The new LUCID-2 detector for luminosity measurement and monitoring in ATLAS

An essential ingredient in all cross section measurements is the luminosity used to normalize the data sample. In this note, we present the final assessment of the integrated luminosity recorded by the D0 experiment during Tevatron Run IIa. The luminosity measurement is derived from hit rates from the products of inelastic proton-antiproton collisions registered in two arrays of scintillation counters called the luminosity monitor (LM) detectors. Measured LM rates are converted to absolute luminosity using a normalization procedure that is based on previously measured inelastic cross sections and the geometric acceptance and efficiency of the LM detectors for registering inelastic events. During Run IIa, the LM detector performance was improved by a sequence of upgrades to the electronic readout system and other factors summarized in this note. The effects of these changes on the reported luminosity were tracked carefully during the run. Due to the changes, we partition the run into periods for which different conversions from measured LM rates to absolute luminosity apply. The primary upgrade to the readout system late in Run IIa facilitated a reevaluation of the overall normalization of the luminosity measurement for the full data sample. In this note, we first review the luminosity measurement technique employed by D0. We then summarize the changes to the LM system during Run IIa and the corresponding normalization adjustments. The effect of the adjustments is to increase D0's assessment of its recorded integrated luminosity compared to what was initially reported during Run IIa. The overall increase is 13.4% for data collected between April 20, 2002 (the beginning of Run IIa data used for physics analysis) and February 22, 2006 (the end of Run IIa).

The LUCID-2 detector is the main online and ofline luminosity monitor of the ATLAS experiment. It is a compact Cherenkov detector made of photomultipliers with a 10 mm diameter quartz window acting as the Cherenkov medium. In order to provide a reliable luminosity measurement during years of data-taking, the LUCID-2 detector can use 104 different luminosity algorithms for each of the LHC colliding bunches. The detector stability is kept at a percent level thanks to an innovative monitoring system based on radioactive Bi-207 sources deposited on the photomultipliers quartz window. Combining the LUCID-2 measurement with those of other four ATLAS subdetectors, the luminosity has been estimated with a total uncertainty of 2.1% in 2015 and 2.2% in 2016.

The LUCID-2 detector is the main online and offline luminosity monitor of the ATLAS experiment. It provides 104 different luminosity measurements from different algorithms for each of the thousands of LHC bunches. The new detector is using the quartz windows of 10 mm diameter photomultipliers and optical quartz fibers as the Cherenkov medium. A main challenge for a luminometer is to keep the efficiency constant during years of data-taking. LUCID-2 is using an innovative calibration system based on radioactive Bi-207 sources deposited on the quartz window of the readout photomultipliers.

A luminosity monitor using photons from radiative bhabha events at the CLEO interaction point (IP) has been installed in the Cornell Electron Storage Ring (CESR) [1]. A key vacuum and detector component is the photon window/converter whose uniformity and thickness are critical for determining the resolution of the total energy deposited in the segmented luminosity monitor. The window design must accommodate the operational requirements of the new monitor at CLEO-c beam energies of 1.5-2.5 GeV and also provide sufficient safety margin for operation at 5.3 GeV beam energies for Cornell High Energy Synchrotron Source (CHESS) running. During 5.3 GeV operation, intense stripes of synchrotron radiation (SR) from the interaction region (IR) superconducting quadrupole magnets (SC Quads) as well as nearby bending magnets strike the window. During the course of window development, several materials and designs were considered. Thermal stresses were calculated using ANSYS for various beam conditions to guide the cooling design. A window using aluminum (Al) alloy 6061-T6 was ultimately chosen to provide optimal performance for both CLEO-c and CHESS running conditions. The window has been in successful operation since September 2004.

Throughout LHC (Large Hadron Collider) Run 2, the LUCID detector, that is located 10 cm from the beampipe on both sides of the interaction point (17 m on the z axis), has been the reference luminosity detector for the ATLAS experiment, providing the on-line and off-line luminosity measurement with high stability and a preliminary uncertainty of about 1.7%. For the high-luminosity LHC, new beampipe equipment and more demanding luminosity precision requirements and LHC beam conditions are expected. The detector will therefore be completely redesigned, exploiting both new and tried-and-tested technologies. Prototype detectors for the new running conditions and technologies have been developed and installed and will be tested during the upcoming Run 3. These consist of a detector based on PhotoMultiplier Tubes (PMT), which uses the quartz window as a Cherenkov medium and is positioned 30 cm from the beampipe, a low-rate PMT detector, located in the shadow of one of the ATLAS shieldings, and the fiber detector, in which fiber bundles are used as Cherenkov-light emitters and transmitters and that are calibrated with an innovative hybrid LED and radioactive-source system. In these prototypes, the behavior of new Hamamatsu R1635 and R7459 PMTs will be evaluated. In this contribution, the motivations for the detector redesign and a description of the LUCID upgrade are illustrated, as well as a detailed account of the preliminary tests performed with the prototypes, including PMT characterization and a study of the fiber degradation under irradiation.

Co‐60 tomotherapy is the treatment modality of choice for developing countries in transition toward IMRT

Pulsed UV laser-induced modifications in optical and structural characteristics of alpha-irradiated PM-355 SSNTD

In order to improve luminosity tuning and maintenance for the CLEO-c high energy physics (HEP) program at the Cornell Electron Storage Ring (CESR), a luminosity monitor using photons from radiative Bhabha events has been installed in the CESR ring. Over 8 meters of CESR vacuum chambers near the interaction region were modified to accommodate this new device. The vacuum modifications were designed to meet two criteria. First, the new vacuum chambers had to provide sufficient horizontal and vertical aperture for photons originating from the interaction point (IP) over a wide range of colliding beam conditions. Secondly, the new vacuum chambers required adequate safety margins for operation at beam energies up to 5.3 GeV for Cornell High Energy Synchrotron Source (CHESS) running. In order to be certain that the vacuum modifications would not give rise to any localized pressure bumps, a detailed calculation of the expected vacuum pressure distribution due to synchrotron radiation flux was carried out. Careful design and planning enabled a successful installation and resumption of CESR operations in record time.

Safe implementation and translation of FLASH radiotherapy to the clinic requirehs development of beam monitoring devices capable of high temporal resolution with wide dynamic ranges. Ideal detectors should be able to monitor LINAC pulses, withstand high doses and dose rates, and provide information about the beam output, energy/range, and profile. Two novel detectors have been designed and tested for ultra-high dose-rate (UHDR) monitoring: a multilayer nano-structured 3-layer high-energy-current (HEC3) detector, and a segmented large area, 4-section flat (S4) detector with the goal of exploring their properties for a future combined design. A Novalis-TX LINAC was converted to produce a 10 MeV electron-FLASH beam. Pulses were monitored using both HEC3 and S4 detectors. The HEC3 detector structure consisted of three electrode layers separated by a nanoporous aerogel (Aero): Al(50µm)-Aero(100µm)-Ta(10µm)-Aero(100µm)-Al(50µm). The S4 structure was comprised of three layers: Cu(100nm)-air(1mm)-Al(100nm) with contact potential for charge collection. Both detectors are self-powered as they do not require an external voltage bias for charge collection. The beam was also characterized using a photodiode, Gafchromic EBT-XD Film, OSLDs, and an Advanced Markus Chamber. The electron-FLASH beam displayed a Gaussian-like profile with 15cm FWHM at isocenter. Electron-FLASH dose rates up to an average of 260Gy/s were measured on the surface of a solid water phantom at isocenter with an instantaneous dose rate of 1.8×105Gy/s and a dose per pulse of up to 1Gy/pulse. Both HEC3 and S4 detectors could record individual pulses for repetition rates of 360Hz with a 4 µs pulse-width. The HEC3 detector signal increased linearly with dose, MU, number of pulses, and dose rate up to 850Gy/s with no loss of functionality at high doses or dose rates. The S4 detector showed linearity with MU and number of pulses at each of the four channels independently showing potential for spatial information and steering but lacked dose rate independence. Two novel detectors, HEC3 and S4, successfully measured electron-FLASH pulses and hence can be considered capable of electron-FLASH beam monitoring in different capacities. HEC3 detector technology is suitable for monitoring high-dose and UHDR beams with high temporal resolution required for pulse counting. We envision the combination of the HEC3 internal structure with the S4 piece-wise design for real-time monitoring of the temporal structure, spatial profiles, energy, and dosimetric properties of UHDR beams.

We report the result of evaluating radiation damage to Bicron BC408 plastic scintillator used in the DOslash Luminosity Monitor during Run IIa. The Luminosity Monitor provides pseudo-rapidity coverage over the range 2.7 < |eta| < 4.4, with the radiation dose in Run IIa estimated to be 0.5 MRad for the region closest to the beams. We find the light yield is degraded by 10-15 % due to radiation damage by comparing new and old scintillator in four observables: (i) visual inspection, (ii) optical transmittance, (iii) response to the radioactive source of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sup> Sr and (iv) light yield for cosmic rays.

We have designed and implemented a fast bunch-by-bunch luminosity monitor for BEPCII. Specially, the high speed electronics design fulfills the requirement to detect and record the event from one bunch pair within 4ns. In order to minimize the influence from very noisy environment of the collider, a couple of methods like discrimination, coincidence window and anti-coincidence techniques are adopted effectively. The preliminary experimental result shows that the hardware and software of the monitor system working well. From the result of the first operation in BEPCII collider, we can see that real time bunch by bunch monitor system will be very beneficial not only for monitoring the status of the collider machine but also for the stage of beam tuning.

A fast luminosity monitor system for PEP II

The luminosity monitor LUCID (LUminosity Cherenkov Integrating Detector) employed in the ATLAS experiment at the LHC had to be upgraded for the second run of LHC (Run 2) that started in spring 2015. The increased energy of the proton beams and the higher luminosity implied that the Photomultipliers of the original LUCID detector had to be replaced for Run 2 to cope with the more demanding conditions. This paper deals with choice and characterisation of the Photomultipliers used for the new version of LUCID.

Extensive use has been made of particle‐induced x‐ray emission (PIXE) analysis over the past several years. The optimization of its detection sensitivity calls for the judicious selection of several parameters including, inter alia, the beam energy used and the x‐ray window thickness. Thin windows are required in order to detect the light elements whose x‐ray energies are so low that they are heavily attenuated by any absorber material between the target and the detector. The choice of beam energy is dependant on the respective x‐ray production cross‐sections for elements of interest, the related background generated, as well as the associated beam energy degradation in the targets. These considerations often lead to a state where protons, elastically scattered from the target, have sufficient energy to penetrate the window and enter the x‐ray detector. The extent to which such protons and their related secondary electron production affect the energy spectrum resolution of intrinsic germanium and Si(Li) x‐ray detectors is demonstrated for a proton beam energy range from 2.1 to 3.5 MeV with a window thickness equivalent to the range of a 2.5 MeV proton.

This paper details the electro-thermal study of the sublimation phase on a zinc oxide surface. This thermodynamic process occurs when a ZnO target is bombarded by a pulsed electron beam source composed of polyenergetic electrons. The source delivers short pulses of 180 ns of electrons with energies up to 16 keV. The beam total current reaches 800 A and is focused onto a spot area 2 mm in diameter. The Monte Carlo CASINO program is used to study the first stage of the interaction and to define the heat source space distribution inside the ZnO target. Simulation of the second stage of interaction is developed in a COMSOL multiphysics project. The simulated thermal field induced by space and time heat conduction is presented. Typically for a pulsed electron beam 2 mm in diameter of electrons having energies up to 16 keV, the surface temperature reaches a maximum of 7000 K. The calculations are supported by SEM pictures of the target irradiated by various beam energies and numbers of pulses.