Electron-RI collider at RIKEN RI Beam Factory

Toshimi Suda

RI Beam Science Lab., RIKEN, JAPAN

RIKEN RI Beam Factory (RIBF) is a next-generation heavy-ion accelerator facility, dedicated to utilizing a short-lived radioactive-isotope (RI) as a secondary RI beam for various fields of basic science. It aims at providing the world's most intense secondary RI beams produced with an intense primary beam of ~1 mA, whose maximum energy will reach 400 MeV/nucleon for light ions and 350 MeV/nucleon for heavier nuclei up to uranium.

The construction of the RIBF project is divided into two phases, namely Phase I and II. In Phase I, which is currently under construction at Wako, three cyclotrons will be newly constructed for further acceleration of a primary beam extracted from the existing K540 RIKEN Ring Cyclotron (RRC). A large acceptance fragment separator, BigRIPS, has been designed to allow an efficient production of RI beams. Both projectile fragmentation and in-flight fission of a high-energy U-beam will be employed to produce RI beams. The in-flight fission process was found to be quite powerful to produce medium-mass neutron-rich nuclei. The first beam will be delivered to an experimental hall in the year 2004.

The second phase of the RIBF project is a new-generation accelerator-complex, called MUSES (MUlti-uSe Experimental Storage rings). It consists of an accumulator-cooler ring (ACR) and an electron-RI (eRI) collider. The ACR cools the produced RI beam extracted from BigRIPS by using both stochastic- and electron-cooling methods. The cooled RI beam in the ACR will be used for precise measurements of the mass and half life of unstable nuclei. Measurements of the nucleon matter distribution by proton elastic scattering with an internal gas target are also proposed.

The eRI collider consists of a 1-GeV electron linac, and two storage rings for electron and cooled RI beams. This collider is to be for structure studies of unstable nuclei by electron scattering, which has never been performed. This is a big challenge to accelerator physics to achieve a sufficiently high luminosity for various electron-scattering experiments, overcoming the short lifetime and the low production cross section of unstable nuclei.

In my talk, I will introduce the RIKEN RIBF project, and discuss mainly on the feasibility of electron scattering experiments at the eRI collider.