Beam Power Density Distribution Research Articles

The effect mechanism of laser beam defocusing on the surface quality of IN718 alloy prepared by laser powder bed fusion

The surface quality issue of the laser powder bed fused (LPBF-ed) parts deteriorates the mechanical properties. Laser beam defocusing (LBD) can effectively improve the surface quality. To reveal the effect mechanism of LBD on the surface quality of the LPBF-ed parts, a laser powder bed fusion (LPBF) numerical model is established. Based on the calculated results, the formation process of the surface defects such as bulges, depressions, partially melted powders and spatters and the corresponding melt pool dynamic behaviors are investigated. The effects of LBD on the melt pool dynamic behaviors during the surface defects formation and the track width are discussed. The results show that LBD can improve the surface quality by reducing Marangoni force and recoil pressure to reduce bulge height and depression depth, increasing track width to decrease partially melted powders, and increasing surface tension and reducing kinetic energy to decrease spatters.

Astigmatic electron beam propagation

An astigmatic electron beam with an ellipticity ratio of approximately 2:1 was examined using the Enhanced Modified Faraday Cup (EMFC) diagnostic to measure its properties and show how the power density distribution varies near the beam waist. Results show that the beam has two power density peaks, one on either side of the beam crossover point, resulting from different focal distances of the major and minor axes of the elliptical beam shape. Quantification of the beam properties was used to establish a depth-of-field where the beam diameter and peak power densities are relatively constant. For the 1 kW beam studied here, the depth-of-field measured approximately ±5 mm from the beam crossover point, illustrating how electron beam diagnostics can be used to identify process control limits for repeatable and reliable welds under non-ideal electron beam power density distribution conditions.

Електронно­променеве зварювання з програмуванням розподілу густини потужності променя

Електронно­променеве зварювання з програмуванням розподілу густини потужності променя

Electron beam welding with programming of beam power density distribution

Electron beam welding with programming of beam power density distribution

Status, scientific results and technical improvements of the NBH on TCV tokamak

The TCV tokamak contributes to physics understanding in fusion reactor research by a wide set of experimental tools, like flexible shaping and high power ECRH. A 1MW, 25 keV deuterium heating neutral beam (NB) has been installed in 2015 and it was operated from 2016 in SPC-TCV domestic and EUROfusion MST1 experimental campaigns (˜50/50%). The rate of failures of the beam is less than 5%.Ion temperatures up to 3.5 keV have been achieved in ELMy H-mode, with a good agreement with ASTRA predictive simulations. The NB enables TCV to access ITER-like βN values (1.8) and Te/Ti ˜1, allowing investigations of innovative plasma features in ITER relevant ELMy H-mode. The advanced Tokamak route was also pursued, with stationary, fully non-inductive discharges sustained by ECCD and NBCD reaching βN˜1.4–1.7.Real-time control of the NB power has been implemented in 2018 and presented together with the statistics of NB operation on the TCV. During commissioning, the NB showed unacceptable heating of the TCV beam duct, indicating a higher power deposition than expected on duct walls. A high beam divergence has been found by dedicated measurement of 3-D beam power density distribution with an expressly designed device (IR measurement on tungsten target).

Signal acquisition and scale calibration for beam power density distribution of electron beam welding

The power density distribution of electron beam welding (EBW) is a key factor to reflect the beam quality. The beam quality test system was designed for the actual beam power density distribution of high-voltage EBW. After the analysis of characteristics and phase relationship between the deflection control signal and the acquisition signal, the Post-Trigger mode was proposed for the signal acquisition meanwhile the same external clock source was shared by the control signal and the sampling clock. The power density distribution of beam cross-section was reconstructed using one-dimensional signal that was processed by median filtering, twice signal segmentation and spatial scale calibration. The diameter of beam cross-section was defined by amplitude method and integral method respectively. The measured diameter of integral definition is bigger than that of amplitude definition, but for the ideal distribution the former is smaller than the latter. The measured distribution without symmetrical shape is not concentrated compared to Gaussian distribution.

Study Of Laser Beam Modulation Influence On Structure Of Materials Produced By Additive Manufacturing

In the article, the study of laser beam modulation influence on the structure of materials produced by one of the methods of additive manufacturing as selective laser melting (SLM) is provided. For the purpose of creating a smoother temperature gradient and the optimal conditions of the heat and mass transfer in the melting pool, an experimental stand for SLM-processing with the system of laser beam power density distribution modulation was created. The laser beam modulation gives promising results for higher parameters’ combinations such as power more than 150W and scanning velocity more than 50 mm/sec. The single track’s formation was produced by different power density distribution as Gaussian, Flat-top and Inverse Gaussian (Donut). All the received single tracks were studied with the use of optical and SEM microscopy. The results produce important data about reducing the width of powder consolidation zone, more even structure and higher productivity. Copyright © 2016 VBRI Press.

Thermographic calorimetry of the neutral beam injectors heating beams at TJ-II

A new beam diagnostic based on infrared thermography has been developed for the neutral beam injectors of the stellarator TJ-II. A highly anisotropic movable target intercepts the beam at its entrance into the stellarator. The thermal print of the beam is captured with a high resolution infrared camera. The infrared images of the target can be translated, with the appropriate analysis, into power density patterns of the beam. The system is calibrated in situ with two thermocouples adiabatically mounted in the target. The two-dimensional beam power density distribution can be accurately characterized allowing beam optimization with respect to the different parameters involved in the beam formation and transport.

A novel ion beam monitor using Kapton foils

Kapton foils can be used as a simple ion beam monitor. These foils act as a self-developing medium and quantitative information about the distribution of the striking beam can be obtained easily. The “burn” pattern on the film due to irradiation by the ion beam is analyzed to determine the beam distribution, here the beam power density distribution. Given the beam voltage this information can be translated to the ion current density distribution. The linearity of response of the Kapton foil with beam current density is shown. The threshold for response of the Kapton foil seems quite good; a clear response is observed with a foil of thickness=50 μm for H− beam current density of about 35 μA/cm2 at 88 kV.

Application of Mark Detection Using the Vibration Method to an Electron Beam Exposure System

The possibility of applying a mark detection method using the vibration method to an electron beam exposure system is investigated. The function V(t) with a period T can be used as the function vibrating the beam when V(t) has the properties: V(t)=-V(-t), V(t)=V(-T/2-t) for t≤0, and V(t)=V(T/2-t) for t≥0. Functions included are triangle, ladder, and discontinuous functions. This leads to the possibility of applying the mark detection technique to an excimer laser lithography system. Fluctuation in the center of gravity of the beam power density distribution is the most serious source of error in determining mark location. The experimental result shows that the vibration method is an effective mark detection technique.