Figure 1. Eli-NP exterior view
1. What is ELI-NP?
Eli-NP can be considered one of the three important components of the Eli system. The European Union plans to build Eli-NP into the world's most advanced research facility in the field of optical nuclear physics research and applications. After completion, the facility will consist of two parts. The first part is two ultra-short pulse lasers with a peak power of up to 10 PW, which can achieve a laser peak power density of up to 1023-1024W/cm2 and provide extreme physical conditions with an electric field strength of 2x1015V/m. The second part is currently the world's brightest (1013 photons/second), quasi-monoenergetic (0.1% bandwidth) gamma ray source, with gamma photon energy up to 19.5 MeV. The gamma ray source is based on the principle of incoherent Compton backscattering and is generated by the opposing collision of an ultra-powerful laser and a beam of 720MeV high-energy electrons generated by a traditional linear accelerator.
Currently, the Lawrence Livermore Experiment is in a leading position in the research of this type of gamma ray source internationally. I believe that ELI-NP will also work closely with them. In addition, the Department of Engineering Physics of Tsinghua University in China has also made many breakthroughs in this direction. Eli-NP will rely on the two tools of ultra-powerful lasers and ultra-bright gamma ray sources to solve cutting-edge problems in the fields of basic physics, nuclear physics and astrophysics, and will also study related topics in materials science and life sciences. Eli-NP has been listed as the core device of the "European Nuclear Science Long-term Development Plan" by NuPECC, the most important academic committee in the field of European nuclear science.
2. Where is Eli-NP?
Eli-NP is located in Romania, Southeast Europe, with a planned area of about 33,000m2. The specific location is in the town of Magurele, only 12 kilometers away from the center of Bucharest, the capital of Romania. Before the establishment of ELI-NP, it was already an important scientific research center in Romania. It has five national R&D institutions, mainly involving nuclear science, laser technology, plasma and space science, materials physics, optoelectronics, etc., a physics school and two professional engineering companies (optoelectronics and nuclear facility design).
Figure 2. Location of Eli-NP
3. Goals of Eli-NP
Eli has currently brought together more than 100 scientists in the fields of high-energy laser and nuclear science from more than 30 countries around the world to formulate a relatively detailed experimental plan for Eli-NP. The currently planned research topics are as follows:
1. Use nuclear physics research methods to study the interaction between ultra-high-power lasers and matter to obtain methods and possibilities for obtaining high-quality accelerated beams of protons and heavy ions through lasers.
2. The extremely high intensity of the laser beam will allow experimental studies of the expected theory of some fundamental physical phenomena, such as vacuum birefringence and electron pair generation under strong electric fields.
3. Use the method of photoinduced nuclear reaction to study and analyze nuclear structure and study astrophysics issues.
4. Research new methods for nuclear material identification and remote characteristic identification. This research will be applied in the field of homeland security such as remote automatic transportation container scanning and nuclear material management.
5. Research new methods to generate new radioisotopes and improve the production capacity of radioisotopes currently used in drug synthesis.
6. Simultaneously use high-intensity γ-rays and laser beams to study the generation of electron pairs in vacuum.
4. The birth of PW Laser technical solution
When ELI-NP began designing a 10PW laser technology solution in 2011, there were three solutions based on gain media. The first solution is to use titanium sapphire as the gain medium and frequency-doubled Nd: Glass laser as the pump source. The typical representative system in China is the Aurora III 1.16PW ultra-intense laser system of the Institute of Physics, Chinese Academy of Sciences. The advantage of this solution is that titanium sapphire can provide a fairly wide spectrum. Even if there is gain narrowing during the amplification process, the final output pulse width can still be compressed to less than 30fs using mature technical means. However, the obstacle to achieving higher energy output in this solution mainly comes from the limitation of the size of the gain medium. Obtaining high-quality, uniformly doped large-diameter titanium sapphire crystal is the key to improving the amplification limit, but it is also very difficult.
Figure 3. Ti:sapphire crystal in ELI-NP laser system, diameter: 200mm
The second solution uses DKDP as the gain medium and adopts the OPCPA amplification structure. The advantage is that the DKDP crystal can grow very large, and the problem of aperture limitation is almost non-existent. However, the problem with this solution is that it has high requirements on the pulse width and energy of the pump laser (limited by the efficiency of the OPA process). A typical representative laser system is the 10PW ultra-powerful laser device of the Shanghai Institute of Optics and Mechanics in my country.
The third solution uses Nd: Glass as the gain medium and adopts the OPCPA amplification structure, so that the energy of the pump laser can be higher (no frequency doubling is required). However, this solution is limited by the gain bandwidth of Nd: Glass. The final output pulse width of this solution is generally in the order of hundreds of fs. The representative system is the British VULCAN laser system (1PW).
Figure 4. Comparison of the advantages and disadvantages of the three options for obtaining PW pulses. The "+" sign represents the advantage, and the -"" sign represents the disadvantage.
After comprehensively considering the advantages and disadvantages of the three options, the designer believes that the first option, which is the titanium sapphire-based CPA solution, is most likely to achieve a pulse output of 10PW in the next five years.
At the same time, in order to obtain high contrast output, this solution uses a pulse purification method combining non-collinear OPCPA and XPW in the front stage, and the traditional titanium sapphire amplifier structure is selected for the rear stage amplification. At the same time, the third solution, the OPCPA solution based on Nd: Glass, is used as a backup solution and is being designed and considered at the same time. The design and construction of Eli-NP's two 10PW systems was undertaken by the French company Thales (another example of technological poverty alleviation and the benefits of developed countries!). The picture below shows the final design plan of Eli-NP (refer to the ELI-NP white paper for detailed design).
Figure 5. Eli-NP’s 10PW technical solution diagram (currently only this definition can be found on the Internet)
As can be seen from the figure, Eli-NP is equipped with two broadband high-contrast preamplifiers: the broadband titanium sapphire seed light is broadened and amplified to 100mJ, while maintaining a bandwidth of 15fs and a contrast ratio of
1012. This is because considering the complexity of OPCPA, the alignment and maintenance time of a single front stage will be very long. Setting up two front stages as backup can ensure the long operation of the system and extend the available machine time. The high-contrast seed pulse is further amplified to the order of Joules (10Hz) to tens of Joules (0.1/0.05Hz). The intermediate amplification stage provides independent output and compression, and is suitable for experiments that do not require particularly high energy but require a certain repetition frequency. The final step is to amplify to 200J, and the repetition frequency is expected to drop to every few minutes. It can be used for independent high-energy physics experiments, or in conjunction with gamma ray sources.
Figure 6. Israeli Ambassador visits Eli-NP
Judging from the photos taken during the visit in December 2017, the overall architecture of the PW system should have been completed, although there has been no news of its release yet. In the blink of an eye, it is already
2018. It seems that this system has not yet been fully completed. However, the Shanghai Institute of Optics and Mechanics of the Chinese Academy of Sciences has taken the lead in achieving the world record of 10PW ultra-short pulse output. I can’t help but admire China’s speed!
Due to space limitations, the gamma ray source of Eli-NP is temporarily left out here.
Please continue to pay attention to our approach to European super powerful laser devices: ELI series, the next issue will be more exciting!
【Reference】
http://www.eli-np.ro/documents/ELI-NP-WhiteBook.pdf
http://www.eli-np.ro/