Miniaturized Particle Accelerators

TU Darmstadt joins international research project aiming for electron accelerators of micrometer-sized scale

24.11.2015 von

The American Gordon and Betty Moore Foundation announced on 19th November that they will fund research for microscopic Laser accelerators. The goal of the international project named “Accelerator-on-a-chip“ is to develop a prototype of a miniaturized, laser-driven linear accelerator. The etit department of TU Darmstadt will work on simulations of electromagnetic fields and beam dynamics in the coming five years.

Up to one hundred miniaturized particle accelerators have room on a small chip. Picture: H. Schmidt

Particle accelerators have been crucial for research in physics, medicine and biology for about 75 years. However, due to their large size, conventional accelerators are demanding in infrastructure and costly. In the future, an alternative could be micro-linear-accelerators, which are not only cheaper, but also more flexible for practical applications.

Such micro-linear-accelerators are significantly smaller than a millimeter and made of a dielectric, e.g. fused silica (glass). The structure is made as a tunnel, similarly to conventional accelerators. When the particles pass through the tunnel, they can be accelerated by the electric field of an incident laser, which has to be synchronized with the particles’ arrival. Due to the small size and the choice of structure material, record acceleration gradients can be achieved. However, the number of accelerated particles is still small. This project aims is to increase the number of particles passing through the accelerator chip. Challenges include particle-particle interaction which lead to collective effects and the excitation of radiation, since the particles move faster than light does through the dielectric material.

A tooth of the miniaturized particle accelerator is smaller than the thousandth part of a millimetre. Picture: U. Niedermayer

Simulation data from Darmstadt

The development of such accelerator chips requires simulations of particle dynamics (e.g. focusing) and electrodynamics of the laser fields. These simulations will be performed by the accelerator physics group at the computational electromagnetics lab (TEMF) in collaboration with Stanford University and other American, German, and Swiss institutes. During the course of the project, different structure types shall be analyzed.

There are many applications for such micro-accelerators in medicine, physics research, or material science, which are nowadays not, or only by large effort, possible. An example would be the treatment of stomach cancer from within the body by an accelerator built into an endoscope. Side effects could be strongly reduced in comparison to electron irradiation from outside the body, so healthy tissue is spared.

Press release of the Gordon and Betty Moore Foundation, 19.11.2015

Mr. Niedermayer, you will work in the etit department on an international research project named “Laser Accelerators on a chip“. Can you tell us what it is about?

It is about extremely small linear accelerators. Structures of glass shall be manufactured by means of techniques known from semiconductor fabrication. The size of the structures is in the range of micrometers and lasers serve to drive them in a non-resonant manner. That’s the origin of the name “Dielectric Laser Acceleration”, DLA. Such an accelerator chip works as follows: Particles pass through the tunnel. The electric field of the incident laser is shaped by the glass in a way the particles are accelerated. Since the material can withstand high fields, the particles can be accelerated with record gradients.

What are the advantages of DLAs?

When sophisticated DLAs are available, they provide a low-cost alternative to conventional electron accelerators. Another advantage is the small size, which allows for entirely new application fields. A particular application would be an accelerator endoscope, which allows irradiating tumors from within the body.

What do you think will be the outcome of this project?

So far it was only shown that DLA works in principle. However the achieved beam intensity (particle number) is still small. In order to have an accelerator ready for practical purposes, we have to increase the intensity significantly. This requires developing focusing structures on the micrometer scale. Finally, a complete micro-accelerator shall be developed in the framework of this research project. This means a system that starts off with an electron source and delivers electrons travelling at almost the speed of light.

What is your particular task in the project?

I plan to set up a small research group working on the topic of DLA. We will simulate the electromagnetic fields and the particle dynamics in such microstructures. The goal is to determine theoretical intensity limitations for the DLA structures. A second step includes the collaboration with the partners in order to make sure that those theoretical intensity limits are also reached in the experiment.

Who are those partners you are going to collaborate with?

We will be funded by the Gordon & Betty Moore Foundation. Gordon Moore together with Andy Grove and Robert Noyce founded the Intel corporation in 1968. He is also famous for “Moore’s law“, saying that the number of transistors on a microchip doubles about every two years. The Moore Foundation funds the Stanford University directly, which redistributes the money to sub-contractors (e.g. the TU Darmstadt). We will collaborate with the Stanford University and the FAU Erlangen on the theoretical fields and the acceleration of non-relativistic electrons. The experiments on acceleration of relativistic electrons will be conducted at the Stanford Linear Accelerator Center (SLAC) in California, the Deutsches Elektronen Synchrotron (DESY) in Hamburg, and the Paul-Scherrer-Institut (PSI) in Switzerland.

How do you manage the collaboration with the international colleagues?

We plan to meet twice a year, once in Europe and once in the USA. Moreover, we will conduct video conferences regularly. Especially with the colleagues who work on simulations we plan to do video conferences monthly. In these meetings we will present results and discuss problems. However, it is likely that I have to travel to the collaborators on short notice since not everything can be clarified online.

What are the challenges in the project? What problems do you expect?

In general, this project is fundamental research. This means that in the beginning we are not yet able to estimate what results we will obtain. At the moment we cannot say if the intensity limits that we want to predict are sufficient for practical use. But I am very optimistic: perhaps there will be new applications which are tailor-made for our beam parameters.

What is your personal goal in the project?

Maybe one day we will have a cost-efficient particle accelerator for everyone, or at least at every university. Moreover, I’d be happy to encourage students to do their Master thesis in this field.

Uwe Niedermayer from the accelerator physics group is the coordinator for the Accelerator-on-a-chip project at TU Darmstadt. Picture: Hagen Schmidt