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Robert R. Wilson Prize Talk John Peoples. April APS Meeting: February 14, 2010. Fermilab 1982. Tevatron I Complex (1987-1989). Tevatron I Luminosity Parameters. Luminosity L= (f 0 BN pbar N p Fγ)/(2β* (ε v + ε h )) Tevatron Collider Parameters
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Robert R. Wilson Prize TalkJohn Peoples April APS Meeting: February 14, 2010
Tevatron I Luminosity Parameters Luminosity L= (f0 BNpbar Np Fγ)/(2β* (εv + εh )) Tevatron Collider Parameters Luminosity Goal: L= 10 30 cm -2 s -1 Energy: E= 900 GeV β * = 100 cm ε v , ε h = 24 mm-mr N p , N pbar = 6 x 10 10 Number of Bunches/beam: B = 3 Luminosity Lifetime: T = L(dL/dt) -1 ~ 12 hr TL
Single batch stochastic cooling • The Debuncher cools one batch of ~ 10 8 pbars at a time for 2 - 3 s (one Main Ring cycle) and then transfers the batch to the Accumulator. • The cooling time is proportional to the number of particles (N), the mixing (M), the noise to signal ration (U) and inversely proportional to the bandwidth (W) T = ε (dε/dt) -1α N(M+U)/W • Typical initial cooling times are about 0.5 s .
Stack tail cooling system • The stack tail pickups are placed in a region of high dispersion (9 m). A displacement of 10 mm radially inward corresponds to an energy decrease of 10 MeV. • The gain of the stack tail pickups decreases exponentially with the radial distance from the pickups, which is proportional to energy. • The beam is cooled slowly where dN/dE is large and quickly where dN/dE is small. An exponential increase in dN/dE will provide a constant flux of pbars into the core momentum cooling system.
Phase I Upgrade of the Fermilab Accelerator Complex The elements of the phase I upgrade for run I were: • Matched low beta insertions for CDF (B0) and D0 • System of electrostatic separators to reduce the number of beam-crossings to two (CDF and D0) • Linac energy upgrade from 200 MeV to 400 MeV • Improvements to the pbar target station and cooling systems • Improvements to the controls and beam position monitors systems
Elements of the Phase II Upgrade • Main Injector replaces the Main Ring and does all of its functions much better • Recycler provides a third and substantially better cooling system with electron and stochastic cooling. • A set of injection kickers to enable 36 bunch operation • Bandwidths of all pbar source cooling systems doubled • Significant improvements to the controls and beam position monitor systems to make transfers faster and more efficient (especially pbars).
Main Injector • Main Injector is 150/120 GeV proton synchrotron with a circumference of 3.3 km. • Its functions for colliding beams are: • Accepts 8 GeV protons from the Booster, accelerates them to 120 GeV and delivers them to the Pbar target station for pbar production and subsequent collection in the pbar source. • Accepts short bunch trains of 8 GeV pbars from the Recycler and 8 GeV protons from the Booster, accelerates them to 150 GeV, coalesces them in to 4 bunches for pbars and 2 bunches for protons and then transfers them to the Tevatron.
Recycler • The Recycler is an 8 GeV storage ring for pbars. It is made mainly of permanent alternating gradient magnets. Pbars are transferred from the Accumulator after stacks of 25 x 10 10 have been accumulated. The typical time between transfers is 1 hr. • The accumulator stacking rate for these small stacks is 25- 30 x 10 10 /hr. • The pbars are cooled and stashed by a few x 100 mA cold relativistic electron beam (4.3 MeV). The stash size can be up to 500 x 10 10 and the accumulation rate does not decline with stash size. Typically stashes are mined when the stash is > 400 x 10 10 . • The formation of dense bunches in the Main Injector at 150 GeV and subsequent coalescing is very efficient. Typically the transfer efficiency from Recycler to the Tevatron at low β is > 80%.
Selection of the number of Bunches, B • L is proportional to B • The bunch spacing is determined by the selected sub-harmonic of the Tevatron 53 MHz RF system (h=3 x7 x53 = 1113). • h=53 provides a bunch spacing of 396 ns. It is being used in Run II to produce 3 groups of 12 bunches with 400 ns spacing for each beam. • The separation of the groups, about 2 µ s, is used for aborts, injection and cogging. • 36 bunches/beam is standard in Run II.
Collider Operation with the Main Injector and Recycler • Each beam has 36 bunches and circulates on helical orbits separated by > 5 sigma except at B0 (CDF) and D0 where the beams collide • Np is limited to < 30 x 10 10 /bunch in order to keep the pbar beam-beam tune shift to < .025. When this is exceeded the initial luminosity lifetime decreases < 6 hr quickly • 2.7 x 10 11 protons/bunch are consistently delivered to low β with a bunch coalescing efficiency of 70%. The luminosity lifetime is typically 6 hr. • N pbar is generally in the range of 7 to 9 x 10 10 /bunch. • The peak L is between 2.8 to 3.2 x 10 32 cm -2 s -1 when a full stash of 400 x 10 10 is available. • The record peak L is 3.47 x 10 32 cm -2 s -1 .
Selection of the number of Bunches, B • L is proportional to B • The bunch spacing is determined by the selected sub-harmonic of the Tevatron 53 MHz RF system (h=3 x7 x53 = 1113). • h=3 is the minimum value to provide collisions at B0 (CDF) and D0. h=3 was used in 1987. • 2 groups of h=3 bunches were used to produce 6 bunches/beam in 1988-89 and Run I. • h=53 provides a bunch spacing of 400 ns. It was used Run II to produce 3 groups of 12 bunches with 400 ns spacing for each beam. The separation of groups is about 2 µ s. 36 bunches/beam is standard in Run II.
