The required beam parameters from users are very wide in beam energy, fluence, and size. For example, some users from bio-science or space science require very low-intensity beams with large uniform areas, whereas users studying radiation-resistant materials want as high-intensity beam as possible. In addition, the user-required beam energies range from 3 to 100 MeV, depending on the application fields and specimen types. At KOMAC, we can provide beams with energies ranging from 10 to 100 MeV continuously by both controlling the DTL tank RF timing and using an energy degrader. We started the pilot user service in 2013 with two beamline/target rooms, which we call general-purpose beamlines, and now, we are operating a radio-isotope (RI) production beamline (TR101), a low-flux beamline (TR102), a beamline for secondary RI beam study (TR104), and a neutron production beamline (dump), as well as two general-purpose beamlines (TR23, TR103). In addition, we were certified under the International Organization for Standardization ISO9001 in 2016 to control the quality of beam service.
1. General-purpose beamlines
Since 2013, we have operated two general-purpose beamlines: one for 20 MeV and the other for 100 MeV. The beam power at the target is 10 kW, and a typical irradiation fluence is about 1011 proton/cm2/pulse; however, it can be modulated to meet user requirement. We guarantee an irradiation uniformity of better than 10% with a sample size smaller than 30 mm in diameter, and we can irradiate large samples up to 300 mm in diameter with reduced uniformity (Fig. 6 lower right). We provide an external beam using a beam window made of a 0.5-mm-thick aluminum–beryllium alloy. The target room is equipped with a beam shutter, a sample holder, a remote sample loading system, and a hot cell for irradiated sample manipulation, as shown in Fig. 6. The beamline is mainly used for materials/nanoscience, bio-life science, and semiconductor irradiation.
2. RI production beamline
One of main applications of a high-intensity proton linac is radio-isotope production. Therefore, in 2016, we developed and commissioned a beamline dedicated to the production of proton-enrich RIs, such as 67Cu (cancer therapy) and 82Sr (PET imaging) . The beam power at the target position is 30 kW, and the irradiation area is tuned for the RI production target with a 50-mm diameter. The target room is highly activated during irradiation, so it is equipped with a hot cell for target handling, as well as a target transportation system and a target cooling system with a separate closed loop. We have demonstrated the production of Cu-67 (68Zn(p, 29)67Cu) and Rb-82 (natRb(p, x)82Sr), but in small amounts due to limited a chemical processing capability, as shown in Fig. 7. The chemical processing facility for RI separation and refining is being installed and will be available in 2021.
3. Low-flux beamline
Recently, the demand for electronic devices used in space applications has been increasing with the growth of space industry. Because protons are the dominant source of radiation in the space environment, and cause radiation effects such as single-event effects (SEEs), proton beam from an accelerator can be used for accelerated ground testing of radiation effects on electronic devices to predict their performance in space. The test for space environment simulation usually requires a very-low-intensity beam, especially for determining the threshold of SEEs precisely. To meet the requirements of users from the space industry, we developed a low-flux beamline (Fig. 8) with features such as easy access and real-time data acquisition capabilities, which are essential for SEE tests . To reduce the beam intensity by more than three orders of magnitude (minimum average current ~ 0.1 nA), we installed a locally shielded collimator. Two octupole magnets were installed to provide a uniform beam with a uniformity better than 10% in a 100 mm-by-100 mm area at the sample position (Fig. 8 lower right). The low-flux beam can be further collimated using an in-air collimator to restrict the irradiation to a specific electronic component mounted on a large board. We can reliably provide a proton beam with an intensity as low as 105 proton/cm2/pulse. Even a lower intensity is possible, but precise dose monitoring is very difficult. The low-flux beamline has been in operation since 2017, and the majority of users utilized that beamline during recent 3 years.
4.8Li production beamline
To expand the utilization fields of the KOMAC accelerator, we have conducted a development program to study secondary beams such as 8Li and neutron generated by bombarding a target with primary proton beam. Especially, a 8Li beam is very useful and can be used in beta-detected nuclear magnetic resonance (β-NMR) for advanced surface analysis. Therefore, we allocated one of the beamlines with a 1-kW beam power as a test beamline for studying 8Li beam generation and for developing a target/ion source (TIS). For the development of the TIS, we performed various numerical studies to estimate the rate of 8Li production, the ionization efficiency, and the operation temperature. The main components of the TIS include a beryllium oxide (BeO) disk-shaped target, a graphite target container, a target heater, and a surface ion source made of rhenium. A prototype of the TIS was fabricated and tested at temperatures above 2000 ℃, as shown in Fig. 9 [5, 6]. In addition to the TIS, beam optical components, such as a beam steerer, an electrostatic focusing lens, and a Wien filter, were installed to transport the generated 8Li beam, and a high-energy beta detector was mounted to detect the beta decay of 8Li. We verified the production of a 8Li beam at a rate of 106 particle/s by measuring the characteristic decay curve (Fig. 9 lower right). Additional studies to improve the production and transport of a 8Li beam, along with a detection technique, will be conducted to realize β-NMR capability at KOMAC.
5. Neutron production beamline
In addition to the proton beam, demands for neutron beams from groups in various fields, such as the semiconductor industry, nuclear fusion society, and nuclear data evaluation groups, have been strong. Especially, the terrestrial radiation (mainly neutrons produced by cosmic rays) effects on the semiconductor devices used for aviation, massive data storage system, and autonomous vehicle systems have been important, because the soft error induced by terrestrial radiation can be critical in those systems; neutron tests on semiconductor devices have been gaining interest in recent years. We have provided users with a pilot service using by-product neutrons generated at a beam dump and with a limited primary beam power (~ 1 kW), as shown in Fig. 10. The estimated neutron fluxes based on a numerical simulation at a reference sample position were 8.1 × 106 neutron/cm2/s for neutron energy above 1 keV and 3.64 × 106 neutron/cm2/s with neutron energy above 10 MeV . Currently, the neutron user service is not so user-friendly, and neutron flux is limited; however, we have a plan to improve the neutron beamline by replacing the beam dump with a dedicated neutron generation target and installing user-friendly equipment to meet the increasing user demands for neutron beams.