[en] In this thesis, we present the experimental tuning procedures developed for the Arcs and for the Final Focus Section of the Stanford Linear Collider (SLC). Such tuning is necessary to maximize the luminosity, by minimizing the beam size at the interaction point, and to reduce backgrounds in the experiment. In the final Focus Section, the correction strategy must result from the principles of the optical design, which is based on cancellations between second order aberrations, and on the ability to measure micron-size beams typical of the SLC. In the Arcs, the corrections were designed after the initial commissioning, to make the system more error-tolerant, through a modification in the optical design, and to enable adjustements of the beam phase-space at the injection to the Final Focus System, through a harmonic perturbation technique inspired from circular accelerators. Although the overall optimization of the SLC is not entirely finished, an almost optimal set-up has been achieved for the optics of the Arcs and of the Final Focus Section. Beams with transverse sizes close to the nominal ones, of a few microns, have been obtained at the interaction point. We present and discuss our results and the optical limits to the present performance

[en] Because the SLC final IP spot is produced by an aberration-dominated optical system, all components and couplings between dimensions of transverse phase-space must be controlled in the experimental tuning algorithm. For equal emittances ε/sub x/ = ε/sub y/, this amounts to ten linear optics adjustments. These adjustments are coupled and depend non-linearly on phase-space parameters. A ten-dimensional non-linear fitting program is therefore used to match the lattice in the Final Focus to the input beam. Local orthogonal ''knobs'' are also defined for fine-tweaking around the initial solution, although this is not always practical because of steering from the lenses. The three final waist corrections are however fully orthogonal to the other seven optical adjustments. This means that they do not cause any of the other seven optical distortions. We refer to this as external orthogonality. They can also be made internally orthogonal. This means that each one of the three orthogonalized controls can be applied independently of the two others. It also allows one to simultaneously correct and determine the phase-space at the IP

[en] Among the many models and mechanisms proposed to explain the observed beam-beam effects in storage rings, one -the two dimensional single resonance model- appears to be particularly well suited to investigate and understand the familiar growth of vertical dimensions commonly seen in flat-beam operated e⁺e^- storage rings. In this paper, after a quick derivation of the method and a comparison of the results obtained with existing experimental data, the assumptions are discussed in order to explain why this elementary model does well in this particular feature of the beam-beam interaction

[en] A compact averaging procedure is worked out to study the beam-beam effect in storage rings, in the weak beam-strong beam case. In order to avoid difficulties with polynomial approximations beam-beam potential deriving from the assumed Gaussian charge distribution is used

[en] As soon as two SLC beams make it to the intersection region, both transverse offsets, spot sizes and shapes can be extracted from the pattern of angular deflections produced by the electromagnetic interaction of the two beams, as one is scanned across the other. These deflections, measured in two high resolution Beam Position Monitors (BPM) mounted symmetrically on both sides of the intersection point, will produce detectable signals allowing spot sizes to be tuned, even with the very low luminosities expected at turn on. They will also furnish a good signal to monitor beam centering and will therefore become an important part of the FFS feedback system. This note summarizes the formulae which will allow us to correlate BPM offset readings with the properties of the two beams, and describes the range and limitations of the technique in the case of SLC

[en] The non-linear beam-beam interaction can excite coupling resonances that enlarge vertical beam dimensions in flat-beam operated machines and are hence harmful to luminosity achievements. Two such resonances are examined here using a first order averaging procedure: 2 Qsub(y) - 4 Qsub(x) = integer and 4 Qsub(y) - 2 Qsub(x) = integer. The effect on vertical amplitudes, when frequency split falls within predicted resonance band limits, is investigated. Effective resonance bands, taking into account amplitude distributions, are indicated and the limitations of the method are discussed

[en] A technique is described for non-destructive measurement and monitoring of the steering offset of the electron and positron beams at the interaction point of the SLC, based on using stripline beam-position monitors to measure the centroid of one beam as it is deflected by the opposing beam. This technique is also expected to provide diagnostic information related to the spot size of the micron-size beams

[en] In the original SLC commissioning plans, it was thought that accumulated optical mismatch, generated by focusing errors in the whole machine, would be corrected at the very end, in the Final Focus. Dedicated correctors for optical matching and a special adjustment strategy were planned for this purpose, with a large tuning range of up to about a factor four in any dimension of the beam phase-space. With the present collimation and shielding arrangements, it is necessary to control the beam upstream of the Final Focus in order to inject a nearly matched phase-space there. We have developed and installed a new system of harmonic focusing corrections at the end of the SLC Arcs, to provide such control. The scheme consists of introducing small regular and skew focusing deviations at specific harmonics of the betatron frequency which the phase-space is specially sensitive to. The harmonics in question are the zeroeth harmonic and the second harmonic of the betatron frequency. The focusing deviations are introduced in the Arc lattice by perturbing the strengths of the combined function magnets with a set of appropriately rewired trim windings at their backleg. The corrections provide an efficient way for adjusting both for errors in the Arc lattice and for mismatch at the injection to the Arc, generated by the upstream systems. In this note, we describe the specification of this correction procedure as well as the present installation. Initial operational experience with this new method for adjusting beam-lines is presented elsewhere. 20 refs., 18 figs

[en] In this thesis, we present a phenomenological study of the beam-beam effect in e⁺e^- storage rings. We are in particular interested in the blow-up of the vertical dimension observed in this kind of accelerator. A detailed analysis of the electromagnetic field generated by the very flat bunches stored, and seen by the counter-rotating particles shows that two-dimensional non-linear resonances, which couple vertical and horizontal betatron oscillations, play a very important role. Moreover, the ''weak beam-strong beam'' approximation holds rather well in the case of very flat bunches. Perturbative analysis enables us to predict the effects from the strongest coupling resonance: 20sub(x)-20sub(y) = integer. We find that mainly the tails of the vertical distribution are affected, and we give a criterion concerning the optimal distance to this resonance in the case of a storage ring such as LEP. Finally, the results and in particular the validity of the single resonance approximation are checked through a numerical simulation

[en] Results from DELPHI on the Z⁰ → bb-bar partial width (Γ₍bb-bar)) and on the average B hadron semileptonic branching ratio (B_s.l.) are reviewed. Prospects are given for improving these measurements, using different complementary techniques. A new and potentially powerful method for extracting the branching ratio R_b with minimal errors is suggested, based on using the redundancy provided by two independent discriminators for bb-bar events. (R.P.) 12 refs., 3 figs