Beam Current Monitoring System Research Articles

Machine Protection Features of the ESS Beam Current Monitor System

Machine Protection Features of the ESS Beam Current Monitor System

High dose-per-pulse electron beam dosimetry: Commissioning of the Oriatron eRT6 prototype linear accelerator for preclinical use.

The Oriatron eRT6 is an experimental high dose-per-pulse linear accelerator (linac) which was designed to deliver an electron beam with variable dose-rates, ranging from a few Gy/min up to hundreds of Gy/s. It was built to study the radiobiological effects of high dose-per-pulse/dose-rate electron beam irradiation, in the context of preclinical and cognitive studies. In this work, we report on the commissioning and beam monitoring of the Oriatron eRT6 prototype linac. The beam was characterized in different steps. The output stability was studied by performing repeated measurements over a period of 20months. The relative output variations caused by changing beam parameters, such as the temporal electron pulse width, the pulse repetition frequency and the pulse amplitude were also analyzed. Finally, depth dose curves and field sizes were measured for two different beam settings, resulting in one beam with a conventional radiotherapy dose-rate and one with a much higher dose-rate. Measurements were performed with Gafchromic EBT3 films and with a PTW Advanced Markus ionization chamber. In addition, we developed a beam current monitoring system based on the signals from an induction torus positioned at the beam exit of the waveguide and from a graphite beam collimator. The stability of the output over repeated measurements was found to be good, with a standard deviation smaller than 1%. However, non-negligible day-to-day variations of the beam output were observed. Those output variations showed different trends depending on the dose-rate. The analysis of the relative output variation as a function of various beam parameters showed that in a given configuration, the dose-rate could be reliably varied over three orders of magnitude. Interdependence effects on the output variation between the parameters were also observed. The beam energy and field size were found to be slightly dose-rate-dependent and suitable mainly for small animal irradiation. The beam monitoring system was able to measure in a reproducible way the total charge of electrons that exit the machine, as long as the electron pulse amplitude remains above a given threshold. Furthermore, we were able to relate the charge measured with the monitoring system to the absorbed dose in a solid water phantom. The Oriatron eRT6 was successfully commissioned for preclinical use and is currently in full operation, with studies being performed on the radiobiological effects of high dose-per-pulse irradiation.

Development of a real-time beam current monitoring system for microbeam scanning-PIXE analysis using a ceramic channel electron multiplier

Microbeam scanning-PIXE (micro-PIXE) analysis is a useful method for obtaining information of multi-elemental distribution in samples by two-dimensional images of sample surfaces such as mammalian cells, tissues, and other environmental monitoring species. In addition to elemental distribution information, quantitative analysis is in demand for further investigations of environmental and biomedical studies concerning heavy metals accumulated in terms of cells and sub-cellular organelles. To make quantitative analysis possible, a real-time beam monitoring system that gives a precise number of ions, and an output independent from a sample that enables one to keep a beam resolution of micrometer size is required. In this paper, we report on the development of beam current monitoring. The beam current was monitored using a ceramic channel electron multiplier (CEM) to detect secondary electrons induced from a 50 nm thick carbon film (10 μg/cm 2). This carbon film was attached to a sample holder, which was set at the targeted sample position. The output value of the CEM was proportional to the Faraday cup installed just after the sample position. The beam resolution was measured using off-axis STIM by scanning a copper grid, and was estimated at 1.79 and 1.72 μm for the horizontal and vertical directions, respectively, sufficient for routine micro-PIXE analysis.

The new external beam facility for environmental studies at the Tandetron accelerator of LABEC

At the new 3MV Tandetron accelerator of the LABEC laboratory of INFN in Florence, an external beam facility fully dedicated to measurements of elemental composition of atmospheric aerosol has been installed. The experimental set-up hitherto used for this kind of applications has been upgraded with the introduction of a silicon drift detector and of a beam current monitor system based on the backscattering of protons on the extraction window. The new facility will be presented, together with some methodological results obtained so far for the analysis of airborne particulate matter samples collected on quartz fiber filters.

Electron beam current monitoring system II

A reliable method for absolute calibration of a ferrite electron beam current monitor with a pulse generator has been developed and tested. The absolute accuracy of pulser calibrations and Faraday cup calibrations of the National Bureau of Standards ferrite monitor have been compared by using them both to determine the Faraday cup error. These independent determinations differ by a maximum of 0.11% and an average of 0.03% at six different energies in the 20–120 MeV range, using beam currents between 0.6 and 25 μA. Variation of the Faraday cup error with energy is shown to compare favorably with the predictions of other authors, and the good agreement is used to argue that the influence of beam microstructure on the ferrite calibration is less than 0.1%.

Electron beam current monitoring system

A beam current monitoring system used with the NBS electron linac is described in detail. The system consists of a water-cooled Faraday cup designed to dissipate the energy in a 1 cm diameter, 100 kW beam of 100 MeV electrons, and a non-intercepting ferrite loaded toroidal coil. The ferrite is used for continuous-duty monitoring and can be calibrated in absolute units with the Faraday cup. The Faraday cup errors have been measured with an absolute accuracy of better than 0.1% by bucking the Faraday cup current against the beam current, using the ferrite monitor as a null detector. The Faraday cup losses are about 0.5% at 30 MeV and decrease to less than 0.1% at 120 MeV. These losses are attributed to backscatter of high energy electrons from the front face of the cup. In addition, it is shown that secondary electrons produced by Møller scattering in the Faraday cup entrance foils may lead to spurious measurements of beam current, and a correction for this effect is derived.