Tunable Achromats and CLIC Applications

It is imperative for linear colliders that the bunch length be adjustable. In most cases bunch compression is required, but recently, in the design of the Compact LInear Collider (CLIC) RF Power Source, it was shown that bunch stretching may also be necessary. In some situations, both modes may be needed, which implies the need for tunable magnetic insertions. This is even more essential in a test facility, to span a wide experimental range. In addition, flexible tuning provides a better control of the stability of an isochronous insertion. To start a numerical search for a tunable insertion from scratch is very uncertain because the related phase space is very uneven. However, a starting point obtained with an analytical approximation is often sufficient to ensure convergence. Another advantage of the analytical treatment described in this paper is that it sheds light on the shape of the entire phase space. To achieve this the isochronous achromat developed previously has been given tuning capabilities by expanding the expressions obtained for its main parameters. An application to the future CLIC Test Facility (CTF3) is shown

Multi-step lining-up correction of the CLIC trajectory

In the CLIC main linac it is very important to minimise the trajectory excursion and consequently the emittance dilution in order to obtain the required luminosity. Several algorithms have been proposed and lately the ballistic method has proved to be very effective. The trajectory correction method described hereafter retains the main advantages of the latter while adding some interesting features. It is based on the separation of the unknown variables like the quadrupole misalignments, the offset and slope of the injection straight line and the misalignments of the beam position monitors (BPM). This is achieved by referring the trajectory relatively to the injection line and not to the average pre-alignment line and by using two trajectories each corresponding to slightly different quadrupole strengths. A reference straight line is then derived onto which the beam is bent by a kick obtained by moving the first quadrupole. The other quadrupoles are then aligned on that line. The quality of the correction depends mainly on the BPM's and micro-movers' resolution and on the stability of the quadrupole strengths. Simulation statistics show that the beam offset from the center-of the quadrupoles is typically 1.5 mu m r.m.s. (7 refs)

A Trajectory Correction based on Multi-Step Lining-up for the CLIC Main Linac

In the CLIC main linac it is very important to minimise the trajectory excursion and consequently the emittance dilution in order to obtain the required luminosity. Several algorithms have been proposed and lately the ballistic method has proved to be very effective. The trajectory method described in this Note retains the main advantages of the latter while adding some interesting features. It is based on the separation of the unknown variables like the quadrupole misalignments, the offset and slope of the injection straight line and the misalignments of the beam position monitors (BPM). This is achieved by referring the trajectory relatively to the injection line and not to the average pre-alignment line and by using two trajectories each corresponding to slightly different quadrupole strengths. A reference straight line is then derived onto which the beam is bent by a kick obtained by moving the first quadrupole. The other quadrupoles are then aligned on that line. The quality of the correction depends mainly on the BPM's and micro-movers' resolution and on the stability of the quadrupole strengths which should be at least of the order of 0.05 %. Although the beam follows a broken straight line, its offset from the center of the quadrupoles is typically 1.5 µm r.m.s

Analysis of a Symmetric Triplet and its Application to Ring Insertions

It is interesting to study the matching capability of a triplet for a large range of parameters and to cover all the possible solutions. Fully analytical treatments can be used for this purpose, when working with the thin lens approximation. Closed solutions and the conditions in which they exist are described for the special case of triplets with a symmetric geometrical arrangement. They define all possible matchings, which correspond to the requests or limits on the Twiss parameters that are specified, and then define the range of values that are obtainable for the betatron functions. Numerical extension to thick lenses gives the complete solutions for the retained cases. Applications are presented on insertion and lattice problems, with emphasis on the design for a possible isochronous ring that is part of the injection chain of the CLIC drive beam

Experimental insertions made of two symmetric triplets

The reported study is based on the analytical treatment developed for an experimental collider insertion made of two symmetric triplets,the inner triplet located near the interaction point (IP) and th e outer triplet preceding a regular lattice. These two triplets are assumed to be symmetric in their geometry and quadrupole strengths, but not in their Twiss parameters. The method is applied to an i nsertion of the type of an experimental LHC insertion. The drift between the IP and the first quadrupole is fixed and the inner triplet is constrained to achieve a beta-crossing with equal and opposit e slopes (alpha-values) in the two planes. The outer triplet acts then as a FODO transformer from beta-crossing to beta-crossing in order to match the lattice. The analysis provides in a given paramet er interval all the existing solutions for the distance between triplets and the total insertion length, as functions of one gradient and the quadrupole separation in the inner triplet. The variation of the quadrupole strengths when the beta-functions increase at the IP (detuning) is studied and the extension from thin lens to thick lens illustrated

Analysis of generic insertions made of two symmetric triplets

This paper reports on the study undertaken to explore the capabilities of a symmetric triplet to achieve the optics constraints required by the inner triplet of an insertion and more generally of a co mplete insertion made of two symmetric triplets to match a double focus to a FODO lattice. It is based on analytical treatment formulating a number of constraints equal to the parameters available. Th is thorough and systematic analysis made it possible to establish for an inner triplet as well as for a complete insertion the existence of solutions and to explicitly find out all the solutions, with out resorting to unguided numerical searches. As a by-product, a lattice transformer, made of a single triplet, that matches two different FODO cells has been singled out and studied in details. The r esults should be profitable in a number of cases. Here, the method is applied to an insertion of the type of an experimental LHC insertion in order to investigate its domain of validity and tunability

Preliminary design of the CLIC drive-beam transfer line

In the drive-beam generation complex of CLIC there is an important beam transfer line between the drive-beam accelerator and the drive- beam decelerators, where the 30 GHz RF power is generated in the decelerator structures In the drive-beam generation complex of CLIC there is an important beam transfer line between the drive-beam accelerator and the drive-beam decelerators, where the 30 GHz RF power is generated in the decelerator structures. The design proposed for this transport system is based on building blocks or beam optics subsystems, which have been individually studied in detail and can be combined in order to cover specific functions. One function consists of bending the beams wherever required by the geometrical layout, so as to preserve the bunch length and keep the bending arc compact and compatible with acceptable synchrotron radiation. Other functions are to adjust the path length of each drive beam for synchronism with the main-linac beam and to compress or stretch the bunch according to the needs. Furthermore, there are vertical and horizontal beam translations, isochronous or acting as a compressor, and b-function transformers for matching the optics. All these functions are necessary in the drive-beam transfer that precedes injection into the decelerators