Overview of the COMPASS CODAC system

This paper presents an overview of the Control, Data Acquisition, and Communication system (CODAC) at the COMPASS tokamak: the hardware set-up, software implementation, and communication tools are described.The diagnostics and the data acquisition are tailored for high spatial and temporal resolution required by the COMPASS physics programme, which aims namely at studies of the plasma edge, pedestal, and Scrape-off-Layer (SOL). Studies of instabilities and turbulence are also an integral part of the programme. Therefore, the data acquisition consists of more than 1000 channels, sampled at rates from 500 kS/s up to 2 GS/s.Presently, the feedback system controls the plasma position and shape, plasma current, and density and it includes 32 analogue input channels as well as 1 digital input/output channel and 8 analogue outputs. The feedback control runs within the Multi-threaded Application Real-Time executor (MARTe) framework with two threads, a 500 μs cycle to control slow systems and a 50 μs cycle to control the fast feedback power supplies for plasma position control.In this paper, special attention is paid to the links between the systems, to the hardware and software connections, and to the communication. The hardware part is described, the software framework is addressed, and the particular implementation – the dedicated software modules, communication protocols, and links to the database are described.     

Timing and triggering of the Thomson scattering diagnostics on the COMPASS tokamak

The Thomson scattering diagnostics (TS) at the COMPASS tokamak (operated in the Institute of Plasma Physics ASCR, Prague, Czech Republic) is based on two high-power Nd:YAG lasers, which have a pulse energy of 1.5 J and repetition rate of 30 Hz each.A new timing and synchronization unit (TSU) based on a Field Programmable Gate Array (FPGA) was designed and constructed in order to assure reliable and synchronized control of flash lamps and Q-switches of both lasers. Correct delay between laser pulses is necessary to obtain the highest possible laser energy and to prevent the active medium, the Nd:YAG rod, from thermal damage.An FPGA development kit was chosen as core hardware for the TSU and dedicated input and output circuits were manufactured to adapt the kit interfaces for COMPASS TS needs. In addition, the FPGA firmware, the control software, and the graphical user interface were developed to control the TSU hardware.This paper describes the TS regimes that are addressed by the new TSU. Further, the TSU design, the operation flow, and the firmware and software development are presented. Finally, the results of commissioning are shown.     

Power supplies for plasma column control in the COMPASS tokamak

The main magnetic fields in COMPASS – i.e. The Toroidal, Magnetising, Equilibrium, and Shaping Fields – are created by a set of four corresponding thyristor power supplies controlled in a 0.5 ms loop.The plasma position has to be controlled both radially and vertically by two additional magnetic fields provided by two fast amplifiers (FAs) based on MOSFET technology, each supplying ±100 V and up to ±5 kA.Currently, an ongoing project aims at ELM triggering by fast changes of the vertical position of the plasma column, also referred to as vertical kicks. For this purpose, a new Vertical Kicks Power Supply (VKPS) capable of quick change of vertical plasma position is being constructed. This power supply should operate at up to 1.2 kV with switching frequency up to 5 kHz. It is designed as a H-bridge but based on IGBT transistors which can be operated at higher voltages than MOSFETs.In this paper, we focus on the FAs and VKPS engineering design and required output parameters. Both the power supplies are based on modern components with highest available ratings in their categories. Unique design of the power supplies takes advantage of the short duration of the COMPASS discharge by overloading the transistors above their maximal steady-state rating.The FA is regularly operating, so that in addition to describing its design, we also describe the achieved performance parameters. Finally, the common controller unit, communication, and error handling is described.     

The use of NRA to study thermal diffusion of helium in (U, Pu)O2

A lot of work has been already done on helium atomic diffusion in UO₂ samples, but information is still lacking about the fate of helium in high level damaged UOX and MOX matrices and more precisely their intrinsic evolutions under alpha self irradiation in disposal/storage conditions.The present study deals with helium atomic diffusion in actinide doped samples versus damage level. The presently used samples allow a disposal simulation of about 100 years of a UOX spent fuel with a 60 MW d kg^?1 burnup or a storage simulation of a MOX spent fuel with a 47.5 MW d kg^?1 burnup.For the first time, nuclear reaction analysis of radioactive samples has been performed in order to obtain diffusion coefficients of helium in (U, Pu)O₂. Samples were implanted with ³He⁺ and then annealed at temperatures ranging from 1123 K to 1273 K. The evolution of the ³He depth profiles was studied by the mean of the non-resonant reaction: ³He(d, p)⁴He. Using the SIMNRA software and the second Fick’s law, thermal diffusion coefficients have been measured and compared to the ³He thermal diffusion coefficients in UO₂ found in the literature.     

Fatigue assessment of the ITER TF coil case based on JJ1 fatigue tests

The material of the TF coil case in the ITER requires to withstand cyclic electromagnetic forces applied up to 3 × 10⁴ cycles at 4.2 K. A cryogenic stainless steel, JJ1, is used in high stress region of TF coil case. The fatigue characteristics (S–N curve) of JJ1 base metal and welded joint at 4.2 K has been measured. The fatigue strength of base metal and welded joint at 3 × 10⁴ cycles are measured as 1032 and 848 MPa, respectively. The design S–N curve is derived from the measured data taking account of the safety factor of 20 for cycle-to-failure and 2 for fatigue strength, and it indicates that an equivalent alternating stress of the case should be kept less than 516 MPa for the base metal and 424 MPa for the welded joint at 3 × 10⁴ cycles. It is demonstrated that the TF coil case has enough margins for the cyclic operation. It is also shown the welded joint should be located in low cyclic stress region because a residual stress affects the fatigue life.     

The ITER full size plasma source device design

In the framework of the strategy for the development and the procurement of the NB systems for ITER, it has been decided to build in Padova a test facility, including two experimental devices: a full size plasma source with low voltage extraction and a full size NB injector at full beam power (1 MV). These two different devices will separately address the main scientific and technological issues of the 17 MW NB injector for ITER. In particular the full size plasma source of negative ions will address the ITER performance requirements in terms of current density and uniformity, limitation of the electron/ion ratio and stationary operation at full current with high reliability and constant performances for the whole operating time up to 1 h. The required negative ion current density to be extracted from the plasma source ranges from 290 A/m² in D₂ (D^?) and 350 A/m² in H₂ (H^?) and these values should be obtained at the lowest admissible neutral pressure in the plasma source volume, nominally at 0.3 Pa. The electron to ion ratio should be limited to less than 1 and the admissible ion inhomogeneity extracted from the grids should be better than 10% on the whole plasma cross-section having a surface exposed to the extraction grid of the order of 1 m².The main design choices will be presented in the paper as well as an overview of the design of the main components and systems.     

10 years of engineering and physics achievements by the Large Helical Device project

This article reviews 10 years of engineering and physics achievements by the Large Helical Device (LHD) project with emphasis on the latest results. The LHD is the largest magnetic confinement device among diversified helical systems and employs the world's largest superconducting coils. The cryogenic system has been operated for 50,000 h in total without any serious trouble and routinely provides a confining magnetic field up to 2.96 T in steady state. The heating capability to date is 23 MW of NBI, 2.9 MW of ICRF and 2.1 MW of ECH. Negative-ion-based ion sources with the accelerating voltage of 180 keV are used for a tangential NBI with the power of 16 MW. The ICRF system has full steady-state operational capability with 1.6 MW. In these 10 years, operational experience as well as a physics database have been accumulated and the advantages of stable and steady-state features have been demonstrated by the combination of advanced engineering and the intrinsic physical advantage of helical systems in LHD. Highlighted physical achievements are high beta (5% at the magnetic field of 0.425 T), high density (1.1 × 10²¹ m^?3 at the central temperature of 0.4 keV), high ion temperature (T_i of 5.2 keV at 1.5 × 10¹⁹ m^?3), and steady-state operation (3200 s with 490 kW). These physical parameters have elucidated the potential of net-current free helical plasmas for an attractive fusion reactor. It also should be pointed out that a major part of these engineering and physics achievements is complementary to the tokamak approach and even contributes directly to ITER.     

Design of a large irradiation channel at MNSR facility in Ghana

In the design of new slant tube for large sample irradiation in the Ghana Research Reactor-1 facility, Monte Carlo N-Particle Code version 5 (MCNP-5) was employed to simulate the neutron flux profile of the new design. The results show that the neutron flux peaks at different points, at an average thermal neutron flux of (1.1406 ± 0.0046) × 10¹¹, (1.1849 ± 0.0047) × 10¹¹ and (1.0580 ± 0.0044) × 10¹¹ n cm^?2 s^?1 around the reactor vessel. The first two peaks happened to coincide with pneumatic transfer pipes in the pool, but the third peak happened to be in line with the slant tube position. It was observed that as the diameter of the tube varies from 3.90 cm to 23.40 cm, the average thermal neutron flux decreased exponentially from (1.1849 ± 0.0047)10¹¹ n cm^?2 s^?1 to (3.3241 ± 0.0100) × 10¹⁰ n cm^?2 s^?1. The average thermal neutron flux decreases exponentially along the diameter of the designed slant tube from (1.0366 ± 0.0042) × 10¹¹ n cm^?2 s^?1 to (9.7396 ± 0.0136) × 10⁹ n cm^?2 s^?1. From the results, it is evident that a slant tube of diameter 15.00 cm can be installed at the original slant tube position for large sample irradiation.     

Thermal,structural, and radiological properties of irradiated graphite from the ASTRA research reactor – Implications for disposal

The release of Wigner energy from the graphite of the inner thermal column of the ASTRA research reactor has been studied by differential scanning calorimetry and simultaneous differential scanning calorimetry/synchrotron powder X-ray diffraction between 25 °C and 725 °C at a heating rate of 10 °C min⁻¹. The graphite, having been subject to a fast-neutron fluence from ∼10¹⁷ to ∼10²⁰ n cm⁻² over the life time of the reactor at temperatures not exceeding 100 °C, exhibits Wigner energies ranging from 25 to 572 J g⁻¹ and a Wigner energy accumulation rate of ∼7 × 10⁻¹⁷ J g⁻¹/n cm⁻². The shape of the rate-of-heat-release curves, e.g., maximum at ca. 200 °C and a fine structure at higher temperatures, varies with sample position within the inner thermal column, i.e., the distance from the reactor core. Crystal structure of samples closest to the reactor core (fast-neutron fluence >1.5−5.0 × 10¹⁹ n cm⁻²) is destroyed while that of samples farther from the reactor core (fast-neutron fluence <1.5−5.0 × 10¹⁹ n cm⁻²) is intact, with marked swelling along the c-axis. The dependence of the c lattice parameter on temperature between 25 °C and 200 °C as determined by Rietveld refinement for the non-amorphous samples leads to the expected microscopic thermal expansion coefficient along the c-axis of ∼ 26 × 10⁻⁶ °C⁻¹. However, at 200 °C, coinciding with the maximum in the rate-of-heat-release curves, the rate of thermal expansion abruptly decreases indicating a crystal lattice relaxation. The ¹⁴C activity in the inner thermal column graphite ranges from 6 to 467 kBq g⁻¹. The graphite of the inner thermal column of the ASTRA research reactor has been treated by heating to 400 °C for 24 h in a hot-cell facility prior to interim storage.     

Dose-dependent bonding environment of oxygen implanted in GaN

The bonding environment of oxygen implanted in GaN is studied using Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The implantation of 70 keV O ions in GaN results in the formation of a 200 nm – thick subsurface layer that is highly defective or amorphous depending on the implantation fluence which ranges from 1 × 10¹⁵ to 1 × 10¹⁷ cm^?2. The NEXAFS spectra are simulated using the FEFF8 code assuming models that account for the formation of point defects (various configurations of O interstitial and O substitutional in N and Ga sites) as well as chemical effects such as the formation of various polymorphs of Ga oxides and oxynitrides. The implantation-induced lattice disorder is modeled by displacing atoms from their equilibrium positions by adding to their Cartesian coordinates random numbers that belong to normal distributions. The simulations reveal that when the fluence is 1 × 10¹⁵ cm^?2, the O implants occupy interstitial sites preferentially in the empty channels aligned parallel to the c-axis in the plane that contains the Ga atoms and/or in the columns that consist of Ga and N atoms along the c-axis. When the fluence is equal to 1 × 10¹⁶ cm^?2 the O ions substitute for N while at 1 × 10¹⁷ cm^?2 they participate in the formation of mixed GaO_xN_y phases.     

RF modeling of the ITER-relevant lower hybrid antenna

In the frame of the EFDA task HCD-08-03-01, a 5 GHz Lower Hybrid system which should be able to deliver 20 MW CW on ITER and sustain the expected high heat fluxes has been reviewed. The design and overall dimensions of the key RF elements of the launcher and its subsystem has been updated from the 2001 design in collaboration with ITER organization. Modeling of the LH wave propagation and absorption into the plasma shows that the optimal parallel index must be chosen between 1.9 and 2.0 for the ITER steady-state scenario. The present study has been made with n_|| = 2.0 but can be adapted for n_|| = 1.9. Individual components have been studied separately giving confidence on the global RF design of the whole antenna.     

Optical contrast formation in amorphous silicon carbide with high-energy focused ion beams

Thin films (d ～ 1 μm) of hydrogenated amorphous silicon carbide (a-Si_1?xC_x:H), deposited by RF reactive magnetron sputtering with different carbon content x, have been implanted with high fluences (Φ = 1016–1017 cm^?2) of high-energy (E = 0.2–1 MeV) He⁺ ions as the implant species. The induced structural modification of the implanted material results in a considerable change of its optical properties, best manifested by a significant shift of the optical absorption edge to lower photon energies as obtained from photo-thermal-deflection spectroscopy (PDS) data. This shift is accompanied by a remarkable increase of the absorption coefficient over one order of magnitude (photo-darkening effect) in the measured photon energy range (0.6–3.8 eV), depending on the ion fluence, energy and carbon content of the films. These effects could be attributed both to additional defect introduction and increased graphitization, as confirmed by Raman spectroscopy and infra-red (IR) optical transmission measurements. The optical contrast thus obtained (between implanted and unimplanted film material) could be made use of in the area of high-density optical data storage using focused high-energy He⁺ ion beams.     

Influence of thermal performance on design parameters of a He/LiPb dual coolant DEMO concept blanket design

Spanish Breeding Blanket Technology Programme TECNO_FUS is exploring the technological capabilities of a Dual-Coolant He/Pb15.7Li breeding blanket for DEMO and studying new breeding blanket design specifications. The progress of the channel conceptual design is being conducted in parallel with the extension of MHD computational capabilities of CFD tools and the underlying physics of MHD models. A qualification of MHD effects under present blanket design specifications and some approaches to their modelling were proposed by the authors in [1]. The analysis was accomplished with the 2D transient algorithm from Sommeria and Moreau [2] and implemented in the OpenFOAM CFD toolbox [3]. The thermal coupling was implemented by means of the Boussinesq hypothesis. Previous analyses showed the need of improvement of FCI thickness and thermal properties in order to obtain a desirable liquid metal temperature gain of 300 °C. In the present study, an assessment through sensitivity and parametric analyses of the required FCI thickness is performed.Numerical simulations have been carried out considering a Robin-type thermal boundary condition which assumes 1D steady state thermal balance across the solid FCI and Eurofer layers. Such boundary condition has been validated with a fluid–solid coupled domain analysis.Results for the studied flow conditions and channel dimensions show that, in order to obtain a liquid metal temperature gain of about 300 °C, the required FCI material should have a very small effective heat transfer coefficient ((k/δ) ≤ 1 W/m²K) and fluid velocities should be about 0.2 m/s or less. Moreover, special attention has to be placed on the temperature difference across the FCI layer. However, for a maximised liquid metal thermal gain, higher velocities would be preferable, what would also imply a reduced temperature difference across the FCI layer.     

Vacuum system of SST-1 Tokamak

Vacuum chambers of Steady State Superconducting (SST-1) Tokamak comprises of the vacuum vessel and the cryostat. The plasma will be confined inside the vacuum vessel while the cryostat houses the superconducting magnet systems (TF and PF coils), LN₂ cooled thermal shields and hydraulics for these circuits. The vacuum vessel is an ultra-high (UHV) vacuum chamber while the cryostat is a high-vacuum (HV) chamber. In order to achieve UHV inside the vacuum vessel, it would be baked at 150 °C for longer duration. For this purpose, U-shaped baking channels are welded inside the vacuum vessel. The baking will be carried out by flowing hot nitrogen gas through these channels at 250 °C at 4.5 bar gauge pressure. During plasma operation, the pressure inside the vacuum vessel will be raised between 1.0 × 10^?4 mbar and 1.0 × 10^?5 mbar using piezoelectric valves and control system. An ultimate pressure of 4.78 × 10^?6 mbar is achieved inside the vacuum vessel after 100 h of pumping. The limitation is due to the development of few leaks of the order of 10^?5 mbar l/s at the critical locations of the vacuum vessel during baking which was confirmed with the presence of nitrogen gas and oxygen gas with the ratio of ～3.81:1 indicating air leak. Similarly an ultimate vacuum of 2.24 × 10^?5 mbar is achieved inside the cryostat. Baking of the vacuum vessel up to 110 °C with ±10 °C deviation was achieved with a net mass flow rate of 0.8 kg/s at 1.5 bar gauge inlet pressure and supply temperature of 230 °C at the heater end. Also during gas feed system installation, the pressure inside the VV was raised from 3.01 × 10^?5 mbar to 1.72 × 10^?4 mbar by triggering a pulse of lower amplitude of 25 voltage direct current (VDC) for 100 s to piezoelectric valve. This paper describes in detail the design and implementation of the various vacuum subsystems including relevant experimental results.     

Optimization of aluminum thickness for absorption of undesired Ti K X-rays in the measurement of low energy brachytherapy source strength

The contribution of Ti K X-rays to total air kerma strength for low energy brachytherapy sources (¹²⁵I and ¹⁰³Pd) are calculated for different source-to-aperture distances of an indigenously designed free air ionization chamber. For 30 cm source-to-aperture distance, calculated contribution of Ti K X-rays is 4%. The Ti K X-rays can be eliminated by a relatively thin aluminum filter, but the primary photons emitted by the source will also be attenuated. This effect should be compensated by applying a suitable correction factor. The uncertainty in the attenuation correction factor has been also calculated for different thicknesses of aluminum by a Monte Carlo uncertainty analysis algorithm programmed in FORTRAN. The results show that the optimum thickness of the aluminum absorber is 100 μm, for which the contribution of Ti K X-rays in air kerma strength is reduced to less than one hundredth of the uncertainty in the correction factor, ensuring that the uncertainty in the air kerma strength will be mainly due to the uncertainty in the correction factor. The calculated uncertainties are 1.7 × 10^?3, and 3.4 × 10^?3 for ¹²⁵I and ¹⁰³Pd sources, respectively.     

Improvement of initial vacuum condition along 2008–2010 KSTAR campaign by vessel baking

Korea Superconducting Tokamak Advanced Research (KSTAR) is upgraded for its KSTAR 3rd campaign for new target mission to produce the D-shaped plasma with a target plasma current of 500 kA and/or pulse length of 5 s. New Plasma Facing Components (PFCs) are installed which leads to the increase of the surface area of the vessel by a factor of about 5. The vacuum conditioning such as the vessel baking has been performed in order to remove various kinds of impurities including H₂O, carbon and oxygen for the plasma. The total outgassing rate in the KSTAR 1st campaign was measured as 1.5 × 10^?4 mbar ? s^?1 which is increased by a factor of 3 (6.49 × 10^?4 mbar ? s^?1) in the KSTAR 3rd campaign. Nevertheless, the outgassing rates per unit area have been decreased from 9.31 × 10^?5 mbar ? m^?2 s^?1 to 1.22 × 10^?5 mbar ? m^?2 s^?1 due to the upgrade of baking system and series of baking operation.     

Hydrogen isotope exchange in tungsten: Discussion as removal method for tritium

Hydrogen isotope exchange in re-crystallized polycrystalline tungsten was investigated at 320 and 450 K. In a first step the tungsten samples were loaded with deuterium to a fluence of 10²⁴ D/m² from a low-temperature plasma at 200 eV/D particle energy. In a second step, H was implanted at the same particle energy and similar target temperature with a mass-separated ion beam at different ion fluences ranging from 2 × 10²⁰ to 7.5 × 10²³ H/m². The analytic methods used were nuclear reaction analysis with D(³He,p)α reaction and elastic recoil detection analysis with ⁴He. In order to determine the D concentration at depths of up to 7.4 μm the ³He energy was varied from 0.5 to 4.5 MeV. It was found that already at an H fluence of 2 × 10²⁰ H/m², i.e. at 1/5000 of the initial D fluence, about 30% of the retained D was released. Depth profiling of D without and with subsequent H implantation shows strong replacement close to the surface at 320 K, but extending to all analyzable depths at 450 K especially at high fluences, leading to higher release efficiency. The reverse sequence of hydrogen isotopes allowed the analysis of the replacing isotope and showed that the release of D is balanced by the uptake of H. It also shows that hydrogen does not diffuse through a region of filled traps into a region were unfilled traps can be encounter but transport is rather a dynamic process of trapping and de-trapping even at 320 K. Initial D retention in H loaded W is an order of magnitude higher than in pristine W, indicating that every H-containing trap is a potential trap for D. In consequence, hydrogen isotope exchange is not a viable method to significantly enhance the operation time before the tritium inventory limit is reached but should be considered an option to reduce the tritium inventory in ITER before major interventions at the end of an operation period.     

Ohmic contacts on n-type layers formed in GaN/AlGaN/GaN by dual-energy Si ion implantation

Electrical properties of Si-implanted n-type GaN/AlGaN/GaN layers and contact resistances of ohmic electrodes (TiAl) formed on these layers have been examined. Experimental results have clearly shown that ohmic electrodes with a low specific-contact resistance of 1.4 × 10^?7 Ω cm² can be fabricated on the n-type layer having a low sheet resistance of 145 Ω/sq, which has been formed by the dual-energy Si ion implantation (80 keV:1.01 × 10¹⁵/cm² + 30 keV:1.6 × 10¹⁴/cm²) and subsequent annealing at 1200 °C for 2 min using a Si₃N₄ layer as an encapsulant.     

Study and optimization of boronization in Alcator C-Mod using the Surface Science Station (S3)

A Surface Science Station (S³) on the Alcator C-Mod tokamak is used to study and optimize the location and rate of boron film deposition in situ during electron cyclotron (EC) discharge plasmas using 2.45 GHz radio-frequency (RF) heating and a mixture of helium and diborane (B₂D₆) gasses. The radial profile of boron deposition is measured with a pair of quartz microbalances (QMB) on S³, the faces of which can be rotated 360° including orientations parallel and perpendicular to the toroidal magnetic field B_T ～0.1 T. The plasma electron density is measured with a Langmuir probe, also on S³ in the vicinity of the QMBs, and typical values are ～1 × 10¹⁶ m^?3. A maximum boron deposition rate of 0.82 μg/cm²/min is obtained, which corresponds to 3.5 nm/min if the film density is that of solid boron. These deposition rates are sufficient for boron film applications between tokamak discharges. However the deposition does not peak at the EC resonance as previously assumed. Rather, deposition peaks near the upper hybrid (UH) resonance, ～5 cm outboard of the EC resonance. This has implications for RF absorption, with the RF waves being no longer damped on the electrons at the EC resonance. The previously inferred radial locations of critical erosion zones in Alcator C-Mod also need to be re-evaluated. The boron deposition profile versus major radius follows the ion flux/density profile, implying that the boron deposition is primarily ionic. The application of a vertical magnetic field (B_V ～0.01 T) was found to narrow the plasma density and boron deposition profiles near the UH resonance, thus better localizing the deposition. A Monte Carlo simulation is developed to model the boron deposition on the different QMB/tokamak surfaces. The model requires a relatively high boron ion gyroradius of ～5 mm, indicating a B⁺¹ ion temperature of ～2 eV, to match the deposition on QMB surfaces with different orientation to B_T. Additionally, the boron ion trajectories become de-magnetized at high neutral gas throughput (～0.5 Pa m³ s^?1) and pressure (～2 Pa) when the largest absolute deposition rates are measured, resulting in deposition patterns, which are independent of surface orientation to B_T in optimized conditions.     

Nickel,Zn and Cd localisation in seeds of metal hyperaccumulators using μ-PIXE spectroscopy

Metal hyperaccumulators are a rare group of plant species that accumulate exceptionally high concentrations of metals in above ground tissues without showing symptoms of phytotoxicity. Quantitative localisation of the accumulated metals in seed tissues is of considerable interest to help understand the eco-physiology of these unique plant species. We investigated the spatial localisation of metals within seeds of Ni hyperaccumulating Hybanthus floribundus subsp. adpressus, H. floribundus subsp. floribundus and Pimelea leptospermoides and dual-metal (Cd and Zn) hyperaccumulating Thlaspi caerulescens using quantitative micro-proton induced X-ray emission (μ-PIXE) spectroscopy. Intact seeds were hand-sectioned, sandwiched between Formvar films and irradiated using the 3 MeV high energy heavy ion microprobe at ANSTO. Elemental maps of whole H. floribundus subsp. adpressus seeds showed an average Ni concentration of 5.1 × 10³ mg kg^?1 dry weight (DW) with highest Ni concentration in cotyledonary tissues (7.6 × 10³ mg kg^?1 DW), followed by the embryonic axis (4.4 × 10³ mg kg^?1 DW). Nickel concentration in whole H. floribundus subsp. floribundus seeds was 3.5 × 10² mg kg^?1 DW without a clear pattern of Ni localisation. The average Ni concentration in whole P. leptospermoides seeds was 2.6 × 10² mg kg^?1 DW, and Ni was preferentially localised in the embryonic axis (4.3 × 10² mg kg^?1 DW). In T. caerulescens, Cd concentrations were similar in cotyledon (4.5 × 10³ mg kg^?1 DW) and embryonic axis (3.3 × 10³ mg kg^?1 DW) tissues, whereas Zn was highest in cotyledonary tissues (1.5 × 10³ mg kg^?1 DW). In all species, the presence of the accumulated metal within the cotyledonary and embryonic axis tissues indicates that the accumulated metal was able to move apoplastically within the seed.