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We present the set-up and performances of the TOP-IMPLART accelerator as a proton source for radiation testing of space components. The TOP-IMPLART proton accelerator is a pulsed fully linear machine aimed at active intensity modulated proton therapy with a final energy of 150 MeV under development at ENEA Frascati Research Centre. Presently the machine offers a beam extraction point on the horizontal line at 35 MeV, with a current up to 50 µA in a 3 µs long pulse and maximum repetition frequency of 50 Hz. An in-air irradiation set-up 1.8 m downstream the accelerator exit window is available with an effective beam energy of about 30 MeV, ±5% transverse homogeneity on a 40 mm diameter beam spot, and intensity repeatability within ±5%. While the proton beams main characteristics (energy, intensity, average fluence) are the same of conventional cyclotron-based cancer treatment facilities, already used for space components qualification, its time structure is significantly different, with high instantaneous dose rate. This research aims at demonstrating the possibility to use an accelerator with these characteristics for radiation hardness assurance testing. A commercial 6-axis integrated MEMS inertial navigation system (accelerometer, gyroscope) was selected as device under test. These devices could be used for example as sensors for attitude determination in University Cubesat missions. Irradiation with proton beams allows simultaneous exploration of total dose, displacement damage and some single-event effect of such components. The results of experimental tests aimed to define an operational procedure are reported: the irradiation set-up is described in detail and the characterization of radiation effect on the component is reported highlighting the consequence of the device performance degradation in terms of the overall navigation system accuracy. These results are considered a first step towards the use of the TOP-IMPLART linear accelerator as a meaningful alternative to traditional cyclotron for proper space qualification of electronic components.

Irradiation of lithium fluoride with protons causes the formation of electronic defects, known as colour centres, in the crystal lattice. Two stable defects among them, the F2 and F3+ aggregate ones, under blue light simultaneous excitation show broad photoluminescence in the red and green visible spectral ranges, respectively, their peculiar characteristics being well known for applications in optically-pumped tuneable lasers, broad-band miniaturized light-emitting photonic devices and passive radiation imaging detectors. Recently, exploitation of their radiophotoluminescence has been successfully proposed for proton-beam advanced diagnostics and dosimetry, even at low dose values typical of radiotherapy. In the present study, lithium fluoride crystals were irradiated with 2.3 MeV protons in the dose range from ∼104 to ∼107 Gy and their dynamic range, that is the capability of detecting the widest possible range of radiophotoluminescence intensity emitted by the colour centres, was found to be 114 dB at the F2 peak emission wavelength of 675 nm under continuous-wave laser excitation at 445 nm. Moreover, after including in the analysis a set of lithium fluoride crystals irradiated with 26.1 MeV protons in the dose range from 0.5 to 48 Gy at a much lower dose-rate, it was found that the radiophotoluminescence intensity of the F2 colour centres shows a linear dependence with dose from 0.5 to ∼2 × 105 Gy.

In a medical accelerator, real-time monitoring systems of the beam and dose delivered to the patient are mandatory. In this work, we present a compact current profile detector that has been designed and tested in the framework of the TOP-IMPLART (Intensity Modulated Proton Linear Accelerator for RadioTerapy) project. This project foresees the realization of a proton linear accelerator, currently under construction at ENEA Frascati, for proton therapy applications. The linac produces a pulsed proton beam with 3 µs duration at 50 Hz repetition rate with a pulse current between 0.5 and 50 μA. A large dynamic range and spatial constraints make the use of usual noninterceptive beam diagnostics unfeasible. Therefore, the use of a beam current monitor based on a passive RF cavity working in the TM010 mode has been proposed. This paper reports the electromagnetic design of the device guided by a simplified analytical model. A prototype of such a device has been realized, characterized, and tested on the linac with a 35 MeV beam varying the beam current. The test results in air and in vacuum, together with the signal detection systems used, are presented.

Solid-state radiation detectors based on the visible photoluminescence of radiation-induced F2 and F3+ color centers in lithium fluoride crystals have been used for advanced diagnostics of 18 and 27 MeV proton beams, produced by the TOP-IMPLART linear accelerator, which is under development for protontherapy applications at ENEA C.R. Frascati, Italy. Visible fluorescence microscopy was successfully used to read the latent proton beam images stored in the lithium fluoride crystals, thanks to high emission efficiency of the F2 and F3+ color centers obtained by simultaneous optical excitation in the blue spectral range. High intrinsic spatial resolution and wide dynamic range of these novel LiF detectors allow obtaining two-dimensional images of both the beam transverse intensity distribution and of the Bragg curve. By using a simple defect formation model that takes into account the energy released in the material and the saturation of defect concentration, not only the two-dimensional dose map was obtained from the beam transverse intensity distribution image, but also the full Bragg curve was reconstructed, allowing the thorough characterization of proton beams produced by the accelerator.

The description of thermal non-uniformity in large area power MOSFETs requires the modeling of a thermal network to account for the thermal interaction between adjacent devices. In this work we propose a methodology to derive an equivalent thermal network which is able to predict the thermal transient as a function of the longitudinal distance from the heat source. The thermal resistances and capacitances are calculated by assuming a cylindrical propagation of the heat. Electro-thermal numerical simulations are performed in order to study the heat propagation inside the device and to verify the accuracy of the proposed model.