Eric Anderssen

The evaporative cooling system for the ATLAS inner detector

This paper describes the evaporative system used to cool the silicon detector structures of the inner detector sub-detectors of the ATLAS experiment at the CERN Large Hadron Collider. The motivation for an evaporative system, its design and construction are discussed. In detail the particular requirements of the ATLAS inner detector, technical choices and the qualification and manufacture of final components are addressed. Finally results of initial operational tests are reported. Although the entire system described, the paper focuses on the on-detector aspects. Details of the evaporative cooling plant will be discussed elsewhere.

The MAPS based PXL vertex detector for the STAR experiment

The Heavy Flavor Tracker (HFT) was installed in the STAR experiment for the 2014 heavy ion run of RHIC. Designed to improve the vertex resolution and extend the measurement capabilities in the heavy flavor domain, the HFT is composed of three different silicon detectors based on CMOS monolithic active pixels (MAPS), pads and strips respectively, arranged in four concentric cylinders close to the STAR interaction point. The two innermost HFT layers are placed at a radius of 2.7 and 8 cm from the beam line, respectively, and accommodate 400 ultra-thin (50 μ m) high resolution MAPS sensors arranged in 10-sensor ladders to cover a total silicon area of 0.16 m2. Each sensor includes a pixel array of 928 rows and 960 columns with a 20.7 μ m pixel pitch, providing a sensitive area of ~ 3.8 cm2. The architecture is based on a column parallel readout with amplification and correlated double sampling inside each pixel. Each column is terminated with a high precision discriminator, is read out in a rolling shutter mode and the output is processed through an integrated zero suppression logic. The results are stored in two SRAM with ping-pong arrangement for a continuous readout. The sensor features 185.6 μ s readout time and 170 mW/cm2 power dissipation. The detector is air-cooled, allowing a global material budget as low as 0.39% on the inner layer. A novel mechanical approach to detector insertion enables effective installation and integration of the pixel layers within an 8 hour shift during the on-going STAR run.In addition to a detailed description of the detector characteristics, the experience of the first months of data taking will be presented in this paper, with a particular focus on sensor threshold calibration, latch-up protection procedures and general system operations aimed at stabilizing the running conditions. Issues faced during the 2014 run will be discussed together with the implemented solutions. A preliminary analysis of the detector performance meeting the design requirements will be reported.

Sensor Development and Readout Prototyping for the STAR Pixel Detector

The STAR experiment at the Relativistic Heavy Ion Collider (RHIC) is designing a new vertex detector. The purpose of this upgrade detector is to provide high resolution pointing to allow for the direct topological reconstruction of heavy flavor decays such as the D{sup 0} by finding vertices displaced from the collision vertex by greater than 60 microns. We are using Monolithic Active Pixel Sensor (MAPS) as the sensor technology and have a coupled sensor development and readout system plan that leads to a final detector with a <200 {micro}s integration time, 400 M pixels and a coverage of -1 < {eta} < 1. We present our coupled sensor and readout development plan and the status of the prototyping work that has been accomplished.

Mechanical Performance of Short Models for MQXF, the Nb3Sn Low-β Quadrupole for the Hi-Lumi LHC

In the framework of the Hi-Lumi LHC Project, CERN and U.S. LARP are jointly developing MQXF, a 150-mm aperture high-field Nb3Sn quadrupole for the upgrade of the inner triplet of the low-beta interaction regions. The magnet is supported by a shell-based structure, providing the preload by means of bladder-key technology and differential thermal contraction of the various components. Two short models have been produced using the same cross section currently considered for the final magnet. The structures were preliminarily tested replacing the superconducting coils with blocks of aluminum. This procedure allows for model validation and calibration, and also to set performance goals for the real magnet. Strain gauges were used to monitor the behavior of the structure during assembly, cool down and also excitation in the case of the magnets. The various structures differ for the shell partitioning strategies adopted and for the presence of thick or thin laminations. This paper presents the results obtained and discusses the mechanical performance of all the short models produced up to now.

Assembly Tests of the First Nb 3 Sn Low-Beta Quadrupole Short Model for the Hi-Lumi LHC

In preparation for the high-luminosity upgrade of the Large Hadron Collider (LHC), the LHC Accelerator Research Program (LARP) in collaboration with CERN is pursuing the development of MQXF: a 150-mm-aperture high-field Nb3Sn quadrupole magnet. The development phase starts with the fabrication and test of several short models (1.2-m magnetic length) and will continue with the development of several long prototypes. All of them are mechanically supported using a shell-based support structure, which has been extensively demonstrated on several R&D models within LARP. The first short model MQXFS-AT has been assembled at LBNL with coils fabricated by LARP and CERN. In this paper, we summarize the assembly process and show how it relies strongly on experience acquired during the LARP 120-mm-aperture HQ magnet series. We present comparison between strain gauges data and finite-element model analysis. Finally, we present the implication of the MQXFS-AT experience on the design of the long prototype support structure.

The STAR MAPS-based PiXeL detector

Author(s): Contin, G; Greiner, L; Schambach, J; Szelezniak, M; Anderssen, E; Bell, J; Cepeda, M; Johnson, T; Qiu, H; Ritter, HG; Silber, J; Stezelberger, T; Sun, X; Tran, C; Vu, C; Wieman, H; Wilson, K; Witharm, R; Woodmansee, S; Wolf, J | Abstract:

Experience from the construction and operation of the STAR PXL detector

A new silicon based vertex detector called the Heavy Flavor Tracker (HFT) was installed at the Soleniodal Tracker At RHIC (STAR) experiment for the Relativistic Heavy Ion Collider (RHIC) 2014 heavy ion run to improve the vertex resolution and extend the measurement capabilities of STAR in the heavy flavor domain. The HFT consists of four concentric cylinders around the STAR interaction point composed of three different silicon detector technologies based on strips, pads and for the first time in an accelerator experiment CMOS monolithic active pixels (MAPS) . The two innermost layers at a radius of 2.8 cm and 8 cm from the beam line are constructed with 400 high resolution MAPS sensors arranged in 10-sensor ladders mounted on 10 thin carbon fiber sectors giving a total silicon area of 0.16 m2. Each sensor consists of a pixel array of nearly 1 million pixels with a pitch of 20.7 μm with column-level discriminators, zero-suppression circuitry and output buffer memory integrated into one silicon die with a sensitive area of ~ 3.8 cm2. The pixel (PXL) detector has a low power dissipation of 170 mW/cm2, which allows air cooling. This results in a global material budget of 0.5% radiation length per layer for detector used in this run. A novel mechanical approach to detector insertion allows for the installation and integration of the pixel sub detector within a 12 hour period during an on-going STAR run. The detector specifications, experience from the construction and operation, lessons learned and initial measurements of the PXL performance in the 200 GeV Au-Au run will be presented.

STAR PIXEL detector mechanical design

A high resolution pixel detector is being designed for the STAR [1] experiment at RHIC. This device will use MAPS as the detector element and will have a pointing accuracy of ~25 microns. We will be reporting on the mechanical design required to support this resolution. The radiation length of the first layer (~0.3% X0) and its distance from the interaction point (2.5 cm) determines the resolution. The design makes use of air cooling and thin carbon composite structures to limit the radiation length. The mechanics are being developed to achieve spatial calibrations and stability to 20 microns and to permit rapid detector replacement in event of radiation damage or other potential failures from operation near the beam.

Fabrication and Assembly Performance of the First 4.2 m MQXFA Magnet and Mechanical Model for the Hi-Lumi LHC Upgrade

The LHC accelerator research program (LARP), in collaboration with CERN and under the scope of the high luminosity upgrade of the Large Hadron Collider, is in the prototyping stage in the development of a 150 mm aperture high-field Nb3Sn quadrupole magnet called MQXF. This magnet is mechanically supported using a shell-based support structure, which has been extensively demonstrated on several R&D models within LARP, as well as in the more recent short (1.2 m magnetic length) MQXF model program. The MQXFA magnets are each 4.2 m magnetic length, and the first mechanical long model, MQXFA1M (using aluminum surrogate coils), and MQXFAP1 prototype magnet (the first prototype with Nb3Sn coils) have been assembled at the LBNL. In this paper, we summarize the tooling and the assembly processes, and discuss the mechanical performance of these first two assemblies, comparing strain gauge data with finite element model analysis, as well as the near-term plans for the long MQXF magnet program.

Design and performance of an R-θ fiber positioner for the BigBOSS instrument

The BigBOSS instrument is a proposed multi-object spectrograph for the Mayall 4m telescope at Kitt Peak, which will measure the redshift of 20 million galaxies and map the expansion history of the universe over the past 8 billion years, surveying 10-20 times the volume of existing studies. For each 20 minute observation, 5000 optical fibers are individually positioned by a close-packed array of 5000 robotic positioner mechanisms. Key mechanical constraints on the positioners are: ø12mm hardware envelope, ø14mm overlapping patrol zones, open-loop targeting accuracy ≤ 40μm, and step resolution ≤ 5μm, among other requirements on envelope, power, stability, and speed. This paper describes the design and performance of a newly-developed fiber positioner with R-θ polar kinematics, in which a flexure-based linear R-axis is stacked on a rotational θ-axis. Benefits over the usual eccentric parallel axis θ-φ kinematic approach include faster repositioning, simplified anti-collision schemes, and inherent anti-backlash preload. Performance results are given for complete positioner assemblies as well as sub-component hardware characterization.