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Tevatron Runii Performance and Plans Proceedings of EPAC 2002, Paris, France TEVATRON RUN II PERFORMANCE AND PLANS M. Church†, FNAL*, Batavia, IL 60510, USA Abstract The Fermilab accelerator complex has been operating 2 CURRENT STATUS AND ISSUES Run II for approximately one year. In this mode 36 Table 1 lists the current status of important Collider proton bunches collide with 36 antiproton bunches at 2 parameters along with the Run IIa goals for 2002. interaction regions in the Tevatron at 980 GeV beam energy. The long range goal in Run II is to obtain a total Table 1: Important Run IIa parameters. Column 2 shows -1 best values on 1/1/2002, column 3 shows best values on integrated luminosity of 15 pb . The current status and performance of the accelerator complex is described, 5/25/2002, and column 4 shows goals for 1/1/2003 including the Tevatron, Main Injector, Antiproton Source, Parameter 1/1/02 5/25/02 1/1/03 and Recycler Ring. Future upgrade plans and prospects goal for reaching the admittedly ambitious long range goal are presented. antiproton production 10 11 18 rate (E10/hr) 1 COLLIDER OPERATIONS AT Accumulator core size 115 120 165 FERMILAB (E10) There are 2 basic modes during Collider operation: antiproton transfer .23 .37 .80 antiproton stacking and "shots." A shot is the process of efficiency loading the Tevatron with protons and antiprotons. In stacking mode, a batch of 84 53MHz proton antiprotons/bunch @ 7.6 10.8 33 bunches is extracted from the Booster Ring at 8 GeV and low beta (E9) injected into the MI (Main Injector) every 2.2 seconds. protons/bunch @ low 115 196 270 These are accelerated to 120 GeV and extracted to the beta (E9) antiproton production target. 8 GeV antiprotons from the production target are then delivered to the Debuncher transverse emittance @ 16.0 16.3 17.5 Ring where they are debunched and stochastically cooled. low beta (π-mm-mrad) These are then transferred to the Accumulator Ring where peak luminosity 0.8 2.0 8.6 they are stacked and stochastically cooled into a "core." Every ~14 hours stacking is stopped in preparation for a shot. A batch of 7 53MHz proton bunches is extracted Figures 1 and 2 show the peak luminosity and the from the Booster, injected into the MI, accelerated to 150 proton and antiproton intensities at the start of each store GeV, coalesced into a single bunch, and then injected into for stores from 11/28/01 to 5/25/02. Over the last five the Tevatron. This process is repeated every ~12.5 months significant gains have been made in increasing the seconds until 36 proton bunches are loaded into the proton intensity at low beta, but increasing the antiproton Tevatron on its central orbit. Electrostatic separators are intensity at low beta has been problematic. There are two then turned on in the Tevatron in preparation for major reasons for this: 1) The transverse emittance of the antiproton injection. Antiprotons are extracted from the antiprotons in the Accumulator core is large -- about twice Accumulator in 4 batches of ~7 53MHz bunches, injected as large as it was in Run I for similar core intensities. The into the MI, accelerated to 150 GeV, coalesced into 4 transfer efficiency of antiprotons from the Accumulator single bunches separated by 396 nsec, and then injected core to 980 GeV is dramatically reduced because of this into the Tevatron, counter-rotating with the protons and large transverse emittance (see Table 1). 2) The long separated by the helical orbit. This process is repeated 9 range beam-beam interaction in the Tevatron severely times. The beam in the Tevatron is then accelerated to reduces the antiproton lifetime and causes excessive 980 GeV, a low beta squeeze is executed, and the beams emittance growth at 150 GeV. are finally brought into collisions at the 2 IR’s (Interaction Extensive recent studies indicate that the large Regions). An entire shot typically takes ~3 hours from Accumulator transverse emittance is due to an increase in the end of the previous store to the start of the next store. the IBS (IntraBeam Scattering) contribution to beam A Collider store generally lasts ~14 hours which is heating in the core. The Accumulator lattice was approximately 1 luminosity lifetime. modified between Run II and Run I in order to increase the bandwidth of the stacktail cooling system from 1-2 ______________________________________________ GHz to 2-4 GHz. This bandwidth increase was necessary † [email protected] to support higher stacking rates for Run II. This lattice * Operated by Universities Research Association, Inc. under contract η with the U.S. Department of Energy modification changed the value of , the slip factor, from 11 Proceedings of EPAC 2002, Paris, France .023 to .012 in order to avoid Schottky band overlap in the lattices -- one for shots and one for stacking. It takes stacktail cooling system. about 60 seconds to ramp between the two lattices. The other serious limitation to Run II luminosity is the 2 long range beam-beam interaction in the Tevatron [1]. ) -1 During Run I the number of parasitic beam-beam sec crossings was 12; in Run II it is now 72. Even though the -2 1.5 beam-beam tune shift is relatively small, ~.003, the lifetime of the antiprotons is dramatically reduced by the presence of protons at 150 GeV in the Tevatron. The 1 typical beam separation on the helix is ~5 beam sigmas. Over the last few months improvements have been made in the helical orbit increasing the separation between 0.5 protons and antiprotons. This has improved the antiproton lifetime at 150 GeV and the antiproton efficiency during the transition from the injection helix to Peak Luminosity (E31 cm the collision helix. These modifications have increased 0 Jan/1 Feb/27 Apr/26 the antiproton transfer efficiency (from Accumulator @ 8 GeV to collisions @ 980 GeV) from ~23% to ~37% even date while increasing the proton intensity by 70%. In a shutdown in the Fall of 2002, the limiting aperture Figure 1: Peak luminosity vs. date for Run II from in the Tevatron (3 C0 Lambertson magnets) will be 11/28/01 to 5/25/02 removed and replaced with wider aperture dipole 20 200 magnets, allowing the helix to be opened an additional ~30%. Modification to the lattice at the A0 sector protons (possibly in the Fall 2002 shutdown) will yield additional protons/bunch (E9) 15 150 improvements in the helix. The completion of longitudinal and transverse dampers in the Tevatron in the summer of 2002 will allow the chromaticity to be reduced (currently it is set at ~10 units). This will increase the 150 10 100 GeV lifetime. Also, methods of using the existing octupole circuits to provide differential chromaticity for the protons and antiprotons are being investigated. 5 50 antiprotons/bunch (E9) antiprotons 3 RECYCLER COMMISSIONING 0 0 The Recycler Ring is an 8 GeV antiproton storage ring Jan/1 Feb/27 Apr/26 situated in the MI tunnel enclosure [2] [3]. Its purpose is twofold: 1) provide for final 8 GeV antiproton storage, date beyond the Accumulator; 2) allow for reusing the Figure 2: Proton and antiproton intensity at low beta vs. antiprotons which remain at the end of a Tevatron store. date for Run II from 11/28/01 to 5/25/02 The Accumulator antiproton core size is probably limited to ~200E10 antiprotons. There are two reasons for this. First, as the stack size increases, the efficacy of Unfortunately it was not appreciated that this lattice the core stochastic cooling systems drop (like 1/N). The modification also increased the IBS term heating of the core from the stacktail cooling system does 2 D 2 + ()βD’+αD not decrease with N, therefore the antiproton stacking rate H = β drops as the core size increases. Second, as the core size by a factor of 2.5. Here, D is the dispersion function, D’ increases, trapped ion instabilities become increasing is the derivative of the dispersion, α and β are the normal difficult to control. The Recycler has a circumference 7 lattice functions, and Η is averaged over the ring. times larger than the Accumulator, therefore for a given core size, the line charge density is less and it is probably The plan to mitigate the excessive core heating is not as sensitive to trapped ions. In addition, electron twofold. 1) During a 2 week shutdown in early June a cooling [4] is planned to be installed and commissioned in new Accumulator core stochastic cooling system will be the Recycler in 2004, and the cooling rate in this case installed. This system will increase the cooling does not scale like 1/N. Without the Recycler being used bandwidth by a factor of 2, thus increasing the cooling for 8 GeV antiproton storage and recycling, peak rate by a factor of 4. 2) A second Accumulator lattice is luminosities in the Tevatron above ~1E32 are probably being commissioned to be used only during shots. This very difficult to obtain. lattice will reduce the IBS heating term by a factor of 2.5. The Accumulator will therefore be operated at 2 distinct 12 Proceedings of EPAC 2002, Paris, France Currently luminosity in Run IIa is being produced with 4 PLANS TO INCREASE ANTIPROTON antiprotons delivered from the Accumulator. The PRODUCTION RATE Recycler is still in a commissioning stage but steady improvements in performance is being made. Figure 3 Assuming the number of protons/bunch in the Tevatron shows the antiproton transfer efficiency from the is limited by the beam-beam interaction, the only way to Accumulator to Recycler for a recent series of 3 transfers.
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