High-power Beam Research Articles

Study of the production of radioisotopes at IFMIF-DONES: 177Lu with deuterons

The production of radioisotopes for nuclear medicine is boosted by different international agencies. The International Fusion Materials Irradiation Facility - Demo Oriented NEutron Source (IFMIF-DONES) will be a infrastructure for testing under high neutron flux the materials to be used in future DEMO fusion reactor. IFMIF-DONES will generate neutrons by means of the impact of a high-power deuteron beam onto a lithium-jet target. There is an important effort to take advantage of the outstanding characteristics of the facility in terms of neutrons and deuterons. Thus, a complementary program is being developed, where the production of radioisotopes for medicine is one of the main applications. Here, we discuss the production of 177Lu with deuterons at IFMIF-DONES.

Effects of laser pretreatment on the formation of nanostructured carbon on the surface of chlorinated polyvinyl chloride under high-power ion beam irradiation

The features of formation of surface morphology of chlorinated polyvinyl chloride (pure and with the addition of the catalyst - ferrocene) under the influence of a high-power ion beam of nanosecond duration after the preliminary pulsed laser treatment of the polymer surface have been investigated. It was found that the morphology of the irradiated surface of chlorinated polyvinyl chloride after pulsed laser surface pretreatment differs significantly from the morphology of the irradiated surface of chlorinated polyvinyl chloride after a preliminary stationary heat treatment. For pure chlorinated polyvinyl chloride, pulsed laser pretreatment with increasing power leads to an increase in the porosity of the surface layer after high-power ion beam irradiation, whereas different surface morphologies, including fibers (including polymer fibers) of different diameters, can be obtained for the pre-stationary post-irradiation thermal treatment of this polymer. Pre-stationary thermal pretreatment of chlorinated polyvinyl chloride with the addition of ferrocene (Fe(C5H5)2) leads to a decrease in the diameter of formed carbon nanofibers (with an increase in the treatment temperature). During the pulsed laser pretreatment, an increase in the porosity of the treated layer and a slight increase in the proportion of nanofibers of larger diameter are observed. To explain the obtained differences for pulsed laser and stationary thermal pretreatment, the effect of polymer heating rate on the features of chlorinated polyvinyl chloride decomposition was analyzed.

Cryopanel and fast closing valve system for ISOL beam operation

We designed a cryopanel system based on Molflow+ simulation and constructed for installation in a beam line of 70 MeV H- cyclotron to adsorb back streaming radioactive molecules from ISOL target. Since the target assembly is not hermetically sealed, a target leak can occur especially during high-power beam operation. The cryopanel surrounds the beam path to enhance adsorption efficiency and can be kept at temperature as low as 10 K. A beam test carried out at a current of ∼1 µA showed the panel temperature is not affected by beam pass. The vacuum in the panel region improves to better than 1 × 10-7 mbar so residual gas spectrum has a low background in detection of target leak. As part of the safety system against target damage, a fast closing valve is installed. These safety systems have been tested as essential components for radiation protection in ISOL operation.

Determining the influence of technological parameters of electron beam surfacing process on the microstructure and microhardness of Ti-6Al-4V alloy

This paper reports the devised technology and equipment for manufacturing parts and assemblies with pre-defined properties by 3D printing methods. Underlying the technology is the application of a high-power electron beam to fuse metal powder in a vacuum chamber with the formation of successive layers that repeat the contours of the digital model of the product. The object of research is the process of surfacing products made of Ti6Al4V titanium alloy powder. The influence of technological parameters (speed and power of the electron beam) on the formation of the structure of the deposited metal and its mechanical properties was investigated. 3 samples printed under 3 modes were studied: beam speed, 270, 540, and 780 mm/s; power, 240, 495, and 675 W, respectively. The beam energy density was 44.5 J/mm3; the trajectory displacement step was 0.2 mm; the dynamic focusing current Idf was –0.31 A; and the powder layer thickness was 0.1 mm. The samples were examined by conventional methods. The structures were studied using an optical microscope, images were recorded with a camera. The Vickers hardness was measured with a microhardness meter in the direction from the technological supports to the surface of the sample, as well as along the surface of the product, and in the layers of the middle part of the sample. It was established that the articles had a dense cast structure of surfaced metal. On all samples, large crystallites with a uniform lamellar-acicular structure of α´-phase with a small amount of β-phase are formed along the height, mostly without defects with uniform microhardness both along the height and along the surface. It was determined that the surfacing mode at beam speed, 240 mm/s; power, 270 W is the most rational for practical use. Under this mode, a stronger structure is formed when it is crushed, reducing the width of the crystallites by 1.55 and 1.17 times compared to other modes

High power electrostatic beam splitter for a proton beamline

The High Intensity Proton Accelerator facility (HIPA) delivers a 590 MeV cw (50.6 MHz) proton beam with up to 1.4 MW beam power (2.4 mA) to spallation and meson production targets serving particle physics experiments and material research. The main accelerator is the ring cyclotron, an isochronous proton machine accelerating an injected 72 MeV beam to a final 590 MeV. A few meters downstream of the ring cyclotron, an electrostatic beam splitter was installed in the 1980s and originally designed to peel off from a 200 μA beam up to 20 μA (12 kW beam power). Future initiatives will also make use of the splitter. Specifically, as part of the Isotope and Muon Production using Advanced Cyclotron and Target technologies (IMPACT) upgrade project, Targeted Alpha Tumour Therapy and Other Oncological Solutions (TATTOOS), an online isotope separation facility will allow to produce promising radionuclides for diagnosis and therapy of cancer in quantities sufficient for clinical studies. The TATTOOS facility includes a dedicated beamline intended to operate at a beam intensity of 100 μA (60 kW beam power), requiring continuous splitting of the high-power main beam via the splitter. As a step forward toward reaching the desired beam intensity, a beam study was carried out to test the viability of the existing splitter for TATTOOS. The results of this study show that a record of 90 μA (53 kW beam power) was peeled off a horizontally and vertically enlarged beam by the splitter. The successful beam strategy employed during the study as well as the results of several key measurements are presented in this paper, with particular emphasis on diagnostic measurements. Additionally, to support the measurements, a computational model of the splitter has been implemented using Monte Carlo simulation tools, including realistic geometry, electrostatic fields, beam optics, and power deposition calculations. Overall, the results of this paper show that through the combination of beam measurements and simulations, the existing splitter can be used to reach the 100−μA beam intensity requirement for TATTOOS. Published by the American Physical Society 2024

Materials adopted for particle beam windows in relevant experimental facilities

A beam vacuum window is a thin interface of separation between a volume under vacuum and a volume at a higher pressure traversed by particle beams. Their application is not only limited to particle accelerators, where they are typically installed inside the beamline to separate vacuum sectors, but also extends to other fields of nuclear research and to high-power hadron beam applications, such as spallation neutron sources and accelerator-driven systems. The main issue concerning the beam window technology resides intrinsically in the dual role of these components: the thickness of the window is supposed to be as thin as possible to allow the passage of the particles through matter with minimal interaction but, at the same time, enough resistant to maintain the required differential pressure between the two environments. Published by the American Physical Society 2024

Overview of neutral beam injectors for plasma heating and diagnostics developed at Budker INP

An overview of the neutral beam injectors developed at the Budker Institute of Nuclear Physics in Novosibirsk during the last 10 years is presented. These neutral injectors are used for plasma diagnostics, heating and current drive in modern fusion devices with magnetic confinement. An arc or a radio-frequency (RF) discharge generates a plasma in the ion sources of the injectors, and a positive hydrogen or deuterium ion beam is extracted and accelerated by a multiaperture ion-optical system (IOS). The accelerated ion beam is converted into a neutral one in a gas target. The precision multiaperture IOS with spherically concave electrodes provides ballistic focusing of the neutral beam. The high-energy, high-power beam injector based on negative ions, which is currently under development, is described as well. It comprises a RF negative ion source and a wide-aperture electrostatic accelerator separated from the source by a low-energy beam transport line, thereby improving the injector reliability.

Frequency tripled semiconductor disk laser with over 0.5 W ultraviolet output power.

Semiconductor disk lasers can produce high output power and good beam quality simultaneously. The high intracavity circulating power of about hundreds of watts, along with the flexibility of tailorable emitting wavelengths, make it an attractive light source for obtaining ultraviolet (UV) radiation from near-infrared lasers through nonlinear frequency conversion. This work reports a frequency tripled 327 nm semiconductor disk laser with record output power and wavelength tuning range by using a type-I phase-matched LiB3O5 (LBO) crystal and a type-I phase-matched β-BaB2O4 (BBO) crystal as the frequency-doubling and -tripling crystals respectively. Thanks to the obviously larger nonlinear coefficient of the type-I phase-matched BBO compared to the commonly used type-II phase-matched LBO, as well as the small spot size specifically designed at the crystal location, the maximum output power of UV lasers reaches 538 mW, corresponding to an optical-to-optical conversion efficiency from pump to UV laser of about 1.14%. A wavelength tuning range of about 8.6 nm and good power stability with a standard deviation of about 0.94 are also achieved.

Beam physics design of a superconducting linac

The China initiative Accelerator-Driven subcritical System (CiADS) project aims to design and build the world’s first accelerator-driven subcritical system demonstration facility. The facility will attain 2.5 MW thermal power in 2026 to realize accelerator-target-reactor coupling experiments. As the first approved accelerator-driven subcritical system facility, the CiADS driver linac will adopt cutting-edge accelerator technologies to achieve the challenging goals of high beam power and high reliability. The accelerator will operate in cw mode to produce a 500 MeV, 5 mA proton beam. To meet the extremely high demands on beam availability, the linac design lays strong emphasis on beam loss control and increased fault tolerance via a novel fault-compensation method. The accelerator complex consists of a room temperature front-end section, a main linac that employs superconducting accelerator technologies, and a high-energy beam transport line. The beam-loss-oriented beam dynamics design of the driver linac complex is presented in the paper. Published by the American Physical Society 2024

Coriolis force compensation and laser beam delivery for 100-m baseline atom interferometry

The Coriolis force is a significant source of systematic phase errors and dephasing in atom interferometry and is often compensated by counter-rotating the interferometry laser beam against Earth's rotation. We present a novel method for performing Coriolis force compensation for long-baseline atom interferometry, which mitigates atom-beam misalignment due to beam rotation, an effect which is magnified by the long lever arm of the baseline length. The method involves adjustment of the angle of the interferometer beam prior to a magnifying telescope, enabling the beam to pivot around a tunable position along the interferometer baseline. By tuning the initial atom kinematics and adjusting the angle with which the interferometer beam pivots about this point, we can ensure that the atoms align with the center of the beam during the atom optics laser pulses. This approach will be used in the MAGIS-100 atom interferometer and could also be applied to other long-baseline atom interferometers. An additional challenge associated with long baseline interferometry is that since long-baseline atom interferometers are often located outside of typical laboratory environments, facilities constraints may require lasers to be housed in a climate-controlled room a significant distance away from the main experiment. Nonlinear effects in optical fibers restrict the use of fiber-based transport of the high-power interferometry beam from the laser room to the experiment. We present the design of and prototype data from a laser transport system for MAGIS-100 that maintains robustness against alignment drifts despite the absence of a long fiber.

Dynamics of high-power coupled nonlinear oscillator arrays for electronic beam steering technique: case of the triode based van der Pol oscillator

This paper presents the dynamics of coupled nonlinear oscillator arrays (CNOAs) as phase shifter for electronic beam steering technique. The proposed phase shifter uses oscillators of van der Pol type with a fifth-order nonlinear resistance and is built on the two architectures based injection-locked oscillator array (ILOAs) and coupled oscillator arrays (COAs). The dynamics equations of the phase shifter are proposed in the frequency and time domain. With the help of mathematical tools such as bifurcation diagrams, maximum Lyapunov exponent and Hilbert transform, important cartography of different oscillating states is deduced over large range of system parameters. Different behavior of the CNOAs including chaos, 2D-torus, multistability, locked and unlocked states are depicted. The phase shift between output voltages of each pair of coupled oscillators is presented for both architectures. A detailed analysis of locked states shows that the required phase shift is synthesized by slightly varying the frequency of the injected signal, or simply by detuning the free-running frequencies of the edge oscillators in equal but opposite directions. The proposed circuit of the phased shifter is built using the original van der Pol oscillator based on a vacuum triode. The maximal phase shift reaches 63° and 75° respectively for ILOAs and COAs. With the presence of triode in the circuit, the output voltage of each oscillating element in the array reaches 100V around 60KHz and is boosted by increasing the value of the triode bias potential to more than 420V. This, therefore, increases the total power dissipation of a single oscillator in the array to more than 47dB ( 50.12W ). This circuit is a candidate for high-power electronics beam steering at ultrasonic frequency.

A Tutorial on the One-Dimensional Theory of Electron-Beam Space-Charge Effect and Steady-State Virtual Cathode

The space-charge effects of pulsed high-current electron beams are very important to high-power particle beam accelerators and high-power microwave devices. The related physical phenomena have been studied for decades, and a large number of informative publications can be found in numerous scientific journals over many years. This review article is aimed at systematically summarizing most of the previous findings in a logical manner. Using a normalized one-dimensional mathematical model, analytical solutions have been obtained for the space-charge-limited current of both planar diode and drifting space. In addition, in the case of a beam current higher than the space-charge-limited current, the virtual cathode behavior and beam current reflection are quantitively studied. Furthermore, the criteria of steady-state virtual cathode formation are investigated, which leads to the physical understanding of the unstable nature of the virtual cathode. This review article is expected to serve as an integrated source of related information for young researchers and students working on high-power microwaves and pulsed particle beams.

Electrochemical and Tribological Performance of Ti–Al with xNb Addition Synthesized via Laser In situ Alloying

Additive manufacturing is a growing technique of producing 3D parts directly using metal powders or wires melted with a high-powered intensity beam or laser. It is still a challenging process as to how laser processing parameters such as gas flow rate and powder flow rate can profitably be adopted to significantly produce Ti–Al-based materials from elemental powders to synthesize alloys that are defect-free and have good mechanical properties. The density of titanium aluminide (Ti–Al) intermetallic alloys makes it gain lots of interests due to its potential ability to substitute nickel-based superalloys in gas turbine engines. This work aims to investigate the effects of Niobium (Nb) additions on Ti–Al–xNb ternary alloys created via the use of 3D printing technology, specifically looking at microstructural evolution, microhardness, electrochemical behavior, and tribological properties. Ti–Al–Nb alloy was synthesized at scan speed of 26 in/min and laser power of 450 W. The structural morphology of the alloys produced was investigated using scanning electron microscopy equipped with energy dispersive spectroscopy and the electrochemical studies of the in situ alloyed Ti–Al–xNb were studied using potentiodynamic techniques. Using an Emco microhardness tester, the microhardness characteristics of the produced TiAl–xNb alloys were examined. From the results obtained, it was observed that the microstructure showed not much substantial cracking or crack initiation. The micrographs are evident of refined microstructure associated to increase in Nb feed rate with α-Ti3Al, γ-TiAl and precipitates of β-TiAl phases as the distinctively identified in the microstructure. The highest recorded microhardness value of 679.1 HV0.5 was achieved at Nb feed of 0.5 rpm and gas carrier of 2 L/min. The fabricated Ti–Al–Nb alloys showed good corrosion resistance behavior in HCl and appreciable wear characteristics with coefficient of friction of 0.412, 0.401, and 0.414 µ at B1, B3, and B5, respectively.

Intracavity frequency-doubled external-cavity surface-emitting blue laser with high conversion efficiency

Blue laser with high power and high beam quality has many applications such as in laser display, underwater communication and imaging, and non-ferrous metal processing. Optically pumped external-cavity surface-emitting laser combines the advantages of both surface-emitting semiconductor lasers and solid-state disk lasers, and can produce high output power and good beam quality simultaneously. Its high intracavity circulating power is more conducive to intracavity frequency doubling, achieving high-power and high beam quality blue light through fundamental laser in the near-infrared waveband. This paper reports an efficient intracavity frequency doubled 490 nm high power blue light by using a 980 nm fundamental laser in an external-cavity surface-emitting laser. The V-type resonant cavity is formed by the high reflectivity distributed Bragg reflector (DBR) at the bottom of gain chip, a folded flat concave mirror (high reflectivity coated for 980 nm and anti-reflectivity coated for 490 nm), and a flat concave end mirror (high reflectivity coated for 980 nm and 490 nm). By inserting a nonlinear crystal LBO into the cavity at the beam waist formed by the folded mirror and end mirror, and employing a birefringent filter (BRF) to polarize the fundamental laser and narrow the linewidth of the laser, a high power and high beam quality blue laser with high conversion efficiency is obtained. The effects of different factors including the length of nonlinear crystal, the linewidth of fundamental laser, and the compensation of walk off angle on the output power of the blue laser are studied experimentally. The length of the nonlinear crystal is optimized based on the size of the fundamental laser beam waist at the position of the crystal in the resonant cavity. Under the type-I phase matching condition of LBO, over 6 W output power at 491 nm wavelength is obtained when the crystal length is 5 mm and the BRF thickness is 1 mm. The beam quality <i>M</i><sup>2</sup> factor in the <i>x</i> direction and the <i>y</i> direction are both 1.08, and the conversion efficiency of frequency doubling is 63%. The experimental results also show that symmetrically placed nonlinear crystals can compensate for the walk-off angle during frequency doubling to a certain extent, thereby clearly improving the conversion efficiency of the frequency doubled blue laser.

About the damage mechanisms of thin targets exposed to high-power particle beams

Thin targets, in the forms of wires, stripes, or foils, are often used in accelerators to measure the properties of particle beams. Motivations for a small thickness, typically between several and hundred micrometers, are diverse. The minuscule diameter of a wire allows for precision measurement because it is probing a small fraction of the beam’s transverse profile. In case of high-power beams, the important rationale is also a small energy which beam deposits in the target and a good cooling because of a large surface-to-volume ratio. In certain beam conditions, the temperature of the target is still very high and leads to wire damage. This paper presents detailed analysis of ductile breakage of a molybdenum wire and gives a short overview of other damage mechanisms for various materials.

Long-range underwater wireless optical communication system based on 490 nm vertical-external-cavity surface-emitting laser

The exploration and utilization of marine resources has promoted the rapid development of marine science and technology, and has put forward higher requirements for underwater communication technology. Long distance underwater wireless optical communication (UWOC) requires the selection of light source on the transmitter side. Laser diodes (LDs) have excellent portability and maneuverability, and have been widely used in the UWOC systems. However, their beam quality is not so good and it is difficult to modulate under high power. In recent years, vertical-external-cavity surface-emitting laser (VECSEL) has received much attention due to its high output power and good beam quality. This work is to explore the advantages of using a 490-nm blue VECSEL as a light source in UWOC, and to improve the performance of the UWOC system by the soft-decision pulse-position modulation (PPM). First, the optical power attenuation coefficient of the channel is obtained, and the measured <i>c</i> is about 0.0591 m<sup>–1</sup> in a 96-m-long tap channel. Subsequently, soft-decision and hard-decision are simulated and experimentally verified. Both simulations and measurements show that the bit error rate (BER) can be significantly reduced with soft-decision. Afterwards, we improve the system by using the soft-decision algorithm and investigate the communication performance of 64 PPMs at different bandwidths by adjusting the PPM signal rate. Finally, 50 MHz is chosen as a signal rate in the experiment. Then a UWOC system is demonstrated in this work. The transmitter side consists of a 490-nm VECSEL light source with an acousto-optic modulator (AOM). The pseudo-random binary sequence (PRBS) is loaded into the arbitrary waveform generator (AWG) for digital-to-analog conversion after PPM modulation, and the analog signal is sent to the driver of the AOM for acousto-optic modulation of the incident beam. The laser is focused before entering the AOM and then collimated after having exited to reduce its divergence. The modulated laser beam passes through a distance of 96 m in the tank by using multiple mirrors on both sides of the tank. Then, the beam is focused by a lens to the avalanche photodiode (APD) for photoelectric conversion in the end, and the signal is processed by a mixed signal oscilloscope (MSO) after data acquisition. A soft-decision algorithm is introduced to further optimize the performance of the PPM modulation. When the optical signal passes through a relatively long distance of 96 m, the measured BER is as low as 1.9 × 10<sup>–5</sup>. This indicates that the soft-decision PPM-based 490 nm blue VECSEL UWOC system performs very well.

Low repetition rate passive mode-locked semiconductor disk laser

Semiconductor disk lasers (SDLs) have advantages of high output power and good beam quality. Their flexible external cavity provides convenience for inserting additional optical element to start mode locking and produce ultra-short pulse train with duration from picosecond to femtosecond. However, the very short lifetime in a range from about a few nanoseconds to tens of nanoseconds of the carrier in semiconductor gain medium limits the decrease of pulse repetition rate, thus restricting the increase of peak power of the mode-locked laser pulse to some extent. In this work, by using the relatively shallow In<sub>0.2</sub>GaAs quantum wells, which have a relatively long carrier lifetime in the active region of gain chip, as well as the particularly designed semiconductor saturable absorption mirror (SESAM) that has a relatively small saturation flux, a passively mode-locked SDL with low repetition rate and high peak power is demonstrated. The used six-mirror cavity has a spot radius of about 200 μm on the chip and a 40 μm spot on the SESAM, and the total cavity length is about 1.92 m. The SESAM passively mode-locked SDL produces a stable pulse train with a lowest repetition rate of 78 MHz. When the temperature is 12 ℃ and the transmittance of the output coupler is <i>T</i> = 3%, an average output power value of 2.1 W and a pulse duration of 2.08 ps are achieved. The corresponding pulse peak power reaches 12.8 kW, which is about twice the reported highest peak power in an SESAM mode-locked SDL. When <i>T</i> = 2% and <i>T</i> = 5%, the obtained average output power values are 1.34 W and 1.62 W respectively, and the corresponding pulse peak power values are 8.17 kW and 9.88 kW. Based on the values reported in the literature and the results of pulse repetition rate in our experiments, the estimated lifetime of the carriers of the In<sub>0.2</sub>GaAs quantum wells in the active region of the gain used chip is 16.4 ns. This high peak power mode-locked semiconductor disk laser has important potential applications in biomedical photonics, chemistry, and nonlinear microscopy.

Development of dual-harmonic RF system for CSNS-II

The upgrade of the China Spallation Neutron Source (CSNS-II) encompasses the development of a dual harmonic RF system for the Rapid Cycling Synchrotron (RCS). The objective of this system is to achieve a maximum second harmonic voltage of 100 kV. To meet this requirement, a high gradient cavity is being used in place of the traditional ferrite loaded cavity. Magnetic alloy (MA) loaded cavities, which can attain very high field gradients, have demonstrated their suitability for high-intensity proton synchrotrons. As a result, designing an RF system with MA-loaded cavities has emerged as a primary focus. Over the past decade, substantial advancements have been made in the development of MA-loaded cavities at CSNS. This paper provides an overview of the RF system that incorporates the MA-loaded cavity and presents the high-power test and beam test results of the system.

Beam Profile Measurement Using the Highly-Oriented Pyrolytic Graphite

The mitigation of heat loading is one of the important issues for beam instrumentation to measure the high-power proton beam. Recently, the highly-oriented pyrolytic graphite (HOPG) material was used for the target probe of the bunch-shape monitor at the front end in the Japan Proton Accelerator Research Complex (J-PARC). Since the thermal conductivity of the HOPG is high, it is suitable to measure both transverse and longitudinal beam profiles under the condition of high heat loading. As an application of the HOPG, for example, the thin HOPG may be used as a substitutive material of the target wire for the transverse profile monitor such as the wire scanner monitor. The possibility of the HOPG target for both transverse and longitudinal beam profile monitors is discussed from some results of the test experiment using the 3 MeV negative hydrogen ion beam at the test stand.

Conceptual design of the high-power electron beam irradiator using niobium-tin superconducting cavity

In recent years, there has been an increasing demand for high-intensity beams in the field of electron beam irradiation. This includes mass production of nuclear medicine examinations using 99Mo and high-efficiency production through material modification via material irradiation. Although superconducting cavities can achieve high-current beam acceleration, a compact accelerator is desirable for general-purpose irradiation beams. In this paper, we designed a practical 10 MeV, 50 mA high-current beam irradiator using a new Nb3Sn superconducting cavity.