets Maxwell’s equations. Plasmas don’t exist without an extreme condition generating them and so will quickly relax back down to a gas, getting rid of their excess energy in a flash of light, we is the bit that we observe. 99% of the known or visible (hat tip to you dark matter and energy folk) universe is in this plasma state (the sun is a big burning ball of plasma for example), driven by the extreme conditions of outer space. Here on earth we’ve figured out a few ways to generate our own beautiful plasmas; by driving electrical current through a gas (like in plasma TV’s, neon lights or plasma balls) or by whacking an intense pulse of light (and therefore extreme source of electric field in the electromagnetic wave) onto matter.
I’m intrigued the most by the latter. For a laser-plasma can have properties that liken it to the plasma conditions at the centre of stars and planets or in the blast waves of supernova explosions. And this means that if one wishes to study these great and faraway astrophysical objects and events, all one needs to do is call up a few high energy, high power laser beams and shoot them all into the centre of a target chamber that can be set up with a suite of diagnostics, to help you interpret the physics of what’s really going. And talking of solar cores, if we want to copycat the energy release process that’s going on at the centre of every star, to keep our power stations burning and generating electricity for us all using a clean and abundant fuel, then lasers are most definitely one approach to seeing that dream come true.
My PhD was on the subject of laser-driven proton beams, by which an intense laser pulse is used to drive matter into the 4th state, plasma, and from there set up a micron sized particle accelerator by separating the negative electrons from the positive ions (the laser electric field pushes the electrons out the way). This charge separation state in turn sets up an incredibly large electric field (TV/m for people who know their E fields) inside the plasma bubble. Any charged particles in the vicinity of that hyped up field will be whipped up from 0 to 60 (MeV, for example) over a distance less than the width of a human hair. My PhD mission was to see if, by changing the properties of the laser pulse (it’s energy content, the width and shape of the pulse rise-time, the size of the focal spot), we can control and enhance the particle beam that comes from our micro plasma accelerator (to be exact my PhD thesis title is Laser-driven proton beams: mechanisms for spectral control and efficiency enhancement). We need to be able to demonstrate control over the process if we ever want to use this accelerator technology for applications and especially for use in a clinical environment, for proton beam cancer therapy for example.
Radiotherapy (beams of X-rays that shine through the patient from many angles) is a very common and successful treatment for cancer tumours. Whereas proton therapy is a highly sought after treatment for tumours below the skin, particularly for those that are growing in or alongside vital organs that need to be protected from radiation dose. Protons interact differently, compared to X-rays, with the atoms that make up the building blocks of all matter. They deposit their energy a lot more locally than X-rays and the depth at which they do this depends on the energy of the beam and the tissue that it interacts with (all of which we can predict very well with well-developed theory and codes). This means that we can send a proton beam into a patient and it will only do harmful damage to the exact location where the tumour is and not the healthy tissue around it, which is really useful for treating cancers positioned next to the spinal-chord and brain or for treatment for children who often have secondary cancer growth from their X-ray treatment in later life. There are currently about 50 proton and ion treatment centres around the world. ‘Why the hell isn’t there one in every hospital?’ was my first reaction to hearing this, I was outraged! At which point my PhD supervisor started to explain how big conventional particle accelerator technology is and how much it costs to build and maintain a centre and about cost-benefit analysis blah blah blah……. This is the flame that lit my passion for laser-driven accelerators for applications. I set out to make my mark on the world by joining the world-wide effort that is trying to figure out how we can bring the theoretical idea of using laser light to push particles and turn it into a real prospect for inspiring applications.
I finished my PhD three years ago and since then have moulded myself a role at the CLF that is enabling me to do just that. I’m the CLF’s applications development scientist, specialising in high power laser plasma accelerators for use in medicine through to advanced manufacturing. I bring together collaborations between laser-plasma physicists, high energy radiation detector engineers, industrial R&D departments and conventional radiation technology specialists to work on the task of developing the physics needed to realise the potential (pun intended) of these light-based particle pushers. In fact, this month (March 2015) I’m leading the first experiment that the CLF is running that is dedicated to demonstrating the application of plasma accelerators in high-energy X-ray, gamma ray and neutron generation for imaging of high value, UK manufactured industrial components that need to be non-destructively inspected. And because I am the lead and principle investigator for this experiment on the CLF’s Vulcan high power laser, I truly do get to press FIRE on the most powerful laser in the world.
See my Royal Institution lecture on the subject of Super Intense Lasers: what would YOU do with the most powerful laser in the world?
Ceri Brenner (@CeriBrenner) is an application development scientist at the Central Laser Facility, Rutherford Appleton Laboratory, developing laser-plasmas for applications in medicine through to manufacturing. Her first degree was in Physics at the University of Oxford before going on to complete a PhD in laser-plasma interaction physics with the University of Strathclyde in 2012 and she has since been based at the CLF. Ceri describes herself as ‘solution focused physicist, driven by a passion for contributing to society through applied physics and new technology’. She also enjoys public speaking and acting as a physics ambassador and is regularly invited to speak on local, national and worldwide BBC radio as well as to give public lectures on super intense lasers and their role in society.