Measurement of HL-2A NBI Beam Profile and Beam Power

To optimize the operation parameters of the beam line of NBI on HL-2A, features of the beam line, including the beam profile and the power deposited on components and injected into the tokamak plasma, were measured. The operational parameters of the four sources on the beam line were optimized with the monitor of the beam profile and beam power, and the transmission efficiency of the NBI injected power was therefore increased. A beam diagnostic system for the beam line of the NBI system on HL-2A as well as the diagnosed results was also presented.

Effect of Scanning Beam Profile to Fabricate Fused Fiber Tapers by CO_2 Laser Irradiation Method

Beam uniformity is a crucial building block of CO2 experiments aimed at fusing and stretching optical fibers in a lossless manner. When the irradiation beam is expanded through a galvanometer mirror, ways to achieve beam uniformity are investigated.

Tunable terahertz radiation from arbitrary profile dielectric grating coated with graphene excited by an electron beam

In this paper, the enhanced terahertz radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch, in a structure consisting of a monolayer graphene supported on a dielectric grating with arbitrary profile is investigated. The results show that the grating profile has significant influence on the dispersion curves and radiation characteristics including radiation frequency and intensity. The dependence of dispersion and radiation characteristics on the grating shape for both the symmetric and asymmetric gratings is studied in detail. Moreover, we find that, for an asymmetric grating with certain profile, there exist two different diffraction types, and one of the two types can provide higher radiation intensity comparing to the other one. These results will definitely facilitate the practical application in developing a room-temperature, tunable, coherent and miniature terahertz radiation source.

Radiation Beam Characterization and Dosimetry of Theratron Equinox-80 Telecobalt Machine Using BEAMnrc Monte Carlo Simulation Code

The BEAMnrc code was used for the simulation of the Theratron Equinox-80 telecobalt machine. The phase space of radiation beam was generated at treatment distance of 80 cm for various field sizes. The phase spaces in air were analyzed by BEAMdp data processing program. The electron energy fluence with respect to photon energy was 0.09% and 0.34% for field size of 05 × 05 and 35 × 35 cm2 respectively and it was maximum at the central axis which gradually decreases beyond this. The profiles for photon fluence were in symmetry for all the fields. The full width at half maximum of profiles in photon energy fluence shows good agreement with the field size. The photon energy fluence was flat till the field size of 27 cm2, after which it decreases gradually till the edge in larger field sizes. The air-kerma output factor from the simulation was in good agreement with measured value. We analyzed the dose data scored in the voxels in a large water phantom by simulation using dosxyznrc code. The percentage depth dose for all field sizes was in good agreement with the BJR supplement 25 and the data supplied by the manufacturer of machine. Significant deviation of about 20% in isodose line near the edge of the profile was observed for 35 × 35 cm2 field size. The penumbra widths of all field sizes were comparable except for 35 × 35 cm2, which has a penumbra width of 4.1 cm at 10 cm depth. The significant under dose near the edge as compared to central axis for larger field sizes may be the indication for its careful use in treatment.

Calculation of Beam Intensity Distribution for the Neutral Beam Injection in EAST

Theoretical beam intensity distribution is derived for the neutral-beam-injection ion source with a multi-slot extraction in EAST. The beam intensity profile, both along and perpendicular to the injecting direction and the beam power deposition to the inner elements in the neutral beam injector （NBI） are evaluated. The results indicate that the transverse beam intensity is much higher than the longitudinal one. This study could provide information for the design of vacuum system, structure of inner elements and cooling system of the neutral beam injector in EAST.

STUDY ON THE OPTICAL FLAT PROFILE HIGH PRECISION MEASURING TECHNOLOGY IN THE METHOD OF LASER DATUM

The physical datum method that uses the laser beam as the physical datum is proposed.A high accuracy of the straight movement on the line above 0.01 μm/100 mm is achieved through applying the method of the closed loop feedback control that uses the laser beam as the datum.The measuring accuracy above 0.05 μm is obtained by applying the self making electric eddy displacement sensor to detect the geometric accuracy of the optical flat.It proves that the laser beam datum method can achieve the high accurcy of the straight movement and has the huge advantage.

Beam experiments with a non-intercepting beam induced f luorescence profile monitor for the ADS LINAC

An accelerator-driven subcritical system（ADS） project was launched in China in 2011, aiming to design and build an ADS demonstration facility with the capability of more than 1000 MW thermal power. The driver linac is defined to be a 10 m A current of high energy protons at 1.5 Ge V in continuous wave operation mode. To meet the extremely high power and intense beam accelerator requirements, non-interceptive monitors for the beam transverse profile are required for this proton linac. Taking advantage of the residual gas as active material, the Beam Induced Fluorescence（BIF） monitor exploits gas-excited fluorescence in the visible spectrum region for transverse profile measurements. The advantages of this non-intercepting method are that nothing is installed in the vacuum pipe,component design is compact and there is no need for expensive signal processing electronics. Beam experiments have been performed under constant beam conditions. The helium spectrum has been verified with different optical filters, showing that a proper optical band-pass filter covering 400–500 nm is necessary for fluorescence experiments with helium. By changing gas pressure, it is shown that gas pressure is proportional to the signal amplitude but has no influence on detected profile width. Finally, a comparison experiment between the BIF monitor and a wire scanner shows that the detected profile width results of both methods agree well.

ULTRASONIC INFLUENCE OF POROSITY LEVEL ON CFRP COMPOSITE LAMINATES USING RAYLEIGH PROBE WAVES

It was found that a pitch-catch signal was more sensitive than normal incidence backwall echo of longitudinal wave to subtle flaw conditions in the composites （damages, fiber orientation, low level porosity, ply waviness, and cracks）. Both the strength and stiffness depend on the fiber orientation and porosity volume in the composites. The porosity content of a composite structure is critical to the strength and performance of the structure in general. The depth of the sampling volume where the pitch-catch signal came from was relatively shallow with the head- to-head miniature Rayleigh probes, but the depth can be increased by increasing the separation distance of the transmitting and receiving probes. Also, a method was utilized to determine the porosity content of a composite lay-up by processing micrograph images of the laminate. A free software package was utilized to process micrograph images of the test sample. The results from the image processing method were compared with existing data. Beam profile was characterized in unidirectional CFRP（carbon fiber reinforced plastics） using pitch-catch Rayleigh probes and the one-sided pitch-catch technique was utilized to produce C-scan images with the aid of the automatic scanner.

Transverse beam size measurement system using visible synchrotron radiation at HLS II

An interferometer system and an imaging system using visible synchrotron radiation（SR） have been installed in the Hefei Light Source（HLS） II storage ring. Simulations of these two systems are given using Synchrotron Radiation Workshop（SRW） code. With these two systems, the beam energy spread and the beam emittance can be measured. A detailed description of these two systems and the measurement method is given in this paper. The measurement results of beam size, emittance and energy spread are given at the end.

Design of imaging system for CSNS near-target beam diagnostics

Introduction China Spallation Neutron Source(CSNS)is an accelerator-based pulsed neutron source which produces neutron with spallation reaction induced by proton bombarding tungsten target.With increasing beam powers and influences on target,near-target monitoring becomes extreme necessary.In this situation,an optical imaging system for proton beam diagnostics and monitoring near the target is being developed at CSNS,which can provide real-time images of the beam on target and beam distribution information.Target imaging system design and development In the design of CSNS target imaging system,coating of Cr^(3+):Al_(2)O_(3) is used to convert particle radiation into emission light.According to the geometry limits of CSNS target station,a special optical system was designed and fabricated to collect the emission light.When the proton beams strike on the target,the coating on the target will be excited,emitting luminescence at the same time.The mirrors and lenses of the optical system image the distribution of emission light into a radiation-hard imaging fiber,which transmits the images to the GigE camera located at low-dose area outside of the target station.Software was written on the LabView platform to control the camera and analyze the images on line.Mock-up of the imaging system was manufactured to test and evaluate the performances of the system.Some important characteristics of the system were obtained and studied.Conclusion Tests on the mock-up of the system present reliably expectation for beam diagnostics.The imaging system has been installed at CSNS recently.More work will be continued to improve the properties of the system.

Design study of an improved laser wire system for electron beam measurement

The laser wire （LW） method has been demonstrated to be an effective non-interceptive technique for measuring transverse profile and emittance of electron beams in colliders, storage rings and dumping rings. In this paper, we present an improved design of high repetition LW system for high average power free electron lasers （HAP FELs） and energy recovery linacs （ERLs）. This improved LW utilizes the excess power of the photocathode drive laser, thus making itself much cheaper and simpler. The system main parameters are optimized with numerical calculations and Monte Carlo simulations, indicating that resolutions would be better than 100 ~m and scanning time less than 1 minute. Status of the experiment preparation is also presented.

BEPCⅡ wire scanner system

To monitor the beam profile at the end of the linac non-destructively, a wire scanner as a new diagnostic instrument was designed, manufactured and installed in 2007. Since then, several measurements have been carried out using this device. This paper describes the whole system of the wire scanner and the testing results.

Design and simulation of the wire scanner for the injector linac of BEPCⅡ

BEPC Ⅱ, the upgrade project of Beijing Electron Positron Collider （BEPC）, is an accelerator with large beam current and high luminosity, so an efficient and stable injector is required. Several beam diagnostic and monitoring instruments are used. A new diagnostic instrument - wire scanner, has been designed and will be used to measure the profile of the linac beam of BEPC Ⅱ. This paper describes the prototype of this system and the cause of heat generating of the wire. Some simulation results of the heat and force by using finite element method software-ANSYS are presented and discussed.