Thomson Parabola Spectrometer Research Articles

Absolute energy-dependent scintillating screen calibration for real-time detection of laser-accelerated proton bunches.

Laser-plasma accelerators (LPAs) can deliver pico- to nanosecond long proton bunches with ≳100 nC of charge dispersed over a broad energy spectrum. Increasing the repetition rates of today's LPAs is a necessity for their practical application. This, however, creates a need for real-time proton bunch diagnostics. Scintillating screens are one detector solution commonly applied in the field of electron LPAs for spatially resolved particle and radiation detection. Yet their establishment for LPA proton detection is only slowly taking off, also due to the lack of available calibrations. In this paper, we present an absolute proton number calibration for the scintillating screen type DRZ High (Mitsubishi Chemical Corporation, Düsseldorf, Germany), one of the most sensitive screens according to calibrations for relativistic electrons and x rays. The presented absolute light yield calibration shows an uncertainty of the proton number of 10% and can seamlessly be applied at other LPA facilities. For proton irradiation of the DRZ High screen, we find an increase in light yield of >60% compared to reference calibration data for relativistic electrons. Moreover, we investigate the scintillating screen light yield dependence on proton energy since many types of scintillators (e.g., plastic, liquid, and inorganic) show a reduced light yield for increased local energy deposition densities, an effect termed ionization quenching. The ionization quenching can reduce the light yield for low-energy protons by up to ∼20%. This work provides all necessary data for absolute spectral measurements of LPA protons with DRZ High scintillating screens, e.g., when used in the commonly applied Thomson parabola spectrometers.

Enhanced laser absorption and ion acceleration by boron nitride nanotube targets and high-energy PW laser pulses

Enhancing laser energy absorption with energy transfer to fast electrons is crucial for efficient laser-driven ion acceleration. In this work, we present an experimental demonstration of volumetric laser absorption using boron nitride nanotube (BNNT) targets with an average density of 15 of the solid density. We use a PW laser system operating at a pulse duration of 1.2 ps and an energy of 1.3 kJ, reaching intensities of 2 × 1019 Wcm−2 on target with moderate nanosecond contrast (109), to generate energetic ion streams from a 250 µm thick BNNT target. To characterize laser-accelerated ions, Thomson parabola spectrometers, CR-39 nuclear track detectors, and an electron spectrometer are employed. The results are compared to those achieved using flat targets made of polystyrene (PS) of the same thickness. The comparison reveals a 1.5-fold increase in proton maximum energy and a 2.5-fold increase in the maximum energy of heavy ions (C and N) when comparing the BNNT to PS. Moreover, the high-energy ion flux recorded at CR-39 is orders of magnitude higher for the BNNT after cutting off low-energy ions with Al filters. The enhanced ion acceleration is the result of a 2.3-fold increase in the electron temperature for BNNT, as measured by the electron spectrometer. These experimental findings are further validated through two-dimensional particle-in-cell simulations, which confirm the increase in electron temperature due to enhanced laser absorption ascribable to the low density and nanostructure of the BNNT target compared to the flat foil. Published by the American Physical Society 2024

Design and mathematical modeling of scintillator-based electron–ion Thomson parabola spectrometer

A compact scintillator-based electron–ion Thomson Parabola Spectrometer (ei-TPS) is designed and built up, which is able to measure the spectrum of electron and ion beams simultaneously in the same angular axis and real-time mode. The energy range of electrons is around 0.27–3.8 MeV with a relative energy resolution better than 2.5%, and the energy range of proton is around 0.16–21 MeV with a relative energy resolution better than 4% at the kinetic energy of 1 MeV, which makes it suitable for laser-driven ion acceleration experiments with 100-TW level laser. Detailed mathematical modeling is performed to reveal the dependence of properties, such as energy range and resolution, response, and detection threshold, on various parameters of ei-TPS, which is useful to modify the parameters according to specific requirements of electrons and ions.

Absolute calibration up to 20 MeV of an online readout CMOS system suitable to detect high-power lasers accelerated protons

We present the design and absolute calibration of a charged particle online readout CMOS system tailored for high-power laser experiments. This system equips a Thomson parabola spectrometer, which is used at the Apollon petawatt scale laser facility to measure the spectra of protons produced by high-intensity laser–target interactions. The RadEye1 CMOS matrices array detectors are paired with a custom triggering system for image grabbing. This allows us to register the proton and ion signals remotely. The repetition rate is presently 1 shot/min, but the frame grabbing enables the system to be compatible with modern high-power lasers running, e.g., at 1 Hz. We detail here the implementation, in the harsh electromagnetic environment of such interactions, of the system, and its absolute calibration, which was performed for proton energies from 4 to 20 MeV.

Extended characterization of alpha particles via laser-induced p-11B fusion reaction in silicon hydrogenated boron-doped thin targets

The nuclear fusion channel of the p-11B reaction producing α particles with multi-MeV kinetic energies was induced by a sub-nanosecond laser pulse focused onto 10 μm thick boron-doped thin targets at intensities of ∼ 1016 W/cm2. A full characterization in terms of α particle flux and angular distribution was performed thanks to the simultaneous use of several diagnostics (time-of-flight detectors, nuclear track detectors, and Thomson Parabola spectrometers), which enabled to measure key features of particles produced both in the backward (target front side) and forward (target rear side) directions. Maximum α particle flux and cut-off energy were recorded at small detection angles with respect to the target normal in the backward direction. The maximum kinetic energy shown by the α-particles produced in the nuclear fusion reaction was ascribable to a post-accelerating transient electric field present in the laser-generated plasma, in agreement with our previous preliminary results.

Design of a compact Thomson Parabola Spectrometer for diagnostics of proton-boron fusion reaction products initiated by laser

The proton-boron aneutronic fusion reaction has numerous potential applications varying from controlled nuclear fusion reactor to broad-energy spectrum α-particle source, as well as uses in medicine, where it can serve as a source for radioisotope production, or directly in proton boron capture therapy. However, proton-boron fusion reaction and its by-products should be investigated extensively to provide a stable and controlled secondary ion source. In order to monitor the multi-ion beam emitted and accelerated from the target surface after interaction with laser pulses, a new Thomson Parabola Spectrometer (TPS) has been designed to differentiate proton and alpha traces in the energy ranges 0.5–5 MeV and 1–10 MeV respectively, with a high energy resolution (≤ 1%), while maintaining compactness of the spectrometer (∼ 20 cm).

Capabilities of Thomson parabola spectrometer in various laser-plasma- and laser-fusion-related experiments

Abstract The Thomson parabola spectrometer (TPS) [1] is a well-known, universal diagnostic tool that is widely used in laser plasma experiments to measure the parameters of accelerated ions. In contrast to other popular ion diagnostics, such as semiconductor detectors or ion collectors, the TPS is not greatly affected by electromagnetic pulses generated during high-power laser interaction with matter and can be tuned to acquire data in various energy ranges of accelerated ions, depending on the goal of the experiment. Despite the many advantages of this diagnostic device, processing the collected data is a difficult task and requires a lot of caution during interpretation of gathered results. In this work, we introduce the basic principles of operation and data analysis based on the numerical tool created specifically for the TPS designed at the Institute of Plasma Physics and Laser Microfusion, present a range of data obtained during various recent experiments in which our TPS was used, and highlight the difficulties in data analysis depending on the purpose of the experiment and the experimental setup.

A Methodology for the Discrimination of Alpha Particles from Other Ions in Laser-Driven Proton-Boron Reactions Using CR-39 Detectors Coupled in a Thomson Parabola Spectrometer

Solid-state nuclear track detectors (CR-39 type) are frequently used for the detection of ions accelerated by laser-plasma interaction because they are sensitive to each single particle. To the present day, CR-39 detectors are the main diagnostics in experiments focused on laser-driven proton-boron (p11B) fusion reactions to detect alpha particles, which are the main products of such a nuclear reaction, and to reconstruct their energy distribution. However, the acceleration of multispecies ions in the laser-generated plasma makes this spectroscopic method complex and often does not allow to unambiguously discriminate the alpha particles generated from p11B fusion events from the laser-driven ions. In this experimental work, performed at the PALS laser facility (600 J, 300 ps, laser intensity 1016 W/cm2), CR-39 detectors were used as main detectors for the angular distribution of the produced alpha particles during a p11B fusion dedicated experimental campaign. Additionally, a CR-39 detector was set inside a Thomson Parabola (TP) spectrometer with the aim to calibrate the CR-39 response for low energetic laser-driven ions originating from the plasma in the given experimental conditions. The detected ion energies were ranging from hundreds of keV to a few MeV, and the ion track diameters were measured for etching times up to 9 hours. The goal of the test was the evaluation of the detectors’ ability to discriminate the alpha particles from the aforementioned ions. Within this study, the calibration curves for protons and silicon low energy ions are accomplished, the overlapping of the proton tracks and alpha particles is verified, and a methodology to avoid this problem is realized.

Absolute response of a proton detector composed of a microchannel plate assembly and a charge-coupled device to laser-accelerated multi-MeV protons.

The absolute response of a real-time proton detector, composed of a microchannel plate (MCP) assembly, an imaging lens, and a charge-coupled device (CCD) camera, is calibrated for the spectral characterization of laser-accelerated protons, using a Thomson parabola spectrometer (TPS). A slotted CR-39 plate was used as an absolute particle-counting detector in the TPS, simultaneously with the MCP-CCD detector to obtain a calibration factor (count/proton). In order to obtain the calibration factor as a function of proton energy for a wide range of proton numbers, the absolute response was investigated for different operation parameters of the MCP-CCD detector, such as MCP voltage, phosphor voltage, and CCD gain. A theoretical calculation for the net response of the MCP was in good agreement with the calibrated response of the MCP-CCD detector, and allows us to extend the response to higher proton energies. The response varies in two orders of magnitude, showing an exponential increase with the MCP voltage and almost linear increase with the phosphor voltage and the CCD gain. The calibrated detector enabled characterization of a proton energy spectrum in a wide dynamic range of proton numbers. Moreover, two MCP assemblies having different structures of MCP, phosphor screen, and optical output window have been calibrated, and the difference in the absolute response was highlighted. The highly-sensitive detector operated with maximum values of the parameters enables measuring a single proton particle and evaluating an absolute spectrum at high proton energies in a single laser shot. The absolute calibrations can be applied for the spectral measurement of protons using different operating voltages and gains for optimized response in a large range of proton energy and number.

Online charge measurement for petawatt laser-driven ion acceleration.

Laser-driven ion beams have gained considerable attention for their potential use in multidisciplinary research and technology. Preclinical studies into their radiobiological effectiveness have established the prospect of using laser-driven ion beams for radiotherapy. In particular, research into the beneficial effects of ultrahigh instantaneous dose rates is enabled by the high ion bunch charge and uniquely short bunch lengths present for laser-driven ion beams. Such studies require reliable, online dosimetry methods to monitor the bunch charge for every laser shot to ensure that the prescribed dose is accurately applied to the biological sample. In this paper, we present the first successful use of an Integrating Current Transformer (ICT) for laser-driven ion accelerators. This is a noninvasive diagnostic to measure the charge of the accelerated ion bunch. It enables online estimates of the applied dose in radiobiological experiments and facilitates ion beam tuning, in particular, optimization of the laser ion source, and alignment of the proton transport beamline. We present the ICT implementation and the correlation with other diagnostics, such as radiochromic films, a Thomson parabola spectrometer, and a scintillator.

High-repetition-rate, multi-MeV deuteron acceleration from converging heavy water microjets at laser intensities of 1021 W/cm2

We demonstrate high repetition-rate deuteron acceleration by irradiating a continuously flowing, ambient temperature liquid heavy water jet with the high-intensity ALEPH laser. The laser delivered up to 5.5 J (120 TW, 1.2 × 1021 W/cm2) laser energy on target at 0.5 Hz. A high repetition-rate Thomson parabola spectrometer measured the deuteron beam energy spectra on each shot for 60 sequential shots (two minutes). Peak fluxes of 5×1010 deuterons/sr/pulse, corresponding to an average flux of 1.5×1012 deuterons/sr/min, were demonstrated with deuteron energies reaching up to 4.4 MeV. High shot-to-shot stability is observed up to 40%–50% of the maximum deuteron energy. These deuteron beams are suited for fast neutron production through deuteron breakup in a converter yielding energies similar to deuteron–deuteron (D–D, 2.45 MeV) fusion reactions of importance for material damage studies.

Absolute calibration of Fujifilm BAS-TR image plate response to laser driven protons up to 40 MeV.

Image plates (IPs) are a popular detector in the field of laser driven ion acceleration, owing to their high dynamic range and reusability. An absolute calibration of these detectors to laser-driven protons in the routinely produced tens of MeV energy range is, therefore, essential. In this paper, the response of Fujifilm BAS-TR IPs to 1-40MeV protons is calibrated by employing the detectors in high resolution Thomson parabola spectrometers in conjunction with a CR-39 nuclear track detector to determine absolute proton numbers. While CR-39 was placed in front of the image plate for lower energy protons, it was placed behind the image plate for energies above 10MeV using suitable metal filters sandwiched between the image plate and CR-39 to select specific energies. The measured response agrees well with previously reported calibrations as well as standard models of IP response, providing, for the first time, an absolute calibration over a large range of proton energies of relevance to current experiments.

Angular-Resolved Thomson Parabola Spectrometer for Laser-Driven Ion Accelerators.

This article reports the development, construction, and experimental test of an angle-resolved Thomson parabola (TP) spectrometer for laser-accelerated multi-MeV ion beams in order to distinguish between ionic species with different charge-to-mass ratio. High repetition rate (HHR) compatibility is guaranteed by the use of a microchannel plate (MCP) as active particle detector. The angular resolving power, which is achieved due to an array of entrance pinholes, can be simply adjusted by modifying the geometry of the experiment and/or the pinhole array itself. The analysis procedure allows for different ion traces to cross on the detector plane, which greatly enhances the flexibility and capabilities of the detector. A full characterization of the TP magnetic field is implemented into a relativistic code developed for the trajectory calculation of each pinhole beamlet. We describe the first test of the spectrometer at the VEGA 3 laser facility at CLPU, Salamanca (Spain), where up to protons and carbon ions from a laser-irradiated Al foil are detected.

Calibration of BAS-TR image plate response to GeV gold ions.

The response of the BAS-TR image plate (IP) was absolutely calibrated using a CR-39 track detector for high linear energy transfer Au ions up to ∼1.6 GeV (8.2 MeV/nucleon), accelerated by high-power lasers. The calibration was carried out by employing a high-resolution Thomson parabola spectrometer, which allowed resolving Au ions with closely spaced ionization states up to 58+. A response function was obtained by fitting the photo-stimulated luminescence per Au ion for different ion energies, which is broadly in agreement with that expected from ion stopping in the active layer of the IP. This calibration would allow quantifying the ion energy spectra for high energy Au ions, which is important for further investigation of the laser-based acceleration of heavy ion beams.

Parametric Study of Proton Acceleration from Laser-Thin Foil Interaction

We experimentally investigated the accelerated proton beam characteristics such as maximum energy and number by varying the incident laser parameters. For this purpose, we varied the laser energy, focal spot size, polarization, and pulse duration. The proton spectra were recorded using a single-shot Thomson parabola spectrometer equipped with a microchannel plate and a high-resolution charge-coupled device with a wide detection range from a few tens of keV to several MeV. The outcome of the experimental findings is discussed in detail and compared to other theoretical works.

Carbon nanotubes embedded in a polyimide foil for proton acceleration with a sub-ns laser

A series of thin films made of aligned carbon nanotubes (CNTs) embedded in a polyimide substrate was designed, fabricated and used for the first time to accelerate protons and C ions by interaction with a sub-nanosecond, high power laser beam (600 J energy and 300 ps pulse width) with peak intensity of about 3 × 1016 W/cm2 on target. Each target was 5 µm thick, and the composite material contained CNTs aligned in different directions in the substrate. The results obtained from the analysis of a Thomson Parabola spectrometer, and of the spots imprinted by ions on a series of PM355 nuclear track detectors, indicate high energies (up to 3 MeV for protons and 9 MeV for C ions) and a marked influence of the CNTs’ orientation on the produced proton beam current. An increase of the proton fluxes, more than two orders of magnitude, was recorded with the targets containing CNTs aligned parallel to the target normal, in comparison to the other targets. The presented experimental results demonstrate that the laser-driven proton beam flux can be increased using ad hoc designed targets (with embedded and aligned nanotubes) and sub-nanosecond laser pulses with moderate intensities and poor temporal contrast, thus in an acceleration regime very far from those typically investigated experimentally using relativistic intensities (>5 × 1018 W/cm2) and short laser pulses (10 fs to 10 ps).

Aluminum ion plasma monitored by SiC detectors from low to high laser intensity and from ns up to fs pulse duration

Thick and thin films of Al targets were irradiated in vacuum with different IR lasers at intensities between 1010 W/cm 2 and 1019 W/cm2, with pulse duration ranging between 3 ns and 45 fs. The laser-generated plasma was monitored in forward and backward directions, from thin and thick targets, by using SiC detectors, ion collectors, ion energy analyzer, optical spectrometer, Thomson parabola spectrometer and X-ray streak camera. Ion emission shows a maximum ion acceleration proportional to the laser intensity, which reaches about 1 MeV per charge state at 1016 W/cm2. Using fs laser, Al ion acceleration occurs at energies up to about 26 MeV and protons are accelerated at energies up to about 2.0 MeV.In the used experimental conditions, the maximum ion acceleration can be controlled by the laser parameters, irradiation conditions, and target geometry, such as the pulse energy, the focal position and the target thickness. Although different lasers and irradiation conditions were employed, the produced ion charges per solid angle of detection remain comparable, as it will be discussed.

Absolute response of a Fuji BAS-TR imaging plate to low-energy protons (

This paper reports on the absolute response of a Fuji BAS-TR image plate to relatively low-energy protons (<0.2MeV) and carbon ions (<1MeV) accelerated by a 10-TW-class compact high-intensity laser system. A Thomson parabola spectrometer was used to discriminate between different ion species while dispersing the ions according to their kinetic energy. Ion parabolic traces were recorded using an image plate detector overlaid with a slotted CR-39 solid-state detector. The obtained response function for the protons was reasonably extrapolated from previously reported higher-ion-energy response functions. Conversely, the obtained response function for carbon ions was one order of magnitude higher than the value extrapolated from previously reported higher-ion-energy response functions. In a previous study, it was determined that if the stopping range of carbon ions is comparable to or smaller than the grain size of the phosphor, then some ions will provide all their energy to the binder resin rather than the phosphor. As a result, it is believed that the imaging plate response will be reduced. Our results show good agreement with the empirical formula of Lelasseux et al., which does not consider photo-stimulated luminescence (PSL) reduction due to the urethane resin. It was shown that the PSL reduction due to the deactivation of the urethane resin is smaller than that previously predicted.

Calibration of radiochromic EBT3 film using laser-accelerated protons

We present a proof of principle for onsite calibration of a radiochromic film (EBT3) using CR-39 as an absolute proton-counting detector and laser-accelerated protons as a calibration source. A special detector assembly composed of aluminum range filters, an EBT3 film, and a CR-39 detector is used to expose the EBT3 film with protons in an energy range of 3.65 MeV-5.85 MeV. In our design, the proton beam is divided into small beamlets and their projection images are taken on the EBT3 film and the CR-39 detector by maintaining a certain distance between the two detectors. Owing to the geometrical factor of the configuration and scattering inside the EBT3, the areal number density of protons was kept below the saturation level of the CR-39 detector. We also present a method to relate the number of protons detected on the CR-39 in a narrow energy range to protons with a broad energy spectrum that contribute to the dose deposited in the EBT3 film. The energy spectrum of protons emitted along the target normal direction is simultaneously measured using another CR-39 detector installed in a Thomson parabola spectrometer. The calibration curves for the EBT3 film were obtained in the optical density range of 0.01-0.25 for low dose values of 0.1 Gy-3.0 Gy. Our results are in good agreement with the calibrations of the EBT3 film that are traditionally carried out using conventional accelerators. The method presented here can be further extended for onsite calibration of radiochromic films of other types and for a higher range of dose values.

Compact Thomson parabola spectrometer with variability of energy range and measurability of angular distribution for low-energy laser-driven accelerated ions.

This article reports the development of a compact Thomson parabola spectrometer for laser-accelerated ions that can measure angular distribution with a high energy resolution and has a variable measurable energy range. The angular-resolved energy spectra for different ion species can be measured in a single shot, and the sampling angle can be selected from outside the vacuum region. The electric and magnetic fields are applied to the ion dispersion by using a permanent magnetic circuit and annulus sector-shaped electrodes with a wedge configuration. The compact magnetic circuit consists of permanent magnets, fixed yokes, and movable yokes. The magnetic flux is intentionally leaked to the movable yokes, allowing the magnetic field to be adjusted from 53 mT to 259 mT. The annulus sector-shaped electrodes with a wedge configuration provide better trace separation for high-energy ions, retain the lower-energy part of the ion signal, and subject ions passing through all pinholes to an equivalent Lorentz force. The magnetic and electric fields are designed for measuring protons and carbon ions with an energy range of 0.1-5 MeV. The spectrometer allows for the adjustment of the observable energy range afterward according to the parameters of the accelerated ion.