DAΦNE Upgrade Status - Science Direct

Nuclear Physics B (Proc. Suppl.) 181–182 (2008) 385–389 www.elsevierphysics.com

DAΦNE Upgrade Status David Alesinia , Maria Enrica Biaginia , Caterina Biscaria , Roberto Bonia , Manuela Boscoloa , Fabio Bossia , Bruno Buonomoa , Alberto Clozzaa , Giovanni Delle Monachea , Theo Demmaa , Enrico Di Pasqualea , Giampiero Di Pirroa , Alessandro Dragoa , Alessandro Galloa , Andrea Ghigoa , Susanna Guiduccia , Carlo Ligia , Fabio Marcellinia , Giovanni Mazzitellia , Catia Milardia , Fabrizio Murtasa , Luigi Pellegrinoa , Miro Pregera , Lina Quintieria , Pantaleo Raimondia , Ruggero Riccia , Ugo Rotundoa , Claudio Sanellia , Mario Serioa , Francesco Sgammaa , Bruno Spataroa , Alessandro Stecchia , Angelo Stellaa , Sandro Tomassinia , Cristina Vaccarezzaa , Mikhail Zobova Ivan Koopb , Evgeny Levichevb , Pavel Piminovb , Dmitry Shatilovb , Victor Smalukb , Simona Bettoni c , Marco Schioppad , Paolo Valentee , Kazuhito Ohmif , Nicolas Arnaudg , Dominique Bretong , Patrick Roudeaug , Achille Stocchig , Alessandro Variolag , Benoit Francis Viaudg , Marco Espositoh , Eugenio Paolonii , Paolo Branchinij a

INFN Laboratori Nazionali di Frascati, Frascati (Rome), Italy

b

BINP SB RAS, Novosibirsk, Russia

c

CERN, Geneva, Switzerland

d e f

INFN Cosenza, Cosenza, Italy

INFN, Rome, Italy

KEK, Ibaraki, Japan

g

LAL, Orsay, France

h

University of Rome ”La Sapienza”, Rome, Italy

i

University of Pisa and INFN, Pisa, Italy

j

University of Rome ”Roma 3”, Rome, Italy

The DAΦNE Φ-factory at INFN-LNF has been upgraded in the second half of 2007 with the scope of testing a recently proposed scheme of crab waist collisions. New vacuum chambers and permanent quadrupole magnets have been designed, fabricated and installed to realize the new configuration. The ring injection systems have been also modified with the installation of new stripline fast injection kickers. Moreover the old bellows have been substituted by the new ones and all ion clearing electrodes in the electron ring have been removed. In the talk we describe the new layout as well as several experimental results obtained during the new run.

1. INTRODUCTION DAΦNE [1] is an electron-positron collider working at the c.m. energy of the Φ resonance (1.02 GeV). In its original configuration the collider consisted of two independent rings having two common Interaction Regions (IR) and an injection system composed of a full energy linear ac0920-5632/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2008.09.070

celerator, a damping/accumulator ring and transfer lines. Since 2000 DAΦNE has been delivering luminosity to three experiments, KLOE [2], FINUDA [3] and DEAR [4] steadily improving performances in terms of luminosity, lifetime and backgrounds. The best machine performances were obtained in the KLOE and FINUDA runs. In particular we

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reached a peak luminosity of 1.5 · 1032 cm−2 s−1 , with a maximum daily integrated luminosity of about 10pb−1 . These performances were the best obtainable with the original collision scheme [5]. Recently the Large Piwinski Angle (LPA) and Crab Waist (CW) collision scheme has been proposed for colliders luminosity increase [6]. It holds the promise of increasing the luminosity of storage-ring colliders by more than two orders of magnitude beyond the current state-of-the-art, without any significant increase in beam current and without reducing the bunch length. This scheme has been adopted in 2007 for the design of the DAΦNE new interaction region for the SIDDHARTA experiment [7]. 2. THE LARGE PIWINSKY ANGLE AND CRAB WAIST COLLISION SCHEME The main features of the new collision scheme can be summarized as follows and are discussed in details in [8]: 1. Large Piwinski Angle (Φ = θσz /σx ) at Interaction Point (IP), see Fig. 1a. This is obtained by increasing the beams crossing angle θ and by reducing the transverse horizontal beam size σx . The LPA allows to reduce the beam overlap area and to decrease the vertical and horizontal beambeam tune shifts. Moreover it reduces the detrimental effects of parasitic crossings (PC) because of the higher crossing angle and smaller horizontal beam sizes; 2. vertical β-function at IP (βy∗ ) of the same order of the overlap area length σx /θ (see Fig. 1b). Together with the reduction of the horizontal beam size, this is the main source of the geometric luminosity increase and it allows, also, to strongly reduce the vertical tune shift; 3. CW transformation realized by two crab sextupoles (see Fig. 1c). This gives a further geometric luminosity gain and allows suppressing the synchro-betatron resonances arising from the vertical motion modulation by horizontal particle oscillations. The DAΦNE upgrade beam parameters are listed in Table 1. In the same Table we show

Figure 1. Sketch of the new collision scheme with LPA and CW.

the parameters of the last KLOE run for comparison. With this new scheme it is expected to reach a luminosity > 5 · 1032 cm−2 s−1 . The new interaction region (IR1) layout is reported in Fig. 2. A detailed description of the new magnet configuration and luminometers used to measure the luminosity can be found in [9]. 3. OTHER HARDWARE UPGRADES AND MODIFICATIONS 3.1. Ring crossing region A new crossing section providing complete separation between the two beams has replaced the second interaction region. It is geometrically symmetric to IR1. Independent beam vacuum chambers are obtained by splitting the original

D. Alesini et al. / Nuclear Physics B (Proc. Suppl.) 181–182 (2008) 385–389

Table 1 DAΦNE beam parameters P arameter KLOE Ibunch (mA) 13 110 Nbunch 17 βy∗ (mm) 170 βx∗ (cm) 7 σy∗ (μm) ∗ 700 σx (μm) ∗ 25 σz (μm) θ (mrad) 12.5 Φ 0.36

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U P GRADE 13 110 6 20 2.6 200 20 25 2.5

Figure 3. Ring crossing region.

HFSS simulations in the frequency range from DC to 5 GHz have shown that the new design strongly reduces bellows contribution to the ring coupling impedance.

Figure 2. Half view of old IR1 (top) and new (bottom) layout.

pipe in two half-moon shaped sections, see Fig. 3, providing full vertical beam separation. This aspect is quite relevant because it cancels completely the problems coming from the beam-beam long range interaction, allowing at the same time to relax the ring optics requirements imposed by beam separation at the unused interaction point. 3.2. New bellows Six new bellows have been developed and installed in the new IR1 and in the ring crossing section of each ring. They connect circular cross section pipes of 88 mm diameter, see Fig. 4. Their innovative component is the RF shield [10] implemented by means of Ω shaped Be-Cu strips.

3.3. New fast injection kickers New stripline injection kickers [11] have been installed in the rings (Fig. 5). They can be fed by fast high voltage pulsers (5 ns-40 kV instead of the old 200 ns-25 kV) allowing injection of the single bunch without perturbing the already stored ones. The beam coupling impedance and HOM content of these new devices has been strongly reduced with respect to the previous ones because of their optimized tapered design. The expected benefits of the new injection system are: higher maximum stored currents, improved stability of colliding beams during injection and less background during injection. 4. COLLIDER STATUS AND BEST OBTAINED RESULTS 4.1. Commissioning milestones The machine started-up at the end of November 2007 and both beams have been stored during first days of December with a detuned lattice. Low-β optics has been applied in January 2008

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trigger has been performed at the end of March. 4.2. Achieved optical parameters and best performances The achieved optical parameters are given in Table 2. As an example the comparison between the measured β-functions (positron ring) and the theoretical ones is shown in Fig. 6, demonstrating the very good knowledge of the linear machine model.

Figure 4. Copper-Beryllium strip shielded bellows, mechanical design (left) and real device (right).

Table 2 DAΦNE optical achieved parameters P arameter design e− emitt. (mm.mrad) 0.20 0.26 6.5 9 βy∗ (mm) ∗ 200 270 βx (cm) θ (mrad) 25 27

e+ 0.26 9 270 25

Figure 5. New fast injection kickers

and first collisions have been obtained. Solenoid windings have been installed in the positron ring and 800 mA e+ current has been stored (with pattern not suitable for collisions) in the first week of February. During February CW sextupoles have been put in operation and a luminosity monitor based on Bhabha e+e- elastic scattering has been installed. First L  ≈ 1032 cm−2 s−1 has been measured at the beginning of March. The SIDDHARTA prototype installation has been done in middle of March. New horizontal feedback have been installed in the electron ring first half of March. Optimization of background in the kaon

Figure 6. Comparison between the measured βfunctions and the theoretical ones (positron ring)

The effect of the crab sextupoles on the luminosity can be observed by switching them on and off. Fig. 7 shows, as an example, the effect of the e− sextupoles: if one switches them off there is an increase of the vertical size of the e− beam (vertical blow-up) and, as a consequence, there is a luminosity reduction.

D. Alesini et al. / Nuclear Physics B (Proc. Suppl.) 181–182 (2008) 385–389

Up to now the maximum single beam stored currents have been ≈ 1.2A for the electron ring and ≈ 0.95A for the positron one. The maximum stored currents of interacting beams at the same time have been ≈ 0.7A(e− ) ≈ 0.7A(e+ ) in 95 bunches. The measured peak luminosity was ≈ 1.5 · 1032 cm−2 s−1 (measured by the Bhabha monitor) and the maximum integrated luminosity per day has been ≈ 6.0pb−1 . A first beam injection test on e+ ring with the fast pulsers has also been done successfully. Unfortunately, we had problems with the new fast pulsers after few hours of operation. They are now being recovered by the vendor and will be re-installed in the machine as soon as possible. The bunch length of both beam has also been measured. The results are reported in Fig. 8 showing reductions of the e+ /e− coupling impedances by ≈ 30% and ≈ 40% respectively, with respect to the last FINUDA run.

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Figure 8. Bunch length measurements

chine linear optics model has been reached. Good vacuum conditioning has been done and 1.2A and 0.95A single beam currents have been stored in the e− and e+ ring respectively. A peak luminosity of ≈ 1.5 · 1032 has been measured. Bunch length measurements have been performed showing a reduction of the machine impedance. Test of the fast kickers has been done successfully. Up to now no ”hard to fix” problems have been found and commissioning is well under way. REFERENCES

Figure 7. Observation of the e− crab sextupoles effect on the beam.

5. CONCLUSIONS The DAΦNE Φ-factory at INFN-LNF has been upgraded in the second half of 2007 with the aim of testing a recently proposed scheme of crab waist collisions and the commissioning started at the end of November. Up to now, the new collision scheme with crab sextupoles has been successfully tested and a good knowledge of the ma-

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