High-precision measurements

Power converters in the accelerator context are often required to deliver a performance that is unusual in an industrial context. This paper deals with some of the important aspects of high-precision output voltage and current control and in particular the current measurement transducers and their application

The measurement challenge of the LHC project

The Large Hadron Collider (LHC) is CERN's next accelerator project, to be commissioned in 2005. The project presents unprecedented challenges in the accurate control of high currents up to 13 kA. Arou nd 1700 superconducting magnet circuits are deployed in the underground, 27 km circumference, tunnel. A new concept with quasi-on-line calibration is proposed

Design and verification of a 24 kA calibration head for a DCCT test facility

The Large Hadron Collider (LHC) is CERN's next particle accelerator project, scheduled for commissioning in 2005. The project requires accurate current measurements above 10 kA. Calibration heads have been developed in collaboration with industry to work up to 24 kA at sub-ppm accuracy. The paper describes the design and verification

Developments in high-precision aspects of power converter control for LHC

The initial results from integration testing of the LHC magnet power converters revealed problems of lowfrequency noise, settling time, drift with time and temperature, thermal management and EMC. These problems originated in the use of DSP, the A/D converter (ADC), the DCCT and their respective environments. This paper reports the methods used to improve the performance through hardware and software modifications and the results achieved

High Current, Low Voltage Power Converter [20kA, 6V]: LHC Converter Prototype

The superconducting LHC accelerator requires high currents (~12.5kA) and relatively low voltages (~10 V) for its magnets. The need to install the power converters underground is the driving force for reduced volume and high efficiency. Moreover, the LHC machine will require a very high level of performance from the power converters, particularly in terms of DC stability, dynamic response and also in matters of EMC. To meet these requirements soft-switching techniques will be used. This paper describes the development of a [20kA,6V] power converter intended as a stable high-current source for D CCT calibration and an evaluation prototype for the future LHC converters. The converter is made with a modular concept with five current sources [4kA,6V] in parallel. The 4kA sources are built as plu g-in modules: a diode rectifier on the AC mains with a damped L-C passive filter, a Zero Voltage Switching inverter working at 20 kHz and an output stage (high frequency transformers, Schottky rectifi ers and output filters). The obtained performance (DC stability, bandwidth, efficiency, EMC,...) is presented and discussed

A Strategy for Controlling the LHC Magnet Currents

The LHC will require an unprecedented precision of a few ppm in the control of the current in the major magnetic circuits. As a result of the optimisation of the machine design, the machine will be powered in eight sectors with separate power converters. This scheme, along with other operational constraints, has led to a re-evaluation of the methods needed to ensure adequate performance. An overview of the strategy envisaged to meet this new challenge is presented, along with details of digital control and correction methods, new techniques for analogue to digital conversion and improvements in DC current transducers above 10 kA

High-current performance evaluation of DCCTs

The evaluation of high performance DCCT's to the ppm level has never been an easy task. With the LHC demanding currents up to 13 kA, a whole series of problems has arisen in the accurate measurement of these devices. In order to tackle these problems, new facilities have been designed for laboratory measurements under full power operating conditions. These include a high performance low voltage 20 kA power converter, quasi-coaxial bus-bar structures, Kusters Bridge range extenders and a novel bipolar 0 - 10 A current calibrator with resolution and linearity better than ± 0.5 ppm. This paper will present an overview of the complete facility and give more detail on the new current calibrator. Initial results will be presented, along with application areas which advance the state of the art in this field of measurements

High-precision performance testing of the LHC power converters

The magnet power converters for LHC were procured in three parts, power part, current transducers and control electronics, to enable a maximum of industrial participation in the manufacturing and still guarantee the very high precision (a few parts in 10-6) required by LHC. One consequence of this approach was several stages of system tests: factory reception tests, CERN reception tests, integration tests , short-circuit tests and commissioning on the final load in the LHC tunnel. The majority of the power converters for LHC have now been delivered, integrated into complete converter and high-precision performance testing is well advanced. This paper presents the techniques used for high-precision testing and the results obtained

拍卖法律制度研究

拍卖在我国属舶来品是19世纪中后期才引入并缓慢发展的新制度对拍卖制度的研究更是近几十年的事因此显得相对薄弱然而市场经济体制的确立促成了拍卖实践在我国的迅猛发展客观上要求有完善的立法和理论研究与之相适应本文从我国实际出发借鉴外国的成功经验对拍卖法律制度的基本问题做了探讨全文除前言和结语外共分五大章第一章拍卖制度的概述主要论述了拍卖的性质与历史沿革拍卖的价值及拍卖的种类拍卖是指以公开竞价的形式将特定物品或者财产权利转让给最高应价者的买卖方式从性质上讲它是一种特种买卖经过了产生早期发展到不断完善的过程拍卖制度作为商品经济的产物具有高度的经济价值和社会意义本文主要从三个角度将其分为强制拍卖与任意拍卖法...no学位：法学硕士院系专业：法律系_民商法学(含劳动法学、社会保障法学)学号：19960800