Mechanical design aspects of the LHC beam screen

Cruikshank, P.; Artoos, Kurt; Bertinelli, F.; Brunet, J.-C.; Calder, R.; Campedel, C.; Collins, I.R.; Dalin, J.-M.; Feral, Bruno; Gröbner, O.; Kos, N.; Mathewson, A. G.; Nikitina, L.; Nikitine, I.; Poncet, A.; Reymermier, C.; Schneider, Gerhard; Sexton, Ian; Sgobba, S.; Valbuena, R.; Veness, R.

doi:10.1109/pac.1997.753282

Cited by 10 publications

(8 citation statements)

References 5 publications

(3 reference statements)

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“…rolled sheet material without any particular machining and surface treatment and a 0.05 mm high purity copper layer, co-laminated onto a stainless steel. These samples may be considered as being representative for either conventional stainless steel vacuum chambers or for the proposed material for the LHC beam screen, respectively [2]. The colaminated copper samples have been studied firstly in their as-received state and subsequently after strong oxidation in air.…”

Section: Sample Preparationmentioning

confidence: 99%

Reflection of photons and azimuthal distribution of photoelectrons in a cylindrical beam pipe

Anashin

Malyshev

Fedorov

et al. 2000

Nuclear Instruments and Methods in Physics Research Section A:

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In a cryogenic proton accelerator, such as the LHC, the creation of an electron cloud and generated heat loads resulting from electron bombardment are strongly dependent on the azimuthal distribution of created photoelectrons. In this context, photon reflection and photoelectron yield measurements have been performed using a beam line on the VEPP-2M storage ring. Six electrodes, covering the complete vacuum chamber perimeter, were mounted such that they could be suitably biased, and while one electrode was irradiated with synchrotron radiation the resulting electron current of all others could be measured. A detailed description of the experimental apparatus and the results of the measurements of photon reflection and the azimuthal distribution of generated photoelectrons are presented.

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Section: Sample Preparationmentioning

confidence: 99%

Reflection of photons and azimuthal distribution of photoelectrons in a cylindrical beam pipe

Anashin

Malyshev

Fedorov

et al. 2000

Nuclear Instruments and Methods in Physics Research Section A:

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“…First, a set of Cu-coated high-Mn content stainless steel samples was studied. Such a surface is now considered to be the base line design for the beam screen in the arcs [10]. Thus, it is relevant to study the properties of different surface preparations such that it can be optimized in terms of the resulting electron yield.…”

Section: The Samplesmentioning

confidence: 99%

VUV photoemission studies of candidate Large Hadron Collider vacuum chamber materials

Cimino

Collins

Baglin

1999

Phys. Rev. ST Accel. Beams

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In the context of future accelerators and, in particular, the beam vacuum of the Large Hadron Collider (LHC), a 27 km circumference proton collider to be built at CERN, VUV synchrotron radiation (SR) has been used to study both qualitatively and quantitatively candidate vacuum chamber materials. Emphasis is given to show that angle and energy resolved photoemission is an extremely powerful tool to address important issues relevant to the LHC, such as the emission of electrons that contributes to the creation of an electron cloud which may cause serious beam instabilities and unmanageable heat loads on the cryogenic system. Here we present not only the measured photoelectron yields from the proposed materials, prepared on an industrial scale, but also the energy and in some cases the angular dependence of the emitted electrons when excited with either a white light (WL) spectrum, simulating that in the arcs of the LHC, or monochromatic light in the photon energy range of interest. The effects on the materials examined of WL irradiation and /or ion sputtering, simulating the SR and ion bombardment expected in the LHC, were investigated. The studied samples exhibited significant modifications, in terms of electron emission, when exposed to the WL spectrum from the BESSY Toroidal Grating Monochromator beam line. Moreover, annealing and ion bombardment also induce substantial changes to the surface thereby indicating that such surfaces would not have a constant electron emission during machine operation. Such characteristics may be an important issue to define the surface properties of the LHC vacuum chamber material and are presented in detail for the various samples analyzed. It should be noted that all the measurements presented here were recorded at room temperature, whereas the majority of the LHC vacuum system will be maintained at temperatures below 20 K. The results cannot therefore be directly applied to these sections of the machine until measurements at cryogenic temperatures, i.e., in the presence of cryosorbed gas layers, are obtained. However, these results are directly relevant to all the warm regions of the LHC vacuum system, such as the experimental vacuum chambers and warm element vacuum chambers in the insertion regions. [S1098-4402(99)

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“…The design of the beam screen (figure 1) is based on a 1mm-thick stainless steel tube coated on its inner surface with 50 µm copper 1 . Weakly supercritical helium, flowing in two stainless steel tubes of 3.7 mm inner diameter running on each side of the beam screen, maintain its temperature below 20 K, while intercepting the heat loads deposited by synchrotron radiation, resistive dissipation of beam image currents, and impact of photoelectrons resonantly accelerated by the circulating proton bunches 2 .…”

Section: Introductionmentioning

confidence: 99%

Stability and Control of Supercritical Helium Flow in the LHC Circuits

Hatchadourian

2000

Advances in Cryogenic Engineering

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The circulating particle beams of the Large Hadron Collider (LHC) will induce dynamic heat loads into the cryogenic system. Beam screens, maintained at a temperature between 5 K and 20 K by weakly supercritical helium -in order to avoid-two phase flow-are inserted inside the magnet cold bore to intercept most of these heat loads. Evidence has been presented in experimental and theoretical work that the main type of dynamic instability in long channels is that caused by the propagation of density waves due to multiple regenerative feedback. Oscillations are typically observed in circuits operating with low flow rate and/or high energy input. The study of the system behaviour under different operating cases permits assessment of the time constant of the system as well as its temperature-control parameters. A part of this work also concerns the study of flow stability in the other LHC cryogenic circuits working with supercritical helium. ABSTRACTThe circulating particle beams of the Large Hadron Collider (LHC) will induce dynamic heat loads into the cryogenic system. Beam screens, maintained at a temperature between 5 K and 20 K by weakly supercritical helium -in order to avoid-two phase floware inserted inside the magnet cold bore to intercept most of these heat loads. Evidence has been presented in experimental and theoretical work that the main type of dynamic instability in long channels is that caused by the propagation of density waves due to multiple regenerative feedback. Oscillations are typically observed in circuits operating with low flow rate and/or high energy input. The study of the system behaviour under different operating cases permits assessment of the time constant of the system as well as its temperature-control parameters. A part of this work also concerns the study of flow stability in the other LHC cryogenic circuits working with supercritical helium.

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Mechanical design aspects of the LHC beam screen

Cited by 10 publications

References 5 publications

Reflection of photons and azimuthal distribution of photoelectrons in a cylindrical beam pipe

Reflection of photons and azimuthal distribution of photoelectrons in a cylindrical beam pipe

VUV photoemission studies of candidate Large Hadron Collider vacuum chamber materials

Stability and Control of Supercritical Helium Flow in the LHC Circuits

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