STATUS OF DAΦN E
M. Preger, for the DAΦNE Team1
INFN, Laboratori Nazionali di Frascati, C.P. 13, 00044 Frascati (Roma), Italy
Abstract
DAΦNE is a double ring electron-positron collider,designed to provide very high luminosity at the energy ofthe Φ resonance (1.02 GeV c.m.). After storing the firstbeam in fall 1997, the collider was commissioned withoutsolenoidal detectors until the end of 1998, reaching asingle bunch luminosity of 1.6x1030 cm-2s-1 with 20 mA
in each beam, corresponding to a beam-beam tune shift of≈0.03. A longitudinal bunch-to-bunch feedback has been
implemented, allowing the storage of more than 0.5 A in
30 bunches for both electrons and positrons. The KLOE
detector, embedded into a superconducting solenoid withstrong longitudinal field integral (2.4 Tm, to be compared
to a magnetic rigidity of 1.7 Tm) compensated by twoother solenoids of opposite field, was installed in winter1999 and commissioning resumed with a carefulcorrection of the coupling effects. Particular effort has
been dedicated to the reduction of background in theexperiment, which led to the possibility of injecting thebeams in interaction without switching off data taking.
The total stored current has reached more than 1 A in eachbeam, while a transverse feedback system has beenrealized to counteract vertical instabilities occurring during
injection. The collider is now running in the multibunchmode for KLOE data taking with peak luminosity up to
1.8x1031 cm-2s-1 and integrated luminosity larger than 0.8
pb-1 per day.

1 INTRODUCTION
DAΦNE has been already described in detail [1,2,3,4].
Let us just recall here that it is a high luminosity
electron-positron collider working at the center of massenergy of the Φ resonance (1.02 GeV) to produce a highrate of K mesons to study CP violation. Two 97 m longindependent rings lay in the same horizontal plane,crossing at a small horizontal angle (25 mrad) in two
interaction regions (IR). The first one hosts a large
detector (KLOE [5]) surrounded by a superconducting
solenoid with a field integral of 2.4 Tm; its main physics
goal is the measurement of the CP violating parameterRe(ε'/ε). A small non-magnetic experiment for the studyof the properties of kaonic atoms (DEAR [6]) is presently
installed on the second IR, which will host in the near
future a second magnetic detector (FINUDA [7]) with the1same field integral as KLOE, devoted to the study ofhypernuclei.
Up to 120 bunches can be stored in each ring, leading
to a very large design total current of 5A. The design
luminosity is 5x1032 cm-2s-1, based on the assumption ofreaching equal tune shifts of 0.04 in both planes with aflat beam (1% coupling, 4.5 cm vertical β at the crossing
point (IP) and 1 mm.mrad emittance).
A powerful injection system [8] has been realized tocope with the large stored current and short, Touschek
limited, lifetime. The system, consisting of a Linac andan intermediate damping ring, is designed to deliver single
bunches with the design charge at full energy to thecollider at a repetition rate of 1 Hz. In such way,
operating in a "top off" mode, or from scratch, it ispossible to refill the rings in less than 5 minutes.
Figure 1 shows a schematic layout of the double ring
collider in the final configuration with both magnetic
detectors installed. Presently, the DEAR detector occupies
the IR at the bottom of the figure. The low vertical β is
obtained by means of two symmetric quadrupole triplets,
realized with permanent magnets in KLOE and withconventional ones in DEAR.

2 HISTORY
The installation of DAΦNE was completed at the endof summer 1997. The first electron beam was stored in
September and the positron one followed two months
later. The first interactions were obtained in March 1998
and at the end of November a single bunch peakluminosity of 1.6x1030 cm-2s-1 was obtained, with 20 mA
in each beam. The corresponding tune shifts, estimatedfrom the luminosity measurement, beam currents andsizes, were ≈0.03.
Only a few attempts to run the machine in themultibunch mode were tried, reaching a luminosity of≈1x1031 cm-2s-1 with 13 bunches in each beam. During
this first commissioning phase (called "DAY-ONE") the
low vertical β at the interaction points (see Fig. 1) was
obtained by a symmetric arrangement of 7 quadrupoles,
with the central one sitting on the IP.
The design single bunch current (44 mA) was largely
exceeded, reaching 110 mA in both rings. Ion trapping
was observed in the electron ring and cured with a
distributed system of clearing electrodes.

D. Alesini, G. Benedetti, S. Bertolucci, C. Biscari, R. Boni, M. Boscolo, A. Clozza, G. Delle Monache, S. Di Mitri, G. Di Pirro, A. Drago,
A. Gallo, A. Ghigo, S. Guiducci, F. Marcellini, G. Mazzitelli, C. Milardi, L. Pellegrino, P. Raimondi (SLAC), R. Ricci, C. Sanelli, F. Sannibale,
M. Serio, F. Sgamma, A. Stecchi, A. Stella, C. Vaccarezza, M. Vescovi, G. Von Holtay (CERN), M. Zobov.

Figure 1: The double ring collider layout (symbols indicate quadrupoles Q, sextupoles S, permanent magnet quadrupoles
PMQ, compensating solenoids C, splitters SPL, dipoles D, wigglers W).
Up to 0.3 A were stored without feedback. A bunch-tobunch longitudinal feedback [9] was implemented, allowing the storage of more than 0.5 A in ≈30 bunches inboth rings.
During a long shutdown in winter 1999 the KLOE detector was installed on the IR on the top of Fig. 1. The
structure of the IR changed drastically with respect to the"DAY-ONE" layout with seven quadrupoles: the strong
field integral necessary for the experiment is realized bymeans of a superconducting solenoid with a field integralof 2.4 Tm. This field rotates the betatron oscillation planeby ≈41 degrees. In order to compensate the strong coupling created by this solenoid, two compensators areplaced near the splitters (see Fig. 1) with the same field
integral of opposite direction. A sophisticated assembly
containing two permanent magnet quadrupole triplets anda thin special vacuum chamber was inserted inside thedetector: the last step was to move the whole setup (solenoid magnet, detector and vacuum chamber) on the beamline. At the same time the DEAR experiment was prepared on the other IR, with two conventional quadrupole
triplets around a carbon fiber straight section on the IP.

The introduction of KLOE was a strong perturbation to
the lattice of the two rings for the following reasons:• The field created by the detector solenoid, althoughcompensated, strongly couples the betatron motion, calling for a sophisticated compensation
scheme [10] where the quadrupoles of the two focusing triplets are rotated by different angles following the rotation of the betatron plane inside themagnet.
• The quadrupole sitting on the IP was removed, reducing to 6 the number of IR quads.
• A Beam Position Monitor (BPM) placed exactly on
the IP in the first commissioning phase, which
made the superposition of the two beams at the IP
straightforward, was no more available.
• The symmetry of each ring with respect to the major axis in Fig. 1 was lost.
Commissioning of the collider after KLOE installation
was resumed in April 1999, exploiting the well-known
working point of the "DAY-ONE" structure, with particular attention to the problem of coupling correction. The
vertical beam size was minimized by tuning the mainsolenoid field, the compensators and skew quadrupole correctors inside the ring, reaching coupling values well below the design one (1%). However, the single bunch luminosity was less than 2x1029 cm-2s-1, much smaller than
the results obtained in the "DAY-ONE" configuration.
Since the main change with respect to the "DAY-ONE"configuration was the introduction of the solenoids,
particular care was dedicated to the problem of coupling,also because simulations had shown that even small
relative angles between the two beams in the plane
perpendicular to the trajectory could seriously affect thelimit on attainable luminosity. This angle cannot bedirectly measured at the IP. However, by making verticalscans of one beam on the other one at the IP and detecting
the corresponding luminosity, it was checked that theeffective vertical beam size was consistent with the size
observed on a synchrotron radiation detector in the arcs.
At the end of the year a period of approximately one
month was dedicated to KLOE: working with stored
currents of 300÷400 mA in 30÷40 bunches, with peakluminosity in the range of 5x1030 cm-2s-1 and beam
lifetime in the order of 1 hour, ≈2.5 pb-1 were delivered tothe experiment.
After the modification of the KLOE IR an unstable
quadrupole mode was observed in both rings, with athreshold strongly dependent on bunch length. This
problem was fixed by increasing the momentum
compaction and reducing the cavity voltage.
A rather strong vertical instability was also observed in
the positron beam at currents larger than ≈200 mA. Thisinstability is not harmful to colliding beams operation,
because it is damped by the beam-beam interaction. A
transverse feedback system was also developed to further
improve the instability threshold.

3 PRESENT PERFORMANCE
Collider operation was resumed in March 2000, after along shutdown, with particular attention to multibunch
operation and coupling optimization. Total currents inexcess of 1 A were stored separately in each ring. The
single bunch luminosity was carefully tuned by adjusting
collision parameters and further reducing the coupling to≈0.5%, reaching 5÷6x1029 cm-2s-1. In multibunch modethe maximum luminosity was 1x1031 cm-2s-1 with 30
bunches and ≈0.35 A per beam. It was empirically foundthat setting the two beams on different betatron tunes(5.10/5.14 for the electron beam, 5.15/5.21 for the
positronone)
improvedmachineperformance
significantly. At this point the machine was dedicated todata collection by KLOE for the whole month of July,delivering an integrated luminosity of ≈4 pb-1. However,data collection was affected by high rates of beam induced
backgrounds and short luminosity lifetime (typically half
an hour). Injection had to be performed frequently withdata acquisition switched off because of unacceptablebackground rate which tripped the KLOE drift chamber,leading to poor average luminosity.
At the beginning of September two weeks werededicated to DEAR: this experiment is particularly
sensitive to the signal to background ratio, which waslarger by two orders of magnitude than the minimum
required to start the experiment. By changing the optical
functions near the IR, improving closed orbit correction
and optimizing the position of 4 couples of scrapers
placed upstream the IR's in both rings it was possible todecrease the backgrounds by a factor 5.
The following period, from mid-September to the endof November, was shared (at typically 50% each) between
KLOE data taking and machine development dedicated at
improving the background situation and the averageluminosity. The first important result of this work wasthat the beam losses during injection were reduced to alevel which allowed injection without switching off thedrift chamber, only inhibiting data acquisition for 50 ms
at each injection pulse. In this way the averageluminosity can be kept close to the maximum one byfrequently refilling the stored beams to the maximum
currents allowed by the beam-beam interaction.
The machine is now operated with 45÷48 bunches. The
filling pattern interleaves one empty bucket with a fullone, with a ≈20% gap to avoid ion trapping. The typical
positron current is 15 mA per bunch, limited by beambeam interaction. The corresponding threshold forelectrons is ≈12 mA per bunch: at higher currents the
lifetime of the positron beam becomes very poor. The
peak luminosity obtained so far is 1.8x1031 cm-2s-1, with
≈0.75 A in the positron beam and ≈0.55 A in the electronone. The luminosity per bunch in multibunch operationis therefore ≈30% smaller than the best obtained in the
single bunch mode, due to non perfectly uniform filling
patterns and parasitic crossing effects. The collider runs
with the beams separated in the DEAR interaction region.
800

Lint(nb^-1)
Lpeak(e29)

700
600
500
400
300
200
100
0

Jul

Aug

Sep

Oct

Nov

Figure 2: Peak luminosity (dots, in units of 1029 cm-2s-1)
and integrated luminosity (crosses, nb-1) per day.

In 2.5 months 24 pb-1 were delivered to the experiment.
Figure 2 shows the integrated and peak luminosity perday. The former changes significantly between differentdays because of variable beam time dedicated to machinedevelopment, while the latter exhibits a smooth
improvement with time. It can be seen from Fig. 2 thatthe envelope of the integrated luminosity improves withtime more rapidly than the peak one. This may be
attributed to the fact that, during this period of datataking, no major improvements in the single bunch
luminosity were obtained, but at the same time there has
been a significant increase in the overall efficiency ofmachine operation.
The last two weeks of December 2000 were dedicatedagain to DEAR: by reinforcing the shielding around thedetector and further optimizing the optical functions andclosed orbit, another factor 4 was gained in the signal tobackground ratio. With a new experimental setup, whichis already installed on the second IP and exploiting a newshape for the scrapers (see next section) it should be possible to start data acquisition. In addition, a new luminosity monitor based on the detection of charged kaons fromthe decay of the Φ resonance was also brought into operation. A trial to work with the beams crossing in KLOE
and DEAR at the same time led to a substantial reduction
in luminosity. Studies are under way to find a suitableworking point with two crossings.

4 BACKGROUND STUDIES
During the time allotted to machine development at theend of last year a careful study of the behavior of thescrapers installed upstream the IR's has been carriedout [11]. Each one of the 4 scrapers, placed before thesplitters (see Fig. 1) in the direction of the incoming
beams, consists of a couple of remote controlled rectangular tungsten blocks of 35 mm thickness, which can be
moved in the horizontal direction from the walls of thevacuum chamber towards the beam. The position of thescrapers is chosen in such a way that they intercept
Touschek-scattered particles from the arcs before hitting
the vacuum chamber inside the IR's. The background ratemeasured by KLOE for an electron beam as a function of
the scraper position is shown in Fig. 3: it can be seenthat the external scraper reduces the background up to a
distance of ≈25 mm from the beam, while the internal one
has only a harmful effect.
The dynamics of Touschek-scattered particles has been
simulated by means of tracking programs and GEANT3:
it was found that most particles are scattered by thetungsten instead of being absorbed and that a different
shape is necessary to improve background rejection. New
scrapers have been built and installed on the rings withthe thickness increased to 55 mm. This thickness isdivided into two flat surfaces: the first one is 10 mm longand bent by 100 mrad with respect to the beam trajectoryin order to increase the impinging angle for mostparticles, the second one (45 mm in thickness) is bent by

10 mrad in the opposite direction to avoid scattering theelectrons towards the center of the beam pipe. First results
show an increased efficiency of the scrapers.

103

BKGD rate (Hz/mA2 )beam position(-2.7 mm)

102

X (mm)

101
-50

-25

0

25

50

Figure 3: Normalized background versus position of
scraper edge.

5 NON LINEARITIESAnother important result from the machine development shifts was the discovery of a strong "octupole-like"term in the wigglers (see Fig. 1). The presence of nonlinear terms in the magnetic structure was already known
from the behavior of the betatron tunes versus energy(obtained by changing the RF frequency) shown in Fig. 4,
which exhibits (with wigglers on) a non linear shape evenwith all sextupoles off in the ring. In a different latticewith all wigglers off, instead, the tunes are linear.

0.30
0.25
∆QY
0.20
0.15

∆QX

0.10
0.05
-4

∆p/p*1000
-2

0

2

4

6

8

10

Figure 4 - Betatron tunes versus energy with sextupoles
off (full dots = wigglers off, empty dots = wigglers on).
A closed orbit "bump" was performed in each wiggler
by means of 4 horizontal correctors. The currents were
adjusted in such a way that the beam position was
perturbed only in the region between the first and lastcorrector. The energy change induced by the correctors was
carefully corrected by changing the RF frequency. Fig. 5
shows the dependence of the betatron tunes on theamplitude of the closed orbit bump in the wiggler. The
horizontal tune fits well with a quadratic behaviour,
typical of an "octupole-like" term. The peak of the curveis slightly displaced from the origin because of a residual
orbit displacement in the wiggler.

0.02
0.01

∆Q

∆QY

0.00
-0.01
∆QX

-0.02
-0.03
-10

∆X(mm)

-5

0

5

10

Figure 5: Change in tune versus horizontal bump
amplitude (full dots = horizontal, empty dots = vertical).
Since the correctors required for a closed symmetricbump are at least four, the beam is displaced in the twodipoles of each achromat as well as in the wiggler (seeFig. 1). The horizontal β function is larger than thevertical one by a factor ≈3 in the wiggler, while thesituation is opposite in the dipole.
We have therefore attributed the dependence of thevertical tune on bump amplitude to the displacement in
the dipole. To verify this assumption, a lattice withwigglers off and similar functions in the achromat has
been realized and the measurement of tunes with bump
amplitude repeated. By subtracting the measurement withwigglers off from the corresponding one with wigglers
on, the result shown in Fig. 6 has been obtained,

0.010

∆Q

0.000
-0.005∆QX-0.010-0.015-0.020-10∆x(mm)-5

6 CONCLUSIONS
Data collection for the KLOE experiment has started at
the end of year 2000 with an integrated luminosity per day
approaching 1 pb-1. Recent improvements on machinelattice have doubled the single bunch luminosity, opening
the way to a substantial improvement of the overallmachine performance. Studies are in progress on theeffects of nonlinearities on the luminosity and their cures;
we are also working on the limits on stored current tocope with the larger total current expected from theimproved single bunch operation, on beam lifetime andon the level of background in the experiments.

REFERENCES

∆QY

0.005

the wiggler (≈25 mm peak-to-peak) with a fourth orderterm in the field. The measured value is in agreement withthe field measurement at the center of the wiggler poles.
After a shutdown in January 2001 for the maintenanceof the cryogenic systems a new "detuned" optics (withhigh vertical β value in DEAR, ≈12 m) has recently beentested to better separate the beams at the second IP. A
single bunch luminosity of 1x1030 cm-2s-1 has beenmeasured at the first attempt. However, this detuned
lattice has lower horizontal β values at the wigglers, thus
decreasing the effect of the octupole term. Work is inprogress to establish to which amount the improvementin luminosity comes from better separation in DEAR andfrom reduced non linearity effects, and to set up
multibunch operation with this new lattice in order tosubstantially improve DAΦNE luminosity performance.

0

5

10

Figure 6 - Tune dependence on bump amplitude after
subtracting measurements with wigglers off
full dots = horizontal, empty dots = vertical).
This result is compatible with an "octupole-like" term.
We cannot demonstrate that it is a real octupole since themeasurement with a vertical beam displacement could not
be performed due to the limited aperture of the vacuum
chamber. The chromatic behavior of the tunes is linear
and the decoherence time measured by applying atransverse kick to the beam by means of the injection
kickers also improves in the lattice with wigglers off.
The measured tune shift on amplitude corresponds to an
integrated third order term of 0.8x103 m -3 per wiggler, andcomes from the combination of the beam trajectory inside[1] G. Vignola, DAΦNE Project Team, “DAΦNE, The
Frascati Φ-factory”, PAC’93, Washington, May 1993.
[2] G. Vignola, DAΦNE Project Team, “DAΦNE, The First
Φ-factory”, EPAC’96, Sitges, June 1996.
[3] S. Guiducci, DAΦNE Commissioning Team, “DAΦNE
Operating experience”, PAC’99, New York, March
1999.
[4] M. Zobov, DAΦNE Commissioning Team, “Status
Report on DAΦNE Performance”, EPAC’2000, Vienna,
June 2000.
[5] The KLOE Collaboration, “KLOE: a General Purpose
Detector for DAΦNE”, LNF-92/019 (IR), April 1992.
[6] The DEAR Collaboration, "DAΦNE Exotic Atom
Research" (DEAR Proposal) LNF 95/055 (IR), 1955.
[7] The FINUDA Collaboration, “FINUDA: a Detector for
Nuclear Physics at DAΦNE”, LNF-93/021 (IR), May
1993.
[8] R. Boni et al., “The Frascati Φ-factory Injection
System”, PAC'91, S. Francisco, May 1991.
[9] M. Serio et al., “Multibunch Instabilities and Cures”,
EPAC'96, Sitges, June 1996.
[10] M. Bassetti et al., “DAΦNE Interaction Region Design”,
PAC'93, Washington, May 1991.
[11] M. Boscolo et al., “Study of the Machine Induced
Background in KLOE”, DAΦNE Tech. Note IR-9, October
2000.