Design Document for Control Dewar and Vacuum Pump Platforms

A liquid helium cryostat has been designed and operated for the purpose of testing visible light photon counter (VLPC) chips at 6.5 K. To achieve the desired operational characteristics for the VLPC devices their operating temperature is restricted to 6.5 K +/− 0.1 K. They will be used in a scintillating fiber tracker being proposed as part of an upgrade of the DO detector at Fermilab. The final version of the scintillating fiber tracker will contain roughly 100000 VLPC channels. Two cryostats with identical thermal design (a 128 channel and a 3072 channel design) have been built to perform the initial VLPC testing. The heat transfer needed to maintain the VLPC at its operating temperature occurs by conduction across an annular helium gas gap to a liquid helium reservoir. Helium boiloff is used to intercept conduction heat leak to the liquid reservoir. ANSYS finite element heat transfer analysis was utilized in the thermal design of the cryostat. The cryostat design and thermal performance (predicted and measured) are presented.

The upgrade of the D/spl phi/ detector at Fermilab is scheduled to run in 1999. One component of the upgrade is a cylindrically shaped preshower detector, placed on the outside of a solenoidal magnet that will surround the tracking volume. The technology for this detector will be plastic scintillating strips, with axial wavelength shifting (WLS) fiber and Visible Light Photon Counter (VLPC) readout. The VLPCs, with their quantum efficiency of /spl sim/70%, perform much better than traditional photomultipliers. We have performed extensive tests on different detector variations; investigating different scintillators, WLS fibers, and construction techniques. Prototype modules were placed in a cosmic ray test stand and over 120000 clean events per detector variant were collected. The large event sample and superior performance afforded by the VLPCs allow precise characterisation of the detector response. In this paper, we present results of our test programs, including uniformity of response, yields and interchannel crosstalk. We have achieved effective attenuation lengths exceeding 11 meters and yields of 4.5 photoelectrons per millimeter of scintillator traversed. An additional factor of 2 increase in yield seems achievable.

The Visible Light Photon Counter (VLPC) has the capability to discriminate photon number states, in contrast to conventional photon counters which can only detect the presence or absence of photons. We use this capability, along with the process of parametric down-conversion, to generate photon number states. We first investigate single photon generation, using a modified Hanbury-Brown Twiss (HBT) intensity interferometer to verify the single photon nature of the light. We then use a second VLPC to experimentally demonstrate generation of 2,3 and 4 photons with high fidelity. We investigate the effect of the detection efficiency of the VLPC on the generation rate and fidelity of the created states.

This paper reviews the research work on the Visible Light Photon Counters (VLPC) that have been developed for the scintillating fiber tracking at high luminosity colliders and high rate fixed target experiments. The devices originated from the joint work between UCLA and Rockwell International Science Center. The VLPCs are capable of counting photons very efficiently down to a single photon level with high avalanche gain, producing pulses at very high rates with very short rise times. Due to small gain dispersions they can be used in counting photons with high quantum efficiencies, therefore they are excellent devices for charged particle tracking using small diameter scintillating plastic fibers. In this paper, fiber tracking for the CDF and D0 upgrades and a possible usage of the VLPC readout for the experiment E803 at Fermilab will be discussed.

Visible light photon counters (VLPCs) offer many attractive features as photon detectors, such as high quantum efficiency and photon number resolution. We report measurements of the single-photon timing jitter in a VLPC, a critical performance factor in a time-correlated single-photon counting measurement, in a fiber-coupled closed-cycle cryocooler. The measured timing jitter is 240 ps full-width-at-half-maximum at a wavelength of 550 nm, with a dark count rate of 25 000 counts per second. The timing jitter increases modestly at longer wavelengths to 300 ps at 1000 nm, and increases substantially at lower bias voltages as the quantum efficiency is reduced.

The low signal to noise ratio produced by the VLPC (Visible Light Photon Counter) chip in the detection of a single photon necessitates the use of a filtering capacitor. Maximum performance of the filtering capabilities dictate the placement of the capacitor be as close to the VLPC chip as possible. However, the chip operates at extremely low temperatures (7K). In addition, available space within the VLPC cassette is limited. Therefore it is desired to find a capacitor which provides good temperature stability at cryogenic temperatures within a minimal space (e.g. surface mounted). This engineering note presents the results from a test of the effect of low temperature on surface mounted capacitors. Preliminary testing suggested that capacitors of the tantalum type would provide the best te mperature stability at cryogenic temperatures, therefore two different tantalum capacitors were tested. A ceramic capacitor was also included in the results as a comparison, even though preliminary results suggested the ceramic type would not provide sufficient temperature stability.

The load and resistance factor design (LRFD) specification developed by the American Institute of Steel Construction allows the designer to consider the partial restraint in a steel connection. A generated nonlinear equation is fitted to available experimental data on partially restrained steel connections for six different types of connections. The connections analyzed are single web angle, double web angle, top and seat angle, end plate with column stiffeners, end plate without column stiffeners, and header plate. The statistics of parameters governing the moment‐rotation curves of the connection are determined. Design examples from the American Institute of Steel Construction Load and Resistance Factor Design Manual are used as an application of the use of statistical data in finding the reliability of a uniformly loaded, partially restrained beam. The reliability is evaluated by imposing end rotations and calculating the reliability index for each imposed deformation. The connection reliability index ...

Design method for determining appropriate stiffness for end point braces

Because beams with web holes are being used increasingly in buildings, the American Institute of Steel Construction (AISC) is considering including provisions for such beams in a future addition to its Specifications for the Design, Fabrication, and Erection of Structural Steel for Buildings. To aid in preparing this addition, the ASCE Committee on Beams with Web Openings has prepared a list of suggestions which are presented herein. The paper first considers the applicability of both the allowable-stress design and plastic design parts of the AISC specification to beams with web holes are required. This paper presents material that is believed to be accurate and reliable for design purposes. However, this material should not be used for any specific application without independent examination and verification of its suitability for such application. ASCE disclaims any warranties regarding this report and anyone making use thereof assumes all risk and liability arising from such use.

This study presents optimum design of plane steel bridges considering corrosion effect by using teaching-learning based optimization (TLBO) method. Optimum solutions of three different bridge problems are linearly carried out including and excluding corrosion effect. The member cross sections are selected from a pre-specified list of 128 W profiles taken from American Institute of Steel Construction (AISC). A computer program is coded in MATLAB to carry out optimum design interacting with SAP2000 using OAPI (Open Application Programming Interface). The stress constraints are incorporated as indicated in AISC Allowable Stress Design (ASD) specifications and also displacement constraints are applied in optimum design. The results obtained from analysis show that the corrosion effect on steel profile surfaces causes a crucial increase on the minimum steel weight of bridges. Moreover, the results show that the method proposed is applicable and robust to reach the destination even for complex problems.

The paper presents a simple yet efficient optimal design method based evolutionary structural optimization (ESO) to determine the minimum member sizes complying with an AISC-LRFD (an acronym for American Institute of Steel Construction – Load and Resistance Factor Design) specification. The influences of nonlinear (second-order approximation) geometry are realistically incorporated using an AISC 2010 direct analysis method. The optimization minimizes the total weight of structures subjected to the challenges associated with the simultaneous presence of nonlinear design formulations and discrete design variables realistically considering the availability of standard steel sections. This leads to a non-convex and/or non-smooth optimization program. The ESO algorithm overcomes the problem by performing iterative elimination procedures of ineffective sections, where the feasible design domain progressively converges to the minimum distribution of steel members satisfying limit state (ultimate strength and serviceability) criteria. The ESO design process is encoded within a visual basis application (VBA) framework having a direct interface with the commercial analysis and design software, called SAP2000. An illustrative example motivated by practical engineering applications has been successfully proceeded and hence highlighted robustness of the proposed approach in obtaining the optimal design of steel structures under applied forces.

With the demise of the Superconducting Supercollider (SSC) Project, there was great concern that the technological developments for that accelerator and its associated detectors might well be lost in the aftermath. In the case of scintillating fiber tracking, such as not been the case. During the period 1990--1993, several tracking technologies were under development for SDC, including Scintillating Fiber Tracking, Straw-tubes, and Microstrip Gas Chambers. In summer 1990, several members of the Fiber Tracking Group (FTG) proposed the use of Scintillating Fiber Tracking to the D0 experiment at Fermilab. This proposal was accepted, and D0 now is building a 75,000 fiber channel tracking detector with readout via Visible Light Photon Counters (VLPC) which were devices pioneered by the SDC Fiber Tracking Group. In addition, all the preshower detectors for D0 also make use of fiber readout (in this case waveshifting fibers) and VLPC for photosensing. In February 1993, a full 7 months prior to cancellation of the SSC project by Congress, the SDC experiment rejected scintillating fiber tracking for further development. Fortunately for all concerned, the D0 experiment had already embraced this technology, so this important detector concept could be further developed, refined, and utilized for physics experimentation. In early 2000, data will be taken with the D0 fiber tracker to study Top Quarks, Beauty Particles, Electroweak Physics, QCD phenomena, and to search for new phenomena. The University of Notre Dame has played a fundamental and seminal role in the development and implementation of this detector technology. R. Ruchti has served as cospokesman of the Fiber Tracking Group since its inception in 1989, and has been a pioneer of fiber tracking technology since 1980. In addition, at least one other experiment at Fermilab, E835, has utilized scintillating fibers with VLPC readout to study Charmonium in proton-antiproton collisions using a gas-jet target in the Tevatron antiproton accumulator ring. This fiber detector has been operated successfully for over 1 year of actual beam conditions.

The multi-photon counting capability of the Visible Light Photon Counter (VLPC), along with the process of parametric downconversion, is used to experimentally generate photon number states containing 1,2,3 and 4 photons with high fidelity.

The continuous strength method for the design of aluminium alloy structural elements

Full‐scale testing of double‐row bolted‐web connections was performed on coped and uncoped specimens. Parameters considered were the end and edge distance, bolt arrangement, and the type of hole (standard or slotted). All of the specimens failed in a block shear mode with factors of safety lower than predicted by the 1978 American Institute of Steel Construction (AISC) specification. An elastic finite element model was used to study the experimental behavior and develop a modified block shear failure model which shows good agreement with the test results. The finite element analysis also indicated the compression bending stresses at the cope to be twice that predicted by normal beam theory.