Close Proximity Operations Research Articles

Effects of Clamping on the Laser Forming Process

Although considerable effort has gone into characterizing the laser forming process in terms of process parameters and conditions, there has been little emphasis on the effects of the mechanical and thermal constraints introduced by the clamping method utilized for a desired application. This research suggests means for investigating and predicting the resulting geometry of a specimen due to laser operation in close proximity to an array of imposed thermo-mechanical constraints for both the single and multiple scan cases; specifically, the resulting average bending angle as well as bending angle variations throughout the part. This is accomplished by initially only considering these effects on the thermal field. Conclusions are then drawn about the nature of the mechanical effects. These conclusions are validated through numerical simulation as well as physical experimentation. An analytical solution of the thermal problem is also presented for further validation of the temperature field as a constrained edge is approached.

A high-efficiency internal WLAN antenna for wireless devices operating in close proximity to a lossy medium

This paper presents a dual-loop patch antenna capable of providing high radiation efficiency for operation in close proximity to a lossy medium with permittivity and conductivity close to those of a human torso or arm. For operation as an internal WLAN (wireless local area network) antenna in a wireless device, the dual-loop patch antenna with a low profile of 3 mm can cover the operating bandwidth of the 2.4-GHz band (2400–2484 MHz), showing a high radiation efficiency of about 88%, when placed very close to the lossy medium with only 1-mm spacing. The obtained results make the proposed antenna very promising for body-worn or wearable antenna applications. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 233–236, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21134

A new optically pumped tandem magnetometer: principles and experiences

In this paper we describe a new design for an optically pumped tandem magnetometer situated at the GeoForschungsZentrum Potsdam. A tandem magnetometer combines the fast response of a self-oscillating vapour magnetometer with the accuracy of a narrow line Mz-type magnetometer. A newly patented method of coupling the two sensors avoids any stray magnetic fields and so allows a compact design of the instrument itself, as well as facilitating its operation in close proximity to other magnetometers. A prototype Cs-K tandem magnetometer for use in magnetic observatories is described. We then show typical results of a long-term comparison with both a second type of optically pumped magnetometer and an Overhauser proton magnetometer. Finally, a resuméis given of four years of continuous operation of this new type of magnetometer with respect to the data quality produced and its operational reliability.

High fusion power steady state operation in JET DT plasmas

Because of its large size, single null divertor and flexible magnetic geometry, JET is capable of producing the most reactor relevant plasmas of any present generation tokamak. In recent DT experiments, the fusion performance of these plasmas was tested for the first time. Over 4 MW of fusion power was produced in a high power, steady state pulse of 5 s, limited by the duration of the heating power. The fusion QE, defined simply as the fusion energy produced divided by the input energy over this 5 s interval, was 0.18. These DT ELMy H mode discharges performed up to expectations based on DD preparation pulses and thus establish a firm basis for extrapolating to a next step machine. Operation at low q95 is possible in JET with no degradation in the confinement enhancement factor and provides an improved margin to ignition when extrapolated to ITER. Considerable uncertainties remain, nonetheless. In particular, access to high density, relative to the Greenwald limit, and operation in close proximity to the H mode threshold may both result in a degradation of the confinement in the next step machine.

Rock Blasting Operations in Close Proximity to Tuen Mun Road for the Ting Kau Bridge and Approach Viaduct

In 1994, the Highways Department awarded a contract for the construction of the Ting Kau Bridge and the Approach Viaduct. Being part of Route 3, Ting Kau Bridge will form a vital link between the new airport and the north-west New Territories. The scope of works includes a triple-tower coble-stayed bridge spanning over the Rambler Channel, its connecting viaduct to the new Tai Lam Tunnel, as well as two ramps linking with Tuen Mun Road. To make space for the ramps, the existing rock slopes adjacent to Tuen Mun Road had to be cut back and part af this was achieved by blasting. The work was carried out under a number of constraints, the main concerns being the safety of the general public, disruption to traffic flow, as well as the tight schedule. This paper describes the planning and assessment made prior to blasting, the blast design and fleid trials, execution of blasting, safety measures undertaken and vibration monitoring carried out. As a result of careful planning and good construction control, the e...

Cryopump measurements relating to safety, pumping speed, and radiation outgassing

A test cryopump has been constructed to investigate operation in close proximity to a neutral beam, to determine static and dynamic pumping speeds, and to study outgassing such as might be produced by a pulse of nuclear radiation. No difficulty was encountered in operating the cryopump close to a deuterium neutral beam source suitable for a fusion-reactor injector. Static and dynamic pumping-speed measurements agreed well, but were somewhat lower than expectations, probably due to the unusual method chosen to supply liquid helium. Safety tests showed that hydrogen could not be ignited at any subatmospheric pressure resulting from a leak-up-to-air accident. The possible hazard of liquid-oxygen condensation in such accidents was not explored. Tests made with pulses of neutrons and gamma rays produced by a TRIGA reactor showed that the cryopump could be partially outgassed by radiation pulses of sufficient intensity. However, the effect is ascribed to the gamma-ray component of the TRIGA pulse which is about 103 times that expected from a fusion reactor such as TFTR.