X-ray laser pulses at the Fourier transform limit

The temporal output of a Ni-like Ag x-ray laser of wavelength 13.9 nm has been recorded using a streak camera with ultrashort (700 fs) temporal resolution. We present a model to calculate the degree of coherence and Fourier transform limit of x-ray laser pulses produced by amplified spontaneous emission and relate the results from the model to previous interferometric measurements of the coherence length of the same Ni-like Ag x-ray laser and our measured duration of temporal output. Our modeling shows that the interferometer and streak camera results are consistent and close to the Fourier transform limit at longer gain medium lengths

The Complexities of Being a Pro-Choice Catholic: How Religion and Politics Collide

The separation of church and state has been indicated in the United States Constitution since the ratification of the Bill of Rights in 1791. Ideally, this was intended to ensure that no one religion would receive privilege over another in the political arena, and that citizens have the freedom to practice their own faith without fear of persecution. In contemporary United States, religion has become a powerful influence in modern day politics and the line distinguishing church from state has become hazy. This is especially prevalent in the realm of reproductive rights. The fight for access to reproductive healthcare, such as contraception and safe, legal abortions, become more combative, as proven by the “pro-life” vs. “pro-choice” dichotomy. The implication that being pro-choice means you do not believe in the sanctity of life, while being pro-life means that you do not believe women should have control of their own bodies, increasingly alienates more and more people who are able to see the complexities surrounding abortion. Unfortunately, it is not just United States citizens that are affected by changes in policies surrounding family planning; it is also women in developing countries who have even less access to these services than we do. This paper addresses the complexities that come with the Catholic Church participating in politics, in addition to examining the way Catholicism and conflicting ideologies surrounding female reproductive health affect the United States and other cultures worldwide

Free electron degeneracy effects on collisional excitation, ionization, de-excitation and three-body recombination

Collisional-radiative models enable average ionization and ionization populations, plus the rates of absorption and emission of radiation to be calculated for plasmas not in thermal equilbrium. At high densities and low temperatures, electrons may have a high occupancy of the free electron quantum states and evaluations of rate coefficients need to take into account the free electron degeneracy. We demonstrate that electron degeneracy can reduce collisional rate coefficients by orders-of-magnitude from values calculated neglecting degeneracy. We show that assumptions regarding the collisional differential cross-section can alter collisional ionization and recombination rate coefficients by a further factor two under conditions relevant to inertial fusion

Investigations of the MAST SOL using the reciprocating probe system

Parallel flow in the scrape-off layer is a major area of interest in tokamak research, impacting on impurity transport, tritium retention and H-mode access. The work presented here is the first major investigation of SOL flow in the Mega Ampere Spherical Tokamak (MAST), using a Gundestrup probe specifically designed for the task. The results of a parameter scan in poloidal field, Bѳ, and temperature, T, of parallel velocity at the outboard mid-plane are presented, and the results and scalings compared to B2SOLPS5.0 simulations of MAST and a simple analytical model, in order to identify the relative importance of drift mechanisms (such as Pfirsch-Schluter and E × B) for driving parallel flow. The results show the predicted linear scaling with temperature and poloidal field strength, but also suggest a density dependence. Another major are of interest is the discovery in recent years of coherent filamentary structures that are radially convected through the L-mode SOL. These filaments are believed to contain sharp gradients in temperature, density and plasma potential, complicating probe analysis. An investigation to characterise the intermittency of the MAST SOL, it’s dependencies on poloidal field strength, density or temperature, and the impact of the filaments on probe measurements was also carried out, and a probe was built to further investigate the structure and dynamics of the filaments. Based on these experiments a method for resolving the flow in the filaments and background plasma was developed and applied in the flow experiments described above. It is found that the parallel Mach numbers are lower in the filaments than the ambient plasma in the far SOL — suggesting either ion temperatures are at least on the order of 4 times the electron temperature — or parallel flow velocity is substantially lower in the filaments than in the background plasma

Challenging, Exciting, Impersonal, Nervous: Academic experiences of large class teaching

Massification of Higher Education has resulted in a rapid increase in undergraduate populations, without an increase in the number of teaching staff. One consequence is that students are typically taught in larger classes. While the impact of class size on student satisfaction and attainment is debated, there has been little attention paid to the academic experience of large class teaching. We present results of a questionnaire completed by 80 academics, primarily based in the UK. Academics perceived classes of 100 or more as large, and most had taught classes of several hundred students. Academic perceptions of large class teaching varied considerably. We find no evidence that institution type or contract type affects perceptions of large class teaching. We also find a lack of training that specifically addresses the demands of large class teaching. We call on academic developers to support academics teaching large cohorts to ensure effective education at scale

Optimization of double drive pulse pumping in Ne-like Ge x-ray lasers

Pumping of the Ne-like Ge x-ray laser with two 100 ps duration pulses (a prepulse and main pulse) is investigated using a fluid and atomic physics code coupled to a 3D ray tracing postprocessor code. The modeling predicts the optimum ratio of the irradiance of the two pulses for the maximum x-ray laser output resulting from the balance between the relative lower electron density gradients and wider gain region which is produced with a larger prepulse and the higher peak gain coefficients produced with a small prepulse. With a longer pulse interval between prepulse and main pulse, a relatively lower optimum pulse ratio is found. The threshold irradiance of the main driving pulse with a prepulse required to make an order of magnitude enhancement of laser output compared to irradiation without a prepulse is also found at 3-4x10(13) W/cm(2) for Ne-like Ge. (C) 1998 American Institute of Physics

Ionization rate coefficients in warm dense plasmas

We recast the atomic processes in a warm, dense plasma using Fermi-Dirac statistics and compare them to the rates of the usual Maxwell-Boltzmann approach of many collisional-radiative models. Population calculations show insignificant differences to calculations assuming nondegenerate free electrons of plasmas at solid density close to local thermodynamic equilibrium, but show departures in average ionization in the presence of strong photoionization. For example, we show that electron degeneracy affects the evolution of plasmas created by ultraviolet free electron laser interaction with solid targets

Efficient calculation of atomic rate coefficients in dense plasmas

Modelling electron statistics in a cold, dense plasma by the Fermi-Dirac distribution leads to complications in the calculations of atomic rate coefficients. The Pauli exclusion principle slows down the rate of collisions as electrons must find unoccupied quantum states and adds a further computational cost. Methods to calculate these coefficients by direct numerical integration with a high degree of parallelism are presented. This degree of optimization allows the effects of degeneracy to be incorporated into a time-dependent collisional-radiative model. Example results from such a model are presented

Determinación del potencial y los requerimientos para aplicar la tecnología de gasificación por plasma en el tratamiento de desechos y la producción de energía eléctrica en el país

Proyecto de Investigación. Instituto Tecnológico de Costa Rica. Vicerrectoría de Investigación y Extensión (VIE). Escuela de Física, 2012Este informe se enfoca en la implementación de tratamientos con plasmas térmicos como una alternativa o complemento para métodos existentes para el manejo de desechos en Costa Rica. Se tomó en cuenta varios desechos posibles y se evaluó la factibilidad de comprar sistemas existentes o crear versiones locales de estas tecnologías

Generation of Warm Dense Matter using an Argon based Capillary Discharge Laser

Argon based capillary discharge lasers operating in the extreme ultra violet (EUV) at 46.9 nm with output up to 0.5 mJ energy per pulse and repetition rates up to 10 Hz are capable of focused irradiances of 109–1012 W cm−2 and can be used to generate plasma in the warm dense matter regime by irradiating solid material. To model the interaction between such an EUV laser and solid material, the 2D radiative-hydrodynamic code POLLUX has been modified to include absorption via direct photo-ionisation, a super-configuration model to describe the ionization-dependent electronic configurations and a calculation of plasma refractive indices for ray tracing of the incident EUV laser radiation. A simulation study is presented, demonstrating how capillary discharge lasers of 1200 ps pulse duration can be used to generate warm dense matter at close to solid densities with temperatures of a few eV and energy densities up to 1 × 105 J cm−3. Plasmas produced by EUV laser irradiation are shown to be useful for examining the properties of warm dense matter as, for example, plasma emission is not masked by hotter, less dense plasma emission that occurs with visible/infra-red laser target irradiation