Interactions between ultra-intense fields and electron beams from accelerators will be much different from what we have observed so far, as incoherent interactions between electrons and laser photons. It is a region where we have not experienced to date as well as where we may encounter a new field of fundamental physics. In this article we introduce examples of interactions between intense fields and electrons and discuss its aspect of fundamental sciences.

Accelerator mass spectrometry (AMS) has developed wide application of radiocarbon (¹⁴C) dating. The AMS system requires only 1 mg of carbon in precise determination of ¹⁴C/ ¹²C and ¹³C/ ¹²C isotope ratios, and this advantage has broadened the applicability of ¹⁴C measurements. Nowadays, AMS contributes to the researches that utilize ¹⁴C dating in archeology, cultural property science, geology, and those that employ ¹⁴C tracer in environmental sciences, medical sciences and even forensic studies.

A Tandetron AMS system dedicated to ¹⁴C measurement was installed at Nagoya University, and its routine operation for ¹⁴C measurement was started in 1983 for the first time in Japan. In 1996, another AMS system (HVE-Model-4130-AMS) was purchased and has been used for high precision ¹⁴C measurements. By repeating a 30 minutes measurement of carbon isotopes for consecutive three days for a sample, one-sigma uncertainty of ±17 to ±30 years has been achieved. A reproducibility test for 2000-year-old archeological samples yielded a fluctuation error as small as ±11 years. We also have evaluated accuracy in our ¹⁴C measurements by participating in international ¹⁴C inter-comparison tests, and confirmed that our ¹⁴C results were quite consistent with those evaluated by the majority of participants. After the critical tests, we are sure that our AMS system is applicable to historical samples that require high precision as well as high accuracy ¹⁴C measurements.

The L-band linac at the Institute of Scientific and Industrial Research, Osaka University has been renewed and upgraded for higher stability, improved reproducibility of operation modes and easier operation. Almost all the power supplies and peripheral facilities are replaced with new ones and a computer control system is newly introduced. The remodeling and the subsequent commissioning are successfully completed. To evaluate stability of the linac, the beam intensities are measured with time in two operational modes of the linac used in the various experiments. The intensity fluctuations in both the operational modes are reduced to one-tenth of previous values before renewal.

Current status of MeV energy heavy ion accelerators of Kyoto university (Faculty of Engineering) is reported. Two types of ion accelerators with terminal voltages 2.5 MV (VdG) and 1.7 MV (Tandem) are utilized for both fundamental and application researches covering atomic collision physics, materials science and element analysis. A brief introduction is given of experimental techniques, developed in our laboratory, concerning multi-coincidence for 3D-imaging of molecular fragmentation, liquid-in-vacuum for ion interactions with liquid targets and positron annihilation for in-situ observation of ion-irradiated materials.

KEKB started the first crab crossing operation in February 2007 with two superconducting crab cavities. After four months operation dedicated for machine tuning, physics run with high-current beams resumed in October with the crab crossing. The crab cavities have been working stably for one and a half years. The crab cavity RF system, commissioning process and performance of the crab cavities with high-current beams are presented.

The SPring-8 compact SASE source (SCSS) test accelerator for XFEL/SPring-8 was constructed in 2005 to perform proof-of-principle experiments for stable SASE FEL operation. The first lasing at 49 nm, though not reached saturation, was observed with the 250-MeV electron beam in June 2006. Towards the saturation, we started stabilizing the RF system for the injector section, which dramatically facilitated the lasing condition. The stable operation enables us to tune each of the machine parameter, for instance transversal beam focusing and a beam trajectory in the two undulators, much more precisely by using the lasing response. The second undulator, which did not sufficiently contribute to the first lasing because of large multipole field errors, was replaced by new one. These improvements led us to the successful observation of continuous SASE saturation at the wavelength ranging from ～50 to 60 nm in September 2007. A pulse-energy of 30 μJ is routinely obtained at 60 nm. The stable and intense EUV SASE FEL has been offered for user experiments since October 2007. Analysis of the obtained SASE saturation data with a 3D-FEL simulation code, SIMPLEX, suggests that the electron beam emittance of 0.6 πmm·mrad is unffected by the bunch compression process with over three hundred compression factor. This result proves the validity of our bunch compression scheme that starts from velocity bunching of uniform and long cylindrical electron beam instead of initially short and intense electron beam from a RF photo-cathode.