Extraction at the Tevatron  updated October 25, 2007  D. Carrigan carrigan@fnal.gov (subject line must be sensible)

Channeling Formulary

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This page is dedicated to the memories of Thornton Murphy and Tim Toohig, key participants in the Fermilab channeling program.

Introduction

In the early 1990’s a fixed target experiment was proposed for the Superconducting Super Collider (SSC) program to study heavy-flavor physics using a tiny fraction of the 20 TeV circulating beam extracted with bent crystal channeling. Conventional methods of beam extraction at such high energies posed problems with no obvious cost-effective solutions. E853 at Fermilab was designed to study the feasibility of this approach. The goals of E853 were to extract 106 900 GeV/c protons/second with 1012 protons circulating in the Tevatron, to study the extraction efficiency, to show that the luminosity lifetime of the circulating beam was not adversely affected, and to investigate the backgrounds created at the two Tevatron collider experiments. Losses at the  collider experiments, CDF had to be kept to a tolerable level. A central concern for the E853 operation was that losses be minimized so that the superconducting Tevatron magnets were not quenched. The experiment was wildly successful. All the goals were met. Channeling extraction was observed at a collider, a superconducting one at that, for the first and only time so far. E853 demonstrated that usewful beams can be extracted from a superconducting accelerator during high luminosity collider operations without unduly affecting the background at the collider detectors.

History

  • First seen at Dubna - 1979
  • investigated at Serpukhov, CERN - 1980s
  • Tevatron - 1995 to 1996
E853 produced the highest energy extracted particle beam ever (900 GeV) and in the process observed particle channeling at the highest energy yet reached. Luminosity driven extraction, where collisions in a collider create halo, was observed for the first time..

In fact, E853 was perhaps the most successful experiment conducted under the ill-fated SSC program.

References

 CERN collimation workshop presentation on E853 (2005), Preprint Fermilab-CONF-05-206-AD
First Results from Bent Crystal Extraction at the Fermilab Tevatron C. Murphy et al., Nucl. Instr. Methods Phys. Res., B119, 231 (1996)
First observation of luminosity-driven extraction using channeling ... R. Carrigan, et al., Phys. Rev. ST - Acc  & Beams 1, 022801 (1998)
Beam extraction studies at 900 GeV using a channeling crystal R. Carrigan, et al., Phys. Rev. AB, vol. 5, E043501 (2002)
Bent crystal layout at C0

The apparatus

The bent crystal for E853 was located at B48. The abort magnet string of kickers replaced by the E853 crystal consisted of four 1.8 m long kicker modules with peak fields of 3.7 kG giving a vertical deflection of 640 µrad. Removal of the upstream kicker module provided sufficient space for the crystal goniometer. The bent crystal was on the outside of the ring and deflected protons up through the quadrupoles (Q) into the field-free region of the Lambertson magnets. Extraction consisted of two parts: a vertical kick into the field-free region of a Lambertson magnet string and horizontal separation of the circulating beam from the extracted beam by the Lambertsons. After the Lambertson magnets the extracted beam traversed two instrumented air gaps approximately 100 meters downstream of the crystal and then entered a beam dump. Air gaps, separated by 40 meters, were instrumented with several scintillators. Thin movable counters could scan the beam profile. A fluorescent screen coupled to a CCD camera in the first air gap also provided a digital readout of the beam‑profile for run‑time diagnostics. 
First extraction at C0

Extracted beam

Images of the extracted beam during the first E853 observation of 900 GeV channeling extraction. In this series the vertical deflection magnet was swept up through a 230 mrad scan, from 130 mrad below the channeling peak to 100 mrad above the peak. Notice that the main extracted beam spot moves up following the crystal orientation. The spot is brightest at the best alignment. The length of the dechanneling tail grows because the beam spot moves up and the Lambertson magnet aperture eclipses less of it. For scale, the width of the dechanneling tail is 3 mm.

E853 successes

  • extracted significan beams from the Teavatron  in parasitic, kicked and RF stimulated
  • first-ever luminosity driven extraction
  • highest energy particle channeling ever
  • useful collimation studies
  • extensive information on time-dependent behavior
  • very robust
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