Table of contents

The ATLAS TRT barrel is a tracking drift chamber using 52,544 individual tubular drift tubes. It is one part of the ATLAS Inner Detector, which consists of three sub-systems: the pixel detector spanning the radius range 4 to 20 cm, the semiconductor tracker (SCT) from 30 to 52 cm, and the transition radiation tracker (TRT) from 56 to 108 cm. The TRT barrel covers the central pseudo-rapidity region |η|< 1, and the TRT while endcaps cover the forward and backward eta regions. These TRT systems provide a combination of continuous tracking with many measurements in individual drift tubes (or straws) and of electron identification based on transition radiation from fibers or foils interleaved between the straws themselves. This paper describes the recently-completed construction of the TRT Barrel detector, including the quality control procedures used in the fabrication of the detector.

A straw proportional counter is the basic element of the ATLAS Transition Radiation Tracker (TRT). Its detailed properties as well as the main properties of a few TRT operating gas mixtures are described. Particular attention is paid to straw tube performance in high radiation conditions and to its operational stability.

We report promising initial results obtained with new resistive-electrode GEM (RETGEM) detectors manufactured, for the first time, using screen printing technology. These new detectors allow one to reach gas gains nearly as high as those achieved using ordinary GEM-like detectors with metallic electrodes. However, due to the high resistivity of its electrodes the RETGEM, in contract to traditional hole-type detectors, have the advantage of being fully spark protected. A primary benefit of these new RETGEMs is the availability of screen printing technology to many research laboratories; this accessibility encourages the possibility to manufacture these GEM-like detectors with the electrode resistivity easily optimized for particular experimental or practical applications.

For an efficient data taking, the Electromagnetic Calorimeter data of the CMS experiment must be limited to 10% of the full event size (1MB). Other requirements limit the average data size to 2kB per data acquisition link. These conditions imply a reduction factor of close to twenty on the data collected. The data filtering in the readout of the Electromagnetic Calorimeter detector is discussed. Test beam data are used to study the digital filtering applied in the readout channels and a full detector simulation allows to estimate the energy thresholds to achieve the desired data suppression factor.

Forward calorimeters, located near the incident beams, complete the nearly 4π coverage for high p_T particles resulting from proton-proton collisions in the ATLAS detector at the Large Hadron Collider at CERN. Both the technology and the deployment of the forward calorimeters in ATLAS are novel. The liquid argon rod/tube electrode structure for the forward calorimeters was invented specifically for applications in high rate environments. The placement of the forward calorimeters adjacent to the other calorimeters relatively close to the interaction point provides several advantages including nearly seamless calorimetry and natural shielding for the muon system. The forward calorimeter performance requirements are driven by events with missing E_T and tagging jets.

The main objective of this research is to introduce a newly developed device called "Adaptive Quality Control Phantom" (AQCP) designed to perform the QC tests. AQCP is the computer-controlled phantom which positions and moves a radioactive source in the Field of View (FOV) of an imaging nuclear medicine device on a definite path to produce any spatial distribution of gamma rays to simulate QC phantoms. To establish and prove the proper functionality and the accurate performance of AQCP, different tests that include systematic uniformity, collimator hole angulation and center of rotation were conducted by this device and the results, findings and differences of these tests as compared with the QC classic method tests are discussed and analyzed in detail in this paper. According to the different tests carried out by AQCP, the authors achieved the following: the performance of systematic uniformity test shows a considerable reduction in the technologist dose compared to the IAEA-TECDOC-602 method. The collimator hole angulation for LEHR, LEUHR and LEHS collimators were measured by using a point source and computer-controlled cylindrical positioning, the results of which show that the measurement accuracy for absolute angulation errors is better than 0.018 degrees. A method for center of rotation assessment by AQCP is introduced and the results of this proposed method as compared with the routine QC test and their differences are discussed in detail. Based on the discussion made in this paper regarding AQCP, the authors believe that this device is able to simulate QC phantoms.

A precise and efficient quantized multiple sinusoids signal estimation algorithm is presented. For different initial conditions obtained using classical spectral estimation algorithms the final solution of our algorithm is not unique. We start to minimize a nonlinear cost function. The accuracy of the initial values of iterations has a large influence on the speed of convergence. An iterative process is performed to reduce the cost function. Algorithm stops when quantization conditions are satisfied. Our algorithm is computationally efficient.

The ATLAS SemiConductor Tracker (SCT) is one of the largest existing semiconductor detectors. It is situated between the Pixel detector and the Transition Radiation Tracker at one of the four interaction points of the Large Hadron Collider (LHC). During 2006-2007 the detector was lowered into the ATLAS cavern and installed in its final position. For the assembly, integration and commissioning phase, a complete Detector Control System (DCS) was developed to ensure the safe operation of the tracker. This included control of the individual powering of the silicon modules, a bi-phase cooling system and various types of sensors monitoring the SCT environment and the surrounding test enclosure. The DCS software architecture, performance and operational experience will be presented in the view of a validation of the DCS for the final SCT installation and operation phase.

Ionization chambers working in ambient air in current detection mode are attractive due to their simplicity and low cost and are widely used in several applications such as smoke detection, dosimetry, therapeutic beam monitoring and so on. The aim of this work was to investigate if gaseous detectors can operate in ambient air in pulse counting mode as well as with gas amplification which potentially offers the highest possible sensitivity in applications like alpha particle detection or high energy X-ray photon or electron detection. To investigate the feasibility of this method two types of open- end gaseous detectors were build and successfully tested. The first one was a single wire or multiwire cylindrical geometry detector operating in pulse mode at a gas gain of one (pulse ionization chamber). This detector was readout by a custom made wide -band charge sensitive amplifier able to deal with slow induced signals generated by slow motion of negative and positive ions. The multiwire detector was able to detect alpha particles with an efficiency close to 22%. The second type of an alpha detector was an innovative GEM-like detector with resistive electrodes operating in air in avalanche mode at high gas gains (up to 10⁴). This detector can also operate in a cascaded mode or being combined with other detectors, for example with MICROMEGAS. This detector was readout by a conventional charge -sensitive amplifier and was able to detect alpha particles with 100% efficiency. This detector could also detect X-ray photons or fast electrons. A detailed comparison between these two detectors is given as well as a comparison with commercially available alpha detectors. The main advantages of gaseous detectors operating in air in a pulse detection mode are their simplicity, low cost and high sensitivity. One of the possible applications of these new detectors is alpha particle background monitors which, due to their low cost can find wide application not only in houses, but in public areas: airports, railway station and so on.

New type of radiation in crystals is predicted and investigated in computer simulation. It is shown that process of volume reflection of electrons and positrons in bent crystals is accomplished with high-power radiation of photons. Volume reflection radiation has intensity comparable with known channeling radiation, but it is less sensitive to entrance angle and sign of charge of a particle. Simulated spectra of radiation power are presented for 10 GeV and 200GeV particles.

Beam conditions and the potential detector damage resulting from their anomalies have pushed the LHC experiments to build their own beam monitoring devices. The ATLAS Beam Conditions Monitor (BCM) consists of two stations (forward and backward) of detectors each with four modules. The sensors are required to tolerate doses up to 500 kGy and in excess of 10¹⁵ charged particles per cm² over the lifetime of the experiment. Each module includes two diamond sensors read out in parallel. The stations are located symmetrically around the interaction point, positioning the diamond sensors at z = ±184 cm and r = 55 mm (a pseudo- rapidity of about 4.2). Equipped with fast electronics (2 ns rise time) these stations measure time-of-flight and pulse height to distinguish events resulting from lost beam particles from those normally occurring in proton-proton interactions. The BCM also provides a measurement of bunch-by-bunch luminosities in ATLAS by counting in-time and out-of-time collisions. Eleven detector modules have been fully assembled and tested. Tests performed range from characterisation of diamond sensors to full module tests with electron sources and in proton testbeams. Testbeam results from the CERN SPS show a module median-signal to noise of 11:1 for minimum ionising particles incident at a 45-degree angle. The best eight modules were installed on the ATLAS pixel support frame that was inserted into ATLAS in the summer of 2007. This paper describes the full BCM detector system along with simulation studies being used to develop the logic in the back-end FPGA coincidence hardware.

Since the summer of 2005, the vacuum ultra-violet Free-electron LASer in Hamburg (FLASH) has operated as a user facility at the Deutsches Elektronen-Synchrotron (DESY), delivering ultra-short laser pulses of tens of femtosecond duration with a high peak brilliance of up to 10²⁸ photons/(s mm² mrad² 0.1% bandwidth). Due to the statistics of the Self-Amplified Spontaneous Emission (SASE) process, each photon pulse differs from the previous one in the number of modes per pulse, the wavelength (0.5% fluctuations) and the intensity, making experiments more complicated. Thus, for certain experiments the detailed knowledge of the beam properties on a shot-to-shot basis is mandatory. In this paper we describe an online method to gain spectral information about the individual Free-Electron Laser (FEL) pulses that is based on rare-gas photoionization and photoelectron spectroscopy.

One of the two ATLAS Forward Calorimeters (FCal), consisting of three modules, one behind the other, was exposed to particle beams of known energies in order to obtain the energy calibration. The data were taken in the H6 beamline at CERN in the summer of 2003, using electron and hadron beams with energies from 10 to 200 GeV. The beam test setup and collected data samples are described in detail. Using data samples taken with a minimal amount of material upstream of the calorimeter, the FCal response to electrons and pions, as measured by the linearity and resolution as a function of energy, is extracted and compared to ATLAS performance requirements.

The influence of air contamination on the VUV scintillation yield in gaseous argon at atmospheric pressure is investigated. We determine with a radioactive α-source the photon yield for various partial air pressures and different reflectors and wavelength shifters. We find that the time constant of the slow scintillation component depends on gas purity and is a good indicator for the total VUV light yield, while the fast component is not affected. This dependence is attributed to impurities destroying the long-lived triplet argon excimer state. The population ratio between the slow and the fast decaying excimer states is determined for α-particles to be 5.5 ± 0.6 in argon gas at 1100 mbar and room temperature. The measured decay time constant of the slow component is 3.140 ± 0.067 μs at a partial air pressure of 2 × 10⁻⁶ mbar.

Results of the first beam emittance measurements obtained at the SARAF 20 keV/u protons and deuterons low energy beam transport line were analyzed using the SCUBEEx code from SNS. In most of the measurements the code provides with robust emittance evaluation. However significant problems were encountered in the special cases of low currents beams. We found that use of the minimum ellipse rather than RMS ellipse as a SCUBEEx filter ellipse resulted in significant improvement in these cases.