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This paper discusses the capture of an ion beam in a magnetized plasma of an Electron Cyclotron Resonance Ion Source based Charge Breeder, as modelled by numerical simulations. As a relevant step forward with respect to previous works, here the capture is modeled by considering a plasma structure determined in a self-consisent way. The plasmoid-halo structure of the ECR plasma - that is consisting of a dense core (the plasmoid) surrounded by a rarefied halo - is further confirmed by the self-consistent calculations, having also some fine structures affected by the electromagnetic field distribution and by the magnetostatic field profile. The capture of Rb1+ ions has been investigated in details, vs. various plasma parameters, and then compared to experimental results., Comment: New results about a self-consistent modeling of magnetized plasmas

Axions, originally proposed to solve the strong CP problem of quantum chromodynamics, emerge now as leading candidates of WISP dark matter. The rich phenomenology associated to the light and stable QCD axion can be described as an effective magnetic field that can be experimentally investigated. For the QUAX experiment, dark matter axions are searched by means of their resonant interactions with electronic spins in a magnetized sample. In principle, axion-induced magnetization changes can be detected by embedding a sample in an rf cavity in a static magnetic field. In this work we describe the operation of a prototype ferromagnetic haloscope, with a sensitivity limited by thermal fluctuations and receiver noise. With a preliminary dark matter search, we are able to set an upper limit on the coupling constant of DFSZ axions to electrons $g_{aee}<4.9\times10^{-10}$ at 95\% C.L. for a mass of $58\,\mu$eV (i.\,e. 14\,GHz). This is the first experimental result with an apparatus exploiting the coupling between cosmological axions and electrons., Comment: 10 pages, 8 figures

This note presents a method to tune the resonant frequency $f_{0}$ of a rectangular microwave cavity. This is achieved using a liquid metal, GaInSn, to decrease the volume of the cavity. It is possible to shift $f_{0}$ by filling the cavity with this alloy, in order to reduce the relative distance between the internal walls. The resulting modes have resonant frequencies in the range $7\div8\,$GHz. The capability of the system of producing an Electron Paramagnetic Resonance (EPR) measurement has been tested by placing a 1 mm diameter Yttrium Iron Garnet (YIG) sphere inside the cavity, and producing a strong coupling between the cavity resonance and Kittel mode. This work shows the possibility to tune a resonant system in the GHz range, which can be useful for several applications., Comment: 7 Pages, 5 Figures

We present a proposal to search for QCD axions with mass in the 200 $\mu$eV range, assuming that they make a dominant component of dark matter. Due to the axion-electron spin coupling, their effect is equivalent to the application of an oscillating rf field with frequency and amplitude fixed by the axion mass and coupling respectively. This equivalent magnetic field would produce spin flips in a magnetic sample placed inside a static magnetic field, which determines the resonant interaction at the Larmor frequency. Spin flips would subsequently emit radio frequency photons that can be detected by a suitable quantum counter in an ultra-cryogenic environment. This new detection technique is crucial to keep under control the thermal photon background which would otherwise produce a too large noise., Comment: To appear on Physics of the Dark Universe

Astronomers have been using the measured luminosity to estimate the {\em luminous mass} of stars, based on empirically established mass-to-light ratio which seems to be only applicable to a special class of stars---the main-sequence stars---with still considerable uncertainties. Another basic tool to determine the mass of a system of stars or galaxies comes from the study of their motion, as Newton demonstrated with his law of gravitation, which yields the {\em gravitational mass}. Because the luminous mass can at best only represent a portion of the gravitational mass, finding the luminous mass to be different or less than the gravitational mass should not be surprising. Using such an apparent discrepancy as a compelling evidence for the so-called dark matter, which has been believed to possess mysterious nonbaryonic properties and present a dominant amount in galaxies and the universe, seems to be too far a stretch when seriously examining the facts and uncertainties in the measurement techniques. In our opinion, a galaxy with star type distribution varying from its center to edge may have a mass-to-light ratio varying accordingly. With the thin-disk model computations based on measured rotation curves, we found that most galaxies have a typical mass density profile that peaks at the galactic center and decreases rapidly within $\sim 5%$ of the cut-off radius, and then declines nearly exponentially toward the edge. The predicted mass density in the Galactic disk is reasonably within the reported range of that observed in interstellar medium. This leads us to believe that ordinary baryonic matter can be sufficient for supporting the observed galactic rotation curves; speculation of large amount of non-baryonic matter may be based on an ill-conceived discrepancy between gravitational mass and luminous mass which appears to be unjustified.

An accurate computational method is presented to determine the mass distribution in a rotating thin-disk galaxy from given rotation curve by applying Newtonian dynamics for an axisymmetrically rotating thin disk of finite size with or without a central spherical bulge. The governing integral equation for mass distribution, resulting from the balance between the Newtonian gravitational force and centrifugal force due to rotation at every point on the disk, is transformed via a boundary-element method into a linear algebra matrix equation that can be solved numerically for rotation curves with a wide range of shapes. To illustrate the effectiveness of this computational method, mass distributions in several mature spiral galaxies are determined from their measured rotation curves. All the surface mass density profiles predicted by our model exhibit approximately a common exponential law of decay, qualitatively consistent with the observed surface brightness distributions. When a central spherical bulge is present, the total galactic mass increases only slightly but the mass distribution in the galaxy is altered in such a way that the periphery mass density is reduced while more mass appears toward the galactic center. By extending the computational domain beyond the galactic edge, we can determine rotation velocity outside the cut-off radius which appears to continuously decrease and gradually approach the Keplerian rotation velocity out over twice the cut-off radius. Am examination of the circular orbit stability suggests that galaxies with flat or increasing rotation velocities with radius are more stable than those with decreasing rotation velocities especially in the region near the galactic edge. Our results demonstrate the fact that Newtonian dynamics can be adequate for describing the observed rotation behavior of mature spiral galaxies., Comment: 24 pages, 9 figures

We present an efficient, robust computational method for modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies. For a disk galaxy with a typical flat rotation curve, our modeling results show that the surface mass density monotonically decreases from the galactic center toward periphery, according to Newtonian dynamics. In a large portion of the galaxy, the surface mass density follows an approximately exponential law of decay with respect to the galactic radial coordinate. Yet the radial scale length for the surface mass density seems to be generally larger than that of the measured brightness distribution, suggesting an increasing mass-to-light ratio with the radial distance in a disk galaxy. In a nondimensionalized form, our mathematical system contains a dimensionless parameter which we call the "galactic rotation number" that represents the gross ratio of centrifugal force and gravitational force. The value of this galactic rotation number is determined as part of the numerical solution. Through a systematic computational analysis, we have illustrated that this galactic rotation number remains within $\pm 10%$ of 1.70 for a wide variety of rotation curves. This implies that the total mass in a disk galaxy is proportional to $V_0^2\,R_g$, with $V_0$ denoting the characteristic rotation velocity and $R_g$ the radius of the galactic disk. The predicted total galactic mass of the Milky Way is in good agreement with the star-count data., Comment: 20 pages, 7 figures

By numerically solving the mass distribution in a rotating disk based on Newton's laws of motion and gravitation, we demonstrate that the observed flat rotation curves for most spiral galaxies correspond to exponentially decreasing mass density from galactic center for the most of the part except within the central core and near periphery edge. Hence, we believe the galaxies described with our model are consistent with that seen through the eyes of Newton. Although Newton's laws and Kepler's laws seem to yield the same results when they are applied to the planets in the solar system, they are shown to lead to quite different results when describing the stellar dynamics in disk galaxies. This is because that Keplerian dynamics may be equivalent to Newtonian dynamics for only special circumstances, but not generally for all the cases. Thus, the conclusions drawn from calculations based on Keplerian dynamics are often likely to be erroneous when used to describe rotating disk galaxies., Comment: 19 pages, 6 figures

Observations reveal that mature spiral galaxies consist of stars, gases and plasma approximately distributed in a thin disk of circular shape, usually with a central bulge. The rotation velocities quickly increase from the galactic center and then achieve a constant velocity from the core to the periphery. The basic dynamic behavior of a mature spiral galaxy, such as the Milky Way, is well described by simple models balancing Newtonian gravitational forces against the centrifugal forces associated with a rotating thin axisymmetric disk. In this research, we investigate the effects of adding central bulges to thin disk gravitational models. Even with the addition of substantial central bulges, all the critical essential features of our thin disk gravitational models are preserved. (1) Balancing Newtonian gravitational and centrifugal forces at every point within the disk yields computed radial mass distributions that describe the measured rotation velocity profiles of mature spiral galaxies successfully. (2) There is no need for gravity deviations or ``massive peripheral spherical halos of mysterious Dark Matter''. (3) The calculated total galactic masses are in good agreement with star count data. (4) The addition of central bulges increases the calculated total galactic masses, possibly more consistent with the presence of galactic gases, dust, grains, lumps, planets and plasma in addition to stars. (5) Compared with the light distribution, our mass distributions within the disk are larger out toward the galactic periphery which is cooler with lower opactiy/emissivity (and thus darker). This is apparent from edge-on views of galaxies which display a dark disk-line against a much brighter galactic halo., Comment: 13 Pages Text + 4 Figures

For mature spiral galaxies, the rotation velocities quickly increase from the galactic center and achieve a constant velocity from the core to the periphery. This dynamic behavior is described by models balancing Newtonian gravitational and centrifugal forces in rotating thin axisymmetric disks. Freeman's disk assumes a mass density decreasing exponentially with radius which correctly produces rotational velocities which increase from the galactic center to a maximum near the outer core, but then decreases out to the periphery contrary to measurements. Mestel's disk assumes a mass distribution decreasing more slowly (inversely with radius) that yields a constant rotational velocity across the entire disk, but has an unrealistic central mass singularity and does not describe the core rotation properly. Thus combine the Freeman and Mestel disks to utilize their strengths and eliminate their deficiencies. Utilize the Freeman formula for the central core, and the Mestel formula beyond the core to the galactic rim. This combined model produces rotation curves comparable to the measurements of mature spiral galaxies. For a more general thin-disk model, we develop an alternative computational method to solve for the mass density distributions for various measured rotation curves We compute radial mass densities that balance the Newtonian gravitational and centrifugal forces at every point. The computational solutions show mass densities which decrease approximately exponentially in the central core (similar to Freeman), and transition to a slower inverse radial decrease (similar to Mestel) to the periphery. Thus these diverse approaches yield similar results and are mutaully self-consistent with Newtonian gravity/dynamics., Comment: 13 Pages + 8 Figures

The measured rotation velocity profiles of mature spiral galaxies are successfully described with a gravitational model consisting of a thin axisymmetric disk of finte radius. The disk is assumed uniformly thin but with variable radial mass density. The governing integral equation is based on mechanical balance between Newtonian gravitational and centrifugal forces (due to galaxy rotation) at each and every point in a finite set of concentric rings. The nondimensionalized mathematical system contains a dimensionless parameter we call ``galactic rotation parameter'' which concisely crystallizes perspective. Computational solutions are obtained for the radial mass distributions that satisfy the measured rotational velocity profiles. Together with a constraint equation for mass conservation, the galactic rotational parameter is also determined from which the total galactic mass is calculated from measured galactic radii and maximum rotation velocities. These calculated total galactic masses are in good agreement with data. Our deduced exponentially decreasing mass distributions in the central galactic core are in agreement with almost all others. However our mass distributions differ toward the galactic periphery with more ordinary baryonic mass in these outer disk regions which are cooler with lower opactiy/emissivity (and thus darker)., Comment: 13 pages + 3 figures = 16 pages total