Pre-experiment of 70 MeV H - cyclotron for producing ISOL RI beam.

The Rare Isotope Science Project (RISP) is currently constructing equipment and facilities for the Rare Isotope Accelerator complex for ON-line experiments (RAON). The first experiment being conducted involves the acceleration of a proton to 70MeV using a cyclotron, which is then delivered to a SiC target to generate a radioactive isotope beam in the ISOL system. However, before conducting this experiment, a preliminary experiment was performed to confirm the exact location and shape of the proton beam to prevent loss of the proton beam. The pre-experiment involved configuring a faraday cup, wire grid scanner, collimator, and slit inside the proton beam diagnostic module to understand the characteristics of the proton beam at the target position. The beam current ranged from 1 μA to 1.5 μA, and the beam size was confirmed to be within the 2×2cm 2 slit size.

1. Introduction RAON (Rare Isotope Accelerator complex for ON-line experiments) heavy ion accelerator facility was designed to produce rare isotope beams using the Isotope Separation ON-Line (ISOL) system (combined ISOL+IF).The ISOL system delivers neutron-rich rare isotope beams to a postaccelerator (super-conducting linear accelerator) and ISOL experiment hall.To produce the rare isotope beams, the ISOL system uses a commercial proton driver, a 70 MeV H − cyclotron, to deliver a proton beam to a target ion source system (TIS) [1].The TIS system produces the radioactive ion beam (RI beam) which is then accelerated to a pre-mass separator, a Radio-Frequency Quadrupole Cooler Buncher (RFQ-CB), an Electron-Beam Ion Source Charge Breeder (EBIS-CB), and an A/q separator for injection into the post-accelerator.The layout of the ISOL system is shown in Figure 1.In 2019, a contract was signed with IBA, and in 2022, acceptance tests were conducted using a proton beam in two target caves.The first RI beam commissioning experiment of the ISOL system was carried out using a proton beam ranging from 1 to 1.5 µA.The cyclotron was operated as a proton driver, and a pre-experiment was performed to confirm the characteristics of the proton beam.This paper describes the pre-experiment and the results obtained from it.

Proton Driver
We utilized the C70 cyclotron as a proton driver, and its specifications are provided in Table ?? as a result of the site acceptance tests conducted to match the operational conditions of the RI beam delivery.Two beam transport lines are connected to Cave A and Cave B, both located in an ISOL bunker(see Fig. 2).The site acceptance tests were performed in both caves.Beam uniformity tests were carried out in Cave A, and the high-power beam test was conducted in Cave B using beam dumps.The beam dump in Cave A was located at the position of the ISOL target, which is 9 m away from the cyclotron vault wall, while the other beam dump was located after the wobbling magnet, almost in the same position as the outside wall in Cave B. The beam uniformity tests were conducted by operating doublet quadrupoles and a wobbling magnet under the conditions of 20 mm and 50 mm (diameter) collimators.The beam line transmission efficiency was measured to be 97 % at the ISOL target position.The high-power beam test, reaching up to 70 MeV, 700 µA-49 kW, was carried out in cave B, while the proton beam transmission tests were conducted in cave A, where the TIS system was located, using a beam dump to check for uniform beam formation by wobbling.The uniformity of the proton beam was found to be within diameters of 2-5 cm.

Target/Ion Source System
The ISOL TIS system has three modules which are proton beam diagnostic module, TIS module, and RI module(see Fig. 3).These modules are connected with pillow seals for the connection and disconnection [2].
Two ion sources(surface and laser) are in the TIS module with a target, an extraction electrode, and a steer.We can remotely handle this module for target exchange maintenance.The TIS module is located between the proton beam diagnostic module and the RI module.The proton beam diagnostic module is developed for diagnosing proton beam before colliding target.It contains a wire grid scanner, a faraday cup, and a collimator.While, the RI module contains electric quadrupole triplets(EQT) and a faraday cup for focusing and measuring the RI beam.

Experiment Method
The main purpose of proton beam diagnostic module is checking the proton beam before colliding targets.The wire grid scanner has 16 channels at one axis on the effective area(50 × 50mm 2 ).The pitch of the tantalum wires is 3 mm.The faraday cup is used to measure the total number of protons passing through the wire grid scanner.
The collimator inside the proton beam diagnostic module is a device used to shape and check the proton beam position as it travels towards the target.It was made of aluminum and is designed to block any protons that are not traveling directly towards the target.The diameter of collimator is 30 mm and it has 4 sides(can withstand 1 kW proton beam by water cooling) to check the current of proton beam for ensuring that the beam is properly focused and aligned with the target.IT can also help to reduce unwanted scattering or other interactions that can affect the experimental results.
We used a high density (¿ 3.0 g/cm 3 ) SiC for the first RI beam producing experiment.The TIS chamber is supplied with 20 kV through a high voltage transfer bus bar and duct.The RI beams are produced in this chamber via proton-induced fission and moved to the ion source by thermal motion.These ionized isotopes are extracted by this high voltage.The double slit is installed before the target to confirm the high-energy proton beam reaches the target correctly.The slit size is 20 × 20mm 2 .We can get information about the proton beam current in the four sides, which can be used to monitor the position and intensity of the beam.

Characteristic of Proton Beam
The multicusp ion source current was 10 µA and the radial probe current was 1.5 µA(@70 MeV) same as beam line current.Measurements of ion beam current were obtained at various points in the system, including at the source faraday cup, through a radial probe,in the beam line, and via the proton beam diagnostic devices.The beam line current measurement was found to be in agreement with the radial probe current measurement, suggesting that the beam line transmission efficiency was 100 %.These results indicate that the ion beam was successfully transmitted through the beam line without significant losses.We selected the widest beam as the initial model and accelerated it to the target, and characterized the incoming proton beam through the wire grid scanner, the faraday cup, the collimator in the proton beam diagnostic module and the slit in the TIS module.First of all, we adjust the beam center position to the proton beam diagnostic module collimator by changing the current of bending magnet SM5, SM6 as shown in Fig. 4. Fig. 5 shows that the beam shape of the proton beam at this condition.The proton beam size is 12 mm in X axis, 18 mm in Y axis.We fixed the dipole magnet parameters, and scanned with the quadrupoles for measuring the proton beam current in the collimator and the slit.First of all, it was confirmed that the proton beam collided with the right slit at 113.56 A as shown We set the current of Q14 to 108.5 A and the current of Q15 to 90.3A on the condition that the proton beam did not collide with the collimator and the slit as shonw in Fig. 6.
We can produce the Na RI beam with these configurations.The Na RI beam was detected by a scintillator and photomultiplier tube configuration(PMT) after the pre-mass separator.We can see the RI beam intensity(see Fig. 7

SUMMARY
The pre-experiment was done with the 1.5 µA, 70 MeV proton beam confirmed by the faraday cups, the wire grid scanner, the 4-jaw collimator and the slits.The proton beam diagnostic module checked the proton beam before colliding it with the target.The proton beam was successfully transmitted through the beamline without significant losses.

Figure 1 .
Figure 1.Layout of the ISOL system.

Figure 2 .
Figure 2. The cyclotron and beam transport line.

Figure 3 .
Figure 3. TIS system-proton beam diagnostic module, TIS module and RI module

Figure 4 .
Figure 4.The beam line configuration from cyclotron

Figure 7 .
Figure 7.The RI beam intensity by changing the proton beam size

Table 1 .
The specifications of the cyclotron