Weiren Chou

The Fermilab Main Injector: high intensity operation and beam loss control

From 2005 through 2012, the Fermilab Main Injector provided intense beams of 120 GeV protons to produce neutrino beams and antiprotons. Hardware improvements in conjunction with improved diagnostics allowed the system to reach sustained operation at ~400 kW beam power. Transmission was very high except for beam lost at or near the 8 GeV injection energy where 95% beam transmission results in about 1.5 kW of beam loss. By minimizing and localizing loss, residual radiation levels fell while beam power was doubled. Lost beam was directed to either the collimation system or to the beam abort. Critical apertures were increased while improved instrumentation allowed optimal use of available apertures. We will summarize the improvements required to achieve high intensity, the impact of various loss control tools and the status and trends in residual radiation in the Main Injector.

8 GeV H - Ions: Transport and Injection

Fermilab is working on the design of an 8 GeV superconducting RF H-linac called the Proton Driver. The energy of H-beam will be an order of magnitude higher than the existing ones. This brings up a number of technical challenges to transport and injection of H-ions. This paper will focus on the subjects of stripping losses (including stripping by blackbody radiation, field and residual gas) and carbon foil stripping efficiency, along with a brief discussion on other issues such as Stark states lifetime of hydrogen atoms, single and multiple Coulomb scattering, foil heating and stress, radiation activation, collimation and jitter correction, etc.

Electron cloud studies at Tevatron and main injector

Estimates indicate that the electron cloud effect could be a limiting factor for Main Injector intensity upgrades, with or without the presence of a new 8 GeV superconducting 8 GeV Linac injector. The effect may turn out to be an issue of operational relevance for other parts of the Fermilab accelerator complex as well. To improve our understanding of the situation, two sections of specially made vacuum test pipe outfitted for electron cloud detection with ANL provided retarding field analyzers (RFAs) were installed in the Tevatron and the Main Injector. In this report we present some measurements and discuss future plans for studies.

A wide aperture quadrupole for the Fermilab main injector synchrotron

During the design of the Fermilab Main Injector synchrotron it was recognized that the aperture was limited at the beam transfer and extraction points by the combination of the Lambertson magnets and the reused Main Ring quadrupoles located between the Lambertsons. Increased intensity demands on the Main Injector from antiproton production for the collider program, slow spill to the meson fixed target program, and high intensity beam to the high energy neutrino program have led us to replace the aperture-limiting quadrupoles with newly built magnets that have the same physical length but a larger aperture. The magnets run on the main quadrupole bus, and must therefore have the same excitation profile as the magnets they replaced. We present here the design of the magnets, their magnetic performance, and the accelerator performance.

Operational aspects of the main injector large aperture quadrupole (WQB)

A two-year Large Aperture Quadrupole (WQB) Project was completed in the summer of 2006 at Fermilab. [1] Nine WQBs were designed, fabricated and bench-tested by the Technical Division. Seven of them were installed in the Main Injector and the other two for spares. They perform well. The aperture increase meets the design goal and the perturbation to the lattice is minimal. The machine acceptance in the injection and extraction regions is increased from 40pi to 60pi mm-mrad. This paper gives a brief report of the operation and performance of these magnets. Details can be found in Ref [2].

New kind of beam pipe for rapid cycling proton synchrotrons

A thin metallic beam pipe reinforced by multi-layer spiral metallic ribs is proposed for rapid cycling proton synchrotrons. The pipe is made of Inconel 718 with thickness of a few tenths of nuts. Each spiral rib has a cross section of about 0.3 mm/sup 2/ and can be bonded to the pipe by using laser deposition technique (e.g., precision metal deposition, or PMD). Compared with other designs (e.g.., ceramic beam pipe with a metallic cage used in the ISIS at the RAL), this new pipe will reduce the magnet aperture significantly, which, in turn, reduces the construction and operating cost of a synchrotron. Numerical simulations and analytical modeling are used to investigate the structural strength and deformation, and the eddy current effects, including heating, magnetic field distortion and the electro-magnetic force on the beam pipe. The results show that this new beam pipe will work. It can be employed to high intensity rapid cycling proton synchrotrons, such as the proton driver at FERMILAB and the JHF at JAERI/KEK. Effort to build a prototype is under way.

Fast beam stacking using RF barriers

Two barrier RF systems were fabricated, tested and installed in the Fermilab Main Injector. Each can provide 8 kV rectangular pulses (the RF barriers) at 90 kHz. When a stationary barrier is combined with a moving barrier, injected beams from the Booster can be continuously deflected, folded and stacked in the Main Injector, which leads to doubling of the beam intensity. This paper gives a report on the beam experiment using this novel technology.

Some physics issues of carbon stripping foils

Carbon foils are widely used in charge-ex change injection in high intensity hadron accelerators. There are a number of physics issues associated with the use of carbon foils, including stripping efficiency, energy deposition and foil lifetime (temperature rise, mechanical stress and buckling, etc.). This paper will give a brief discussion of these issues.