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A compact proton synchrotron using combined function magnets is proposed to help realize the wider availability of charged particle cancer therapy facilities. This combined function magnet was designed with the help of three-dimensional magnetic field calculations to take account of a realistic fringe and the interference among the magnetic poles. An evaluation scheme for tune values based on particle tracking was developed to improve the magnet design. To verify the magnet design, a model magnet was fabricated and measured. In order to achieve a tune value evaluation from the measured magnetic field, schemes for accurate field mapping and field interpolation were developed. From the tune value evaluation of the measured magnetic field, it was thought that the performance of the model magnet was good enough to construct a synchrotron. In this paper, we report details of the design and the evaluation scheme for the combined function magnet and the results of the field measurements of the model magnet.

A two-dimensional density distribution of metastables Ar(1s₅) (in Paschen notation) in an inductively coupled plasma (ICP) reactor in argon, driven by one-turn radio-frequency current coil at 13.56 MHz, has been investigated by laser absorption spectroscopy. Measurements were made over a pressure range of 15–300 mTorr, and powers between 20 and 400 W. In these conditions, metastable density varied between 1×10¹⁰ and 2.3×10¹¹ cm^-3. Even for the the position far from the coil, 140 mm far from the source region, metastable density remained comparatively high (of the order of 10¹⁰ cm^-3). As the power increases the metastable density drops down significantly especially for the center of the discharge where the highest electron density is anticipated. In general, the metastable profiles can be explained by combining the expected profile of efficient excitation with diffusion and with the radial dependence of the density of the electrons that can quench the metastable levels by inducing transitions to higher excited states. Therefore we have compared the data for metastable profiles with the excitation rates for one radiative level with a relatively short lifetime and with the radial dependence of electron density obtained by using a Langmuir probe.

We present the space-time resolved excitation data for a single coil inductively coupled plasma (ICP) reactor operating in collision dominated regime in argon and oxygen at 13.56 MHz. Robot assisted scanning was used in order to obtain Abel inverted radial profiles of emission and subsequently of the net excitation rate as well as the number density of excited states. The net excitation rate in argon has modulation close to the walls due to the azimuthal field time dependence and a large bulk value independent of the time presumably due to low energy electron-metastable atom collisions. The time resolved profile in oxygen shows a much more pronounced modulation due to the azimuthal field and a much lower degree of excitation for the center of the tube. At low pressures a structure is observed in the temporal dependence of the net excitation rate that is consistent with two different mechanisms of electron acceleration with phase shift of π/4: (I) by azimuthal field and (II) due to the drift motion in crossed electric and magnetic fields that leads to a motion in the azimuthal or radial direction and consequently to energy gain.