F. Sannibale

Effects of nonlinear terms in the wiggler magnets at DA/spl Phi/NE

Analysis of the experimental observations and comparison with magnetic measurements have pointed out relevant nonlinear terms in the DA/spl Phi/NE wigglers and in the C corrector magnets. Different optics configurations aimed at reducing the impact of nonlinear terms have been studied and their effects on the collider performances are presented.

Status report on DA/spl Phi/NE

DA/spl Phi/NE, the Frascati LNF /spl Phi/-factory, is providing luminosity for the KLOE experiment since July 2000. A steady increase of daily integrated luminosity in KLOE has been obtained, due to interspersed machine physics studies. The main results are: increase of single bunch luminosity by reduction of the effects of nonlinear terms in the machine, background reduction, refill of the colliding beams while keeping the KLOE detector taking data and increase of stable stored current. A fraction of machine time has been used to tune luminosity and reduce background in the DEAR configuration. The luminosity delivered to DEAR was sufficient to conclude the first phase of the experiment.

The DAΦNE luminosity monitor

DAΦNE, the Frascati Φ-factory, is an e+/e− collider with 2 interaction points (IPs). The center of mass energy is 1020 MeV and the design luminosity 4.2×1030u200acm−2u200as−1 in single bunch mode and 5×1032u200acm−2u200as−1 in multibunch mode. Between the possible electromagnetic reactions at the interaction point, single bremsstrahlung (SB) has been selected for the luminosity measurement. The SB high counting rate allows real-time monitoring, which is very useful during machine tune-up and moreover the narrow peak of the SB angular distribution makes the counting rate almost independent from the beam position at the IP. A description of the experimental set-up, calibration results and luminosity measurements is presented.

DAΦNE beam instrumentation

DAΦNE, the Frascati Φ-Factory, is now under commissioning. The accelerator complex is composed of a linac, an accumulator-damping ring, and two separate main rings, one for electrons and the other for positrons, with two interaction regions in which the experiments will be placed. In order to achieve the luminosity goal, high performance instrumentation and beam diagnostics have been installed. Some of the relevant beam measurements performed are: beam emittance, transverse and longitudinal dimensions, beam positions and tunes, overlap in the interaction points, and luminosity. An overview of the diagnostic instrumentation of the accelerator complex is given together with measurement examples and discussion of operational experiences.

Proposal of an Experiment on Bunch Length Modulation in DAφNe

Obtaining very short bunches is an issue especially for colliders but also for CSR sources. The modulation of the bunch length in a strong rf focusing regime had been proposed, corresponding to a high value of the synchrotron tune. A ring structure where the function R56 along the ring oscillates between large positive and negative values will produce bunch length modulation. The synchrotron frequency can be tuned both by the rf power and by the integral of the function R56, up to the limit of zero value corresponding to the isochronicity condition. The proposal of a bunch length modulation along the ring in DAΦNE is here described. DAΦNE lattice can be tuned to positive or negative momentum compaction values, or to structures in which the two arcs are respectively set to positive/negative integrals of the R56 function. With the installation of an extra rf system at 1.3 GHz, experiments on bunch length modulation both in the regime of high and low synchrotron tune can be realized.

Non Linear Beam Dynamics at DAPHINE

Studies and measurements have been performed at DAΦ NE to improve dynamic aperture, beam lifetime and beam-beam performance. Measured tune scans for different working points are presented. After the measurement of an octupole-like term in the wiggler field, decoherence meas- urements with wigglers on and off have been performed. The effect of this cubic term on the chromaticity and dy- namic aperture is presented. . The Kloe experiment is routinely collecting data. The non-linearities present in the machine play a major role affecting the dynamic aperture, the beam lifetime, (with relation to the background and the integrated luminosity), and the beam-beam behaviour (single bunch luminosity). The study moved from extensive beam lifetime measurements vs. betatron tunes in both rings resulting in a high sensitivity of the machine to high order resonances (section 2). The deco- herence measurements, (dynamic tracking), with the wig- glers powered on and off show the effect of a strong dependence of the tune on the betatron amplitude oscillation, (section 3). The presence of a cubic term in the wiggler is accounted for the residual non-linear chromaticity of the machine even with sextupoles off. The strength of the octupole thin lens to be taken into account in each pole, found from the chromaticity measurements, agrees with the value obtained from the measurements of the betatron tunes vs. the localised orbit bumps inside the wiggler (6). The effect on the dynamic aperture is described in section 5.

Beam-beam experience at DA/spl Phi/NE

This paper summarizes the results of experimental observations and measurements of beam-beam interactions in DA/spl Phi/NE, the Frascati Phi-factory. The achieved results are reported with analysis of present limitations in both single and multibunch operation modes and compared with numerical simulations.

Non-linear beam dynamics at DA/spl Phi/NE

Studies and measurements have been performed at DA/spl Phi/NE to improve dynamic aperture, beam lifetime and beam-beam performance. Measured tune scans for different working points are presented. After the measurement of an octupole-like term in the wiggler field, decoherence measurements with wigglers on and off have been performed. The effect of this cubic term on the chromaticity and dynamic aperture is presented.

Beam steering and orbit control at DAFNE

The commissioning phase without experiments of DAFNE, the Frascati double ring F-factory, has been completed. Single bunch luminosity exceeding cm -2 sec -1 has been obtained. Accurate beam position control is mandatory for luminosity achievement. Each ring, 100 m long, is equipped with 45 Beam Position Monitors and 31 correctors per plane. The integer part of both betatron tunes is 5. The closed orbit of the two Main Rings of DAFNE is essentially dominated by the magnetic cross-talk between the two rings due to fringing fields of dipoles and wigglers, the cross-talk between some of the transfer line magnets and the rings, and the effect of the ion clearing electrodes in the electron ring, since the residual misalignments of the magnets are much better than the required tolerances. The horizontal reference for the closed orbit is complex because of the off-axis trajectories in the interaction regions (IR), the splitters which separate the two beams at the IR ends, the presence of wigglers, and finally the four different types of dipoles. The line along which quadrupoles and sextupoles have been aligned corresponds to the line defined by the nominal bending radius of the dipoles, and this line is taken as reference for the closed orbit. The aim of the closed orbit correction is the optimization of the coupling and the exact overlap of the two beams at the interaction points (IPs). Several closed orbit correction methods have been implemented and used: best corrector method, harmonic method, orbit decomposition by eigenvalue of the measured Response Matrix. Coupling of the order of few , well below the 1% design value, has been achieved in both rings, by correcting the vertical orbit within mm and the horizontal one within mm with respect to the reference line. Coupling tuning over a large range is easily obtained using the skew quadrupoles. The vertical overlap of both beams at the IP, critical since the vertical dimension of the interacting bunches is 20 mm, is obtained with localized steering bumps with 5 mm accuracy.