Development of a Laser-based Alignment System for the J-parc Linac

A high-intensity proton accelerator facility named Japan Proton Accelerator Research Complex, or J-PARC, has been proposed as a joint project between KEK (High Energy Accelerator Research Organization) and JAERI (Japan Atomic Energy Research Institute), and the construction of its first phase has been approved by the government [1]. The construction of the linac part has recently been started at JAERI Tokai-campus. Figure 1 shows the layout of the J-PARC linac, which consists of a 50-keV IS (Ion Source), a 3-MeV RFQ (Radio Frequency Quadrupole linac), a 50-MeV DTL (Drift Tube Linac), a 190-MeV SDTL (Separate-type DTL), and a 400-MeV ACS (Annular Coupled Structure linac). The output beam of the linac is led to a 3-GeV RCS (Rapid Cycling Synchrotron) by a beam transport line named L3BT. In highintensity proton accelerators, suppressing excess beam loss is essentially important to avoid serious radiation problems. To lower the beam loss along the linac, an accurate alignment of accelerator components, especially quadrupole magnets, is indispensable. An accurate alignment is also important to avoid beam quality deterioration, such as emittance growth. It should be noted here that it is necessary not only to perform an accurate alignment initially but also to maintain the alignment accuracy for a long period of time. To preserve the alignment accuracy, we need to continuously watch the long-term ground (floor level) motion, and re-alignment should be performed easily. To meet these requirements, we have been developing a laser-based alignment system for the linac part. The total length of the linac is about 280 m, including the straight section of the following beam transport line. The goal accuracy of this alignment system is ± 50 μm transversely. In this paper, the outline of the alignment system is presented together with some preliminary results of the feasibility tests performed with a 50 m test beam line.