Spectral detection of simplicial communities via Hodge Laplacians

19 pages, 8 figures19 pages, 8 figures19 pages, 8 figure

Studies of the beam-beam interaction for the LHC

We have used the beam-beam simulation code CBI to study the beam-beam interaction for the LHC. We find that for nominal LHC parameters, and assuming only one bunch per beam, there are no collective (coherent) beam-beam instabilities. We have investigated the effect of sweeping one of the beams around the other (a procedure that could be used as a diagnostic for head-on beam-beam collisions), We find that this does not cause any problems at the nominal current, though at higher currents there can be beam blow-up and collective beam motion. (4 refs)

Start-Up of FEL Oscillator from Shot Noise

In free-electron laser (FEL) oscillators, as inself-amplified spontaneous emission (SASE) FELs, the buildup of cavitypower starts from shot noise resulting from the discreteness ofelectronic charge. It is important to do the start-up analysis for thebuild-up of cavity power in order to fix the macropulse width from theelectron accelerator such that the system reaches saturation. In thispaper, we use the time-dependent simulation code GINGER [1]toperformthis analysis. We present results of this analysis for theparameters of the Compact Ultrafast TErahertz FEL (CUTE-FEL) [2]beingbuilt atRRCAT

Free-electron lasers

Free-electron lasers (FELs) are lasers that use an electron beam from an accelerator to produce widely tunable, high power, ultrafast pulses of coherent radiation. FELs are today important sources of infrared and far-infrared radiation the world. Quasi-CW high-power FELs are also operational. FELs that operate on the self-amplified spontaneous emission principle are leading candidates for X-ray lasers and fourth-generation light sources. We discuss the physics, technology, advantages and applications of FELs, and explore the frontiers of X-ray and high-power FELs. We also present details of plans for a compact, ultrafast, terahertz free-electron laser in India

Energy transparency and symmetries in the beam-beam interaction

We have modified the beam-beam simulation code CBI to handle asymmetric beams and used it to look at energy transparency and symmetries in the beam-beam interaction. We find that even a small violation of energy transparency, or of the symmetry between the two beams, changes the character of the collective (coherent) motion; in particular, period-n oscillations are no longer seen. We speculate that the one-time observation of these oscillations at LEP, and the more ubiquitous observation of the flip-flop instability in colliders around the world, may be a consequence of breaking the symmetry between the electron and positron beams. We also apply this code to the asymmetric collider PEP-II, and find that for the nominal parameters of PEP-II, in particular, the nominal tune-shift parameter of ξ_{0}=0.03, there are no collective beam-beam issues. Collective quadrupole motion sets in only at ξ_{0}=0.06 and above, consistent with earlier observations for symmetric beams