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Vacuum

"Much ado about nothing", a popular title from English literature, has been quoted often to vacuum technologists relative to our work. In the real world there is much to do to obtain the nothingness of a good vacuum! There is even more to achieving the good ultra-high vacuum (UHV) needed for the NSLS storage rings. Today's vacuum technologist must be familiar with a large variety of pumps, gauges, chambers, materials, processes, valves, controls, diagnostics, etc., related to vacuum. A practical example would be to measure, find, and fix a system vacuum leak - a task easily compared to finding a needle in a haystack. A good knowledge of vacuum systems and skill with mass spectrometers is required for success. The vacuum technologist must also be familiar with the workings of the entire Light Source and its beamlines in order to resolve vacuum issues and to ensure smooth operation.

vacuum ranges

The NSLS storage ring vacuum has to be in the ultra-high range.

The ongoing mission of the NSLS Vacuum group is to provide the best possible vacuum for the operation of the Light Source. Good vacuum is one of several main ingredients for good stored beam lifetime; without it, the many collisions between electrons and gas molecules in poor vacuum would result in short lifetimes and excessive radiation. The Vacuum group is part of the Mechanical Section.

Along with the Operations group, we continually monitor beamline front ends in both rings to ensure that one beamline problem does not affect an entire ring. Pressure and partial pressure requirements must be met to open a beamline to the VUV or the X-Ray Ring. The rings and front ends are continually monitored with residual gas analyzers to protect beamline optical components from hydrocarbon and other contaminants. Clean dry nitrogen is used for controlled vent-up of vacuum sections when necessary, and pressure-interlocked portable turbo-molecular pumping stations are used to recover vacuum. Special procedures have been developed by the Vacuum group for bake-out, argon plasma cleaning and conditioning of parts and assemblies for installation in the rings or beamlines. These procedures were used during the recent VUV shutdown where one quarter of the bending chambers were replaced to add new IR beam lines. Without these procedures, quick recovery of the stored beam lifetime would have been impossible.

In addition to the NSLS storage rings, booster and injection vacuum systems, and front-ends, the Vacuum group works on other projects. We have been involved in vacuum R&D programs for the Advanced Light Source, the Advanced Photon Source, B-meson Factory, Daphne, LHC and SSC UHV beam chambers. Measurements of accelerator construction materials were studied and measured on beamlines U10B and X28A. The measurements involved photon interaction with internal vacuum surfaces. This photon interaction causes the pressure to rise which limits the stored electron beam lifetime. In addition to measuring internal vacuum surfaces, we have coated internal surfaces with various metals, for example, ceramic beam chambers.

The Vacuum group monitors the new cleaning facility, which is managed by the BNL Central Shops. This facility cleans vacuum parts for the NSLS and other BNL Departments such as Physics, AGS, RHIC, and Central Shops. The new cleaning procedures for the Central Shops were evaluated and tested for NSLS UHV.

The Vacuum group interfaces with the NSLS staff and User community to resolve vacuum issues or problems. We routinely Helium leak test vacuum parts and assemblies for NSLS staff and Users. In addition, time and schedule permitting, we rebuild various types of vacuum pumps and electronics for our selves and NSLS users. Included are: mechanical pumps, Balzers turbo molecular pumps, Varian ion pumps, and Perkin Elmer ion pumps and controllers.

heating tape

Aluminum foil and heater tapes are used for vacuum bakeout.

The Vacuum Group is led by Conrad Foerster and is responsible for the design and repair of the NSLS vacuum system. Both the VUV and X-ray rings require a constant pressure of 10-10 torr, a vacuum better than that of space. But why is such an incredible vacuum needed? When the electrons are accelerated inside the rings, they inevitably collide with free molecules. These collisions degrade the beam strength, and in turn, its lifetime.

One method of perfecting the vacuum uses a process called a "bakeout". During a bakeout, the pipes are heated to 150˚C-200˚C using heating tape. This causes gas molecules that are attached to the pipes to become free. The gas is then drawn out using pumps.

HMS

Helium Mass Spectrometer Leak Detector

Finding and sealing leaks in the beam pipe is one part of the maintenance process. Leaks occur less than once a month, and are usually prevented before they occur. When there is a suspected leak, the vacuum engineers use a Helium Mass Spectrometer to pinpoint the location of the leak. In the same way you can listen for air escaping from a hole in a basketball, the spectrometer detects helium escaping from microscopic holes in the pipe. The leak is temporarily sealed with epoxy while the new part is being shipped.

Inside of a Mechanical Rotary Pump

Inside of a Mechanical Rotary Pump

Some of the pumps used by the vacuum engineers include:

  • Diode and Triode ion pumps
  • Titanium sublimator pumps
  • Non Evaporable Getter pumps(NEG)
  • Mechanical pumps
  • Turbo-Molecular Pumps(TMP)
  • Diffusion Pumps