The Alpha Magnetic Spectrometer (AMS) on the international space station: Part II — Results from the first seven years

The Alpha Magnetic Spectrometer (AMS) is a precision particle physics detector on the International Space Station (ISS) conducting a unique, long-duration mission of fundamental physics research in space. The physics objectives include the precise studies of the origin of dark matter, antimatter, and cosmic rays as well as the exploration of new phenomena. Following a 16-year period of construction and testing, and a precursor flight on the Space Shuttle, AMS was installed on the ISS on May 19, 2011. In this report we present results based on 120 billion charged cosmic ray events up to multi-TeV energies. This includes the fluxes of positrons, electrons, antiprotons, protons, and nuclei. These results provide unexpected information, which cannot be explained by the current theoretical models. The accuracy and characteristics of the data, simultaneously from many different types of cosmic rays, provide unique input to the understanding of origins, acceleration, and propagation of cosmic rays.</p

Characterization of GaN HEMT Low-Frequency Dispersion Through a Multi-Harmonic Measurement System

In this paper, the experimental characterization of low-frequency dispersion (i.e., long-term memory effects) affecting microwave GaN HEMTs is carried out by adopting a new nonlinear measurement system, which is based on low-frequency multiharmonic signal sources. The proposed setup, which has been fully automated by a control software procedure, enables given source/load device terminations at fundamental and harmonic frequencies to be synthesized. Different experimental results are provided to characterize well-known effects related to low-frequency dispersion (e.g., knee walkout and drain current collapse) and to demonstrate the validity of assumptions commonly adopted for electron device modeling

A Low-Cost and Accurate Technique for the Prediction of Load-Pull Contours

Load-pull measurement systems are the most common and powerful instruments used for the design of power amplifiers. They allow to directly obtain output power, efficiency and gain contours which give a clear idea of the electron device optimum termination for the selected operation. Nevertheless, such measurement systems are also very expensive, especially if high frequencies and high power levels are addressed. In this paper, a new technique for drawing load-pull contours is presented which jointly exploits both large-signal low-frequency I/V device measurements and a nonlinear capacitance-based model, the latter one being obtained on the bases of bias- and frequency-dependent small-signal S-parameters. The proposed approach achieves the same level of accuracy of high-frequency measurement systems, using general purpose instrumentation available in microwave laboratories. Different experimental examples, based on power GaN FETs, are provided to demonstrate the validity of the described technique

Characterization of Electron Device Breakdown Under Nonlinear Dynamic Operation

In this paper a new methodology to characterize the breakdown of microwave electron devices under realistic device operation is described. Different experimental examples will be provided in order to demonstrate the validity of the proposed characterization technique with respect to the ones commonly adopted

“Hybrid” Approach to Microwave Power Amplifier Design

A new “hybrid” approach to microwave power amplifier design is presented which is based both on experimental large-signal low-frequency I/V load-line characterization and a model-based description of the device capacitances. Such a technique allows to get the same information obtained through nonlinear measurement setups operating at microwave frequencies. Several simulated and experimental data are proposed, based on GaN technology, in order to prove the effectiveness of the methodology

GaN power amplifier design exploiting wideband large-signal matching

The present manuscript details a wideband high power amplifier design, based on a 5-mm GaN power bar. In particular, a broadband input large-signal matching condition has been realized, that ensures optimal power transfer under actual device operation. The measured performance of the PA perfectly matches the expected predictions based on large-signal measurements carried out on a 1.25-mm GaN elementary cell

Empirical Investigation on Device-Degradation Indicators Under Nonlinear Dynamic Regime

Electron device degradation, although not directly accounted for, represents a key issue in microwave circuit design. This is especially true when the particular applications involved (e.g., satellite, military, consumer) do not allow or strongly discourage any kind of in itinere maintenance. As a matter of fact, in order to account for device degradation in circuit design, a suitable electron device model is needed which is able to predict the performance degradation as a function of the actual electrical regime involved in the device operation. Such a kind of model is not available in literature. In this paper, quantitative results are provided for devicedegradation indicators which correlate DC and RF stress experiments. These results can be considered an important step toward the definition of a nonlinear model accounting for device degradation

Experimental Investigation of LF dispersion and IMD asymmetry within GaN based HEMT technology

An experimental investigation of the lowfrequency dispersion affecting the behaviour of microwave devices is reported in this work. The study has been carried out by exploiting two different measurement techniques and experiments have been performed on a GaN based HEMT. In particular, bias and frequency dependence of dynamic characteristics has been clearly observed. Moreover, asymmetric behaviour not exclusively ascribed to the measurement environment (e.g., termination impedance networks) manifests in the non-linear response of the considered device

Breakdown Walkout Investigation in Electron Devices Under Nonlinear Dynamic Regime

In this paper, the breakdown walkout in microwave electron devices is investigated by means of a recently proposed measurement set-up. This innovative setup allows to apply a stress procedure not only in classical static conditions, but also under dynamic regime by applying a large-amplitude excitation signal at moderately high frequency at either the input or the output port of the device. As a matter of fact, for the very first time, experimental data can be collected for fully investigating the walkout behaviour under both static and dynamic operations