JANNuS-Saclay

Introduction

At CEA Paris-Saclay, a triple beam facility has been installed for simultaneous ballistic damage, gas implantation and/or electronic excitation. Samples can be irradiated in the wide temperature range from liquid nitrogen to 1000°C. Evolution in the ion-irradiated material microstructure and changes in the service properties (mechanical, thermal…) are then characterized by on line Raman spectrometry or post mortem. Simulation can greatly help in validating the transposition of material laws derived from ion irradiations –formation and evolution of defect loops and of cavities, segregation, amorphization– to in-reactor conditions.

Ion beams available

The JANNuS-Saclay facility comprises three electrostatic accelerators (respectively named Épiméthée, Japet and Pandore) connected to a triple beam chamber for single-, dual- and triple beam irradiations. Three other chambers are linked to Épiméthée and Pandore for single beam irradiation and/or Ion Beam Analysis.

The three accelerators offer a wide range of beams and more ions have still to be tested. Four gases and two metals are available on Épiméthée. Pandore produces different H and He isotopes. Japet uses a single solid cathode that can be rapidly changed. Combining these many beams enables a variety of dual beam and triple beam conditions that mark the richness of JANNuS-Saclay.

Ion sources and accelerators

Épiméthée is a 3 MV single-ended electrostatic accelerator (3-UH-2 Pelletron, National Electrostatics Corp.) equipped with an electron cyclotron resonance (ECR) source (Pantechnik, Nanogan type) able to provide highly damaging beams with large energies and ranges, and also gases: hydrogen, oxygen, noble gases. The ECR source produces high charge states of a variety of ion species, which in combination with the 3 MV acceleration potential can produce ion beams with energies as high as 36 MeV. The source is equipped with four bottles for such gases as O2, He, Ar, Kr, Xe, CH4 and two cartridges of volatile organometallic compounds such as ferrocene and W(CO)6 for producing Fe and W ions.

Japet is a 2 MV Tandem Pelletron (6SDH-2, National Electrostatics Corp.) equipped with an external SNICS-II ion source (negative ions by cesium sputtering) which can deliver electronegative ions such as H, Cl, I, C, Si, V, Cu, Zr, Ag, Au… This system is capable to produce energies of 0.5 to 4.0 MeV for single-charged ions (like H ions), up to 6 MeV for double-charged ions, and correspondingly higher energies for ions of higher charge states (up 16 MeV for Au ions).

Pandore is a 2.5 MV single-ended electrostatic accelerator (7.5SH-2 Pelletron, National Electrostatics Corp.) equipped with a RF source which produces single-charge ions. Six gas bottles are installed in the vessel that allow producing protons, deuterium ions, helium-4 and helium-3 ions. This accelerator is used for implantation as well as for IBA.

Irradiation chambers

The triple beam chamber receives one beam line coming from each of the accelerators, allowing single, dual or triple beam irradiations. Each one of the beam lines, converging towards the triple beam chamber with an incidence angle of 15 °, is equipped with a raster scanner unit able to spread the beam homogeneously over an area 2 cm in diameter on the sample surface. A heating-cooling sample stage has been developed to provide precise temperature control from Liquid Nitrogen temperature to 800°C.
Two other vacuum chambers are linked to Épiméthée that can be used for single beam irradiation. In these chambers, samples are irradiated at normal incidence. This layout allows connecting a user-designed station behind the single beam chamber and performing in situ diagnostics such as mechanical test or mass spectrometry analysis. A heating-cooling sample stage has been developed to provide precise temperature control from Liquid Nitrogen temperature to 800°C for the single beam irradiation.

Current integration provides an accurate measurement of implanted species concentration. On the top of the chambers, a pneumatic system holds a group of Faraday cups designed to control the beam intensity. During irradiation, current is intermittently measured (typically for 30 seconds, every 10 or 20 minutes) using the mobile multi-pin Faraday cups device. Beam profiler monitoring and dose post-controls performed by IBA confirm the validity of this approach. Currents, numbers of incident particles and accumulated doses are regularly monitored during irradiation and the beam intensities can be adjusted at any time in order to attain the requested dose for each ion in the same irradiation time. A new continuous current measurement device is currently being developed.

Low temperature irradiation/implantations (at -172 °C and from 1°C to 20 °C) are managed by flowing LN in the sample stage. Higher temperature (from 20 °C to 800°C) is obtained by heating the sample stage. One to five thermocouples are used to measure the sample temperature and another thermocouple is used for temperature regulation via PID control. A 2D infrared thermal imaging camera records the sample surface temperature during irradiation. At higher temperature, a bi-chromatic pyrometer can be implemented. Robust coupling of the samples to the sample holder and of the sample holder to the stage is important to achieve homogenous temperature. In most cases, sample holders are custom-built for each experiment. Another sample stage made of copper is used to cool samples down to liquid nitrogen temperature under higher beam intensities.
For the triple beam chamber, each beam line can be equipped with an energy degrader in order to produce a roughly homogeneous irradiation damage and implantation(s) along the whole ion range. The degraders are constituted by rotating wheels mounted with suitable thin foils, typically 25 to 250 µg.cm-2 carbon foils or aluminum from 0.8 to 5 µm thick. Degraders induce ion loss due to divergence after scattering in the foils and straggling in the thickest foils. These phenomena have to be taken into account for the calculation of the implantation profiles. Self-ion effect due to the superimposition of the damage region with implantation is taken into account by selecting an appropriate observation depth in the sample.

In situ Raman spectroscopy

Raman spectroscopy is an efficient technique for studying the evolution of the microstructure of materials under irradiation such as to determine existing phases before and after irradiation, to outline the stress induced by irradiation, to evidence phase transition under irradiation and to monitor the damage build-up. For that purpose, a confocal Raman spectrometer has been installed in the triple beam chamber, which allows characterizing a variety of materials of nuclear interest. On line Raman spectrometry allows to monitor in real time the evolution of the damage induced by single-, dual- or triple beam irradiations.

In situ Raman is performed with frequency-doubled Nd:YAG (532 nm) laser, ex situ analyses with a Renishaw Invia Reflex device equipped with a Leica DM2500 microscope with 5 objectives (x5, x20, x50, x50L and x100) are also available. In addition to the 532 nm laser, He:Ne (633 nm) and DPSS (457 nm) laser sources complete the experimental set up.

Introduction

Ion beams available

Ion sources and accelerators

Irradiation chambers

In situ Raman spectroscopy

Ion Beam Analysis

New setup development

High and low temperature chambers