Development of the Dual-Beam Ion Irradiation Facility for Fusion Materials (DiFU).

The Dual-beam ion irradiation facility for Fusion materials (DiFU) has been developed and installed at the Ruder Boskovic Institute with the purpose to perform irradiation of samples of fusion materials by one or two ion beams. Ion beams are delivered to the DiFU chamber by a 6 MV EN Tandem Van de Graaff and a 1 MV HVE Tandetron accelerator, enabling irradiation of areas up to 30 × 30 mm2. The sample holder enables the three-dimensional positioning of samples that can be irradiated while being heated, cooled, or kept at room temperature. Ion fluxes are measured indirectly by the insertion of two large Faraday cups. Besides, the ion flux is monitored continuously by two sets of horizontal and vertical slits, which, in turn, define the limits of the irradiation area on the sample. Sample temperature and conditions during irradiation are additionally monitored by a set of thermocouples, an IR camera, and a video camera. Particular care is dedicated to the mitigation of carbon contamination during ion irradiation.

Ion Microprobe Study of the Polarization Quenching Techniques in Single Crystal Diamond Radiation Detectors.

Synthetic single crystal diamond grown using the chemical vapor deposition technique constitutes an extraordinary candidate material for monitoring radiation in extreme environments. However, under certain conditions, a progressive creation of space charge regions within the crystal can lead to the deterioration of charge collection efficiency. This phenomenon is called polarization and represents one of the major drawbacks associated with using this type of device. In this study, we explore different techniques to mitigate the degradation of signal due to polarization. For this purpose, two different diamond detectors are characterized by the ion beam-induced charge technique using a nuclear microprobe, which utilizes MeV energy ions of different penetration depths to probe charge transport in the detectors. The effect of polarization is analyzed by turning off the bias applied to the detector during continuous or discontinuous irradiation, and also by alternating bias polarity. In addition, the beneficial influence of temperature for reducing the effect of polarization is also observed. Finally, the effect of illuminating the detector with light is also measured. Our experimental results indicate that heating a detector or turning off the bias, and then applying it during continuous irradiation can be used as satisfactory methods for recovering the CCE value close to that of a prepolarized state. In damaged regions, illumination with white light can be used as a standard method to suppress the strength of polarization induced by holes.

Imaging of Organic Samples with Megaelectron Volt Time-of-Flight Secondary Ion Mass Spectrometry Capillary Microprobe.

Time-of-flight Secondary Ion Mass Spectrometry (TOF SIMS) with MeV primary ions offers a fine balance between secondary ion yield for molecules in the mass range from 100 to 1000 Da and beam spot size, both of which are critical for imaging applications of organic samples. Using conically shaped glass capillaries with an exit diameter of a few micrometers, a high energy heavy primary beam can be collimated to less than 10 µm. In this work, imaging capabilities of such a setup are presented for some organic samples (leucine-evaporated mesh, fly wing section, ink deposited on paper). Lateral resolution measurement and molecular distributions of selected mass peaks are shown. The negative influence of the beam halo, an unavoidable characteristic of primary beam collimation with a conical capillary, is also discussed. A new start trigger for TOF measurements based on the detection of secondary electrons released by the primary ion is presented. This method is applicable for a continuous primary ion beam, and for thick targets that are not transparent to the primary ion beam. The solution preserves the good mass resolution of the thin target setup, where the detection of primary ions with a PIN diode is used for a start trigger, reduces the background, and enables a wide range of samples to be analyzed.

Monitoring Ion Track Formation Using In Situ RBS/c, ToF-ERDA, and HR-PIXE.

The aim of this work is to investigate the feasibility of ion beam analysis techniques for monitoring swift heavy ion track formation. First, the use of the in situ Rutherford backscattering spectrometry in channeling mode to observe damage build-up in quartz SiO₂ after MeV heavy ion irradiation is demonstrated. Second, new results of the in situ grazing incidence time-of-flight elastic recoil detection analysis used for monitoring the surface elemental composition during ion tracks formation in various materials are presented. Ion tracks were found on SrTiO₃, quartz SiO₂, a-SiO₂, and muscovite mica surfaces by atomic force microscopy, but in contrast to our previous studies on GaN and TiO₂, surface stoichiometry remained unchanged. Third, the usability of high resolution particle induced X-ray spectroscopy for observation of electronic dynamics during early stages of ion track formation is shown.