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DAΦNE & KLOE: a nice interaction
   

In May 2010, the DAΦNE accelerator begins operation with the new, improved KLOE detector, KLOE-2. The detector has been rolled into place and as researchers put the finishing touches to the high luminosity interaction region (IR), we look at the work that has lead to this upgrade.

DAΦNE and KLOE - early history

DAΦNE pronounced "Dafnee" has the full name: Double Annular Phi-factory for Nice Experiments. It is an accelerator complex at INFN, Frascati, Italy that includes a double ring collider (see right-hand image) and an injection system.

In its original configuration the collider consisted of two independent rings, each roughly 97m long, sharing two 10m long interaction regions (IR1 and IR2) where the KLOE and FINUDA or DEAR detectors were respectively installed. A full energy system, including an S-band linear accelerator (linac), 180 m long transfer lines and an accumulator/damping ring, provides fast and high efficiency positron/electron injection.

    



The DAΦNE accelerator's layout after the KLOE-2 detector upgrade - "IR" shows the Interaction region. DAΦNE is a double ring lepton collider producing phi (Φ) particles by colliding electrons and positrons at the energy of the Φ-resonance (1.02 GeV) (see Physics at DAΦNE for more information).  Image courtesy of LNF, INFN. Thumbnail image main page courtesy of Rob Owen-Wahl, stock.xchng.
 
 

DAΦNE began steady operations in 2001 and in the next seven years provided high K meson rates to the three experiments, which logged ~ 4.4 fb-1 total integrated luminosity in dedicated runs. In the same period the collider performances have been significantly improved by several progressive upgrades.

In 2007 DAΦNE achieved a peak luminosity of 1.6*1032 cm-2s-1 and a daily integrated luminosity of about 10 pb-1. Thanks to the collider performances, the KLOE experimental programme was completed in 2006, collecting about 3.0 fb-1.

The DAΦNE upgrade

In the second half of 2007, a major upgrade was implemented on DAΦNE in order to test a novel collision scheme, capable, in principle, to boost the luminosity towards 1033 cm-2s-1. The higher luminosity is due to smaller beam sizes at the collision point and the suppression of beam-beam resonances.

The main ingredients of the new configuration are a large Piwinski angle and Crab-Waist (CW) collisions. The large Piwinski angle results in thinner bunches of particles crossing with an increased angle and small overlap. Crab-Waist (CW) collisions are achieved by two sextupole magnets installed symmetrically with respect to the Interaction Point to focus the beam throughout the overlap region and suppress beam-beam resonances.

The new configuration has been used to give beam-beam events to the SIDDHARTA experiment, a compact device and the heir of DEAR, without a solenoidal magnetic field providing a simple environment for the CW test.

The results obtained have been striking. The luminosity has been increased by a factor of 3 with a peak value of 4.53x1032 cm-2s-1. The highest daily integrated luminosity measured in a moderate injection regime, suitable for the SIDDHARTA operation, has been ~15 pb-1. An almost continuous injection regime provided ~1.0 pb-1 hourly integrated luminosity indicating a monthly integrated luminosity of < 0.5 fb-1 for an upgraded KLOE experiment (KLOE-2).

KLOE and KLOE-2

KLOE is a multipurpose experiment devoted, mainly, to the study decays of K mesons (particles containing a single strange quark), as well as to several hadronic physics and low energy quantum chromodynamics studies.

 



The KLOE-2 detector emerges from the pit to reach its work position in the DAΦNE Interaction Region (IR). KLOE was parked away from the collider during the high luminosity test with the SIDDHARTA experiment. Image courtesy of LNF – INFN

     

The detector consists of a large cylindrical drift chamber, < 3.5 m long and 2 m in radius, surrounded by a lead-scintillating fibre electromagnetic calorimeter. A superconducting coil around the detector provides a magnetic field of 0.52 T.

With respect to the original design, KLOE-2 will have additional detector layers, including new tracking and calorimeter devices. It will also extend its investigation capabilities to the study of gamma-gamma (γ γ) reactions, by means of dedicated detectors tagging the scattered electron and positron, typical of those events.

Work within EuCARD

The successful test on DAΦNE confirms that the new collision scheme can be applied to the design of future lepton colliders, as well as to other existing machines, in order to reach unprecedented luminosities.
 
 

For this reason a research programme within the "Assessment of Novel Accelerator Concepts" work package (ANAC - WP11) has been approved. The main purpose of the EuCARD research is to prove the compatibility of large magnetic detectors with the new collision scheme. Tasks involve designing a new IR region according to the new collision scheme for the KLOE-2 detector and studying a possible IR for the upgrade of one out of the four LHC IRs.

The DAΦNE Interaction Region for the KLOE-2 run

Integrating the high luminosity collision scheme with the KLOE-2 detector introduces new challenges in terms of IR layout and optics, beam acceptance and coupling correction.
 

The IR magnetic layout has been defined in order to keep the beam vertical trajectory within reasonable values providing, at the same time, the maximum aperture for the beam.

In fact due to the larger crossing angle to the stronger first low-b quadrupole magnet and to the magnetic field of the experiment detector, the vertical displacement of the beam in the IR is an order of magnitude larger than in the last KLOE run. Permanent magnet dipoles are used for this purpose.

The IR optics have been designed in order to fulfill all the requirements in terms of tight focussing at the interaction point, inclusion of the crab sextupole magnets and coupling correction. The IR vacuum chamber mechanical design has been completed and all the parts are being delivered.

In the next months the efforts will address defining and optimizing the DAΦNE main rings optics including the new IR, as well as to perform simulation studies about beam dynamics, beam-beam and backgrounds hitting the experimental detector. At the same time the feedback systems, transverse and longitudinal, will be upgraded. With the current schedule, DAΦNE operation with the KLOE-2 experiment will start in May 2010.

- Catia Milardi, INFN-Frascati, EuCARD-ANAC (WP11)

  



Technical drawing showing the KLOE-2 detector (large, cylindrical structure in the centre of the image) and the DAΦNE high luminosity interaction region (IR). The horizontal, grey, x-shaped tubes running through the detector are the IR vacuum pipes. The small reds and yellows at either side of the image are the magnetic elements - quadrupole magnets to focus the beams and dipole magnets to keep the beam trajectories under control. Image courtesy of LNF-INFN
 
           

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