To reach design luminosity, the International Linear Collider (ILC) must be able to create and reliably maintain nanometer size beams. The ATF damping ring is the unique facility where ILC emittances are possible. In this paper we present and evaluate the proposal to create a final focus facility at the ATF which, using compact final focus optics and an ILC-like bunch train, would be capable of achieving 37 nm beam size. Such a facility would enable the development of beam diagnostics and tuning methods, as well as the training of young accelerator physicists

/KEK, Tsukuba /Beijing, Inst. High Energy Phys. /Novosibirsk, IYF /Daresbury /CERN /Hiroshima U. /Orsay, LAL /LLNL, Livermore /North Carolina A-T State U. /Oxford U. /Pohang Accelerator Lab. /Queen Mary, U. of London /Royal Holloway, U. of London /DESY /SLAC /University Coll. London /Oregon U. /Tokyo U.

Araki, S.

Hayano, H.

Higashi, Y.

Honda, Y.

Kanazawa, K.

Kubo, K.

Kume, T.

Kuriki, M.

Kuroda, S.

Masuzawa, M.

Naito, T.

Okugi, T.

Sugahara, R.

Takahashi, T.

Tauchi, T.

Terunuma, N.

Toge, N.

Urakawa, J.

Vogel, V.

Yamaoka, H.

Yokoya, K.

UNT Digital Library

Work supported in part by Department of Energy contract DE-AC02-76SF00515PROPOSAL OF THE NEXT INCARNATION OF ACCELERATOR TESTFACILITY AT KEK FOR THE INTERNATIONAL LINEAR COLLIDERS. Araki, H. Hayano, Y. Higashi, Y. Honda, K. Kanazawa, K. Kubo, T. Kume, M. Kuriki, S. Kuroda,M. Masuzawa, T. Naito, T. Okugi, R. Sugahara, T. Takahashi, T. Tauchi, N. Terunuma, N. Toge,J. Urakawa, V. Vogel, H. Yamaoka, K. Yokoya, KEK, Ibaraki, J. Gao, W. Liu, G. Pei,J. Wang, IHEP, Beijing, B. Grishanov, P. Logachev, F. Podgorny, V. Telnov, BINP, Novosibirsk,D. Angal-Kalinin, R. Appleby, J. Jones, A. Kalinin, CCLRC, Daresbury, O. Napoly,J. Payet, CEA, Gif-sur-Yvette, H. Braun, D. Schulte, F. Zimmermann, CERN, Geneva,T. Takahashi, Hiroshima University, Y. Iwashita, T. Mihara, Kyoto ICR, P. Bambade, LAL, Orsay,J. Gronberg, LLNL, Livermore, M. Kumada, NIRS, Chiba-shi, S. Danagoulian,S. Mtingwa, North Carolina A&T State University, N. Delerue, D. Howell, A. Reichold,D. Urner, Oxford, J. Choi, J.-Y. Huang, H.S. Kang, E.-S. Kim, S. Kim,I.S. Ko, Pohang Accelerator Laboratory, P. Burrows, G. Christian, S. Molloy,G. White, Queen Mary University of London, I. Agapov, G. Blair, G. Boorman, J. Carter,C. Driouichi, M. Price, Royal Holloway, University of London, N. Walker, DESY, Hamburg,K. Bane, A. Brachmann, T. Himel, T. Markiewicz, J. Nelson, N. Phinney, M. Pivi, T. Raubenheimer,M. Ross, R. Ruland, A. Seryi, C. Spencer, P. Tenenbaum, M. Woodley, SLAC, Stanford,S. Boogert, A. Liapine, S. Malton, UCL, London, E. Torrence, University of Oregon,T. Sanuki, T. Suehara, University of TokyoAbstractTo reach design luminosity, the International Linear Col-lider (ILC) must be able to create and reliably maintainnanometer size beams. The ATF damping ring is the uniquefacility where ILC emittances are possible. In this paperwe present and evaluate the proposal to create a final focusfacility at the ATF which, using compact final focus opticsand an ILC-like bunch train, would be capable of achieving37 nm beam size. Such a facility would enable the devel-opment of beam diagnostics and tuning methods, as well asthe training of young accelerator physicists.MOTIVATIONS AND GOALS FOR THEINTERNATIONAL ATF2 PROJECTThe future International Linear Collider (ILC) must fo-cus electron and positron beams to sizes as small as a fewnanometers at the Interaction Point (IP), and stablize themto the sub-nanometer level. Experience with handling,measuring and tuning such tiny beams would be invalu-able preparation for future ILC performance. The Acceler-ator Test Facility (ATF) at the KEK laboratory in Tsukuba,Japan, is the unique facility worldwide with ultra-low emit-tance beams extracted from the damping ring. The goals ofthe proposed ATF2 facility are to focus the beam to 37 nmsize using the compact final focus optics, develop experi-ence with reliably achieving and maintaining small beamsizes, provide a test bed for ILC instrumentation and BeamDelivery System (BDS) related studies, create a facility totrain young physicists, and finally be a model of design,construction and operation of a truly international facility.The ATF2 facility will be a continuation of the success-Table 1: The achieved ATF beam parameters and the pa-rameters for the ATF2, goals A and B. The ring energy isE0 = 1.28 GeV, the typical bunch length and energy spreadare σz ∼ 8 mm and ∆E/E = 0.08 %.Measured ( A ) ( B )Single bunchNbunch (1010) 0.2-1.0 0.5 -DR γεy (10−8m) 1.5 3 -Extr. γεy (10−8m) 3.0-6.5 3 -Multi bunchNbunch (1010) 0.3-0.5 0.5 0.5nbunches 20 1-20 3-20DR γεy (10−8m) 3.0-4.5 3 3Extr. γεy (10−8m) - 3 3IP σ∗y (nm) 37 37IP ∆y/σ∗y (%) 30 5ful results achieved at the Final Focus Test Beam [1]. TheFFTB, which achieved a beam size of 70 nm, provided in-valuable experience and confidence in the final focus sys-tem design and operation. However, it could not addressquestions of reliably maintaining the beam size over thelong term or of beam stability. Between 1994 and 1997,there were a number of short runs of 1-3 week duration.The small beam size was achieved in about half of theruns. The measured beam size was also much larger thanthe 40 nm value expected given the input beam emittances.The difference was attributed to significant jitter of the fo-cused beam and was partly due to limited accuracy of tun-ing the linear optics and the aberrations [3]. Since FFTBruns were not compatible with SLC operation, detailed in-vestigations of these important issues could not be pursued.SLAC-PUB-11202May 2005Contributed to Particle Accelerator Conference (PAC05), Knoxville, TN, May 16-20, 2005Figure 1: ATF2 layout, the conservative version which assumes that crab-cavity tests continue in 2006.Since the FFTB era, the ILC BDS design has changedsignificantly. The recently proposed compact final focusoptics with local chromaticity correction [2] has better per-formance in a much shorter system and can more easily beextended to multi-TeV. This is now the basis of ILC BDSdesign but has never been tested experimentally. Prior toILC construction, it will be important to obtain real experi-ence with the compact final focus optics design. The ATF2facility, to be built in 2005-2006 with first beams avail-able in early 2007, would give important operating expe-rience during preparation of the ILC Technical Design Re-port (TDR), construction and early years of operation, andwill become the alma mater for the generation of physicistsneeded to complete the ILC design and operate the ILC.0.0 10. 20. 30. 40. 50. 60. 70. 80. 90. 100.s (m)ATF2: EXT + Final Focus (FF6)SUN version 8.23/06 13/04/05  16.20.440.020.40.60.80.100.120.β1/2(m1/2 )-3.0-2.5-2.0-1.5-1.0-0.50.00.51.01.52.02.5D x(m)βx1 / 2 βy1 / 2 DxFigure 2: ATF2 Optics (“conservative” version, crab cavityspace not released).The ATF2 will address two major challenges of the ILCBDS: focusing the beams to nanometer size and providingsub-nanometer stability. The ATF has the high qualitybeams required to achieve these goals – it has successfullyproduced beams with the lowest emittance ever achieved,in both single and multi-bunch [4, 5] mode, which are verysimilar to those for ILC. Further development of hardwareand diagnostics and improvement of the extracted beamquality are needed for ATF2. The schedule for ATF2 andhardware development will successively address the twomajor goals:(A) Achievement of 37nm beam size.(A1) Demonstration of a compact final focus systembased on local chromaticity correction [2].(A2) Maintenance and verification of the small beamsize.(B) Control of beam position.(B1) Demonstration of beam orbit stabilization withnanometer precision at IP.(B2) Establishment of beam jitter control techniquesat nanometer level with ILC-type beam.Ultimately, the ATF2 will aim at achieving the small beamsize and nanometer beam stability simultaneously.The high quality beams available at ATF2 would gener-ate many other opportunities for experiments. As an op-tion, a photon linear collider (PLC) test facility has beenconsidered. At the PLC test facility, a photon beam wouldbe produced with high intensity and multi-bunch structuresimilar to the ILC. Experiments could also be conducted totest QED in the strong field of a high intensity laser.ATF2 DESIGNTwo possible final focus (FF) designs were consideredfor ATF2. The first was proposed in 2002 [6], and the sec-ond is the Next Linear Collider (NLC) compact final focus[7] scaled down in length. Both designs were evaluated forthe proposal [8]. The first design has fewer magnets andwould be less expensive, but the chromaticity correctionis not purely local, the tolerances on magnet strength andposition are tighter, the bandwidth is narrower and scalingto TeV energy is more difficult. Therefore, the NLC-likeoptics was chosen as a baseline design for the ATF2.The final focus beam line of the ATF2 is about 37 meterslong extending the existing ATF extraction line as shownin Fig.1. The optics in Fig.2 has L∗ = 1 m (distance fromlast focusing quadrupole to IP), η′ = −0.14 (derivative ofdispersion at IP) with IP beta-functions β∗x/y = 4/0.1 mm.The beam parameters are shown in Table 1. The total chro-maticity of this optics is approximately the same as in theILC FF. The vertical beam size will be focused to 37 nmwith the aspect ratio of about 100:1 similar to the ILC.In addition to the final focus proper, the ATF2 designincludes a snake-like optics with six bends which displacethe final focus beamline to the South (toward the bottomof Fig.1). This may be necessary to avoid the KEK-B crabcavity test area (shown by a blue rectangular bar), assumingconservatively that the crab-cavity development continuesinto 2006. If the first crab-cavity tests are successful andthe space is no longer needed, an “ideal optics” without thesnake bends will be used.To fully realize the ATF2 program and fulfill both goalsA and B, a number of hardware developments and otherimprovements are needed to the ATF damping ring and ex-traction system.For goal (A), an interferometer-based beam size moni-tor (BSM, also called Shintake monitor) will be installedat the IP. The laser will operate with higher modes thanthose used for the FFTB measurements [1]. To measure thebeam orbit and maintain the beam size with feedback, thebeamline magnets will be equipped with 100 nm resolutioncavity-BPMs and will be placed on movers. Tuning meth-ods will be established based on BSMs as well as BPMs.To achieve the goal (B1), a set of precision nano-BPMswill be installed at the IP. A set of BPMs with a resolutionof better than 2 nm are now being developed by the Japan-US group. The possibility of combining the two goals, withboth the BSM at the IP and nano-BPMs nearby to achieveboth the small beam size and nanometer stability, is underinvestigation.The beam quality must also be improved for ATF2. Thepresent normalized emittance in the ATF extraction line isestimated to be 4.8 × 10−8 m, three times larger than thatin the damping ring. The emittance can be improved to thenominal value of 3×10−8m by correcting the x-y coupling.The beam jitter must be reduced to about 30% of the beamsize for the goal (A), and 5% for the goal (B). The verticalbeam jitter in the ATF extraction line is now typically about30% of the beam size (up to 100% on the time scale of sev-eral minutes), which is much larger than the 10% beamjitter observed in the damping ring. The slow component isbelieved to come from the extraction kicker system, whichmay be improved by a double kicker scheme together withan additional feed-forward system. This is expected to re-duce the jitter to the same level as in the damping ring.The beam stability can be further improved with a new300 nsec kicker which will make it possible to extract thebeam-train in 3 bunches separated by 150 nsec. A fastfeedback system being developed by KEK and UK groups,FEATHER and FONT, will be used to further stabilizethe third bunch. The nano-BPM system will be able toverify the performance of the fast feedback system at thenanometer level. Further beam jitter control at nanometerlevel with ILC-type beam (goal B2), will require a veryfast kicker with less than a nsec rise time and stable pulseheight, which will make it possible to extract an ILC-typetrain, i.e. 20 bunches with about 300 nsec separation at5Hz. These developments may continue during the ILCconstruction.Finally, before installation of the ATF2 components, thefloor under the new beamlines must be reinforced in a simi-lar way as was done for the ATF damping ring. Studies withseismometers and tiltmeters have shown that the presentfloor in the ATF2 area is much less stable and has a largesensitivity to temperature variation. Reinforcement of theATF2 floor will be done during Summer of 2006.ATF2 COLLABORATION AND ATF2SCHEDULEThe ATF2 test facility is being developed by an inter-national team of more than sixty people worldwide, withthe aim to produce a detailed proposal by mid-2005. Thetentative schedule includes start of hardware construction(magnets, BPMs, etc.) in the Fall of 2005. Reinforcementof the ATF floor will happen in Summer of 2006, prior tothe beamline installation. The first beams could be avail-able in early 2007. The ATF2 construction plan is similarto a possible ILC model: the host laboratory (KEK) will besolely responsible for the conventional facility constructioncosts, while the beamline hardware will come as contribu-tions from participating labs and institutions. This processmay provide useful experience for the ILC.SUMMARYThis paper describes the proposal for an international fi-nal focus ATF2 facility for consideration by the worldwideInternational Linear Collider collaboration. The ATF2 fa-cility will benefit from the uniquely small beam emittancesachievable at KEK ATF, and will provide valuable expe-rience in achieving, maintaining and stabilizing nanome-ter scale beams. Such a facility will be invaluable for thesuccessful design and operation of ILC, provide a test bedfor development of instrumentation and accelerator physicsideas, train the next generation of accelerator physicists andpromote truly international collaboration building a new fa-cility.REFERENCES[1] V.Balakin et. al., PRL, 74, 2479, (1995).[2] P. Raimondi and A. Seryi, Phys. Rev. Lett. 86, 3779 (2001).[3] P. Tenenbaum, ATF2 workshop, SLAC, January 5, 2005,http://www-conf.slac.stanford.edu/mdi/ATF2.htm[4] K. Kubo et. al., PRL, , 88, 194801, (2002).[5] Y. Honda et. al., PRST, 6, 092802, (2003).[6] S. Kuroda et al., KEK-Preprint-2002-138, Nanobeam 2002.[7] A. Seryi et al., SLAC-PUB-10554, EPAC 2004.[8] ATF2 proposal, in preparation by ATF2 collaboration,http://lcdev.kek.jp/ILC-AsiaWG/WG4notes/atf2/

Proposal of the Next Incarnation of Accelerator Test Facility at KEK for the International Linear Collider

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Proposal of the Next Incarnation of Accelerator Test Facility at KEK for the International Linear Collider

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