Design and implementation of synchrotron radiation masks for LEP2

Estimates of photon flux for LEP2 have predicted unacceptable background levels within the detectors of the four LEP experiments. As part of the solution to this problem, synchrotron radiation masks have been installed within the experimental vacuum Chambers close to the interaction points. The photon flux calculations and specification for the masks have been laid-out by von Holtey et.al. [1]. This paper describes the design of the masks and outlines the principal technical issues overcome for their installation and alignment

Mechanical and Vacuum Stability Design Criteria for the LHC Experimental Vacuum Chambers

Four colliding beam experiments are planned for the Large Hadron Collider (LHC) requiring experimental vacuum chambers in the interaction region. The beam pipe should be as transparent as possible to scattered particles and detectors should be as close as possible to the interaction point, resulting in small diameter beam pipes. This, together with the bunched beam structure, makes ion induced pre ssure bump instability, well known from the Intersecting Storage Rings (ISR) at CERN, a potential problem. Adequate conductance, cleanliness of the beam pipes and efficient pumping are required to avo id this instability. Suppression of electron multipacting requires appropriate surface coatings and cleaning procedures. Small beam pipe diameters must provide the required beam stay clear and still a llow margin for alignment and stability inside detectors. Design criteria to ensure both local and global stability under static and dynamic mechanical loads are defined

Vacuum Calculations for the LHC Experimental Beam Chambers

The vacuum stability is studied for the LHC experimental beam vacuum chambers of ALICE, ATLAS, and CMS. The present baseline design includes sputtered Non-Evaporable Getter (NEG) coating over the whole chamber inner surface providing distributed pumping and an antimultipactor coating. The data are presented for the dominant gas species (H2, CH4, CO and CO2) in a baked system. It results that the distributed pumping is necessary for vacuum stability of CO. Lumped pumping with Sputter Ion Pumps (SIP) is also indispensable for the stability of CH4. The operational constraints with NEG technology are described

Vacuum Stability for Ion Induced Gas Desorption

Ion induced vacuum instability was first observed in the Intersecting Proton Storage Rings (ISR) at CERN and in spite of substantial vacuum improvements, it remained a limitation of the maximum beam current throughout the operation of the machine. Extensive laboratory studies and dedicated machine experiments were made during this period to understand the details of this effect and to identify ways of increasing the limit to higher beam currents. Stimulated by the recent design work for the LHC vacuum system, the interest in this problem has been revived with a new critical review of the parameters which determine the pressure run-away in a given vacuum system with high intensity beams

Design Aspects of the RF Contacts for the LHC Beam Vacuum Interconnects

The LHC requires a very low longitudinal and transverse beam coupling impedance, in particular at low frequencies. This implies an admissible DC contact resistance of less than 0.1 m$\Omega$ for the RF contacts inside the vacuum bellows which must carry the image current (up to 50 A peak) of the beam at each vacuum chamber interconnect. Technological aspects, measurement methods and test results are presented for the contacts which will be used in the LHC. The modified mechanical design and the justifications for specific choices will be discusse

Microstructural and mechanical characterization of yarns made from carbon nanotubes for the instrumentation of particle beams at CERN

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Beam Vacuum Interconnects for the LHC Cold Arcs

The design of the beam vacuum interconnect is described in this paper. Features include a novel RF bridge design to maximise lateral flexibility during cryostat Cold arcs of the LHC will consist of twin aperture dipole, quadrupole and corrector magnets in cryostats, operating at 1.9 K. Beam vacuum chambers, along with all connecting elements require flexible 'interconnects' between adjacent cryostats to allow for thermal and mechanical offsets foreseen during machine operation and alignment. In addition, the beam vacuum chambers contain perforated beam screens to intercept beam induced heat loads at an intermediate temperature. These must also be connected with low impedance RF bridges in the interconnect zones.alignment and so-called 'nested' bellows to minimise the required length of the assembly

Cutaneous Head and Neck Squamous Cell Carcinoma with Regional Metastases: The Prognostic Importance of Soft Tissue Metastases and Extranodal Spread

Extranodal spread (ENS) is an established adverse prognostic factor in metastatic cutaneous squamous cell carcinoma (cSCC); however, the clinical significance of soft tissue metastases (STM) is unknown. The aim of this study was to evaluate the prognosis of patients with STM from head and neck cSCC, and to compare this with that of node metastases with and without ENS. Patients with cSCC metastatic to the parotid and/or neck treated by primary surgical resection between 1987 and 2007 were included. Metastatic nodes > 3 cm in size were an exclusion criterion. A Cox proportional hazard model was used to determine the effect of STM adjusting for other relevant prognostic factors. The population included 164 patients with a median follow-up of 26 months. There were 8 distant and 37 regional recurrences. There were 22 were cancer-specific deaths, and 29 patients died. STM was a significant predictor of reduced overall (hazard ratio 3.3; 95% confidence interval 1.6-6.4; P = 0.001) and disease-free survival (hazard ratio 2.4; 95% confidence interval 1.4-4.1; P = 0.001) when compared to patients with node disease with or without ENS. After adjusting for covariates, STM and number of involved nodes were significant independent predictors of overall and disease-free survival. In metastatic cSCC of the head and neck, the presence of STM is an independent predictor of reduced survival and is associated with a greater adverse effect than ENS alone

Biographical interviews and imagined futures essay writing: users of two methods in conversation

This article reports on a conversation between users of two research methods, biographical interviews and imagined futures essay writing. A dialogue form is used to discuss these methods and their potential to be combined. The value of comparing research methods is discussed, and then the two methods are described and points of connection and contrast are explored. Although one method emphasises looking back while the other looks forward, the two have much in common, including the exercise of imagination, and discussion of individual agency and structural constraint. Both involve the construction of narratives that help understanding of people’s lives as individual trajectories set in broader social and historical contexts. The two methods are quite different but complementary, and possibilities for their combination in one project are identified. The article ends by reflecting on the benefits and drawbacks of using dialogue to consider how research methods sit alongside each other