J. Sondericker

Position and timing resolution of interpolating cathode strip chambers in a test beam

Abstract Design and construction details are presented of a four-layer, position sensitive, cathode strip chamber and a low cost, highly multiplexed readout system based on monolithic circuit technology that are well suited for a muon detector at future hadron colliders. Track location is determined by interpolation of the cathode induced charge, using a new design with intermediate strips between readout nodes to reduce the number of channels and improve position resolution and linearity. Results are reported from tests with an 55 Fe source and a 300 GeV/ c muon beam in RD5 at CERN. The beam test demonstrated position resolution of 40 μ m per layer which is less than 1% of the readout pitch. The timing resolution for the entire four-layer detector was 3.6 ns r.m.s. which is adequate for fully efficient beam crossing identification in an LHC experiment.

Liquid ionization calorimetry with time-sampled signals☆

We present the results of a study of amplitude and timing measurements made in a liquid krypton electromagnetic calorimeter, using multiply sampled signals of the shaped waveform. The measurements were designed to emulate the type of data that will be available from a calorimeter operating at future hadron-hadron colliders with short (∼ 20 ns) spacing between bunch crossings. Data have been collected with 18 ns sample spacing on waveforms from individual calorimeter sections with a shaping time of 40 ns and from 5 × 5 tower analog sums with a shaping time of 50 ns. The amplitude was measured using the analog sum signal, and the timing was measured using the signal from the individual sections. The data were processed using the method of optimal filtering, and a reduction in the noise of about a factor of two over that for a single sample is seen when using multiple samples for determining the amplitude. We find an energy resolution of 6.7%E, in agreement with the resolution measured for the same calorimeter using a single sample measured at the peak of the waveform. The timing resolution for a section of a calorimeter tower with deposited energy ∈ can be expressed as (c∈)2 + σcal2, with a value of c of 0.38 GeV ns for the front section (the first 6 radiation lengths) and 0.70 GeV ns for the back section, and a value of 0.15 ns for σcal.

Precision timing with liquid ionization calorimeters

We present timing measurements performed with a liquid krypton electromagnetic accordion calorimeter, measured in an electron beam over an energy range of 5–20 GeV. A novel discriminator with an amplitude-independent timing response was used to extract the inherently accurate timing information from the calorimeter. As expected, the timing resolution στ is observed to vary inversely with the signal amplitude, which is proportional to the deposited energy E. We measure a resolution of στ = 4.15±0.06 GeV ns/E for a sum of 5×5 towers with dimensions 2.7×2.5 cm2 each. From this we deduce that the timing resolution for an individual tower is approximately 0.8 GeV ns/E.

An Experimental Study of Catastrophic Loss of Vacuum for RHIC Dipole in MAGCOOL

Experimental studies of catastrophic loss of insulating vacuum for RHIC dipoles to air and to helium have been performed in the Brookhaven MAGCOOL magnet test facility. A RHIC dipole was cooled to 4.5 Kelvin and powered to its 5000 Ampere design current prior to the test. Ambient air or helium was then introduced into the enclosure to simulate the vacuum loss conditions. The response of the cryogenic system, including the insulating vacuum, pressure, temperature and flow rate for the cooling helium, temperatures on the vacuum tank and heat shield are given as a function of time. The heat load is calculated from the sum of the heat into the magnet and the adjacent helium cooling pipes. The results indicate that for this system the heat load from a sudden loss of vacuum is of the order of 10 kW [0.086 W/cm2] for the helium test and 20 kW [0.17 W/cm2] for the air test. These are approximately one order of magnitude larger than the magnet quench heat load, and thus require special consideration of a pressure relief system for the helium cooling circuit.

Performance of an accordion electromagnetic calorimeter with liquid krypton and argon

Test results of a liquid krypton/argon electromagnetic calorimeter with accordion type electrode structure are presented. The test was carried out at the Brookhaven AGS in a negative beam with good electron identification at momenta 5, 10, 15, and 20 GeV/c. Results on energy resolution, linearity, pointing resolution, and muon response are presented. The results are in good agreement with Monte Carlo calculations. The energy resolution of 6.7%E was achieved using liquid krypton and 7.7%E with liquid argon, with a negligible constant term.

RHIC 25 kW Refrigerator and Distribution System, Construction, Testing, and Initial Operating Experience

The installation and testing of most of the Relativistic Heavy Ion Collider (RHIC) cryogenic system is complete. The RHIC cryogenic system consisting of the modified ISABELLE refrigerator, and other new cryogenic components, has been completed from the 25 kW refrigerator through one sixth of the 3.8 km circumference RHIC accelerator up to the 4:00 valve box. This paper covers the progress to date with respect to construction and installation of the helium distribution system, including the vacuum jacketed piping and valve boxes, recoolers, and controls. In addition, the 25 kW refrigerator has been operated on three seChapaute occasions over the past two years. These first experiences with the operation of the refrigerator and warm compressor system, along with some test results will be discussed here.

A Precision Cryogenic Temperature Data Acouisition System

A multiplexed temperature data acquisition system with an overall precision of ±25 PPM has been designed using state-of-the-art electronics to accurately read temperature between 2.4 K and 600 K from pre-calibrated transducers such as germanium, silicon diode, thermistor or platinum temperature sensors.

Operational Tests of the BNL 24.8 kW, 3.8 K Helium Refrigerator

The BNL 24.8 kW refrigeration system is completely installed and major portions of the acceptance tests have been completed. So far, the equipment tested has performed at or above design levels. The room temperature helium compressor station has been completely tested and accepted. The two-stage oil injected screw compressor system exhibited an isothermal efficiency of 57% while delivering a helium flow in excess of 4400 g/s. Data on the performance of the make-up gas cryogenic purifier is also given.

Design of the LHC US ATLAS Barrel Cryostat

One of the experiments of CERN’s Large Hadron Collider (LHC) is the ATLAS Liquid Argon detector. The Liquid Argon Barrel Cryostat is part of the United States contribution to the LHC project and its design is presented here. The device is made up of four concentric cylinders: the smallest and largest of which form a vacuum vessel enclosing a cold vessel cryostat filled with liquid argon. The Cryostat serves as the housing for an electromagnetic barrel calorimeter, supports and provides space in vacuum for a solenoid magnet while the toroidal opening furnishes room for a tracker detector. Design requirements are determined by its use in a collider experiment: the construction has to be compact, the material between the interaction region and the calorimeter has to be minimal and made of aluminum to reduce the amount of absorbing material. The design complies with code regulations while being optimized for its use in a physics environment.

Design Considerations and Experience of the RHIC Dual Magnet Cryostat Installation

The first RHIC Dual Magnet installation, of eight (8) cold masses in one vacuum vessel, has been completed. Design of the system included the requirement for assembly on location, the need for individual three-direction alignment capability at each cold mass cradle, a fixed position cradle for the entire assembly, longitudinal slide capability for all other cradles, two thermally isolated heat shields, accessible electrical splice boxes, removable interconnects, removability of individual cold mass sections, flexible supply lines for electrical power and cryogenic services and external loads imposed from the supply services. Initially two of the twelve total assemblies were fabricated for the Sextant Test of the RHIC ring. This paper covers an overview of that effort from initial design considerations, fabrication/installation techniques, initial installation problems and the final design solutions.