Loss Of Longitudinal Landau Damping in the LHC Injectors

A large number of collective instability mechanisms act on high-intensity beams. It is necessary to determine under what conditions the beam will remain stable. Space charge is the most fundamental mechanism and it represents the main intensity limitation in low-energy machines, while at high energy the inductive chamber impedance is often dominant. Landau damping provides a natural stabilizing mechanism against collective effects, if particles in the beam have a small spread S in their natural frequencies. The purpose of this report is to study the loss of Landau damping for the longitudinal plane via the âﾜSacherer formalismâ. Stability limits are calculated for several longitudinal beam distributions, including two types of flat bunches, which could be of interest to the LHC upgrade. Landau stability diagrams are computed and presented for different azimuthal modes. A general recipe is given for calculating the threshold intensity in the case of a capacitive impedance below transition or, equivalently, for a purely inductive impedance above transition. Results are finally applied to the case of the PS Booster, as an example of space-charge impedance below transition, and to the SPS, as an example of inductive impedance above transition

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3D UK? 3D History and the Absent British Pioneers

The recent television ‘rediscovery’ of a small cohort of 1950s British 3D films (and the producers who made them) has offered a new route into considering how the historical stories told about 3D film have focused almost exclusively on the American experience, eliding other national contexts. This article challenges both the partiality of existing academic histories of 3D, and the specific popular media narratives that have been constructed around the British 3D pioneers. Offering a rebuttal of those narratives and an expansion of them based around primary archival research, the article considers how the British 3D company Stereo Techniques created a different business and production model based around non-fiction short 3D films that stand in contrast to the accepted view of 3D as an American feature film novelty. Through an exploration of the depiction (and absence) of these 3D pioneers from existing media histories, the article argues for a revision to both 3D studies and British cinema history