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M. Zobov

Publications and source records attributed to M. Zobov.

31 records · Page 2Linked to original sources
arXiv2007

Impact of Ion Clearing Electrodes on Beam Dynamics in DAFNE

Presently clearing electrodes are being considered as a possible cure of e-cloud driven problems in existing and future colliders. 'Invisible' electrodes, made of a thin highly resistive layer pasted on a dielectric plate, have been proposed as one of design solutions for the e-cloud clearing. For the first time such electrodes were successfully used in the electron-positron accumulator (EPA) of LEP. Similar electrodes had been using for a long time for ion clearing purposes in the DAFNE electron ring. Theoretical considerations and experimental measurements at DAFNE have revealed a substantial contribution of the ion clearing electrodes (ICE) to the machine broad-band impedance giving rise to several harmful effects degrading the collider performance. In this paper we discuss the impact of the electrodes on DAFNE beam dynamics, show the results of ICE wake field and impedance calculations and compare them with available experimental data. We also describe the procedure of ICE removal from the wiggler sections of the electron ring that has resulted in remarkable improvements in terms of beam dynamics and geometric luminosity.

physics.acc-ph↗
arXiv2007

Beam-Beam Issues for Colliding Schemes with Large Piwinski Angle and Crabbed Waist

Numerical simulations have shown that a recently proposed 'crabbed waist' scheme of beam-beam collisions can substantially increase the luminosity of a collider. In this paper we give a qualitative explanation why this scheme works. For this purpose we use simple geometrical considerations and analyze peculiar properties of vertical motion modulations by synchrotron and horizontal betatron oscillations. It is shown that in the 'crabbed waist' scheme these modulations, which are the main sources of beam-beam resonances excitation, are significantly suppressed. Some numerical examples demonstrating the effect of the crabbed waist collisions are also given.

physics.acc-ph↗
arXiv2006

Wire Compensation of Parasitic Crossings in DAFNE

Long-range beam-beam interactions (parasitic crossings) are one of the main luminosity performance limitations for the Frascati e+e- Phi-factory DAFNE. In particular, the parasitic crossings lead to a substantial lifetime reduction of both beams in collision. This puts a limit on the maximum storable current and, as a consequence, on the achievable peak and integrated luminosity. In order to alleviate the problem numerical and experimental studies of the parasitic crossings compensation with current-carrying wires have been performed at DAFNE. Two such wires have been installed at both ends of the KLOE interaction region. Switching on the wires in agreement with the numerical predictions, improvement in the lifetime of the 'weak' beam (positrons) has been obtained at the maximum current of the 'strong' one (electrons) without luminosity loss. In this paper we describe the parasitic crossings effects in DAFNE, summarize the results of numerical simulations on their compensation with the wires and discuss the experimental measurements and observations.

physics.acc-ph↗
arXiv2006

DAFNE Experience with Negative Momentum Compaction

There are several potential advantages for a collider operation with a lattice with negative momentum compaction factor (alfa). Since the lattice of the Frascati e+e- Phi-factory DAFNE is flexible enough to provide collider operation even with alfa < 0, we have exploited this possibility for an experimental study of the beam dynamics. The negative momentum compaction lattices have been successfully implemented and stable 1 A currents have been stored in both electron and positron rings without any problem for RF cavities and feedback systems operation. First collisions have been tested at low currents. In this paper we describe the experimental results and compare them with expectations and numerical simulations. Present limitations to DAFNE operation with alfa < 0 and ways to overcome them are also discussed.

physics.acc-ph↗
arXiv2004

Design considerations for future DAFNE upgrade

The Frascati F-Factory DAFNE has been delivering luminosity to the KLOE, DEAR and FINUDA experiments since year 2000. Since April 2004 the KLOE run has been resumed and recently peak luminosity of 1.0x1032 cm-2s-1 and integrated luminosity of 6.2 pb-1/day have been achieved. The scientific program of the three high-energy experiments sharing DAFNE operation will be completed approximately by the end of year 2006. A scientific program for DAFNE beyond that date has not been defined yet and it is matter of discussion in the high-energy physics and accelerator physics communities. In this paper we present some future scenarios for DAFNE, discussing the expected ultimate performances of the machine as it is now and addressing the design for an energy and/or luminosity upgrade. The options presented in the following are not exhaustive and they are intended to give a glance of what is doable using the existing infrastructures.

physics.acc-ph↗
arXiv2004

DAFNE operation with the FINUDA experiment

DAFNE operation restarted in September 2003, after a six month shut-down for the installation of FINUDA, a magnetic detector dedicated to the study of hypernuclear physics. FINUDA is the third experiment running on DAFNE and operates while keeping on place the other detector KLOE. During the shut-down both Interaction Regions have been equipped with remotely controlled quadrupoles in order to operate at different solenoid fields. Among many other hardware upgrades one of the most significant is the reshaping of the wiggler pole profile to improve the field quality and the machine dynamic aperture. Commissioning of the collider in the new configuration has been completed in short time. The peak luminosity delivered to FINUDA has reached 6 10^31 s-1cm-2, with a daily integrated value close to 4 pb-1.

physics.acc-ph↗
arXiv2004

DAFNE

The results of 2002 DAFNE operation for the two experiments KLOE and DEAR are described. During 2003 a long shutdown has been dedicated to the installation of new Interaction Regions (IR) and to hardware modifications and upgrades. In the last section optics studies and performances expectations for the new machine configuration are reported.

physics.acc-ph↗
arXiv2004

Strong RF focusing for luminosity increase: short bunches at the IP

One of the key-issues to increase the luminosity in the next generation particle factories is to reduce the bunch length at the interaction point (IP) as much as possible. This will allow reducing proportionally the transverse beta functions at the IP and increasing the luminosity by the same factor. The strong RF focusing consists in obtaining short bunches by substantially increasing the lattice momentum compaction and the RF gradient. In this regime the bunch length is modulated along the ring and could be minimized at the IP. If the principal impedance generating elements of the ring are located where the bunch is long (in the RF cavities region) it is possible to avoid microwave instability and excessive bunch lengthening due to the potential well distortion.

physics.acc-ph↗
arXiv2004

High Luminosity Issues for DAPhNE Upgrade

We give an overview of presentations and discussions during the Accelerator Working Group Session dedicated to High Luminosity Issues for a future upgrade of the Frascati e+e- Phi-Factory DAPhNE at the Workshop "e+e- in the 1-2 GeV range: Physics and Accelerator Prospects" held at Alghero (Italy) on 10-13 September 2003.

physics.acc-ph↗
arXiv2003

Crosstalk between beam-beam effects and lattice nonlinearities in DAPhNE

Numerical simulations of beam-beam effects in the electron-positron Phi-factory DAPhNE taking into account the measured cubic nonlinearities have shown that the nonlinearities have a strong impact on the collider luminosity performance. The numerical results explain many of experimental observations made during collisions in both single and multibunch regimes.

physics.acc-ph↗
arXiv2003

Strong RF Focusing for Luminosity Increase

A luminosity of a circular collider can be increased by squeezing the bunch length at the interaction point (IP). A natural way to decrease the bunch length is to decrease the momentum compaction factor and/or to increase the RF voltage. However, in such a way we cannot obtain short bunches with high currents since wakefields prevent this due to the potential well distortion and the microwave instability. In present paper we propose to use a strong RF focusing (with high RF voltage and high momentum compaction factor) to obtain very short bunches at the IP with progressive bunch elongation towards the RF cavity. This allows placing the most important impedance generating elements near the RF cavity where the bunch is longest thus minimizing the effect of the wakefields.

physics.acc-ph↗
arXiv2003

Wake Fields and Impedance

Knowledge of the electromagnetic interaction between a beam and the surrounding vacuum chamber is necessary in order to optimize the accelerator performance in terms of stored current. Many instability phenomena may occur in the machine because of the fields produced by the beam and acting back on itself as in a feedback device. Basically, these fields produce an extra voltage and energy gain, affecting the longitudinal dynamics, and a transverse momentum kick which deflects the beam. In this paper we describe the main features of this interaction with typical machine components.

physics.acc-ph↗