Intensity issues and machine protection of the HE-LHC

The HE-LHC study investigates the possibilities for upgrading the beam energy of the Large Hadron Collider CERN from 7 TeV to 16.5 TeV. This paper presents a preliminary investigation of intensity issues and machine protection for the HE-LHC.Comment: 4 pages, contribution to the EuCARD-AccNet-EuroLumi Workshop: The High-Energy Large Hadron Collider, Malta, 14 -- 16 Oct 2010; CERN Yellow Report CERN-2011-003, pp. 124-12

Operational Experience with LHC Collimation

A first sub-set of the collimation system has been installed for the 2008 first beam commissioning of the LHC. It included 88 collimators around the ring and the two injection lines. Each collimator has two jaws for which must be controlled and monitored with high precision. The LHC collimation system was put into operation from July to October 2008. The installed system is described and first results from system operation without and with beam are presented. It is shown that the LHC collimation system achieved the specified accuracy and reproducibility of jaw positioning. Next steps in collimation commissioning are described and planned system upgrades for high beam intensities are outlined

Simulations on a potential hybrid and compact attosecond X-ray source based on RF and THz technologies

We investigate through beam dynamics simulations the potential of a hybrid layout mixing RF and THz technologies to be a compact X-ray source based on Inverse Compton Scattering (ICS), delivering few femtoseconds to sub-femtosecond pulses. The layout consists of an S-band gun as electron source and a dielectric-loaded circular waveguide driven by a multicycle THz pulse to accelerate and longitudinally compress the bunch, which will then be used to produce X-ray pulses via ICS with an infrared laser pulse. The beam dynamics simulations we performed, from the photocathode up to the ICS point, allows to have an insight in several important physical effects for the proposed scheme and also in the influence on the achievable bunch properties of various parameters of the accelerating and transverse focusing devices. The study presented in this paper leads to a preliminary layout and set of parameters able to deliver at the ICS point, according to our simulations, ultrashort bunches (around 1 fs rms), at 15 MeV, with at least 1 pC charge and transversely focused down to around 10 um rms or below while keeping a compact beamline (less than 1.5 m), which has not yet been achieved using only conventional RF technologies. Future studies will be devoted to the investigation of several potential ways to improve the achieved bunch properties, to overcome the limitations identified in the current study and to the definition of the technical requirements. This will lead to an updated layout and set of parameters.Comment: To be published in Nucl. Inst. Meth. A as proceedings of the EAAC17 conference 9 pages, 11 figure

The Beam-Beam Interaction in the Presence of Strong Radiation Damping

The beam-beam interaction in electron-positron storage rings depends strongly on the radiation damping. It has been shown before that the achievable beam-beam tune shift (the beam-beam limit) is a function of the damping decrement (the damping rate per beam-beam interaction). The LEP collider has been operated and has delivered luminosity in the range of 45 GeV to 101 GeV. The beam-beam performance data from LEP is revisited and fitted with a simple model. The scaling of the beam-beam limit with the damping decrement is estimated

The regimes of polarization in a high energy e+e−e^{+}e^{-} storage ring

Several regimes of polarization must be considered for high-energy e /sup +/e/sup -/ storage rings. Based on a theoretical paper by Derbenev, Kontratenko and Skrinsky from 1979 we describe the different cases. Particularly, it is shown that from a certain high energy onwards the polarization degree is expected to increase with energy. This is in sharp contrast to the usually considered regime where the expected polarization level decreases for higher beam energies. The theory of Derbenev, Kontratenko and Skrinsky is applied to the LEP storage ring with its energy range from the Z at 91 GeV to the W at 200 GeV. Though the theoretical expectations for beam polarization at the highest beam energy remain low, it is shown that the depolarization can move into a new regime for LEP above 60 GeV. The high energy LEP is the first storage ring that operates in this new and experimentally unknown regime of beam spin dynamics. (6 refs)

Review of ultra high-gradient acceleration schemes, results of experiments

A dramatic improvement in energy gain per unit cost is mandatory for the future of very high energy accelerators, for which RF-acceleration would be replaced by new tech-niques. Several schemes have been proposed (laser driven, beam driven accelerators) and tested. A critical review of these schemes and experimental results is presented, with considerations on the most promising techniques and the effort still needed. Important parameters for high luminos-ity (efficiency, emittance preservation, ...) are discussed

Measurements of heavy ion beam losses from collimation

The collimation efficiency for Pb ion beams in the LHC is predicted to be lower than requirements. Nuclear fragmentation and electromagnetic dissociation in the primary collimators create fragments with a wide range of Z/A ratios, which are not intercepted by the secondary collimators but lost where the dispersion has grown sufficiently large. In this article we present measurements and simulations of loss patterns generated by a prototype LHC collimator in the CERN SPS. Measurements were performed at two different energies and angles of the collimator. We also compare with proton loss maps and find a qualitative difference between Pb ions and protons, with the maximum loss rate observed at different places in the ring. This behavior was predicted by simulations and provides a valuable benchmark of our understanding of ion beam losses caused by collimation.Comment: 12 pages, 20 figure