Chinese JUNA 400kV Accelerator Delivers Its First Intense Particle Beam

China's Jinping Underground Nuclear Astrophysics (JUNA) 400 kV Accelerator has delivered its first intense beam since its construction. Conducted on the 26th of December, the experiment is the result of a collaboration between the China Institute of Atomic Energy (CIAE) and the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences.

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A historic event for Chinese physics

The beam experiment is part of a project to better understand the complex physics going on in the center of stars. It is here that many of the elements of the universe are created.

However, these reactions almost impossible to measure directly from afar using ground-based laboratories. This is for a variety of reasons, however, one is that cosmic background radiation tends to overwhelm these reaction events.

The Chinese Academy of Sciences press release explains that, "as a result, the corresponding reaction rates suffer from rather large uncertainties and prevent us from a precise understanding of the element synthesis and the energy generation in stars.

The best solution for this difficult problem is to measure the critical reaction cross-section directly at stellar energies and provide reliable reaction rates with the desired accuracy for astrophysical studies."

The JUNA project hopes to provide benchmark data, help verify extrapolation models, constrain theoretical calculations, and solve key scientific questions in nuclear astrophysics.

"This project aims at the direct measurement of (α,γ), (α,n) reactions in hydrostatic helium burning and (p,γ), (p,α) reactions in hydrostatic hydrogen-burning based on Jinping deep underground laboratory, and will provide key input of nuclear physics for understanding evolution of stars and origin of elements." JUNA's website reads.

"The key techniques, which include the accelerator system with high stability and high intensity, the detector system, and the shielding material with low background, will be developed through the above research," it continues. 

JUNA is the deepest of its kind

JUNA, located in the China Jinping deep underground Laboratory (CJPL), is the deepest of its kind in the world. Its location provides unparalleled ultralow background radiation levels to help scientists at the facility conduct nuclear astrophysics experiments. 

The team has developed an electron cyclotron resonance (ECR) ion source system for the accelerator that consists of a 2.45 GHz ECR source and a 14.5 GHz ECR source. This makes the system capable of delivering intense beams of H⁺ at 20 emA or He⁺ at 10 emA.

It can also generate He²⁺ cations at 2.5 emA.

The facility operates several measures to efficiently control the extracted beam quality and stability as well as the beam-induced background. The fluctuation of the beam current is also maintained within +/- 5 %. 

The generated beam delivered by the ECR on the 26th of December is, by all accounts, more than 10 times higher than any similar facilities in other underground laboratories around the world. 

According to a press release from the Chinese Academy of Sciences, "the coupling of the ECR source with the high voltage platform developed by CIAE provides JUNA and the community an unprecedented opportunity to conquer some long-standing problems, such as the direct measurement of ¹²C(a,g)¹⁶O, the holy grail reaction in experimental nuclear astrophysics."

This development is an important step in the development of this interesting project. Who knows what secrets researchers at the facility will be able to uncover about the nature of physics at the center of stars.