Low-Energy Ion Transport Between Two Insulating Parallel Plates

Experimental data are presented for low-energy singly charged ion transport between two insulating parallel plates. Using a beam intensity of approximately 20 pA, measurements of the incoming and transmitted beams provide quantitative temporal information about the charge deposited on the plates and the guiding probability. Using a smaller beam intensity (~1 pA) plate charging and discharging properties were studied as a function of time. These data imply that both the charge deposition and decay along the surface and through the bulk need to be modeled as acting independently rather than as a combined weighted average. A further reduction of beam intensity to ~25 fA allowed temporal imaging studies of the positions and intensities of the guided beam plus two bypass beams to be performed. Because of the parallel plate geometry, SIMION software was used to simulate trajectories of the guided and bypass beams. This provides information about the amount and location of deposited charge and, as a function of charge patch voltage, the probability of beam guiding and how much the bypass beams are deflected. Information about the electric fields which provides insights into the relative charge decay via the surface and bulk is also obtained. An equivalent electric circuit model of the parallel plates is used to associate the deposited charge with the patch voltage. To achieve internal consistency between the various sets of experimental data and the SIMION information, the deposited charge is implied to be distributed primarily on the inner surface of the plates, transverse to the beam direction, rather than being distributed throughout the entire plate.

Medipix3 proton and carbon ion measurements across full energy ranges and at clinical flux rates in MedAustron IR1

The Medipix3, a hybrid pixel detector with a silicon sensor, has been evaluated as a beam instrumentation device with proton and carbon ion measurements in the non-clinical research room (IR1) of MedAustron Ion Therapy Center. Protons energies are varied from 62.4 to 800 MeV with 104 to 108 protons per second impinging on the detector surface. For carbon ions, energies are varied from 120 to 400 MeV/amu with 107 to 108 carbon ions per second. Measurements include simultaneous high resolution, beam profile and beam intensity with various beam parameters at up to 1000 FPS (frames per second), count rate linearity and an assessment of radiation damage after the measurement day using an x-ray tube to provide a homogeneous radiation measurement. The count rate linearity is found to be linear within the uncertainties (dominated by accelerator related sources due to special setup) for the measurements without degraders. Various frequency components are identified within the beam intensity over time firstly including 49.98 Hz with standard deviation, σ = 0.29, secondly 30.55 Hz σ = 0.55 and thirdly 252.51 Hz σ = 0.83. A direct correlation between the number of zero counting and noisy pixels is observed in the measurements with the highest flux. No conclusive evidence of long term radiation damage was found as a result of these measurements over one day.

Dipole–Dipole Broadening in the Selective Reflection of an Intense Laser Beam from the Interface between a Transparent Dielectric and a Dense Resonance Gas

The dipole–dipole broadening of the spectrum of the selective reflection of intense resonance light from the interface between a transparent dielectric and a gas of the natural mixture of Rb isotopes has been studied experimentally. The case of a high gas density where the Doppler broadening can be neglected has been investigated. It has been shown that dipole–dipole broadening is reduced with increasing the number density of excited atoms. When the laser beam intensity is much higher than the saturation intensity of a resonance transition, a significant broadening due to the very high laser beam intensity has not been observed in the reflection spectrum from the transparent dielectric/gas interface. The observed intensity dependence of the spectral width has been explained by the quenching collisions of the excited atoms with the interface.

An Ion Source’s View of Its Plasma

Modeling of ion beam extraction from an ECRIS requires special procedures in order to achieve results similar to what is found experimentally. The initial plasma conditions must be included for consistency between experiment and simulation. Space charge forces and their compensation of the extracted ion beam become important with increasing beam intensity. Here we consider the various beam-plasma conditions that occur along any beam line.