Prototype of curved-electrode, Paul-type, quadrupole, electrodynamic mass filter has the mass-resolution and transmission-factor properties expected from both theoretical considerations and results of experiments using linear quadrupole features

Abramson, R. H.

Fredericks, R. W.

English

NASA Technical Reports Server

20V
October 1969
	 Brief 69-10510 
•	 NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Ion Mass Spectrometer for Special Uses 
Detector 
Ii MM Dia. Aperture 
0.868 Dia.	 I	 0.80 cm. Dia 
rrfl 
Quadruple Electrodes 
FIGURE 1. Curved-Electrode Geometry for Quadrupole Spectrometer 
The problem: 
To develop a highly sensitive ion mass spectrom-
eter for direct measurement of very low ion densities. 
The solution: 
An engineering prototype of a curved-electrode, 
Paul-type, quadrupole, electrodynamic mass filter has 
been built. This instrument has the mass-resolution 
and transmission-factor properties expected, from
both theoretical considerations and results of experi-
ments. using linear quadrupole features. Tests with 
ultraviolet light show that; if the interior of the 
quadrupole is blackened, its photoelectric response is 
negligible. The problem of a far-ultraviolet photo-
emission, in measurement of low count rates by the 
particle-detector, has been solved by bending of an 
electrodynamic quadrupole mass filter to a quarter-
circle (fig.	 1); thus several reflections of the 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000489 2020-03-16T18:06:46+00:00Z
photons entering the entrance aperture are forced 
before the photons strike the surface of the particle-
detector. 
How it's done: 
The prototype operates satisfactorily at high inci-
dent-ion currents, when a simple Faraday-cup current-
detector and a standard laboratory micromicroam-
meter provide adequate measurements. Use of a 
secondary electron-multiplier was studied at lower 
current densities, where either a current-amplifica-
tion or a pulse-counting mode of detection is neces-
sary. 
The special oil-free vacuum system, the radio-fre-
quency power supply, and peripheral electronics were 
specially constructed. Two quadrupole mass-filter 
structures were used in the development: a previ-
ously built aluminum unit weighing 3.5 lb without 
electronics and measuring 500 inch 3 ; and a unit 
specially built of magnesium alloy, of the same volume 
and weighing about 1.5 lb without electronics. A 
special power supply was built in such a breadboard 
form that a flight-type power supply can be evolved 
from it. 
The prime purpose of this development was an in-
strument for direct measurement of the ionized com-
ponent of the lunar atmosphere. All aspects of the 
spectrometer are discussed. Extensive tests and 
reexamination of the project lead to the following 
conclusions: The principle of the curved-rail ion-mass 
filter is valid. An instrument yielding moderate reso-
lution, with a reasonable transmission factor, is 
feasible; its sensitivity will depend on successful
design of a low-noise, low-count-rate particle-
detector—the major requirement in development of 
an adequate flight instrument; present knowledge can 
cope with the problems in electronics. An instrument 
is feasible measuring about 10 by 10 by 6 inches, 
weighing 5 to 6 lb, and consuming less than 5 W of 
power. 
The present instrument is significantly limited in 
long-range stability; further refinement is required. 
Limitations in resolution and sample-handling ability 
disqualify it from normal chemical analyses. The in- 
strument's portability and sensitivity render it useful 
for measurement in vacuum, detection of leaks, and, 
with minor modification, determination of certain 
atmospheric contaminants of low molecular weight. 
Notes: 
I. Radiologists, designers of instruments, and air-
pollution controllers may be interested in this 
spectrometer. 
2. Requests for further information may be directed to: 
Technology Utilization Officer 
Headquarters 
National Aeronautics and Space Admin. 
Washington, D.C. 20546 
Reference: TSP69-105 10 
Patent status:	 - 
No patent action is contemplated by NASA. 
Source: R. W. Fredericks and R. H. Abramson of 
TRW, Incorporated 
under contract to 
NASA Headquarters 
(HQN- 104 18)
. 
. 
. 
Brief 69-10510	 Category 02


Ion mass spectrometer for special uses

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