RAON Accelerator Research Articles

Lattice design and beam dynamics studies of the high energy beam transport line in the RAON heavy ion accelerator

In RAON heavy ion accelerator, beams generated by superconducting electron cyclotron resonance ion source (ECR-IS) or Isotope Separation On-Line (ISOL) system are accelerated by lower energy superconducting linac and high energy superconducting linac. The accelerated beams are used in the high energy experimental hall which includes bio-medical and muon-SR facilities, after passing through the high energy beam transport lines. At the targets of those two facilities, the stable and small beams meeting the requirements rigorously are required in the transverse plane. Therefore the beams must be safely sent to the targets and simultaneously satisfy the two requirements, the achromatic condition and the mid-plane symmetric condition, of the targets. For this reason, the lattice design of the high energy beam transport lines in which the long deflecting sections are included is considered as a significant issue in the RAON accelerator. In this paper, we will describe the calculated beam optics satisfying the conditions and present the result of particle tracking simulations with the designed lattice of the high energy beam transport lines in the RAON accelerator. Also, the orbit distortion caused by the machine imperfections and the orbit correction with correctors will be discussed.

Start-to-end simulation for the RISP test facility

The RAON accelerator of Rare Isotope Science Project (RISP) has been developed to accelerate heavy ion beams generated by superconducting electron cyclotron resonance ion source (ECR-IS). The beams produced by the ECR-IS are transported through Low Energy Beam Transport (LEBT) section to Radio Frequency Quadrupole (RFQ), Medium Energy Beam Transport (MEBT) section, and low energy superconducting linac (SCL1). Prior to the construction of the RAON accelerator, the components of the LEBT section, the RFQ, the MEBT section, and the part of the SCL1 need to put to the test with the beams generated by the ECR-IS. For that reason, a test facility is under development and will be installed within a few year. Also, in order to build the test facility more efficiently within its restrictive space requirements, we designed the lattice of the test facility newly and then, with this newly designed lattice, in order to demonstrate that the test facility performs well, the start-to-end beam simulation needs to be carried out. In this paper, we will describe the new lattice design of the test facility and the result of the start-to-end beam simulation for the test facility. In addition to the simulation for the single charge state beam, the transportation and acceleration of the three charge state beams will be also examined in the test facility.

Achromatic and isochronous lattice design of P2DT bending section in RAON accelerator

In RAON heavy ion accelerator, generally, the In-flight Fragmentation (IF) and Isotope Separation On-Line (ISOL) systems are employed in order to produce various isotope beams. Out of the isotope beams, the beams generated by the ISOL system are transported from the low energy linac SCL3 to the high energy driver linac SCL2. The post-accelerator to the driver linac transport (P2DT) section that consists of the charge stripper section, the 180° bending section, and the SCL2 matching section is placed between the SCL3 and the SCL2. In this P2DT section, however, the transverse and longitudinal emittance growth can aggravate the beam acceptance of the SCL2. Besides, the growth at the P2DT 180° bending section is considered a significant issue because of the unexpected achromatic effect. Therefore an achromatic and isochronous lattice design should be devised to prevent the transverse and longitudinal emittance from increasing while the multi-charge beams flow through the bending section. This study reports an improved design for the achromatic and isochronous lattice up to the second-order. After satisfying the first-order achromatic and isochronous condition by adjusting the field strength of quadrupoles with this design, the simple and efficient method will be utilized with the aim of getting the minimum number of sextupoles. The research on the collimator for the charge selection at the bending section will be also represented by using the designed lattice.

Design study for the KOBRA (KOrea Broad acceptance Recoil spectrometer and Apparatus) at RAON

The KOBRA (KOrea Broad acceptance Recoil spectrometer and Apparatus) is a multi-purpose recoil spectrometer for low-energy nuclear experiments at the RAON accelerator complex. It is divided into two stages based on the operational function: the first stage (F0–F3) is an in-flight separator or beam transport line, and the second stage (F3–F5) is a large acceptance spectrometer. For spectrometers using radioactive ion (RI) beams, high performance, such as high resolution and large acceptance, are especially required due to the limit of quality of RI beams. In this respect, a dispersion-matching technique and a movable magnet system were employed for high resolution and large acceptance, respectively. Reaction spectra at the focal plane for the dispersion matching mode were obtained and analyzed using a Monte Carlo simulation code. In addition, the geometrical angular acceptances with respect to the distance between the reaction target and the first Q-pole doublet of the second stage were calculated, and the expected maximum solid angle of the spectrometer was estimated.

Design of the Superconducting Magnet System for a 28-GHz ECR Ion Source of RAON Accelerator

The linear accelerator, RAON, has been being developed as a part of the Rare Isotope Science Project (RISP) at Institute for Basic Science (IBS) in the Republic of Korea. In this paper, it is dealt with the design of a low Tc superconducting magnet system for an electron cyclotron resonance (ECR) ion source to utilize a 28-GHz radio frequency source. The superconducting magnet system for a 28-GHz ECR ion source consists of four solenoid coils and six saddle coils (a sextupole coil) (Taylor et al. IEEE Trans. Appl. Supercond. 10, 224–227, 2000). The detail specifications of each superconducting coil are designed by analyzing magnetic field to enhance the efficiency of beam extraction and electromagnetic force to improve the mechanical stability of a superconducting coil by using finite elements method (FEM) simulation. The definitive design parameters for manufacturing the superconducting magnet system for a 28-GHz ECR ion source of RAON accelerator are suggested considering electromagnetic characteristics.

Design of the RAON accelerator systems

The RAON is the name of the heavy ion accelerator facility under construction in Korea that includes the In-flight Fragment (IF) and Isotope Separation On-Line (ISOL) facilities to support cutting-edge research in various science fields. The superconducting linac is the driver for the IF facility that can accelerate beams from proton to uranium with 200 MeV/u, 400 kW (for uranium beam). A 70-MeV, 1-mA H− cyclotron is the driver for the ISOL facility and is followed by a post-accelerator consisting of s superconducting linac that can accelerate rare-isotope (RI) beams and deliver them to experimental halls. These facilities provide high-intensity stable ion and rare isotope (RI) beams for domestic and international users. In this paper, design and prototyping efforts for the RAON accelerator systems are presented.

Design of the multi-reflection time-of-flight mass spectrometer for the RAON facility

Electrodes design for the multi-reflection time-of-flight mass spectrometer (MR-TOF-MS) has been performed for the high precision mass measurement system in RAON accelerator facility, which will be constructed in Korea. Calculated mass res- olution is 10 5 for the condition of an energy spread of 30 eV and an emittance of 0.75 mm mrad. MR-TOF-MS will be used for the isobar separation and the mass measure- ment for very short-lived isotopes.

Design of the plasma chamber and beam extraction system for SC ECRIS of RAON accelerator

The RAON accelerator is the heavy ion accelerator being built in Korea. It contains a 3rd generation SC ECRIS which uses 28 GHz/18 GHz microwave power to extract 12 puA uranium ion beams. A plasma chamber for that ECRIS is made of aluminum machined from bulk Al. That chamber contains cooling channels to remove dumped power and another access port for microwave introduction and plasma diagnostics. Beam extraction electrodes were designed considering the engineering issues and preliminary beam extraction analysis was done. That plasma chamber will be assembled with a cryostat, and beam extraction experiment will be done.