Demonstrating Plasma-Modulated Plasma Accelerators (Demonstrating P-MoPA).
Abstract
Particle accelerators are used in many areas of the physical and biological sciences. For example, fundamental studies of the building blocks of matter are carried out with huge accelerators at institutions such as CERN. On a smaller scale, synchrotrons use accelerated electron beams to create light which is widely tunable from the infra-red to X-rays. The conventional accelerators used in these machines employ radio-frequency electric fields to accelerate charged particles. The maximum electric field that can be used is limited by electrical breakdown within the accelerator structure, and so increasing the energy of the accelerated particles requires a larger accelerator. To give some idea of the scale, synchrotron machines are about the size of a football stadium, and the largest machine at CERN is 27 km in circumference! Laser-driven plasma accelerators offer a way to make particle accelerators much more compact. In these devices an intense laser pulse propagates through an ionized gas (a plasma). As it does so, the laser pulse pushes the electrons away from it and sets up a plasma wave which follows the laser pulse at the speed of light. This behaviour is analogous to the water wake which trails a boat crossing a lake. At the peaks of a plasma wave there are more electrons than average, and at the troughs there are fewer, and this charge separation forms very large electric fields. In fact, the field is equal to that which would be generated by placing 100 million volts across two electrodes spaced by one millimetre. This field is about 1000 times larger than the maximum electric field used in conventional accelerators, and as a direct consequence a plasma accelerator can be 1000 times shorter and still produce particles of the same energy. Laser-driven plasma accelerators have already generated electron beams with energies comparable to those used in today s large-scale synchrotron and free-electron laser facilities | and in a plasma accelerator stage only a few centimetres long. Furthermore, the pulses of electrons (known as `bunches ) produced by laser-plasma accelerators have many desirable properties, such as a duration of only a few millionths of a nanosecond. These properties, and the small size of the accelerator, make laser-plasma accelerators ideally suited to driving very compact, and potentially transportable, sources of radiation and energetic particles | with myriad potential applications in science, medicine, and industry. However, a roadblock to realizing these exciting applications is the low pulse repetition rate of the driving lasers that are used today. This is typically only a few pulses per second, which is too low for the most demanding applications, especially those that require a high data rate to achieve a sufficiently high signal-to-noise ratio. In this project we seek to overcome this roadblock by employing a new approach for driving the plasma wave that takes advantage of advances in industrial lasers that can already provide laser pulses with the necessary energy (around 1 joule) at kilohertz repetition rates. The duration of the laser pulses provided by these lasers is too long to drive the plasma wave directly, and so a new approach has to be employed- the plasma-modulated plasma accelerator (P-MoPA). A P-MoPA has three sections. First, in the modulator section the spectrum of a long, high-energy `drive laser pulse is modulated by propagating it along with the (low-amplitude) plasma wave driven by a short, low-energy `seed pulse. This modulates the spectrum of the drive pulse. Second, the spectrally-modulated drive pulse is converted to a train of short pulses by passing it through a special optical system known as a `compressor . Third, the pulse train generated this way is focused into a second plasma.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 05, 2025
- Source ID
- FA86552417030
Entities
People
- Simon M. Hooker
Organizations
- Air Force Office of Scientific Research
- United States Air Force
- University of Oxford