This one-day short course is intended for those who wish to understand and operate a residual gas analyzer (RGA), and a helium mass spectrometer leak detector (MSLD). The course will focus on operation, use, data analysis and interpretation, process control, leak detection, and problem solving using the RGA.

The construction and operation of each component part: ionizer, mass filter, and detector is explained. Decoding a real mass spectrum is not always easy. Here we discuss individual ionization processes and how they combine to form signatures (cracking patterns) for gases and vapors of practical interest. Numerous cracking patterns for useful gases, vapors, lubricants, pump fluids, and elastomers are described, as well as practical methods for identifying these sources when they are hidden within the mass analysis of real environments.

We describe how the RGA can be used as a leak detector with a range of tracer gases to test both small and very large chambers.

The description, operation, and practical aspects of using an MSLD are covered in detail, including an extensive compilation of Best Practices for both MSLD and RGA that have been collected from decades of personal use. Commercial software will not be covered; however, this course will give technologists the understanding and practical knowledge they need to operate commercial equipment, to solve problems, and to communicate and explain their results with assurance and confidence.

Optional Text: J.F. O’Hanlon, and T.A. Gessert, A User’s Guide to Vacuum Technology, Fourth Edition, John Wiley, New York (2023). Its cost is not included in the course registration, but may be purchased via: https://www.wiley.com/en-us/A+Users+Guide+to+Vacuum+Technology%2C+4th+Edition-p-9781394174133

Course Outline:

1. Background Concepts
This section reviews the basic gas laws and gas flow concepts that are needed to understand the behavior of residual gas analyzers and leak detectors. Common terms, components, and system concepts that all participants should understand are defined and explained.

  • Gas laws
  • Gas flow
  • Distinguishing between a mass spectrometer, a residual gas analyzer, and a helium leak detector

2. Residual Gas Analyzer: Instrument and Component Parts
The two main types of mass filters: magnetic, and electric separation are described along with common types of ionizers and ion counters.

  • Instrument description
  • Ionization methods
  • Closed and open ionization sources
  • Magnetic sector mass analyzer
  • Quadrupole mass analyzer
  • Detection methods

3. Analyzing Mass Spectra
Bombard of gases by energetic electrons creates numerous ion fragments. These fragments can confuse spectral analysis. This section describes the ways in which fragments are created and explains the advantages and limits of using an RGA to understand a vacuum environment. Numerous useful practical examples of ion fragment patterns (cracking patterns) of typical materials used in a vacuum environment are described and explained.

  • Dissociative, multiple, and isotopic ion fragments
  • Quantitative versus qualitative analysis
  • Cracking patterns of commonly used gases, fluids, and solids
  • Practical Examples

4. Additional RGA Techniques
This section discusses additional RGA concepts. Where a sensor is located and what it sees in the chamber affect its response. Gasket materials, nearby hot filaments, and nearby cryogenic and heated surfaces all contribute to the observed spectra, and sometimes confuse the analysis. These effects must be understood in order to accurately describe the gas environment. RGAs can also be excellent leak detectors.

  • Sampling background gases
  • Sampling high pressure process environments
  • Permeation and outgassing of materials
  • Using an RGA to detect leaks
  • Outgassing from hot filaments
  • Atmospheric pressure ionization mass spectroscopy, a specialized technique

5. Leak Detectors
A leak detector is either a bench mounted, or portable, self-contained residual gas analyzer that is optimized for use with helium or perhaps hydrogen-containing sampling gas. Leak detectors can be configured to find leaks in one of several ways that best depend on the system being tested. Methods for detecting leaks will be described followed by a detailed discussion of instrument types, connection methods, and response limits. This section concludes with an extensive list of Best Practices for leak detection.

  • Need for a leak detector
  • Leak detector connection methods
  • Classical and counter-flow leak detectors
  • Leak sensing response time and sensitivity
  • Permeation of gaskets and probe time constants
  • Sampling pressurized containers
  • Safety: high voltage, helium, and Paschen's Law
  • Leak testing very large chambers
  • Hydrogen-based leak detection
  • Best Practices for using leak detectors

6. Case Studies
Residual gas analyzers are capable of solving complex production and development problems quickly and efficiently. This concluding section describes five case studies that illustrate the utility and speed with which the RGA can solve production problems.

  • Leaking supply gas valve
  • Leaking external gasket
  • Oil contamination from mechanical roughing and oil diffusion pumps
  • Background residue from an improperly cleaned system
  • Leak testing a very large thermal vacuum chamber

Instructor: John F. O'Hanlon, Professor Emeritus of Electrical and Computer Engineering, University of Arizona