Design study for a magnetically supported reaction wheel

Results are described of a study program in which the characteristics of a magnetically supported reaction wheel are defined. Tradeoff analyses are presented for the principal components, which are then combined in several reaction wheel design concepts. A preliminary layout of the preferred configuration is presented along with calculated design and performance parameters. Recommendations are made for a prototype development program

Surfatron and stochastic acceleration of electrons in astrophysical plasmas

Electron acceleration by large amplitude electrostatic waves in astrophysical plasmas is studied using particle-in-cell (PIC) simulations. The waves are excited initially at the electron plasma frequency $\omega_{\rm pe}$ by a Buneman instability driven by ion beams: the parameters of the ion beams are appropriate for high Mach number astrophysical shocks, such as those associated with supernova remnants (SNRs). If $\omega_{\rm pe}$ is much higher than the electron cyclotron frequency $\Omega_{\rm e}$, the linear phase of the instability does not depend on the magnitude of the magnetic field. However, the subsequent time evolution of particles and waves depends on both $\omega_{\rm pe}/\Omega_{\rm e}$ and the size of the simulation box $L$. If $L$ is equal to one wavelength, $\lambda_0$, of the Buneman-unstable mode, electrons trapped by the waves undergo acceleration via the surfatron mechanism across the wave front. This occurs most efficiently when $\omega_{\rm pe}/\Omega_{\rm e} \simeq 100$: in this case electrons are accelerated to speeds of up $c/2$ where $c$ is the speed of light. In a simulation with $L=4\lambda_0$ and $\omega_{\rm pe}/\Omega_{\rm e} = 100$, it is found that sideband instabilities give rise to a broad spectrum of wavenumbers, with a power law tail. Some stochastic electron acceleration is observed in this case, but not the surfatron process. Direct integration of the electron equations of motion, using parameters approximating to those of the wave modes observed in the simulations, suggests that the surfatron is compatible with the presence of a broad wave spectrum if $\omega_{\rm pe}/\Omega_{\rm e}> 100$. It is concluded that a combination of stochastic and surfatron acceleration could provide an efficient generator of mildly relativistic electrons at SNR shocks

Konsumsi Bbm Premium di Indonesia dan Faktor-faktor yang Mempengaruhinya

This study examines the factors that & determine 'premium' petroleum demand in Indonesia, focusing on the period of 1980-1995. Employing a logarithmic model this study also measures price-elasticity, income-elasticity, and the cross-elasticity of premium petrol with lubricants. It is found that the demand is inelastic towards income, inelastic towards price, and that lubricants arc strong complementariness for premium petrol. Thus it can be concluded that premium petrol is a normal good (neither superior nor inferior), a relatively basic need with little or no substitutes and its demand is complementary with the demand or lubricants. Since premium petrol is a basic need for Indonesian people Government with almost no substitutes, the should not take rash steps that would cause the price of petrol apparent that if Indonesia would like to re4uce the consumption of premium petrol, price policies would not be very effective as price-elasticity is low. Non-price policies, eg., introduction of alternative energy, would probably be more potent

PENGGUNAAN BAHASA PADA PAPAN NAMA DI RUANG PUBLIK JALAN PROTOKOL JAKARTA

Abstrak. Penggunaan bahasa pada papan nama menarik diteliti, setiap papan nama memiliki bentuk dan makna tertentu. Penelitian ini bertujuan untuk mengidentifikasi dan mengetahui penggunaan bahasa pada papan nama di ruang publik jalan protokol Jakarta. Metode yang digunakan dalam penelitian ini adalah metode deskriptif kualitatif. Objek penelitian satuan ini adalah satuan lingual yang terdapat papan nama di ruang publik jalan protokol Jakarta, yaitu Jalan Jendral Sudirman, Jalan M.H. Thamrin dan Jalan Gatot Subroto. Hasil penelitian ini menunjukkan bahwa penggunaan bahasa pada papan nama terbatas pada satuan sintaksis kata dan frasa. Penggunaan dalam bentuk frasa sebanyak 152 data dan dalam bentuk kata sebanyak 13 data, dengan rincian 7 data dalam bentuk kata dan 6 data dalam bentuk abreviasi. Bentuk frasa lebih sering muncul karena frasa lebih memiliki keakuratan dalam mengekspresikan nama sebagai identitas, kepemilikan, asal, bidang, waktu, lokasi, petunjuk, dan media iklan, sementara kata tidak mampu mewakili hal tersebut. Pola frasa inti-pewatas dalam bahasa Indonesia sebanyak 70 data, dalam bahasa asing sebanyak 14 data dan dalam bahasa campuran (Indonesia-asing) sebanyak 5 data, sementara pola frasa pewatas-inti dalam bahasa Indonesia sebanyak 11 data, dalam bahasa asing sebanyak 41 data dan dalam bahasa campuran (Indonesia-asing) sebanyak 11 data. Kata Kunci: Penggunaan Bahasa, Frasa/Kata, Papan Nama di Ruang Publi

A sandpile model with tokamak-like enhanced confinement phenomenology

Confinement phenomenology characteristic of magnetically confined plasmas emerges naturally from a simple sandpile algorithm when the parameter controlling redistribution scalelength is varied. Close analogues are found for enhanced confinement, edge pedestals, and edge localised modes (ELMs), and for the qualitative correlations between them. These results suggest that tokamak observations of avalanching transport are deeply linked to the existence of enhanced confinement and ELMs.Comment: Manuscript is revtex (latex) 1 file, 7 postscript figures Revised version is final version accepted for publication in PRL Revisions are mino

Self-consistent nonlinear kinetic simulations of the anomalous Doppler instability of suprathermal electrons in plasmas

Suprathermal tails in the distributions of electron velocities parallel to the magnetic field are found in many areas of plasma physics, from magnetic confinement fusion to solar system plasmas. Parallel electron kinetic energy can be transferred into plasma waves and perpendicular gyration energy of particles through the anomalous Doppler instability (ADI), provided that energetic electrons with parallel velocities v ≥ (ω + Ωce )/k are present; here Ωce denotes electron cyclotron frequency, ω the wave angular frequency and k the component of wavenumber parallel to the magnetic field. This phenomenon is widely observed in tokamak plasmas. Here we present the first fully self-consistent relativistic particle-in-cell simulations of the ADI, spanning the linear and nonlinear regimes of the ADI. We test the robustness of the analytical theory in the linear regime and follow the ADI through to the steady state. By directly evaluating the parallel and perpendicular dynamical contributions to j · E in the simulations, we follow the energy transfer between the excited waves and the bulk and tail electron populations for the first time. We find that the ratio Ωce /(ωpe + Ωce ) of energy transfer between parallel and perpendicular, obtained from linear analysis, does not apply when damping is fully included, when we find it to be ωpe /(ωpe + Ωce ); here ωpe denotes the electron plasma frequency. We also find that the ADI can arise beyond the previously expected range of plasma parameters, in particular when Ωce > ωpe . The simulations also exhibit a spectral feature which may correspond to observations of suprathermal narrowband emission at ωpe detected from low density tokamak plasmas