Operation In Strong Magnetic Fields Research Articles

A Fluidic Adder Circuit Based on a Microfluidic System

Automation based on pneumatic soft actuators (PSAs) offers extensive benefits for operation in strong magnetic fields, at ultrahigh electric potentials and in underwater environments. However, due to the lack of automated pneumatic control systems, most of the PSAs require external electronic controls, such as programmable logic controllers (PLCs), pumps, and solenoid valves. Recently, researchers have investigated the use of microfluidic logic gates as a promising alternative for the control of submillimeter-scale fluidic components. In this letter, we demonstrate the use of microfluidic logic gates for addition operations. Based on functionally integrated fluidic components with local and global physical characteristics, we examine a fundamental class of the basic NOT gate. In addition, an adder application is described in this letter. We also introduce a calculation signal into a flip latch that is then connected to a microfluidic decoder. The system can avoid the need for cumbersome and fragile external electronic controllers.

An ionization pressure gauge with LaB6 emitter for long-term operation in strong magnetic fields.

We report here on a potentially significant improvement in the design of neutral pressure gauges of the so-called ASDEX-type which were first used in the Axially Symmetric Divertor EXperiment (ASDEX). Such gauges are considered state-of-the-art and are in wide use in fusion experiments, but they nonetheless suffer from a relatively high failure rate when operated at high magnetic field strengths for long times. This is therefore a significant concern for long-pulse, high-field experiments such as Wendelstein 7-X (W7-X) and ITER. The new design is much more robust. The improvement is to use a LaB6 crystal instead of a tungsten wire as the thermionic emitter of electrons in the gauge. Such a LaB6 prototype gauge was successfully operated for a total of 60 h in B = 3.1 T, confirming the significantly improved robustness of the new design and qualifying it for near-term operation in W7-X. With the LaB6 crystal, an order of magnitude reduction in heating current is achieved, relative to the tungsten filament based gauges, from 15-20 A to 1-2 A. This reduces the Lorenz forces and the heating power by an order of magnitude also and is presumably the reason for the much improved robustness. The new gauge design, test environment setup at the superconducting magnet, and results from test operation are described.

Novel micropixel avalanche photodiodes (MAPD) with super high pixel density

In many detectors based on scintillators the photomultiplier tubes (PMTs) are used as photodetectors. At present photodiodes are finding wide application. Solid state photodetectors allow operation in strong magnetic fields that are often present in applications, e.g. some calorimeters operating near magnets, combined PET and MRT, etc. The photon detection efficiency (PDE) of photodiodes may reach values a few times higher than that of PMTs. Also, they are rigid, compact and have relatively low operating voltage. In the last few years Micropixel Avalanche PhotoDiodes (MAPD) have been developed and started to be used. The MAPD combines a lot of advantages of semiconductor photodetectors and has a high gain, which is close to that of the PMT. Yet, they have some disadvantages, and one of them is a limited dynamic range that corresponds to a total number of pixels. The novel deep microwell MAPD with high pixel density produced by the Zecotek Company partially avoids this disadvantage. In this paper characteristics of these photodetectors are presented in comparison with the PMT characteristics. The results refer to measurements of the gain, PDE, cross-talks, photon counting and applications: beam test results of two different “Shashlyk” EM calorimeters for COMPASS (CERN) and NICA-MPD (JINR) with the MAPD readout and a possibility of using the MAPD in PET.

Structural aspect of the problem of designing superconducting materials based on Bi-2212 ion-plasma coatings for operation in strong magnetic fields

The Bi-2212 crystal structure parameters and the structural states of the material of thick ion-plasma coatings are analyzed during their production. These structural states include the amorphization of the coating material; changes in the modulated structure of Bi-2212; the formation of a basal texture, which characterizes oriented grain growth during heat treatment; and the improvement of integrain contacts. Problems related to the creation of high-current superconducting Bi-2212-based composites and those related to Chevrel phases, which began to be studied a decade earlier, are considered to be common. The differences in the changes of the critical currents of these materials in an applied magnetic field are associated with the difference in the superconducting fragments in their crystal structures. The development of studies dealing with the creation of superconducting composites containing ion-plasma coatings and intended for operation in strong magnetic fields is considered.

Compact vacuum phototriodes for operation in strong magnetic field

The results of tests of 1″ vacuum phototriodes in a magnetic field up to 4.5 T are presented. It was found that output amplitude decreases by about 6% per tesla in the magnetic field range from 2.0 to 4.0 T . For devices with an anode mesh pitch of 16 μm , the output amplitude at 4.0 T is 30% lower than that at zero field.

Development of the gas electron multiplier (GEM)

We describe recent developments of the gas electron multiplier (GEM), a thin composite mesh acting as proportional avalanche amplifier in gas counters. In beam tests we have verified the excellent efficiency, time resolution and localization accuracy for a GEM with micro-strip read-out. Efficiency, localization accuracy and operation in strong magnetic fields has been verified; operation at rates above 10/sup 6/ Hz/mm/sup 2/ and lifetimes corresponding to at least 10 mC/cm of collected charge have been demonstrated. Refinements in the manufacturing technology have permitted the realization of large size detectors (27 by 25 cm/sup 2/), to be used in conjunction with microstrip gas chambers. With an improved design, stable gains above two thousand have been reached (GEM2000); larger gains can be obtained increasing the thickness of the foils, cascading two GEMs at some distance or in electrical contact. Further developments of the technology and prospective applications are discussed.

Performance and testing of Russian mesh photomultiplier tubes for high magnetic field environments

Future experiments on RHIC and LHC require the performance of photodetectors with stable operation in strong magnetic fields, 0.5 T for the STAR (RHIC) Time of Flight system (TOF) and more than 3 T for the CMS (LHC) electromagnetic calorimeter. Such photodetectors have to possess a good energy and time resolution, for TOF measurements less than 100 ps [1] simultaneously being radiation hard up to some Mrad. Fine mesh dynode proximity photomultiplier tubes FMPMT developed and produced in recent years by Hamamatsu are the most promising detectors for the above specified goals. Different kinds of PMT were tested by some experimental groups in axial magnetic field up to 1.5 T [2–4]. The obtained PMT time resolution in beam test together with Bicron scintillator was better than 100 ps [1].

Helium and hydrogen atom detection in the recycling gas using optical measurements on an ASDEX pressure gauge

The so-called ASDEX pressure gauge is a hot cathode ionization gauge specially designed for operation in strong magnetic fields and under high, noise conditions. It has been employed for investigations of total particle fluxes in or nearby high recycling zones in several tokamaks in the pressure range 10−5 to 10−1 mbar, by analyzing the ion current. However, partial pressures are also of great importance, e.g. the density of helium in pumping ports, because the helium ash removal is a crucial issue for a burning plasma. The partial pressure of hydrogen atoms in molecular hydrogen is a parameter which can be easily compared with the results of neutral gas simulations, and it is therefore an important parameter for the validation of such calculations. A spectroscopical approach using the photons produced in the gauge has been implemented to investigate such issues and to distinguish different atomic species. The degree of dissociation of hydrogen can be determined analysing the Lyα intensity using an oxygen cell as high transparent narrow band filter for Lyα light. Due to the lack of such a convenient filter for the resonant He lines in the VUV the He content in the recycling gas has to be measured with visible He I lines.

A fluid theory of ion collection by probes in strong magnetic fields with plasma flow

A one-dimensional fluid theory of Langmuir probe operation in strong magnetic fields is presented. Cross-field diffusion of ions both into and out of the the collection region is consistently accounted for, in effect taking momentum and particle diffusivity to be equal. The results differ by significant factors from previous analyses, which did not account for outward diffusion but in effect set momentum diffusivity to zero. The differences are especially large when parallel flow of the external plasma is present. It is thus clear that the value assumed for the momentum diffusivity strongly affects the interpretation of recent probe measurements. It is argued that the present results offer a more reliable basis for this interpretation.