Experimental study of the fast scintillating behavior of ZnO:Ga crystal under MeV electron beam.

An experimental study on the scintillating behavior of ZnO:Ga crystals was conducted using a 7-MeV electron accelerator. The ZnO:Ga crystals were grown using both hydrothermal and chemical vapor transport methods. One of the ZnO:Ga crystals grown via the hydrothermal method exhibited a 1.5-ns afterglow time when excited by an MeV electron beam. The ultra-short scintillation was captured using both an ultrafast streak camera and a framed camera. The experimental results also confirm its potential for diagnosing electron beam trains with a repetition rate of hundreds of MHz.

Rhodotron and rotating target: A solution towards micro-spot for high energy and high dose rate bremsstrahlung sources.

High energy over MeV bremsstrahlung sources that employ normal conducting radio frequency linear accelerators have expanding applications in industrial computerized tomography (CT) for non-destructive inspection and evaluation. The X-ray spot size that mainly affects the imaging quality is yet limited by the electron beam width in the high resolution CT systems. In a short exposure time, high beam power is required to generate sufficient photons to improve the signal to noise ratio of imaging. However, with ∼kW level of average beam power these linear accelerators usually have a beam spot size over 1 mm since the temperature rising due to the beam energy deposition in the target should be far below its melting point. We propose a concept of using a Rhodotron-based accelerator to provide high power electron beams in a long duration pulse and a rotating target to mitigate the overheating issue, such that the gap between micro-spot and high dose rate can be bridged in the high energy bremsstrahlung sources. This article presents an in-depth simulation work to discuss and evaluate this scheme of X-ray source. The simulations of beam dynamics in the accelerator and bremsstrahlung process in the target predict the generated X-rays with a spot size as small as 68 µm at full-width half-maximum and a dose rate as high as 4700 cGy/min from a 9 MeV electron beam interacting with a 1 mm thickness tantalum target. Further thermal analysis in the rotating target indicates a significant improvement of beam power handling in comparison with the conventional stationary one.

Correction of coupled higher-order modes in the S-parameter characterization of wideband cavity beam position monitors.

Wideband RF cavity beam position monitors (CBPM) have been increasingly employed for short bunch interval operations in several linear accelerators. At a few nanoseconds of bunch spacing, the loaded quality factor of the CBPM TM110 dipole eigenmode is required to be sufficiently low to minimize the signal interference between consecutive bunches. Moreover, the bunched beam also couples to several unwanted higher-order modes (HOM), such as the TM210 and TE111 eigenmodes, which also may result in an error of the bunch position measurement if no precautions are taken. In the fabrication phase of CBPMs, the mode coupling can alter the TM110 mode frequency and therefore causes an error in its tuning, e.g., 0.3% for a 4.875 GHz CBPM with QL = 22.5. This error needs to be identified so that the precise tuning is enabled since the dipole mode frequency becomes critical for the position evaluations as the signal processing is relatively phase-sensitive. This paper presents an approach to extract the pure unperturbed frequency of the dipole mode, not altered by the response to coupled HOMs. An analytic model based on the superposition law applied to electromagnetic fields has been developed to characterize the response of coupled HOMs in the S-parameter measurement. The model has been further verified with numerical simulation in the CST-Studio software by analyzing an approximate single-mode response CBPM. The correction method was applied on a wideband CBPM prototype for the pre-research plan of future high repetition rate hard XFEL at the Chinese Academy of Engineering Physics.

First demonstration of simultaneous measurement of beam current, beam position, and beam tilt on induction linac using combined B-dot monitor.

The authors previously reported that the axial B-dots can be used to directly measure the beam tilt and demonstrated that the axial B-dots are applicable to a coaxial calibration stand. In this study, a combined B-dot monitor composed of four axial B-dot loops and four azimuthal ones is tested for the simultaneous measurement of the time-varying beam current, beam offset, and beam tilt at the output of the injector of the DRAGON-I induction linac. In the experiments, the beam offset and beam tilt at the position of the monitor are proportionally adjusted using a pair of steering coils. Eight waveforms acquired from the B-dot monitor are analyzed to reconstruct the time-varying beam current, beam offset, and beam tilt. The original signals of both the azimuthal B-dot and the axial B-dot ports change significantly with respect to the current applied to the steering coils. The measured beam tilt is linearly dependent on the current applied to the steering coils and agrees well with the measured beam offset.

Demonstration of low energy proton radiography on an 11-MeV cyclotron.

Lens focused proton radiograph on thin objects is demonstrated using an 11-MeV proton cyclotron at China Academy of Engineering Physics. The proton beam exiting from the tested objects is focused onto the image plane by a magnetic lens system mitigating image blur caused by multiple Coulomb scattering. Both simulations and experiments show that clear images can be obtained with a lens system for the objects with thickness up to 2.7 × 10-2 g/cm2 and the error for the areal density measurement is measured to be less than 2.3%. For the objects with thickness between 2.7 × 10-3 g/cm2 and 2.7 × 10-2 g/cm2, 100-200 µm of spatial resolution is achieved.