Low Temperature Effects: Surface Mount Capacitors

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.

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 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.

This study focuses on investigating the reliability of ceramic and tantalum capacitors by enhancing the stress effect of moisture with voltage on/off-periods. Display units with ceramic and tantalum capacitors were tested at 85degC-85-percent relative humidity (85/85) with an operating voltage of 15 V for the first 1620 hours. A voltage cut-off of 70 hours was done after 1620 hours, after which the test continued. On the basis of the results, it seems that in the case of tantalum capacitors the combined stress effect of moisture and voltage can be enhanced with periodic off times. In contrast, ceramic capacitors seem to maintain their integrity despite the off-period during 85/85 testing. The ceramic capacitors outlasted the tantalum ones since the tantalum capacitors were noticed to absorb moisture during the off period. Enhancement of the stress effect was not discovered without the initial 1620 hours temperature-humidity test. Possible reasons are discussed in the paper.

Multilayer ceramic capacitors (MLCCs) prepared using Ba1−xSrxTiO3 (BST) ceramics exhibit high dielectric constants (~1000), low dielectric loss (<0.01), and high breakdown voltage, with particularly significant tunability in dielectric properties (>50%) and with poor temperature stability. Doping-dominated temperature stability improvements often result in unintended loss of dielectric properties. A non-doping method has been proposed to enhance the temperature stability of BST capacitors. The composite gradient multilayer (CGML) ceramic capacitors with BaxSr1−xTiO3, where 0.5 < x < 0.8, as the dielectric, were prepared using a tape-casting method and sintered at 1250 °C. There exists a dense microstructure and continuous interface between the BaxSr1−xTiO3 thick film and the Pt electrodes. CGML ceramic capacitors feature a high dielectric constant at 1270, a low dielectric loss of less than 0.007, and excellent frequency and temperature stability. The capacitor showcases remarkable dielectric properties with a substantial tunability of 68% at 100 kV/cm, along with a notably consistent tunability ranging from 20% to 28% at 15 kV/cm across temperatures spanning from 30 to 100 °C, outperforming single-component BST-MLCCs in dielectric performance.

Remarkable energy storage performances of tungsten bronze Sr0.53Ba0.47Nb2O6-based lead-free relaxor ferroelectric for high-temperature capacitors application

Electromechanical response and piezoelectric properties in (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 piezoceramics using nano-sized AlN modification

Dielectric capacitors exhibiting high energy-storage properties and excellent pulse performance are critical components in advanced pulsed power systems. The multilayer ceramic capacitors (MLCCs) are the most widely used capacitors, due to the high integration and excellent high-temperature endurance. Nevertheless, achieving high energy density and reliable performance at wide temperature range and prolonged cycling remains the major challenge for existing commercial MLCCs based on linear dielectrics or Pb-based antiferroelectrics. Herein, we developed BaTiO₃-based relaxor ferroelectric MLCCs with X9S characteristic for high-voltage applications. The BaTiO₃-based MLCCs exhibiting a good energy density of 6.09 J cm^-3 and an ultrahigh efficiency of 98.2%, with a superior stability in temperature (&lt;10%, 24~250 ℃) and fatigue (after 10⁶ cycles, &lt;4% at 200 ℃). The pulse properties of MLCCs show a minimal variation (&lt;4.5%, 22~200 ℃). Moreover, 6878-size MLCCs with 300 nF can release a peak current of 3600 A at rated voltage of 3000 V, which exhibit higher peak currents than linear MLCCs and better stability than Pb-based MLCCs. The excellent performance and superior stability demonstrate that the relaxor ferroelectrics MLCCs have great potential for advanced energy-storage and pulsed power applications.

This engineering note documents the design of the control dewar and vacuum pump platform that is to be installed on the D-Zero detector. It's purpose is twofold. Firstly it is a summary and repository of the final design calculations of the structure. Secondly, it documents that design follows the American Institute of Steel Construction (AISC) manual and applicable OSHA requirements with respect to walking working surfaces. The information contained in the main body of this note is supported by raw calculations included as the appendix. The platform is a truss type frame strucrure constructed primarily of rectangular steel tubing. The upper platform is for support of the control dewar (cryogenic/electrical interface for the solenoid), visible light photon counter (VLPC) cryogenic bayonet can, and infrequently, personnel during the connection and disconnection of the detector to building services. Figure 1 shows a layout of the structure as mounted on the detector and with the installed equipment. The connection of the platform to the detector is not conventional. Two main booms cantilever the structure to a location outside of the detector. The mounting location and support booms allow for the uninhibited motion of the detector components.

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.

Ultrahigh energy storage performance in AN-based superparaelectric ceramics

In this work, the process of two-stage modifications for (Ba0.97Ca0.03)(Ti0.96Sn0.04-xHfx)O3 (BCTS4-100xH100x) ceramics was studied. The trade-off composition was obtained by Hf substitution for Sn and MnO2 doping (two-stage modification) which improves the temperature stability and piezoelectric properties. The phase structure ratio, microstructure, and dielectric, piezoelectric, ferroelectric, and temperature stability properties were systematically investigated. Results showed that BCTS4-100xH100x piezoelectric ceramics with x=0.035 had a relatively high Curie temperature (TC) of about 112 °C, a piezoelectric charge constant (d33) of 313 pC/N, an electromechanical coupling factor (kp) of 0.49, a mechanical quality factor (Qm) of 122, and a remnant polarization (Pr) of 19μC/cm2. In addition, the temperature stability of the resonant frequency (fr), kp, and aging d33 could be tuned via Hf content. Good piezoelectric temperature stability (up to 110 °C) was found with x =0.035. BCTS0.5H3.5 + a mol% Mn (BCTSH + a Mn) piezoelectric ceramics with a = 2 had a high TC of about 123 °C, kp ∼ 0.39, d33 ∼ 230 pC/N, Qm ∼ 341, and high temperature stability due to the produced oxygen vacancies. This mechanism can be depicted using the complex impedance analysis associated with a valence compensation model on electric properties. Two-stage modification for lead-free (Ba0.97Ca0.03)(Ti0.96Sn0.04)O3 ceramics suitably adjusts the compositions for applications in piezoelectric motors and actuators.