The JUNA (Jinping Underground Nuclear Astrophysics collaboration) 400kV accelerator installed at China JinPing deep underground Laboratory (CJPL) successfully delivered its first intense beam on December 26. The accelerator is jointly developed by China Institute of Atomic Energy (CIAE) and the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS). 

The reactions happening inside of stars play an important role in the origin of elements in the universe. But these reaction cross sections are too small to be measured directly at the stellar energies in the ground-based laboratories as the cosmic background overwhelms the rare reaction events. 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.  

CJPL is currently the deepest underground laboratory in the world. The excellent ultra-low background environment in CJPL offers a great opportunity for the underground nuclear astrophysics experiments.  

A team of IMP developed an ECR ion source system for the accelerator, which consists of a 2.45 GHz ECR source and a 14.5 GHz ECR source. The system is capable to deliver intense beams including H⁺ beam at 20 emA, He⁺ at 10 emA and He²⁺ at 2.5 emA. Several measures were implemented to efficiently control the extracted beam quality and stability as well as the beam induced background. The fluctuation of the beam currents is in the range of +/-5%.  

The beam intensity delivered by the ECR source at CJPL is more than 10 times higher than the similar facilities in the other underground laboratories.  

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.   

 Fig. 1 The profile of the intense beam delivered by the Jinping ECR ion source. The outer ring structure results from the reflection of the surroundings. (Image by IMP) 

                         Fig. 2 The Jinping ECR ion source system installed at CJPL. (Image by IMP) 

Contact :

LIU Fang

Institute of Modern Physics

Email: fangliu@impcas.ac.cn