Modern laser technology makes it possible to generate ultrashort pulses with a very high peak power. At the Lund Laser Centre, a high-power laser facility in Lund, Sweden, laser pulses having a duration of approximately 30 femtoseconds are generated with a maximum peak power of up to 40 terawatts. When these pulses are focused, extreme light intensity is achieved. For example, when atoms in a gas are hit by these pulses, they are ionised almost instantaneously, resulting in the main part of the laser pulse interacting with a plasma consisting of free, negatively charged electrons and positively charged ions. The electrons are quickly displaced by the laser pulse whereas the heavier ions largely remain in place, resulting in a very strong electrical field.
The research conducted in the field is spurred by the potential to create applications where charged particles are accelerated to relativistic energies over very short distances in the strong electrical fields. This technology may allow for the development of new and much smaller types of accelerators for applications where for instance linear accelerators are used today.
Ionising radiation occurs around these laser plasma accelerators in connection with a range of different processes, both when the laser pulse interacts with the plasma, and when the accelerated particle beam is slowed down. It is well documented in the literature that ionising radiation is generated when this technology is used; however, the Swedish Radiation Safety Authority (SSM) has, from the perspective of radiation protection, identified the need for both an overall analysis and in-depth knowledge relating to the radiation environment around laser plasma accelerators.
This report demonstrates that the ionising radiation generated around laser plasma accelerators has a strong correlation to the peak power of the laser pulses. Nonetheless, the experimental arrangements can show great variation, for which reason general conclusions cannot be drawn.
This report gives insight into the radiation environment around laser plasma accelerators from the perspective of radiation protection, and may be used as a tool for supporting SSM’s licensing reviews and regulatory supervision in this field.
Need for further research
Depending on technological progress and its possible impact on the radiation environment around the equipment in question, a follow-up study may eventually be required, not only as a basis for updating SSM’s framework of rules, but also to underpin licensing reviews and supervisory work in the field.