DAFNE

In order to follow the latter line of research in subnuclear physics, we need accelerators capable of delivering beams of extremely high intensity and accurate energy calibration; in this way a wide variety of data even on the most rare phenomena can be obtained.

The italian National Institute for Nuclear Physics (INFN) is realising in the Frascati National Laboratory the first of this special kind of accelerators, dedicated to the an abundant production of F (Phi) particles coming from the annihilation of electrons and positrons at the energy of the F resonance.

The F particle is unstable and decays in a very short time into other lower energy particles, the most interesting being K mesons. This kind of particles showed up, right at their discovery in 1947, such unexpected features that a new physical entity, called "strangeness", was introduced to explain them.

The study of neutral K mesons led to the discovery of a unique phenomenon, the violation of a fundamental symmetry of nature, which is strictly respected in any other reaction: the CP symmetry, which states that any reaction must not change if it undergoes a simultaneous mirror reflection and change of all particles into their antiparticles. The detailed measurement of the fundamental parameters of CP violation and its inclusion into a coherent conceptual framework is one of the most challenging open problems in physics, and it represents the main research program at DAFNE.

The extremely precise study of the different decays of F and K mesons at DAFNE will deliver clear experimental information on many critical items of the subnuclear world and of the forces which drive the interactions between its constituents. The KLOE collaboration has been set up to follow this line of research on DAFNE.

However, CP violation and K meson physics are not the only goals of the DAFNE Project: the abundant production of K mesons opens a wide range of experiments in nuclear physics, with unique characteristics of energy resolution and kind of observable reactions. A second experiment, FINUDA, will be installed on one of the two interaction straights of the DAFNE Main Rings to perform studies on the spectroscopy and decay modes of hypernuclei, e.g. special nuclei, where a nucleon is replaced by a baryon made up of "strange" quarks (Lambda, Sigma, Csi). The "strangeness" degree of freedom adds a new dimension to our knowledge of the nuclear world, by creating new dynamic systems whose spectroscopy can show up symmetries which are forbidden in ordinary nuclei. In DAFNE, Lambda hypernuclei will be produced by stopping K mesons of known energy inside nuclear targets.

Design strategy

Injection system and layout

Linac

Accumulator

Main Rings

Interaction Regions

Status

Who's who in the LNF Accelerator Division Staff DAFNE DESIGN STRATEGY @ Schematic representation of the two-ring colliding beams concept. @ Crossing flat beams at an angle in the horizontal plane. DAFNE is a F-factory, mainly dedicated to the study of CP violation. The F-resonance (1.02 GeV c.m) can be created by annihilating electrons and positrons in a storage ring with a peak cross-section of Å5x10^3 nanobarn. Å50% of the F decay into a couple of charged K mesons, while Å35% create a couple of neutral Klong + Kshort. The Klong decays normally into 3 pions, the Kshort into 2 pions. In the CP violating decay, the Klong decays into only 2 pions and this happens in only 0.3% of the decays. Sufficient statistical accuracy in the observations for the KLOE experiment requires Å2x10^7 CP violating decays per year. Under normal operating conditions, a luminosity near 10^33 cm^-2 s^-1 is needed to fulfil this requirement. The luminosity is a typical figure of merit of a storage ring collider, proportional to the number of interactions per unit time between the particles of the counterrotating beams. In the case of an electron/positron collider, it is the product of the number of electrons stored in each bunch times the number of positrons stored in each bunch times the frequency of bunch crossings at the interaction point, divided by the cross section area of the beam at the crossing point. The number of particles which can be stored in a bunch is limited by the beam-beam interaction, which introduces a strong non-linearity in the beam dynamics, leading to beam blow-up and loss. This limit becomes less severe when the energy of the stored particles increases. The effect of beam-beam interaction can be reduced by strongly focusing the beam at the interaction point (the so called "low-beta" technique) by means of strong magnetic lenses. Of course, these lenses create chromatic perturbations in the particle motion, which need to be corrected outside the crossing region. For this reason, only a limited number of low-beta crossing points (one or two) can be realised in a small low energy collider such as DAFNE. The luminosity required for the CP violation experiment is two orders of magnitude larger than the maximum obtained until now in a collider at the same energy, namely at the VEPP-2M storage ring in Novosibirsk. This is a "conventional" storage ring, where a single bunch of electrons and a single one of positrons circulate in opposite directions in the same vacuum vessel, crossing in a low-beta interaction point and being separated at the opposite point in the ring by means of electrostatic fields. This separation can be easily performed in the case of a single bunch but becomes a critical item when many bunches are stored in the ring. The luminosity given by VEPP-2M is at the limit of the beam-beam instability at the F resonance energy. In order to gain the required improvement in luminosity, an alternative collider scheme has been proposed for DAFNE, where the beams are stored into two separated rings, both lying in the same horizontal plane, and crossing in two opposite low-beta sections at a small horizontal angle. In this way, many bunches can be stored in each ring, each bunch being perturbed by the beam-beam interaction only twice during each revolution in the ring. The luminosity is then proportional to the number of stored bunches, up to 120 for the DAFNE Main Rings. Numerical simulations and accelerator studies have shown that the crossing at an angle of the beams does not introduce additional limitations to the beam-beam interaction, provided the transverse size of the beam in the plane of the crossing (horizontal in the case of DAFNE) is larger, typically by an order of magnitude, than the bunch length times the crossing angle. For this reason a flat shape has been chosen for the beam, the horizontal size at the crossing point being 100 times larger than the vertical one. This choice implies also that strong focusing is needed only in the vertical plane at the crossing point, thus simplifying the design of the low-beta region and the chromatic correction system. Accelerator experiments performed on storage ring in operation or already shut down have shown that radiation damping, an effect coming from the intense synchrotron radiation emission form the particles inside the storage ring bending fields, is a relevant parameter in the beam-beam interaction limitation to the maximum achievable luminosity. High energy storage rings can in fact achieve much higher luminosities than low energy ones, and this is due not only to the larger mass of the interacting particles, but also to the larger amount of synchrotron radiation produced at high energy. The radiation, however, can be increased in low energy rings by inserting in the lattice special magnets of alternating polarity, called "wigglers". In the DAFNE Main Rings 8 wigglers will increase by a factor of 2 the synchrotron radiation power emitted by the particles in the bending magnets. All the above described choices for DAFNE make the realisation of the facility mainly a technological challenge, the feasibility of all "fundamental" items, such as beam-beam interaction, being already demonstrated in operating storage rings. Damping of instabilities due to the large number of stored bunches and vacuum problems related to the large total stored currents are the major technological challenges of the DAFNE Project. DAFNE BEAM-BEAM DESIGN PARAMETERS Single beam energy (GeV) 0.51 Number of particles per bunch 8.9x10^10 Number of bunches per ring up to 120 Crossing frequency (MHz) up to 368.25 Horizontal emittance (mm.mrad) 1.0 Vertical emittance (mm.mrad) 0.01 Coupling factor 0.01 Horizontal b function at crossing (m) 4.5 Vertical b function at crossing (m) 0.045 Total crossing angle in the horizontal plane (mrad) 25 Horizontal beam-beam tune shift per crossing 0.04 Vertical beam-beam tune shift per crossing 0.04 Bunch length (mm r.m.s.) 30 Horizontal beam size at crossing (mm r.m.s.) 2.0 Vertical beam size at crossing (mm r.m.s.) 0.02 Synchrotron radiation loss per turn (KeV) 9.3 Horizontal betatron damping time (msec) 36 Vertical betatron damping time (msec) 36 Longitudinal damping time (msec) 17.8 Maximum stored current per ring (A) 5.2 Maximum luminosity (cm-2s-1) 5.3x10^32 INJECTION SYSTEM AND LAYOUT @ Schematic layout of the DAFNE accelerator complex. @ Modification of the ADONE hall for the installation of the DAFNE Main Rings and experiments. In order to gain substantial saving of funds and construction time, the double ring collider and its injector system have been designed to cope with the buildings where ADONE was installed. After the final shut down in April 1993, the old storage ring, its injector Linac, the transfer lines from the Linac to the storage ring and all the experimental beamlines were dismantled and the buildings completely renovated to host the new accelerator complex. The injection system of DAFNE consists of a Linac, an intermediate Accumulator Ring, and Å180 m of Transfer Lines from the Linac to the Accumulator and from the Accumulator to the Main Rings. This rather long and complicated arrangement was dictated by the necessity of utilising the existing buildings, keeping new civil constructions at a minimum. The new Linac and its power supplies are located in the old Linac building. The Accumulator with its transfer lines is installed in an experimental hall, where the old Linac beam was extracted and used for nuclear physics experiments. The Main Rings are assembled in the ADONE hall, where two large reinforced pits have been built to host the large and heavy magnetic detectors of KLOE and FINUDA. The DAFNE injection system has been designed to fill in few minutes from scratch the large required current in the Main Rings in the single bunch mode to ensure the maximum flexibility in the stored bunch patterns. The whole system runs at the operating energy of the collider, so that the current decay (mainly due to the Touschek effect) can be compensated by refilling the rings on top of the already circulating current (this injection mode is called "topping up"). The injection scheme is the following: ¥ positrons are accelerated in the Linac (converter target in) in 10 ns pulses at 50 Hz ¥ positrons are injected into a single Accumulator bunch up to a pre-set current ¥ the positron beam is cooled down in the Accumulator by waiting for 5 damping times ¥ the positron bunch is extracted from the Accumulator and injected into the positron Main Ring ¥ the sequence is repeated for all the bunches to be injected into the positron Main Ring ¥ Electrostatic separators are switched on to separate the beams at the crossing point ¥ The converted target is extracted and the whole sequence is repeated for the electrons ¥ Separators are switched off and beams are brought into collision. LINAC @ The DAFNE Linac during installation in Frascati. The heart of the DAFNE injection system is a Å60 m long Linac built by TITAN BETA (San Diego, California) on the basis of a turn-key contract. It is an S-band accelerator (2.865 GHz) driven by four 45 MW klystrons each followed by a SLED peak power doubling system. It delivers 10 ns pulses at a repetition rate of 50 Hz. A quadrupole FODO focusing system is distributed along the entire structure. A triode gun delivers up to 10 A electrons at 120 KV. The beam is then accelerated at 250 MeV by six 3 m long accelerating sections up to a removable target, where it is focused by a quadrupole system to a 1 mm radius spot to produce positrons with an efficiency of Å0.8%. The positrons are collected by a high field pulsed magnetic lens, separated from the electrons by means of a "chicane" of dipoles, and then accelerated up to a maximum energy of 550 MeV by 10 accelerating sections. The expected positron current during the pulse is 36 mA within ±1% energy spread and 5 mm.mrad emittance. In the electron mode the converter is removed from the beam and the electrons are accelerated through the whole structure up to 800 MeV. The pulse current is 150 mA within ±0.5% energy spread and 1 mm.mrad emittance. @ The DAFNE Linac spectrometer magnet. The average energy of the accelerated particles and the width of its distribution is measured by a spectrometer system consisting of a pulsed magnet, which deviates the beam from the Transfer Line, and a 60¡ bending magnet, which focuses the beam on a hodoscope of secondary emission metallic strips. The beam from the Linac can also be directed by means of a DC magnet, in a dedicated mode which is not compatible with injection into the collider, towards a Test Beam area, mainly conceived for detector calibration. For this purpose, a system of absorbers, energy and phase- space scrapers can statistically reduce the beam intensity down to a single electron per pulse. LINAC PARAMETERS GENERAL RF frequency (MHz) 2856 Klystron power (MW) 45 Number of klystrons 4 Number of SLED peak power doublers 4 Number of accelerating sections 16 Repetition rate (Hz) 50 Beam pulse width (ns) 10 HIGH CURRENT ELECTRON LINAC Number of accelerating sections 6 Input current from gun (A) ² 10 Input energy from gun (KV) 120 Output current (A) > 4 Output energy (MeV) 250 Output emittance (mm.mrad) ² 1 Energy spread (%, total) 10 Beam spot radius (mm) 1 POSITRON LINAC MODE Number of accelerating sections 10 Output energy (MeV) 550 Input energy (MeV) 8 Output current (mA) 36 Output emittance (mm.mrad) ² 5 Energy spread (%, total) 2 HIGH ENERGY ELECTRON LINAC MODE Output energy (MeV) 800 Output current (mA) 150 Output emittance (mm.mrad) ² 1 Energy spread (%, total) 1 DAFNE ACCUMULATOR @ The Accumulator during installation. The DAFNE Accumulator is a small storage ring, which has been included into the DAFNE injection system for the following reasons: ¥ With the design positron output current from the Linac and the DAFNE Main Rings longitudinal acceptance, injection of the full design current into one of the two rings requires Å2x10^4 Linac pulses at 100% efficiency. Due to its Gaussian particle distribution, a small fraction of the stored beam hits the septum which separates the ring vacuum vessel from the injection line at each injection pulse and gets lost. In order to avoid saturation, this fraction should be much smaller than the inverse of the number of injected pulses (in our case 5x10^-5). By injecting, as an example, 50 pulses into the Accumulator, and then extracting and injecting into the Main Rings, the tolerable fraction of lost particles drops to Å0.1%. ¥ The R.F. system runs at a very high harmonic of the revolution frequency (120) in order to allow storage of a large number of bunches to reach high luminosity. This is not necessary in an intermediate ring, where only a single bunch is needed. It is therefore possible to run the Accumulator R.F. cavity at a sub-multiple frequency of the Main Rings one, increasing the longitudinal acceptance (from 2.7 to 13.4 ns) and therefore accepting the full charge in the Linac pulse. ¥ After accumulating the desired current, injection into the Accumulator can be stopped for a short time to allow the beam to damp down to its equilibrium energy spread and emittance, which are typically two orders of magnitude smaller than the corresponding Linac values. In this way a high quality beam can be extracted from the Accumulator and injected into the Main Rings, thus avoiding the necessity of designing the Main Rings lattice with a larger physical and dynamic acceptance, and relaxing the requirements on the Main Rings magnets with substantial savings on the overall cost of the facility. @ Schematic layout of the DAFNE Accumulator. The Accumulator is a quasi-octagonal ring with a total length of 32.5 m on the nominal trajectory. Its lattice is made of four almost achromatic arcs, each consisting of two 45¡ full iron H-type sector dipole magnets with a small gradient to optimise the damping distribution, a quadrupole triplet and two sextupoles to correct the ring chromaticity. All the dipoles are powered in series. The quadrupoles are connected into three independent families, the sextupoles in two families. @ The DAFNE Accumulator dipole on the magnetic measurement bench. @ The DAFNE Accumulator quadrupole under measurement with a rotating coil system. @ The DAFNE Accumulator sextupole. The electron beam coming from the Linac is injected into the ring by means of a system of two septum magnets, the first bending the beam by 34¡ and the second performing the final deflection of 2¡ into a special 3.5 m vacuum vessel between two achromats. The stored beam is extracted by a mirror symmetric system placed in the opposite straight section. The positron beam follows the opposite path. The remaining two straight sections host the pulsed kicker magnets used to deflect the beam at injection and extraction and the R.F. cavity. @ The DAFNE Accumulator R.F. cavity. A system of 8 correctors and 10 position monitors allows a careful correction of the closed orbit in the ring with the purpose of optimising injection efficiency. Two synchrotron light monitors and two stored current monitors are also part of the diagnostic system. A transverse feedback system is also implemented on the ring by means of a stripline pick-up and a stripline kicker. The vacuum chamber is fully stainless steel and a pumping system consisting of 18 sputter ion pumps is designed to reach an average dynamic pressure in the ring of 5 nTorr. The Accumulator has been realised by OXFORD INSTRUMENTS (U.K.). All the magnets have been sub-contracted to TESLA Engineering (U.K.). DAFNE ACCUMULATOR PARAMETERS Energy (MeV) 510 Circumference (m) 32.56 Emittance (mm.mrad) 0.26 Horizontal betatron tune 3.12 Vertical betatron tune 1.14 R.F. frequency (MHz) 73.65 R.F. voltage (KV) 200 Bunch average current (mA) 150 Bunch length (cm) 3.8 Synchrotron radiation loss (KeV/turn) 5.2 Horizontal betatron damping time (msec) 21.4 Vertical betatron damping time (msec) 21.4 Longitudinal damping time (msec) 10.7 Number of bending magnets 8 Bending radius (m) 1.1 Bending angle (deg) 45 Operating field (T) 1.55 Gradient (T/m) -0.66 Number of quadrupoles 12 Bore diameter (mm) 100 Operating gradient (T/m) 8 Maximum gradient (T/m) 12 Magnetic length (cm) 30 Number of sextupoles 12 Bore diameter (mm) 108 Operating gradient (T/m^2) 135 Maximum gradient (T/m^2) 180 Magnetic length (cm) 10 MAIN RINGS Due to the peculiar geometry of the crossing in the horizontal plane, each Main Ring of the DAFNE collider consists of two 180¡ bends of different length, the "short arc" and the "long arc". @ Schematic layout of the two DAFNE Main Rings. The trajectories of the electron and positron beams cross at the two interaction points at an angle of 25 mrad with respect to each other. The separation between them increases along the interaction region (5 meters on each side of the interaction point), reaching Å12 cm at the entrance of a special septum magnet, called "splitter", which bends the two beams in opposite directions. In this magnet there is sufficient distance between the two beams to let them travel in two separate vacuum chambers and at the end of the magnet the distance is large enough to accommodate the magnetic elements of the arcs. The short straight sections between the splitter and the first dipole in the arc are used to match the optical functions in the interaction region, where a low vertical beta value is required to reach high luminosity, to those in the arcs. Matching is realised by means of quadrupole triplets of the same kind of those installed in the Accumulator. A sextupole in each straight, where the dispersion is very low, is used to control high order aberrations introduced by the chromaticity correction sextupoles in the arcs. Also these sextupoles are of the same kind of those in the Accumulator. A special design of the vacuum chamber and large aperture quadrupoles and sextupoles allows the installation of tagging counters downstream the KLOE interaction region. The original design of the Main Rings had vanishing dispersion at the crossing points and in all the four straight sections at 90 degrees with respect to the interaction regions. The arcs consisted therefore of two achromats, each composed of 2 dipoles, 3 quadrupoles, 2 sextupoles for chromaticity correction and one wiggler to increase the total radiation damping. In the long arc the dipoles bend the beam by 99 degrees each, in the short one by 81 degrees to compensate for the opposite deflection of the two arcs in the splitter. Further improvements in the lattice design have led to a non-vanishing dispersion in the straight section of the long arc, where injection is performed. The short arc still preserves vanishing dispersion to avoid synchro-betatron coupling in the R.F. cavity. The definition of "achromat" in the long arc is therefore not correct, at least in principle. However, this name is still used, because the magnetic structure is flexible enough to make dispersion vanish also in the long straight. The dipoles in the achromats are C-shaped with flat poles. In each achromat one of the two dipoles has parallel ends, while the other is a sector type one. The magnets have a rather large gap and pole width to provide a large acceptance for the relatively high beam emittance. The quadrupoles and sextupoles are also large, in order to cope with the peculiar design of the vacuum chamber in the achromat, described in the following. All the magnets in the achromat are being built by ANSALDO (Genova, Italy). @ Parallel ends dipole prototype on the magnetic measurement bench. @ Large quadrupole prototype. The wigglers used to double the synchrotron radiation power emitted by the beam are conventional electromagnets, each made of five central poles and two end poles. The peak field in the poles is 1.85 T, to be compared to the 1.2 T in the bending magnet. Due to the strong power consumption of these magnets, it is foreseen to change them with superconducting ones in the future. The magnets are built by DANFYSIK (Denmark). @ Wiggler prototype. In the long arc, the straight section between the achromats is used for injection. A first septum magnets, consisting of a thin copper sheet of 1.5 mm thickness, and carrying 2000 A direct current, separates the vacuum vessel of the ring from the injection channel coming from the Accumulator, and performs the final 2 degrees deflection of the injected beam. A system of 3 pulsed kickers provides a local single turn closed orbit deformation, which merges the injection pulses into the already stored beam. 8 quadrupoles in this section are used to control the betatron tunes of the ring and to optimise the phase advance between the kickers and the injection septum, while two sextupoles help in reducing high order aberrations. All the magnets in the straight are of the same type of the Accumulator ones. The structure of the straight section in the short arc is similar to the long arc one, with 7 quadrupoles instead of 8: the R.F cavity of the ring is placed in this straight. All the dipoles in the same ring (one short arc plus a long one) are connected in series, while all the other magnets have their independent power supply, in order to ensure the maximum flexibility in the operation of the machine. Particular care has been taken in the design of the Main Rings vacuum system, to cope with the very high radiation power emitted by the beam. At the full design current (Å5 A per beam), Å50 KW must be dissipated in each ring, under the constraint of keeping the average pressure in the chamber below 1 nTorr for beam lifetime reasons. In addition, the requirement of low beam generated background to the detectors in the interaction regions, calls for lower pressure near the interaction points. In order to achieve this performance, a special vacuum chamber has been designed in the achromats, consisting of three parts, the central one around the beam separated from two "antechambers" by means of a narrow slot allowing the passage of photons radiated by the electron beam in the wigglers. The same arrangement, but with only one antechamber towards the outside of the ring has been adopted for the bending magnet. @ Vacuum vessel cross sections in the Main Ring achromats. The achromats are the "hottest" region from the point of view of emitted synchrotron radiation power. The vacuum vessel in each achromat has been designed as a single piece Å10 m long aluminum chamber, including the two achromat dipoles and the straight section with the wiggler in between. The radiation from the dipoles and the wiggler travels through the slots to the antechamber, where it hits special water-cooled copper absorbers. @ The first vacuum vessel of the Main Ring achromats. @ Schematic of the achromat vacuum vessel with synchrotron radiation absorbers. Near each synchrotron radiation absorbers, where the gas load is concentrated, there is a titanium sublimation pump with a pumping velocity of Å2000 litres per second, and a sputter ion pump to extract those kind of gases which are not efficiently pumped by the sublimators. Special NEG pumps are foreseen in the interaction regions, where a lower pressure is needed to avoid excessive backgrounds to the experiments. The radiofrequency system of each ring consists of a normal conducting single cell cavity running at 368 MHz on the 120th harmonic of the revolution period. Each cavity is fed by a 150 KW/cw klystron, protected against the reflected cavity power by a ferrite circulator. In order to reduce the interaction of the beam with the high order modes of the cavity, the latter is equipped with long tapered beam tubes and three waveguides to couple out the parasitic modes that are then dissipated into external 50 Ohm loads by means of special broadband transitions between the waveguides and coaxial vacuum feedthroughs. @ The prototype Main Ring radiofrequency cavity under construction at ZANON. @ The high order mode absorber with the broadband transition from the waveguide to coaxial external load. The central body of the R.F. cavity is obtained from a single forged OFHC copper billet and the internal surface is fully manufactured with an automatic milling machine. The cavity is built in Italy by ZANON. The basic design choice of achieving the required luminosity with a large total current distributed over a large number of bunches makes the operation very critical with respect to longitudinal coupled bunch instabilities caused by parasitic higher order modes in the ring, mainly in the R.F. cavity. These instabilities have been identified as a potentially severe limit to the ultimate achievable luminosity. Even though the high order modes in the cavity are strongly damped by the waveguides absorbers, the probability for a damped high order mode to cross a coupled bunch mode frequency is large and, due to the large total current, the growth rate of unstable modes can be stronger than the radiation damping by up to two orders of magnitude. The required additional damping is provided by a longitudinal feedback system, based on digital signal processors, which acts on each bunch individually. The digital section is under construction at SLAC in the framework of a collaboration with the SLAC-LBL PEPII group on feedback systems for the next generation of "factories" with intense beams and a large number of bunches. The first realisation of this kind of feedback has been successfully tested at the synchrotron radiation source ALS in Berkeley. The active element of the feedback chain for DAFNE is a special overdamped cavity running at 1.2 GHz (3.25 times the main R.F. frequency). The cavity has a diameter of 20 cm and is 7.2 cm long. To obtain the large required bandwidth (Å180 MHz for operation with 120 bunches), the cavity is loaded with 6 ridged waveguides followed by broadband transitions. @ CAD view of the longitudinal feedback kicker cavity. @ Prototype longitudinal feedback kicker cavity. Additional instrumentation for the Main Rings consists in a distributed orbit correction system made of button pick-ups, striplines and horizontal/vertical correctors, sensitive to the beam position also in a single-turn mode. Synchrotron radiation monitors and single bunch current detectors will also be available for beam diagnostics purposes. A system of skew quadrupoles is foreseen to control the beam coupling at the interaction point, as well as a beam deflection system to separate the beams during injection and to finely control the superposition of the beams at interaction. The luminosity will be measured both by the experimental detectors through the rate of well-known electromagnetic reactions, and by a special system of counters situated right after the splitter magnets measuring the rate of single beam-beam bremsstrahlung produced at the interaction points. INTERACTION REGIONS The splitter magnets described in the Main Rings section represent the boundaries of the two interaction regions, where the electron and the positron beams travel together inside a common vacuum vessel and cross at the interaction points at a total angle of 25 mrad in the horizontal plane. The interaction points (IP) are both completely surrounded by the experimental detectors, which use a longitudinal solenoidal field to detect the charge and momentum of the particles produced in the electron/positron interactions. The KLOE detector exploits a solenoidal field of 0.6 T along a distance of 5 m, while the FINUDA experiment requires a higher field (1.1 T) on a shorter distance (Å2 m). Both solenoidal magnets are superconducting. The KLOE experiment is mainly dedicated to the study of CP violation in the decay of the F resonance and requires the maximum possible free solid angle around the IP. This requirement is in conflict with the necessity of putting the strong focusing quadrupoles of the low-beta insertion as close as possible to the interaction point to avoid large contributions to the aperture and the chromaticity of the ring. For this reason a very compact solution has been adopted for these quadrupoles, by realising them with permanent magnets: in this way the magnetic structure of the machine is completely contained within two narrow cones of 9 degrees half aperture around the vacuum chamber axis, and the acceptance of the experiment is near 99%. Moreover, the iron of conventional quadrupoles represents a strong perturbation to the solenoidal field required for the experiment, while permanent magnets do not interfere with it. In the KLOE interaction region there are six such quadrupoles, three on each side of the IP. In the FINUDA interaction region, due to the shorter length of the solenoidal, there are only four permanent magnet quadrupoles. A third layout for the interaction regions, called the DAY-ONE structure has also been designed to operate without solenoidal fields: it will be used during the commissioning of the collider, and it is realised with conventional quadrupoles. @ Schematics of the KLOE detector with the solenoid and permanent magnet quadrupoles. @ Permanent magnet quadrupole prototype. The design strategy of DAFNE foresees flat beams to overcome the difficulties which may come from the crossing angle at the IP. The solenoidal fields of the detectors are a strong source of coupling and must there be carefully compensated to avoid the growth of the vertical beam size. The compensation is achieved by means of a couple of superconducting solenoids, one on each side of the experimental detectors, near the splitters, with a longitudinal field opposite to the main solenoid one and with the same total integrated field. In addition, since the solenoid field rotates the plane of betatron oscillation proportionally to its field integral, the permanent magnet quadrupoles must be rotated accordingly. A complicated support, allowing a rotational degree of freedom for the quadrupole triplets is foreseen for fine adjustment of the coupling. The overall focusing effect of the low-beta quadrupoles and fringing field of the solenoids is the same for the KLOE, FINUDA and DAY-ONE insertions. This helps a lot in changing the operation mode of the collider from one to another configuration. In particular, the low- beta quadrupoles and the vacuum vessel section around the IP are completely embedded into the experimental detectors. If one of the detectors needs to be taken away from the beamline for maintenance, it is possible to replace it with the corresponding DAY-ONE straight section without changing the optics of the remaining part of the collider. One of the most critical items of the whole project is the KLOE vacuum vessel near the IP. It is important that the Kshort coming from the decay of the F resonance cross the minimum possible amount of material to avoid regeneration. For this reason the first idea for the vacuum chamber shape near the IP was a sphere with a radius large enough for the decay of the Kshort (Å10 cm). However, it appeared immediately clear that such a shaped chamber could trap R.F. fields induced by the high current beam, leading to R.F. losses and overheating. It was therefore decided to shield the sphere from the beam by means of an extremely thin (50 microns) beryllium cylinder of the same radius of the beam pipe outside the IP. The sphere is also made of beryllium (500 microns thickness to minimise the radiation lengths seen by the other decay particles). Prototypes of this vessel sections are being developed by specialised factories. Beam diagnostics in the interaction region is also a critical item for the overall reliability of the collider. A system of directional striplines is used to detect the position of the electron and positron beams even if they travel in the same vacuum chamber, while special button pickups are used near the splitter, where the distance between the two beams is sufficient to allow an efficient independent position detection. The luminosity monitor described in the Main Rings section will also be used to optimise the superposition of the beams. The main source of particle losses in the DAFNE Main Rings is the Touschek effect, namely intrabeam scattering between particles in the same bunch, which leads to an energy change of the scattered particles. This effect limits the beam lifetime to Å2 hours. The lattice structure is such all the particles scattered in the achromat upstream the interaction point are deflected by the second bending magnet and reach their maximum oscillation amplitude in the detector region. They constitute therefore a potential source of severe background to the experiment. In order to avoid this intrinsic drawback of the collider lattice, a system of adjustable scarpers has been designed, which trap the scattered particles before the splitter, at the price of a small reduction of beam lifetime. PROJECT STATUS Buildings and utilities The Linac and Transfer Lines tunnel, the Linac Modulator Hall and the Accumulator Hall upgrading is complete. The Main Rings Hall is almost completed: it is expected to be available for machine assembling beginning November 1995. The new building for the KLOE detector is under construction. The end of the construction is foreseen at the end of January 1996. Out of the four water cooling systems of the facility, the first one, dedicated to the Linac and part of the Transfer Lines, is operating since September 1994. The second system, for the Accumulator and the remaining part of Transfer Lines, will be completed in January 1996. The last two systems, connected to the Main Ring Hall, will be ready in November 1996. Four electrical power distribution systems are foreseen in the DAFNE project, with the same layout of the cooling systems. The first one (Linac and Transfer Lines) is available since December 1994; the second (Accumulator and Transfer Line) will be ready in November 1995: the last two systems (Main Rings) are due for April 1996. The contract for the DAFNE Hall air conditioning system is expected to be awarded in November 1995. The tender for the realisation of the refrigerator/liquefier plant for the superconducting elements in the DAFNE Hall has been authorised at the end of September 1995. The contract is expected to be awarded in November. Linac The installation of the machine has been completed and the accelerator sections put under vacuum. They are now being conditioned with R.F. power. A first test of beam transport up to the converter target at 250 MeV has been successfully performed in May 1995. Commissioning of the Linac with electrons up to 800 MeV is scheduled to start in October. Operation with positrons at the injection energy (550 MeV) is expected by the end of the year. Accumulator The electrical, mechanical, thermal and magnetic properties of all the magnets (8 dipoles, 12 quadrupoles and 8 sextupoles) have been measured at LNF, including the position of the magnetic centres for alignment purposes. The field quality of all the magnets has been found to be excellent and remarkably constant among the different elements of the same groups. The quadrupoles and sextupoles have been then shipped back to Oxford where they have been assembled with the vacuum chambers and aligned on girders. The assemblies have been delivered, ready for installation, to LNF in August 1995. The first phase of the Accumulator installation has been completed at the beginning of October. The dipoles have been installed on their supports and carefully aligned. The four girders of the achromats have been placed in their positions and will be aligned as a whole during October, as well as one of the two injection/extraction sections, the kicker section and the R.F/kicker one. The remaining injection section, placed just in front of the entrance door of the Accumulator Hall will be installed later to leave space for bringing heavy equipment (Transfer Line injection branches and power supplies) inside the Hall. The sputter ion pumps have been mounted on their supports and connected to the dipole vacuum chambers. The two branches of Transfer line inside the Accumulator Hall will be installed by ANSALDO during October 1995. The cooling water pipes will be installed during the same period. The power supplies of the Accumulator magnets, built by DANFYSIK, will be delivered in November. Unfortunately, a vacuum chamber section containing the striplines of the transverse feedback system has been damaged during its delivery to Frascati and is being repaired at Oxford. It is expected to be delivered again to LNF at the end of November. A specialised team from Oxford will then make the final welding on the vacuum chamber and perform, together with the LNF staff, the leak test required for the acceptance of the whole system. The ring will be left under vacuum. The synchrotron light monitors will be installed as well. The last phase of the installation will be the installation of the second injection/extraction straight and the connection of water cooling and power supplies to the magnets. The final check of the whole machine will be performed before the start of commissioning with beam at the end of March 1996. The R.F. cavity and its power supply have been delivered to LNF. The system has been tested at full operation power successfully in a dedicated test area. It has been then transported into the Accumulator Hall and installed in the ring. Main Ring Magnets 60 "small" quadrupoles, of the same kind of the Accumulator ones, have been delivered to LNF from TESLA Eng. The remaining part of the Contract (6 quadrupoles and 8 sextupoles) will be concluded in October. All the "large" magnets to be installed in the achromats are being produced by ANSALDO. The Contract includes 28 quadrupoles of 10 cm bore diameter, 16 dipoles of four different types (the parallel end short, the parallel end long, the sector short and the sector long), 18 sextupoles and 8 large bore (20 cm diameter) quadrupoles. The prototype of the 10 cm diameter quadrupole has been delivered to LNF. The magnetic measurement showed a satisfactory field quality, and the magnet has been accepted with minor mechanical modifications. It is now almost ready for series production. The dipole lamination, the same for all the four magnet types, was not acceptable because of poor quality of the steel and insufficient control of the sub-contractor responsible of punching the lamination. It was however decided to assemble a prototype and machine the pole gap in order to meet the requirements on the field quality. The gap height was therefore increased by 0.5 mm. The magnet is presently under measurement at LNF, and the results are acceptable from a magnetic point of view. Punching of all the lamination has therefore been authorised, under the condition of improving the stacking procedure. The first trial of producing the laminations for the sextupole was unsuccessful, and the punching tool is being modified, while until now no work has been done on the large aperture quadrupoles. According to the latest ANSALDO schedule, all magnets will be delivered by July 1996. The prototype of the wiggler magnets, built by DANFYSIK, has been successfully measured at LNF, accepted and sent back to the factory for minor modifications. The first 5 magnets are ready for shipment to Frascati, and the last 3 will be delivered in November 1995. R.F. System The first cavity has been completely machined on the inner side. All its main components, cooling system, waveguide absorbers, tuner and supports are ready. Final tuning will be performed at the seller's plant at the end of October. The vacuum test will follow and power test is foreseen at LNF within November 1995 with a dedicated 50 KW tetrode amplifier. The Klystrons have been successfully tested at LNF up to 180 KW c.w. The power supplies are undergoing a few minor modifications. The acceptance test is foreseen at the end of October 1995. The low power controls and R.F. feedback electronics are operational. Next milestones for the R.F. system are the construction of the second cavity, to be started in November 1995, the power test of ferrite circulators (January 1996) and the installation of the power supplies in the Main Rings Hall (June 1996). A prototype of the longitudinal feedback kicker cavity has been realised and low power tested in the laboratory. Vacuum system The first 10 m long aluminum vacuum vessel of the achromat has been delivered to LNF and tested. After bake-out at 150 degrees for 48 hours, the residual gas pressure reached 0.16 nTorr. A second vessel has been completed and the remaining six will be delivered at a rate of one vessel per month. All the sputter ion pumps have been purchased and delivered to the Laboratory. The vessels of the titanium sublimator pumps are under construction. The final drawing of the sources has been completed and the tendering procedure has started. The copper absorbers design has been finalised and the material is being purchased. WHO'S WHO IN THE LNF ACCELERATOR DIVISION STAFF Ordinary Mail Address: INFN, Laboratori Nazionali di Frascati, Divisione Acceleratori Casella Postale 13 00044 Frascati (Rome), Italy FAX Number: +39-6-94032265 BASSETTI Mario - Associate Director, F-factory Physics Telephone: +39-6-94032273 E-mail address: BASSETTI@LNF.INFN.IT BIAGINI Maria Enrica - Accelerator Physics Group Telephone: +39-6-94032435 E-mail address: BIAGINI@LNF.INFN.IT BISCARI Caterina - Accelerator Physics Group Telephone: +39-6-94032435 E-mail address: BISCARI@LNF.INFN.IT BONI Roberto - Leader, Radiofrequency Group Telephone: +39-6-94032252 E-mail address: BONI@LNF.INFN.IT CASTELLANO Michele - ARES-L Group Telephone: +39-6-94032210 E-mail address: MICHELE@LNF.INFN.IT CATTONI Aldo - Associate Director, F-factory General Organization Telephone: +39-6-94032271 E-mail address: CATTONI@LNF.INFN.IT CHIMENTI Virgilio - Associate Director, F-factory Vacuum and Mechanics Telephone: +39-6-94032257 E-mail address: CHIMENTI@LNF.INFN.IT CLOZZA Alberto - Leader, Vacuum Group Telephone: +39-6-94032537 E-mail address: CLOZZA@LNF.INFN.IT DELLE MONACHE Giovanni - Mechanical Engineering Group Telephone: +39-6-94032544 E-mail address: DELLEMONACHE@LNF.INFN.IT DE SIMONE Sergio - Leader, Pulsed Magnets Group Telephone: +39-6-94032277 E-mail address: DESIMONE@LNF.INFN.IT DI PIRRO Giampiero - Accelerator Physics Group, DAFNE Control System Telephone: +39-6-94032269 E-mail address: DIPIRRO@LNF.INFN.IT DRAGO Alessandro - Electronics, Diagnostics and Controls Group Telephone: +39-6-94032585 E-mail address: DRAGO@LNF.INFN.IT FERRARIO Massimo - ARES-L Group Telephone: +39-6-94032216 E-mail address: FERRARIO@LNF.INFN.IT GALLO Alessandro - Radiofrequency Group Telephone: +39-6-94032639 E-mail address: GALLO@LNF.INFN.IT GHIGO Andrea - Electronics, Diagnostics and Controls Group Telephone: +39-6-94032213 E-mail address: GHIGO@LNF.INFN.IT GUIDUCCI Susanna - Accelerator Physics Group Telephone: +39-6-94032221 E-mail address: GUIDUCCI@LNF.INFN.IT MARCELLINI Fabio - Radiofrequency Group Telephone: +39-6-94032639 MIGLIORATI Mauro - Accelerator Physics Group Telephone: +39-6-94032636 E-mail address: MIGLIORATI@LNF.INFN.IT MILARDI Catia - Accelerator Physics Group, DAFNE Control System Telephone: +39-6-94032377 E-mail address: MILARDI@LNF.INFN.IT MODENA Michele - Leader, Cryogenic Engineering Telephone: +39-6-94032267 E-mail address: MODENA@LNF.INFN.IT PATTERI Piero - ARES-L Group Telephone: +39-6-94032465 E-mail address: PATTERI@LNF.INFN.IT PELLEGRINO Luigi - Mechanical Engineering Group Telephone: +39-6-94032510 E-mail address: PELLEGRINO@LNF.INFN.IT PREGER Miro Andrea - Leader, Accelerator Physics Group Telephone: +39-6-94032272 E-mail address: PREGER@LNF.INFN.IT RAFFONE Guido - Leader, Mechanical Engineering Group Telephone: +39-6-94032510 E-mail address: RAFFONE@LNF.INFN.IT SANELLI Claudio - Leader, Electrotechnical Engineering Group Telephone: +39-6-94032251 E-mail address: SANELLI@LNF.INFN.IT SANNIBALE Fernando - Electronics, Diagnostics and Controls Group Telephone: +39-6-94032213 E-mail address: SANNIBALE@LNF.INFN.IT SERIO Mario - Leader, Electronics, Diagnostics and Controls Group Telephone: +39-6-94032276 E-mail address: MSERIO@LNF.INFN.IT SGAMMA Francesco - Mechanical Engineering Group, Design Subgroup Telephone: +39-6-94032379 E-mail address: SGAMMA@LNF.INFN.IT SPATARO Bruno - Accelerator Physics Group Telephone: +39-6-94032253 E-mail address: SPATARO@LNF.INFN.IT STECCHI Alessandro - Accelerator Physics Group, DAFNE Control System Subgroup Telephone: +39-6-94032377 E-mail address: STECCHI@LNF.INFN.IT TAZZIOLI Franco - Associate Director, ARES-L Group Telephone: +39-6-94032275 E-mail address: TAZZIOLI@LNF.INFN.IT VACCAREZZA Cristina - Vacuum Group, Design Subgroup Telephone: +39-6-94032537 E-mail address: VARESE@LNF.INFN.IT VESCOVI Sandro - Electrotechnical Engineering Group Telephone: +39-6-94032267 E-mail address: SVESCOVI@LNF.INFN.IT VIGNOLA Gaetano - Head, Acccelerator Division and DAFNE Project Leader Telephone: +39-6-94032268 E-mail address: VIGNOLA@LNF.INFN.IT FAX : +39-6-94032203 ZOBOV Mikhail - Accelerator Physics Group Telephone: +39-6-94032277 E-mail address: MIKHAIL@LNF.INFN.IT