Notes

Outline

The Fermilab Accelerator Complex: Status and Challenges Eric Prebys FNAL Beams Division

Outline Basic Accelerator Physics Concepts Horizontal motion (lattice functions, emittance) Tune plane Longitudinal motion (phase stability, longitudinal emittance) The Accelerator Complex Proton Source (Preac, Linac, Booster) Main Injector Pbar source (target, debuncher, accumulator) Tevatron Recycler Operational modes The Challenges Run II MiniBooNE NUMI

Dipole Field, Thin Lens Approximation.

Quadrupole Fields (focusing elements)

Betatron Motion

Tune and Tune Plane

Emittance

Normalized Emittance

Slip Factor/Transition

Phase Stability

Longitudinal Phase Space

Longitudinal Emittance

Fermilab Accelerators

The Fermilab Accelerator Complex

Preac(cellerator) and Linac

Booster

Main Injector

Antiproton Source

Antiproton Source – Debunching and Cooling

Tevatron The Tevatron was the world’s first superconducting accelerator. It accepts protons AND pbars at 150 GeV from the Main Injector. Typically: 36 proton bunches with 180E9 protons in each. (Run IIa goal: 270E9) 36 pbar bunches with 12E9 pbars in each. (Run IIa goal: 33E9) These are accelerated to 980 GeV. Collisions (“low beta”) are initiated at the B0 (CDF) and D0 detector regions. These “stores” are kept for typically 16 hours, while more antiprotons are made for the next “shot”.

Recycler The Recycler is an 8 GeV storage ring in the same tunnel as the Main Injector. The main lattice elements (dipoles and quadrupoles) are made out of permanent magnets). The Recycler can accept 8 GeV antiprotons from The antiproton accumulator. The Main Injector (after deceleration). The Recycler can deliver these antiprotons to the Main Injector for acceleration. The goal of the recycler is To store antiprotons from the accumulator, thereby increasing the total antiproton production capacity. To recover antiprotons from a Tevatron store for use in subsequent stores. At the moment, the recycler is not being used in standard operation.

Primary Modes of Operation Stacking: full booster batches (~5E12 p) are accelerated to 120 GeV by the Main Injector, and delivered to the pbar target about once every 3 seconds (limited by the rate at which they can be debunched and cooled.  It takes 10-16 hours to get enough pbars for a “shot”. Shot setup: various beamline tuning takes place.  Most importantly, pbar transfer lines are tuned with reverse protons. Proton Injection:  about 7  53 MHz booster bunches are injected into the M.I., accelerated to 150 GeV and “coalesced” into a single bunch, which is injected into the Tevatron (x 36). Antiproton Injection:  part of the “core” of the accumulator is manipulated to a separate extraction orbit and about 11 53 MHz bunches are extracted to the M.I., where they are accelerated to 150 GeV, coalesced and injected into the tevatron at 150 GeV. Acceleration/collision:  The protons and pbars are accelerated together to 980 GeV over a few minutes. The beam is scraped, and the beta is reduced (“squeezed”) at the collision regions.  Physics begins.  During this time, the rest of the accelerator complex is totally free to do other things (primarily stacking). MiniBooNE Operation:  While the M.I. Is ramping, a chain of 8 GeV Booster batches is switched to the MiniBooNE beamline. NUMI Operation:  along with the stacking batch, 5 additional batches are loaded into the Main injector.  These are accelerated along with the stacking batch and extracted to the NUMI line after it has been extracted.

How is Run II Going?

Why Haven’t Run IIa Goals been Met? Number of pbars!!! NOT (primarily) due to protons on target or pbar production rate. Typically only around 50% of pbars from the accumulator make it to collisions. Some of this is due to large emittances out of the accumulator. This gets worse with larger stacks. Some is due to aperture and matching problems throughout the system. Long range beam interactions in the Tevatron: Limit total number of protons. Due to aperture and helix problems. General reliability problems: It’s a very complicated system If we lose the antiprotons, it takes at least 12 hours to recover.

The Plan New cooling has been installed in the accumulator and is being tested.  Initial results look good. Studies continue to understand all the transfer efficiencies of the machines. Continue to improve helix and aperture in Tevatron to reduce long range beam interaction. Integrate recycler into accelerator operation some time in 2003.

(Near) Future Challenges Two important neutrino experiments are coming on line soon: MiniBooNE will use the 8GeV Booster beam and a detector 500 m away to look for neutrino oscillations in the range  Dm2~1 eV2 – the range indicated by the LSND experiment. NUMI will use the 120 GeV Main Injector beam and a detector 750 km away to look for neutrino oscillations in the range of Dm2~10-5 eV2 – the range indicated by atmospheric and solar neutrino data. Both of these experiments place a major challenge on the Booster – arguably the only more or less original part of the Fermilab accelerator complex.

What’s so Hard About Neutrino Physics (from the Accelerator Standpoint)? Probability that a proton on the AP target will produce an accumulated pbar:   .000015 (1.5E-5) Probability that a proton on the MiniBooNE target will result in a detected neutrino: .000000000000004 (4E-15) Probability that a proton on the NUMI target will result in a detected neutrino at the MINOS far detector:      .000000000000000025 (2.5E-17) Þ Need more protons in a year than Fermilab has produced in its lifetime!!

What Limits Total Proton Intensity? Maximum number of Protons the Booster can stably accelerate: 5E12 Maximum average Booster rep. Rate:  currently 2.5 Hz, soon 7.5 Hz (NUMI only) Maximum number of booster batches the Main Injector can hold: currently 6, possibly go to 11 (NUMI only) Minimum Main Injector ramp cycle time (NUMI only): 1.4s+loading time Losses in the Booster: Above ground radiation Damage and/or activation of tunnel components

Proton Timelines Everything measured in 15 Hz “clicks” Minimum M.I. Ramp = 22 clicks = 1.4 s MiniBoone batches “don’t count”. Cycle times of interest Stack cycle: 1 inj + 22 MI ramp = 23 clicks = 1.5 s NuMI cycle: 6 inj + 22 MI ramp = 28 clicks = 1.9 s Full Slipstack cycle (total 11 batches):         6 inject + 2 capture (6 -> 3) + 2 inject + 2 capture (2 -> 1) + 2 inject + 2 capture (2 -> 1) + 1 inject + 22 M.I. Ramp ---------------------- 39 clicks = 2.6 s

Summary of Proton Ecomomics

Booster Repetition Rate Limits Presently, the Booster is limited to an average rep. Rate of 2.5 Hz, which would only yield a small fraction of the desired MiniBooNE intensity. The primary limitation is the pulsed extraction septum magnet (MP02). A new power supply will go in in the next few weeks, which will raise this rate to 4.5 Hz, which would give about half the nominal MiniBooNE rate. A new magnet will go in during the January shutdown which will allow the Booster to go to 7.5 Hz – enough for MiniBooNE or NUMI. In order to run both MiniBooNE and NUMI, we need More cables for the extraction septum. Cooling for the RF cavities (or new RF cavities) A new “bump” magnet, which steers beam out during injection.

Above Ground Radiation Main worry are the high occupancy areas in the Booster towers. Shielding has been added both in the tunnel and to the first floor of the Booster towers. Offices have been moved to reclassify some worrisome areas.

Best Performance + Shielding + BooNE Intensities

Booster Tunnel Losses Harder to quantify – no hard limits Major worry is activation of high maintenance components (e.g. RF cavities). Administrative limit set at twice the total power loss during “messy” stacking (for 9 times the beam!!!). If we had to run tomorrow, we could deliver roughly 20% of the nominal MiniBooNE intensity under this scenario. Steps are being taken to reduce beam losses and proton source consistency.

Collimators

Other Improvements Beam control: programmable trim magnet control cards now allow control of the orbit throughout the cycle. Improved beam monitoring: a number of new beam diagnostics, including a real time tune measurement, had been or are being commissioned. New monitoring and analysis tools: we have been pledged support from computing division, which we plan to use to develop improved tools for monitoring and analyzing the performance of the proton source.

Summary The Fermilab accelerator complex is very complex and versatile. It presents many challenges which keep us busy now and in the foreseeable future. We’re always looking for people to help out.