Jefferson Laboratory is developing a set of innovative superconducting magnets for the 12 GeV upgrade in JLAB Hall C. We will report on the finite element analysis (FEA) of the force collar for the ...Super High Momentum Spectrometer Cosine Theta Dipole magnet. The force collar is designed with an interference fit and intended to provide enough pressure after cool down to operating temperature to counteract Lorentz forces acting on the dipole coil during operation. By counteracting the Lorentz forces and keeping the coil pack in overall compression, movement of the coils is expected to be minimized. The dimensional geometry of the cold mass is maintained in the commercial solid modeling code UG/I-DEAS while the magnetic field design is maintained in the commercial TOSCA code from Vector Fields. The three dimensional FEA was conducted in the commercial codes ANSYS and IDEAS. The method for converting the models and calculating the loads transferred to the structure is discussed. The results show the cold mass response to: force collar assembly preload, differential thermal contraction, and operational Lorentz loads. Evaluations are made for two candidate force collar materials and two candidate force collar designs.
The 12 GeV upgrade at Jefferson Lab has identified two new large spectrometers as Physics detectors for the project. The first is a 7.5 Gev/c 35 m-sr. spectrometer that requires a pair of identical ...Combined Function Superconducting Magnets (CFSM) that can simultaneously produce 1.5 T dipole fields and 4.5 T/m quadrupole fields inside a warm bore of 120cm. The second is an 11 GeV/c 2 m-sr. spectrometer that requires a CFSM that simultaneously produces a dipole field of 4.0 T and a quadruple field of 3.0 T/m in a 60 cm warm bore. Magnetic designs using TOSCA 3D have been performed to realize the magnetic requirements, provide 3d fields for optics analysis and produce field and force information for the engineering feasibility of the magnets. A two-sector cos(/spl theta/)/cos(2/spl theta/) design with a low nominal current density, warm bore and warm iron design has been selected and analyzed. These low current densities are consistent with the limits for a cryostable winding. The current paper will summarize the requirement definition of these two magnets. The conceptual design arrived at during the feasibility study involving the choice of conductors, thermal and structural analyses will be presented. A discussion of the manufacturing approach and challenges will be provided.
The GlueX beamline and detector Akondi, C.S.; Barbosa, F.; Barsotti, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2021, Letnik:
987
Journal Article
Recenzirano
Odprti dostop
The GlueX experiment at Jefferson Lab has been designed to study photoproduction reactions with a 9-GeV linearly polarized photon beam. The energy and arrival time of beam photons are tagged using a ...scintillator hodoscope and a scintillating fiber array. The photon flux is determined using a pair spectrometer, while the linear polarization of the photon beam is determined using a polarimeter based on triplet photoproduction. Charged-particle tracks from interactions in the central target are analyzed in a solenoidal field using a central straw-tube drift chamber and six packages of planar chambers with cathode strips and drift wires. Electromagnetic showers are reconstructed in a cylindrical scintillating fiber calorimeter inside the magnet and a lead-glass array downstream. Charged particle identification is achieved by measuring energy loss in the wire chambers and using the flight time of particles between the target and detectors outside the magnet. The signals from all detectors are recorded with flash ADCs and/or pipeline TDCs into memories allowing trigger decisions with a latency of 3.3 μs. The detector operates routinely at trigger rates of 40 kHz and data rates of 600 megabytes per second. We describe the photon beam, the GlueX detector components, electronics, data-acquisition and monitoring systems, and the performance of the experiment during the first three years of operation.
Advances in audio recognition have enabled the real-world success of a wide variety of interactive voice systems over the last two decades. More recently, these same techniques have shown promise in ...recognizing non-speech audio events. Sounds are ubiquitous in real-world manipulation, such as the click of a button, the crash of an object being knocked over, and the whine of activation from an electric power tool. Surprisingly, very few autonomous robots leverage audio feedback to improve their performance. Modern audio recognition techniques exist that are capable of learning and recognizing real-world sounds, but few implementations exist that are easily incorporated into modern robotic programming frameworks. This paper presents a new software library known as the ROS Open-source Audio Recognizer (ROAR). ROAR provides a complete set of end-to-end tools for online supervised learning of new audio events, feature extraction, automatic one-class Support Vector Machine model tuning, and real-time audio event detection. Through implementation on a Barrett WAM arm, we show that combining the contextual information of the manipulation action with a set of learned audio events yields significant improvements in robotic task-completion rates.
We present a search at the Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling α' to electrons. Such a particle A' can be produced in electron-nucleus ...fixed-target scattering and then decay to an e + e- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175-250 MeV, found no evidence for an A'→ e+ e- reaction, and set an upper limit of α'/α ~/= 10(-6). Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.
Our experience with chordoma treatment Brindza, P; Chaloupka, R; Grosman, R
Acta chirurgiae orthopaedicae et traumatologiae Čechoslovaca
76, Številka:
5
Journal Article
Recenzirano
The aim of the study was to evaluate the group of patients operated on for chordoma at our department. We present diagnostic and surgical management options relevant to the localisation of chordoma ...in the spine, and evaluate the results in terms of post-operative complications, tumour recurrence and patient survival.
Between 1989 and 2002 a total of 20 patients diagnosed with chordoma were treated. There were 15 men and five women with an average age of 53 years. The cervical spine was affected in 20 %, thoracic in 15%, lumbar in 25 % and sacral in 40 % of the patients. All of them suffered from back pain, and nine patients (45 %) had neurological symptoms. The average time from the onset of complaints till disease diagnosis was 7.2 months.
The average survival time was 63 months, with eight patients (40 %) surviving for more than five years. Of the patients with chordoma of the mobile spine, 66 % were treated by a combined antero-posterior procedure involving somatectomy, vertebral body replacement and posterior stabilisation; for sacral spine chordoma, a dorsal approach was always used. Of 11 patients (55 %) who required repeat surgery, eight had recurrent tumour and three had wound infection.
Chordomas are rare, slow-growing tumours usually diagnosed with a delay, particularly when localised in the sacral spi- ne. At present magnetic resonance imaging is the essential diagnostic method allowing us to plan the appropriate surgical management.When the mobile spine is affected, a combined antero-posterior procedure including somatectomy, vertebral body replacement with a graft or implant and posterior stabilisation is used.When the sacral spine is involved, some authors prefer en bloc resection from the posterior approach, others use a combined antero-posterior procedure. Chordomas are known to have a high risk of local recurrence. Post-operative radiotherapy, which makes the disease-free interval longer, is recommendedúúú chemotherapy has no effect.
Chordomas are associated with serious diagnostic and therapeutic problems, with frequent local recurrence. Prognosis is good if early diagnosis is made, and en bloc resection is performed.
We report on the design, fabrication, commissioning and operation of a large superconducting magnet system that is an important element of the 8 sector super conducting toroidal G0 Spectrometer ...located at Jefferson Lab (JLAB) in Newport News, VA. The purpose of the G0 experiment is the high precision measurement of polarized electron scattering by protons to isolate the strange quark content of normal baryonic matter by observing parity violation caused by the weak interaction. The G0 spectrometer has been operating for three years and first results are submitted for publication . The G0 SC torus is 4 meters long and 4 meters outside diameter and produces 3 Tesla in the 8 gaps that are accessible to particles. The realization of this 8 sector superconducting toroidal magnet required the development of a number of challenging large scale features including: large total open solid angle, high sector-sector field symmetry, the symmetry axis aligned perpendicular to gravity, the location of the liquid hydrogen (proton) target on axis in the magnet cryostat, and large surface area but thin titanium exit windows on one end of the cryostat. The cryostat consists of a super-alloy welded low permeability stainless steel shell (to minimize magnetization effects) and aluminum end caps. The 8 superconducting coils have unique characteristics including dry pancake wound copper stabilized NbTi conductors, encased in aluminum structure, mechanically preloaded and indirectly cooled by a set of parallel thermo siphon circuits. This magnet was built by BWXT under a fixed price performance contract that included fabrication to a defined ideal cold current spatial distribution. The commissioning and operations will be discussed
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