Spot Parameters Research Articles

Validity of one-time phantomless patient-specific quality assurance in proton therapy with regard to the reproducibility of beam delivery.

Patient-specific quality assurance (PSQA) is a crucial yet resource-intensive task in proton therapy, requiring special equipment, expertise and additional beam time. Machine delivery log files contain information about energy, position and monitor units (MU) of all delivered spots, allowing a reconstruction of the applied dose. This raises the prospect of phantomless, log file-based QA (LFQA) as an automated replacement of current phantom-based solutions, provided that such an approach guarantees a comparable level of safety. To retrieve a reliable LFQA conclusion from a one-time plan delivery before treatment initiation, deviations between planned and logged parameters must either be persistent over all following treatment fractions or, in case of random fluctuations, must not have a relevant impact on the reconstructed dose distribution. We therefore investigated the reproducibility of log file parameters over multiple patient treatment fractions and compared the reconstructed dose distributions. Log file variability was examined at both spot parameter and integral dose levels. The log files of 14 patient treatment plans were analyzed retrospectively for a total of 339 delivered fractions. From the recorded x/y position and MU parameters per spot, the respective mean difference to the planned value (accuracy) and the standard deviation (reproducibility) were calculated for 108,610 planned spots. The dose distributions reconstructed from the log files of each fraction were evaluated against the planned fraction dose using 3D gamma index analysis. The dose-based gamma pass rate was correlated with a new spot-based log file pass rate . Beam timing information from the log files was used to quantify the total plan/field delivery time stability after excluding machine interlocks. The mean spot-wise accuracy with respect to distance from planned positions and MUs was (0.6±0.3)mm and (0.0001±0.0023) MU, respectively. The mean reproducibility of the observed single spot deviations was (0.2±0.1) mm and (0.0004±0.0004) MU (mean±standard deviation). These variations resulted in minimal changes in the reconstructed fraction dose with (2mm/2%)>99% for all studied fractions. Results for more sensitive criteria (1mm/1%) were plan-specific, but on average>92.6% per plan and correlated with (1mm) pass rates (0.51≤rPearson≤0.99). Field delivery times were reproducible within±4 s (2σ) and no treatment interruptions were observed in 92.8% of cases. The log file records of plan-relevant spot parameters are well-reproducible over multiple fractions and deviations have no dosimetrically relevant impact on the reconstructed fraction doses. Results of a one-time pre-treatment LFQA are considered as valid for the entire treatment course and there is no concern in this regard to replace state-of-the-art phantom measurements in the current PSQA workflow.

Multi-objective optimization on the parameters of variable laser spot for the SL printing with a new path planning algorithm

Multi-objective optimization on the parameters of variable laser spot for the SL printing with a new path planning algorithm

Sustainable Application of NATIVO 300 SC Fungicide (Tebuconazole 200 g/L +Trifloxystrobin 100 g/L) in the Control of Brown Spot (Bipolaris oryzae) in Strict Rainfed Rice Cultivation in Côte d’Ivoire

Rice brown spot is a devastating disease caused by Bipolaris oryzae. Various fungicide formulations are used against this phytomycosis, which occurs in all ecologies in Côte d'Ivoire. This study aimed to rationalize the application of a fungicide effective against brown spot in strict rainfed rice cultivation. The experimental design was a Fisher block with three replications. It was carried out in strict rainfed ecology at Biankouma between July and November 2023. The fungicide used was NATIVO 300 SC (Tebuconazole 200 g/L + Trifloxstrobin 100 g/ L). Five different treatments were tested (T0: no fungicide treatment; T1: NATIVO 300 SC at a dose of 350 ml.ha-1, every 10 days interval from the initial appearance of brown spot symptoms until 50% heading stage; T2 : NATIVO 300 SC at a dose of 350 ml.ha-1, at the seedling (4 to 5 leaves), booting and complete heading stages; T3: NATIVO 300 SC at a dose of 350 ml.ha-1, at seedling (4 to 5 leaves), maximum tillering and complete heading stages; T4: NATIVO 300 SC at a dose of 350 ml.ha-1, at early tillering (2 to 3 stems visible), maximum tillering and complete heading stages). Data on disease severity of brown spot and agronomical parameters were recorded ans statistically analysed using SAS 9.4 software. The results proved that treatments T1 and T4 proved more effective, with leaf severity indices of 2.0±0.98 and 3.52±0.78 versus 6.52±0.66 for the control, and yield gains of 67.69 and 60.09% respectively. In conclusion, application of NATIVO 300 SC fungicide at a dose of 350 ml/ha can be recommended at the early tillering, maximum tillering and complete heading stages of rice for effective management of brown spot.

Research on the process parameters and welded joint quality of resistance spot welding of aluminum composite for car bodies

Abstract The test uses a resistance welding machine to implement resistance spot welding of 6061-T6 aluminum alloy thin plate for automobile body and obtains the welding process parameters of resistance spot welding through the test. Using an orthogonal test scheme and extreme difference analysis method to test and further optimize the resistance welding process parameters, after lap resistance spot welding of a 6061-T6 aluminum alloy thin plate with a thickness of 2 mm, we analyze the welding appearance and complete the tensile test. The test results show that when the welding current is 60 KA, the welding pressure is 0.63 MPa, the thickness of the plate is 2.00 mm, the spot weld joints obtained from the specimen have no obvious defects, better molding, good welding quality and appearance, and its tensile shear value is 5.583 KN at maximum.

Assessment of pencil beam scanning proton therapy beam delivery accuracy through machine learning and log file analysis

PurposeComprehensive Quality Assurance (QA) protocols are necessary for complex beam delivery systems like Pencil Beam Scanning (PBS) proton therapy. This study focuses on automating the evaluation of beam delivery accuracy using irradiation log files and machine learning (ML) models. MethodsIrradiation log files of 935 clinical treatment fields and routine QA beams were analysed to evaluate spot parameters and Monitor Unit (MU) accuracy. ML models predicted spot size along the X, Y, major, and minor axes. In-house scripts automated log file analysis and spot size predictions. Predicted spot sizes were compared with expected baselines, and the accuracy of spot position, symmetry, and MU for each spot in the beam was evaluated. ResultsMore than 99.5 % of spot positions were accurate within a 1 mm. The mean and Standard Deviation (SD) of X positional error were −0.021 mm (SD: 0.181 mm), and for Y positional error, they were −0.002 mm (SD: 0.132 mm). ML models accurately predicted spot sizes, with over 95 % of spots demonstrating size variations within 10 % of the baseline. The Root Mean Squared Error (RMSE) of X and Y spot size differences were 0.15 mm and 0.16 mm, respectively. Spot symmetry was within 10 %, and MU accuracy showed 95 % of spots with MU per spot variation less than 2 %. ConclusionThis method can validate the vendor’s beam delivery safety interlock system and serve as a quick alternative to patient-specific QA in adaptive treatment, where time is limited, as well as for routine QA spot parameter evaluations.

Miniaturized optical system of a laser seeker based on a dynamic and static performance co-design

The laser semi-active seeker, crucial for miniaturizing guided munitions, offers high precision, anti-jamming, and rapid response. Current research focuses on system response, spot parameters, and angular velocity accuracy. With small-caliber munitions on the rise, further miniaturization and weight reduction are essential. This paper proposes a design for an optical system that balances dynamic imaging quality and miniaturized static structure. Using quadrant detector principles, factors affecting detection performance are analyzed to determine the optimal spot size and imaging range. Based on imaging requirements and the optical properties of a dual-reflector structure, we determine the design parameters of the system to achieve a combination of dynamic and static performance. Evaluations using ZEMAX and MATLAB confirm that the system achieves ±4∘ linear and ±8∘ full fields of view, 0.12% distortion, 4.52 mrad angular accuracy, a 15.72 mm axial length, and has the possibility of actual production. The system is compact, with excellent spot roundness, stability, and uniform energy distribution, providing a reference for future guided weapon research.

Beam quality measurement and image analysis of RF optical emission system

With the development of radio-over-fiber (ROF), beam quality is also an important parameter in evaluating ROF systems. Therefore, this paper selects the low-frequency to very high frequency (VHF) direct modulated optical emission system to verify its feasibility and excellent performance. It then analyzes the beam quality and image processing. In this paper, MATLAB is selected for the theoretical simulation, then CMOS is used to collect light spots, RayCiV2.5 is used to Gaussian fit the light field intensity distribution, and finally the ideal and actual light spot parameters are compared. Due to the influence of noise, this paper also preprocessed the image by brightness adjustment, filtering, edge fitting, etc. It proposed a fast two-sided filtering algorithm, which obtained a high peak signal-to-noise ratio (PSNR) and strong applicability. The results show that the edge-mode rejection ratio is as high as 33.6 dB, the beam quality is good, and it can be well applied in ROF. The M2 factor is 2.75, the optical field intensity Gaussian fit is 99.8 %, and the signal-to-noise ratio (SNR) is as high as 54.7 dB. Moreover, the image is robust after fast bilateral filtering.

A petrophysically driven seismic inversion method for the total organic carbon content of source rocks

Organic carbon content is the main index for evaluating organic matter abundance of source rocks, and it is still difficult to quantitatively predict total organic carbon (TOC) in source rocks based on seismic data. The study of seismic fluid identification driven by petrophysics can help to understand the fluid characteristics and distribution patterns of subsurface oil and gas reservoirs. First, this paper clarifies the sweet spot parameters (parameters characterizing hydrocarbon enrichment) and sensitive elastic parameters (a parameter characterizing the nature of an ideal elastic body) of source rocks through theoretical petrophysical modeling. Next, the paper establishes the relationship between sensitive elastic parameters and sweet spot parameters TOC and constructs a statistical petrophysical model that can characterize the relationship between the two on this basis. And then we construct the joint distribution of TOC and elastic impedance through the Bayesian theoretical framework to obtain the maximum posterior probability estimate as the final TOC inversion results of source rocks. Our method successfully predicts the spreading of high-quality source rocks in the Wen4 Section of Lufeng 13 Subsag, and the inversion results are within an uncertainty range of ±14 m for well data, which proves the reliability of the method. The prediction results show that the organic matter abundance of source rocks in the Wen4 Section is high, and the organic carbon content is generally higher than 2%, which provides a reliable basis for the further implementation of the resource scale of the depression and the clarification of the hydrocarbon-rich area, which provides technical support for the evaluation of the source rocks of the new depression in the new area.

3D Multi-Phase Sub-Pixel PSF Estimation Based on Space Debris Detection System

The distribution of diffuse spot energy can be used to sensitively evaluate the aberrations and defects of optical systems. Therefore, the objective and quantitative measurement of diffuse spot parameters is an important means to control the detection quality of space debris detection systems. At present, the existing optical system dispersion measurement method can only judge whether the energy distribution meets the index. However, these methods ca not provide an objective quantitative basis to guide the installation process. To solve this problem, a mathematical simulation model of 3D multi-phase sub-pixel PSF distribution is proposed. According to the relation between the CCD target plane and the theoretical image plane (focal plane, defocus, and deflection), the diffuse spot distribution of the optical system is simulated with different phase combinations. Then, Pearson Correlation Coefficient (PCC) is used to evaluate the matching similarity of the diffuse spot image. The simulation results show that when the PCC is greater than 0.96, the distribution of the two diffuse spots can be identified as matching. This also confirms the accuracy of the proposed PSF model. Then, the focusing deviation of the system being tested can be analyzed according to the phase size of the diffuse spot simulation image. This method can quickly and accurately guide the focal surface installation and testing of the system. Therefore, the purpose of improving the detection accuracy of space debris is achieved. It also provides a quantitative basis for the engineering application of optical detection systems in the future.

Hardware and Software Complex for Identification of Displacement Based on a Fiber-optic Sensor

The article deals with developing a hardware and software complex for identifying rock displacement in open pits. The complex allows for continuous measurement of several parameters and timely notification of personnel of mining enterprises engaged in underground and surface development. The software included in the complex is easy to use and allows changing the information interface. The complex collects, processes and analyzes data from fiber-optic sensors that monitor the geotechnical state of the edge massif. It is connected to fiber-optic sensors via optical conductors, which eliminates the use of the expensive copper cable. Fiber-optic sensors are intrinsically safe and explosion-proof, and are highly resistant to electromagnetic interference. The complex with fiber-optic sensors allows monitoring the geotechnical state of mine workings in open pits. The principle of operation of the complex is based on comparison of apertures and intensity of light spots using a high-resolution photodetector. It has been found that diffraction spots and their pixel pattern do not change in the absence of rock displacement of the edge massif. When a displacement occurs, the light wave that passes through the fiber-optic sensor changes its properties, which leads to changing the parameters of the light spot. After processing the data, the complex produces a numerical value of the displacement.

Real-time delivered dose assessment in carbon ion therapy of moving targets

Abstract Purpose:
Real-time adaptive particle therapy is being investigated as a means to maximize the treatment delivery accuracy. To react to dosimetric errors, a system for fast and reliable verification of the agreement between planned and delivered doses is essential. This study presents a clinically feasible, real-time 4D-dose reconstruction system, synchronized with the treatment delivery and motion of the patient, which can provide the necessary feedback on the quality of the delivery.
Methods:
A GPU-based analytical dose engine capable of millisecond dose calculation for carbon ion therapy has been developed and interfaced with the next generation of the Dose Delivery System (DDS) in use at Centro Nazionale di Adroterapia Oncologica (CNAO). The system receives the spot parameters and the motion information of the patient during the treatment and performs the reconstruction of the planned and delivered 4Ddoses. After each iso-energy layer, the results are displayed on a graphical user interface by the end of the spill pause of the synchrotron, permitting verification against the reference dose.
The framework has been verified experimentally at CNAO for a lung cancer case based on a virtual phantom 4DCT. The patient’s motion was mimicked by a moving Ionization Chambers (ICs) 2D-array.
Results:
For the investigated static and 4D-optimized treatment delivery cases, real time dose reconstruction was-achieved with an average pencil beam dose calculation speed up to more than one order of magnitude smaller than the spot delivery. The reconstructed doses have been benchmarked against offline log-file based dose reconstruction with the TRiP98 treatment planning system, as well as QA measurements with the ICs 2D-array, where an average gamma-index passing rate (3%/3mm) of 99.8% and 98.3%, respectively, were achieved.
Conclusion:
This work provides the first real-time 4D-dose reconstruction engine for carbon ion therapy. The framework integration with the CNAO DDS paves the way for a swift transition to the clinics.

Comprehensive analysis of the eclipsing binaries V527 Dra and V2846 Cyg

ABSTRACT This is the first comprehensive study of the eclipsing binaries V527 Dra and V2846 Cyg, based on radial velocities and ground- and space-based light curves. We perform detailed modeling of these data to derive the absolute parameters and the orbital properties of the two systems. V527 Dra is found to be a semidetached, and V2846 Cyg a contact binary. Both show continual out-of-eclipse variations that can be explained by migrating dark spots of magnetic origin. We also perform the eclipse timing variation (ETV) analysis which reveals that V527 Dra has a tertiary companion whose mass (${\sim} 1 \,{\rm M}_{\odot }$) and orbital inclination (${\sim} 70^{\circ }$) are additionally constrained by radial velocities. The ETV diagram of V2846 Cyg displays a quadratic trend accompanied by a low-amplitude cyclic variation, likely due to a magnetic cycle, although further eclipse times are needed to provide a clearer explanation. Lastly, we demonstrate a correlation between the variations in spot parameters obtained via light curve modelling for individual orbital cycles and the residual ETVs, essentially confirming the assumption of magnetic activity in both systems.

A novel rock-physics model of organic-rich shale considering maturation influence

Geochemical parameters, e.g., maturity and total organic carbon (TOC) content, play a crucial role in the prediction of sweet spots and the exploration of oil and gas in organic-rich shales. Thermal maturity significantly affects the conversion of solid organic matter into hydrocarbons and the evolution of microstructures, thereby altering the overall elastic properties of shales. To clarify how maturity affects shale properties, we develop a novel rock-physics model (RPM) of organic-rich shale, in which we consider the continuous process of thermal maturity. First, we present how to estimate the maturity level, TOC content, and organic porosity using logging data. Second, different from only considering the discrete-stage maturity, we establish a novel RPM in which a continuous kerogen maturation process serves as a key control condition. Furthermore, we calibrate the volumetric proportion of each porosity type as a function of maturation. Finally, we apply the RPM to investigate how sweet spot parameters (thermal maturity, TOC content, and brittle mineral content), overpressure, and diagenesis affect the overall elastic properties and anisotropy of shale during thermal maturation. Results demonstrate that using our RPM, we may predict the acoustic velocity of shale formations reliably and that kerogen evolution has a noticeable impact on the elastic properties of shale rocks, particularly during the wet gas window stage of mid-to-high maturation. We conclude that thermal maturity emerges as a crucial sweet spot parameter in the case of the exploration of oil and gas in organic-rich shales.

Simultaneous Photometric and Spectroscopic Analysis of V505 Lacertae, a Photospherically and Chromospherically Active Contact Binary Star

New BVR photometric and high-resolution spectroscopic observations of V505 Lac are presented with Transiting Exoplanet Survey Satellite (TESS) photometric data. The orbital period has experienced a secular decrease during the past 16 yr. A clear anticorrelation in the primary and secondary eclipse timing variation (PSETV) obtained from the TESS data is also identified. A double-lined radial velocity (RV) curve is secured, and the effective temperatures of the less- and more-massive stars (Stars 1 and 2, respectively) are measured. Using a spectral subtraction technique, excess emissions are detected in the time-series Ca ii H and K and Hα lines for Star 2. Simultaneous analysis of the light and RV curves using the Wilson–Devinney (WD) code reveals that V505 Lac is a photospherically and chromospherically active W-subtype contact binary system. The component-star masses and radii are determined to an accuracy of approximately 1%. The WD spot model is individually applied to 221 light curves segmented from the TESS data so as to derive the spot parameters of a cool spot on Star 2. The combined variations in both longitude and colatitude among the spot parameters appear to be strongly associated with those of both the anticorrelation in the PSETV and the O’Connell effect in the TESS light curves. Robust negative linear relationships between the PSETV anticorrelation size and the O’Connell effect magnitude are found for the first time. Mass–radius, mass–luminosity, and mass ratio–mass diagrams of contact binaries, along with the mass ratio frequency distribution, are presented in an attempt to elucidate the evolutionary characteristics of these systems.

Generation of Perfect Vortex Beams with Complete Control over the Ring Radius and Ring Width

We have experimentally created perfect vortex beams (PVBs) by Fourier transformation of Bessel–Gaussian vortex beams, which are generated by modulating the fundamental Gaussian beam with the spiral phase plates and the axicons, respectively. Although the method has been used many times by other authors, as far as we know, few people pay attention to the quantitative relationship between the control parameters of the PVB and ring width. The effects of the waist radius of the fundamental Gaussian beam wg, base angle of the axicon γ, and focal length of the lens f on the spot parameters (ring radius ρ, and ring half-width Δ) of PVB are systematically studied. The beam pattern of the generated Bessel–Gaussian beam for different propagation distances behind the axicon and the fundamental Gaussian beam wg is presented. We showed experimentally that the ring radius ρ increases linearly with the increase of the base angle γ and focal length f, while the ring half-width Δ decreases with the increase of the fundamental beam waist radius wg, and increases with enlarging the focal length f. We confirmed the topological charge (TC) of the PVB by the interferogram between the PVB and the reference fundamental Gaussian beam. We also studied experimentally that the size of the generated PVB in the Fourier plane is independent of the TCs. Our approach to generate the PVB has the advantages of high-power tolerance and high efficiency.

Developing an Intelligent Fiber-Optic System for Monitoring Reinforced Concrete Foundation Structure Damage

This paper presents the results of complex scientific research aimed at developing a prototype fiber-optic system for controlling the technical condition of buildings, structures, and extended objects. The aim is to develop a quasi-distributed type of fiber-optic control system without electrical signals, with the minimum possible cost of one measurement point. The fiber-optic sensors are based on a new method of controlling the parameters of the light spot by means of a hardware-software complex. The proposed monitoring system is quasi-distributed, is able to determine the damaged and most stressed and deformed areas of load-bearing reinforced concrete structures of buildings at the stage of their occurrence, and will allow for the taking of preventive measures for their protection. The research was carried out on a laboratory bench working together with the hardware-software complex; pixel analysis of changes in the area of the spot and its intensity was used as a fiber-optic sensor. A single-mode optical fiber of the G.652.D 9/125 μm standard was used, with a wavelength of 650 nm. The monitoring system can perform the function of pressure measurement on the building structure, establish the damage zone, and signal in case of an abrupt change in parameters in case of structure destruction. Laboratory tests have shown that the number of channels can be increased to 16 or 32. With the help of this system, it is possible to monitor the technical condition of the underground and above-ground parts of buildings or structures and control their integrity in real-time.

Optimization of resistance spot welding with surface roughness dissimilar mild steel with stainless steel

Resistance spot welding plays a critical role in the manufacture dissimilar material industry. However, there are differences in mechanical properties between mild steel and satinless steel so as to reduce the quality of welded joints. In order for differences in mechanical properties to be corrected, surface roughness was treated. The aim of this study was to optimize the welding parameters of DRSW with surface roughness by analysis using the Taguchi and Anova Methods. In this study discusses about investigates the Resistance spot welding parameters on weld geometry, mechanical properties, and SEM EDS on dissimilar materials of mild steel and stainless steel. The material thickness of the mild steel and stainless steel are 1 mm, respectively. The process parameters of the resistance spot welding joint used, example; surface roughness, current, welding time, and electrode force. Quality welding joint test results include weld geometry, mechanical properties, and SEM EDS. Weld geometry testing to determine the weld nugget profile. The mechanical properties test was shear tensile test, while the SEM EDS included macrostruture and microstructure observations. The results showed the highest nugget diameter 6.65 mm highest shear tensile strength 7.66 kN. The most influential parameter is current by 75.08 %, then surface roughness by 12.35 %. The highest tensile strength has fewer defects. Surface roughness treatment before welding is very good to make welding quality joints between mild steel and quality stainless steel increase. Surface roughness treatment was very good to be included when making welding procedures for welding engineers for welding processes resistance spot welding dissimilar mild steel with stainless steel.

Spot Invalid Point Repair Algorithm of Detector Array Measurement System Based on Image Correlation Coefficient

The detector array method has been widely used in the field of high-energy laser far-field spot parameter measurement due to its ability to directly measure the far-field spot of high-energy lasers, wide dynamic range of the detectors, high system sampling frequency, good real-time performance, and suitability for various testing environment requirements. However, during the measurement process, the irradiation of strong lasers or damage to other hardware systems can result in invalid points in the acquired spot images, thereby reducing the measurement accuracy of the system. In order to achieve accurate measurement of laser far-field spot parameters, this paper establishes an experimental model based on the analysis of the sampling spacing of the detector array target and proposes a laser far-field spot invalid point repair algorithm based on image correlation coefficient. Experimental results demonstrate that the algorithm proposed in this paper effectively reduces the impact of invalid points in the measurement system on the measurement accuracy, and achieves accurate measurement of high-energy laser measurement systems.

Influence of Local Electropolishing Conditions on Ferritic–Pearlitic Steel on X-Ray Diffraction Residual Stress Profiling

Layer removal with electropolishing is a well-established method when measuring residual stress profiles with lab-XRD. This is done to measure the depth impact from processes such as shot peening, heat treatment, or machining. Electropolishing is used to minimize the influence on the inherent residual stresses of the material during layer removal, performed successively in incremental steps to specific depths followed by measurement. Great control of the material removal is critical for the measured stresses at each depth. Therefore, the selection of size of the measurement spot and electropolishing parameters is essential. The main objective in this work is to investigate how different electrolytes and electropolishing equipment affect the resulting surface roughness, geometry, microstructure, and consequently the measured residual stress. A second objective has been to establish a methodology of assessing the acquired electropolished depth. The aim has been to get a better understanding of the influence of the layer removal method on the accuracy of the acquired depth. Evaluation has been done by electropolishing one ground and one shot peened sample of a low-alloy carbon steel, grade 1.1730, with different methods. The results showed a difference in stresses depending on the electrolyte used where the perchloric acid had better ability to retain the stresses compared to the saturated salt. Electropolishing with saturated salt is fast and results in evenly distributed material removal but has high surface roughness, which is due to a difference in electropolishing of the two phases, ferrite, and pearlite. Perchloric acid electropolishing is slower but generates a smooth surface as both ferrite and pearlite have the same material removal rates but may cause an increased material removal for the center of the electropolished area. In this work, it is suggested to use perchloric acid electropolishing for the final layer removal step.

The motion and distribution characteristics of cathode spot and its influence on plasma parameters

Cathode spots and plasma are the key factors affecting the breaking capacity of vacuum switches. In order to analyze the motion and distribution characteristics of cathode spot and its influence on plasmas, the experiments of cathode spot observation and plasma diagnosis were conducted in this paper. The cathode spot images were captured by ultra high-speed camera. Based on the continuous spectrum theory, the electron density was measured by the colorimetric thermometry. According to the cathode spot images and method of cathode spot recognition, the parameters of cathode spots including number, size and current were obtained. The changes of these parameters with arcing time and current amplitude were analyzed. The dependence of the cathode spots average size on spot current and spot expansion velocity was discussed. The axial and radial distributions of electron density were obtained which is related to the cathode spot distribution on the cathode surface. The significant fluctuation in the radial direction for electron density was observed.