An apparatus to measure the incident charged particle beam flux while effectively eliminating losses to reflection and/or secondary emission of the charged particle beam being measured is described. It comprises a sense cup through which the charged particle beam enters. A sense cone forms the rear wall of the interior chamber with the cone apex adjacent the entry opening. An outer case surrounds the sense cup and is electrically insulated therefrom. Charged particles entering the interior chamber are trapped and are absorbed by the sense cup and cone and travel through a current measuring device to ground

Gregory, D. A.

Stocks, C. D.

English

NASA Technical Reports Server

United States Patent 1191 
Gregory et al. 
11 11 4,455,532 
[451 Jun. 19. 1984 
APPARATUS FOR MEASURING CHARGED 
PARTICLE BEAM 
Inventors: Don A. Gregory; Charles D. Stocks, 
both of Huntsville, Ala. 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Assignee: 
Appl. No.: 342,857 
Filed: Jan. 26,1982 
Int. Cl2 ............................................. GOlR 29/12 
U.S. Cl. ................................... 324/457; 324/71.3; 
324/72.5; 250/305 
Field of Search ...................... 324/457, 71.3, 464, 
324/72.5; 250/305, 389, 397 
References Cited 
U.S. PATENT DOCUMENTS 
FOREIGN PATENT DOCUMENTS 
472425 8/1973 Australia ............................. 324/464 
Primary Examiner-Micheal J. Tokar 
Assistant Examiner-Kevin D. O'Shea 
Attorney, Agent, or Firm-Joseph H. Beumer; John R. 
Manning; Leon D. Wofford, Jr. 
ABSTRACT 
The apparatus 11 according to the present invention 
effectively eliminates losses to reflection and/or sec- 
ondary emission of the charged particle beam 13 being 
measured. It comprises a sense cup (17) with an interior 
chamber and an entry opening (25) through which the 
charged particle beam (13) enters. A sense cone (19) 
forms the rear wall of the interim chamber with the 
cone apex adjacent the entry opening (25). An outer 
case (21) surrounds the sense cup (17) and is electrically 
insulated therefrom. Charged particles entering the 
interior chamber are trapped and are absorbed by the 
sense cup and cone and travel through a current mea- 
suring device (15) to ground. 
t571 
4,251,775 2/1981 Michel ............................... 32W72.5 6 Claims, 2 Drawing Figures 
nj5 ELECTROMETER 
https://ntrs.nasa.gov/search.jsp?R=19840020506 2020-03-22T10:09:28+00:00Z
U.S. Patent Jun. 19, 1984 4,455,532 
ELEC TROM E TE R u’5 
4.455,532 
APPARATUS FQR MEASURING CHARGED 
PARTICLE BEAM 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the United States Government and may be manu- 
factured and used by or for the Government of the 
United States of America for governmental purposes 
without the payment of any royalties thereon or there- 
for. 
DESCRIPTION 
1. Technical Field 
This invention relates to apparatus for measuring the 
number of charged particles per area per time, or flux, 
of a charged particle beam. 
It is often desired to measure low and high energy 
charged particle beams and the present invention ac- 
complishes that purpose without causing a large error in 
the measurement of the incident flux. 
2. Background Art 
Previously, various devices and methods have been 
used to measure the incident charged particle beam flux 
(electron, proton, etc.). Some of these devices and 
methods are discussed in the U.S. Pat. No. 3,239,664. 
There appears to be no standard to compare the effec- 
tiveness of any design and whether it was efficiently 
trapping the charged particles. While the prior designs 
depend on stopping the particle and its secondary emis- 
sions and forcing them to travel through a current mea- 
suring device to ground, it has been noticed that a large 
percentage of the incident beam is lost and not con- 
verted into measurable current, thereby causing a large 
error in the measurement of the incident flux. 
DISCLOSURE OF INVENTION 
The present invention has a sense cup with an interior 
chamber and an entry opening through which a 
charged particle beam enters. Within the sense cup is a 
cone with its base closing the rear wall and its apex 
adjacent to the entry opening. Charged particles enter- 
ing the chamber impinged on the cone and are either 
absorbed or deflected to the side walls of the chamber. 
The arrangement effectively traps the particles even if 
they undergo multiple reflections so the particles will be 
absorbed and conducted by the metallic sense cup and 
metallic cone to a current meter. 
The sense cup is mounted within an interior chamber 
of an outer case and insulated therefrom. The particles 
absorbed by the cone and surrounding sensing cup 
travel through a current meter whereby the flux can be 
calculated with great accuracy. 
It is a principal object of the invention to provide an 
apparatus for measuring an incident charged particle 
beam flux with improved accuracy. 
It is another object to provide an apparatus for effec- 
tively eliminating losses due to reflection and/or sec- 
ondary emissions of the charged particle beam being 
measured. 
BRIEF DESCRIPTION OF DRAWINGS 
DETAILED DESCRIPTION OF THE 
INVENTION 
Referring to the drawing, FIIG. 1 illustrates the appa- 
5 ratus ll of the present invention which is able to trap 
charge particles of a beam 13 and measure them 
through a current measurement device 15 without sig- 
nificant losses due to reflection and/or secondary emis- 
sion. The apparatus 11 has an inner sense cup 17 with a 
10 sense cone 19 therein supported by an outer case 21 by 
separated therefrom by electrical insulating material 23 
and suitable air gaps 25. The sense cup 17 with its sense 
cone 19 and the outer case 21 are made of a metal such 
as aluminum. A suitable electrical insulating material is 
The sense cup 17 as illustrated is cylindrical with an 
interior cylindrical chamber, and a forward entry pas- 
sageway 25 for the entering charged particle beam 13 to 
be measured. The sense cone 191 is fitted within the back 
20 passageway of the cup 17 and has its cone 19 extending 
forward so its apex is adjacent and near the exit of the 
forward passageway 25. The sense cone 119 has a shaft 
27 extending rearwardly and outwardly from the sense 
cup 17 and the outer case 21. 
The base portion 29 of the sense cone 19 is cylindrical 
and has a diameter smaller than the bottom or base 
diameter of the cone. The base portion 29 fits within a 
complementary opening at the rear of the cup 17. As 
illustrated, the bottom diameter of the cone 19 corre- 
30 sponds to the diameter of the interior cylindrical cham- 
ber of the cup. The interior planar angle of the cone 
apex is approximately 40 degre'es. 
The outer case 21 is similar to the sense cup 17 with 
an interior cylindrical chamber within which the inner 
35 sense cup 17 is fitted, and with a forward aperture pas- 
sageway 29 for the charged particle beam 13 to enter. A 
rear threaded plug 31 closes the interior chamber 
whereby the interior sense cup 17 with its outer insulat- 
ing material 23 is held tightly in a fixed position. The 
40 plug 31 has circular passageway 33 at its center through 
which the sense cone shaft 27 extends. The diameter of 
the passageway 33 is slightly larger than the diameter of 
the sense cone shaft 27, so an air gap 25 of about 0.12 
inches is formed to electrically isolate the sense cone 
The distal end portion of the sense cone shaft 27 is 
threaded, and a nut 35 is screwed thereon together with 
a metal washer 37 and insulating washer 39 of Teflon to 
fit snugly against the outer surface of the plug closure 
50 31. Another nut 41 is also screwed onto the sense cone 
shaft 27 to clamp a washer-like electrical lead 43 be- 
tween the two nuts. 
A protective metallic cup 45 of aluminum or other 
metallic material is fitted over the rear of the outer case 
55 21 and held there by screws 47 to shield against stray 
radiation. An electrical conductor 49 suitably insulated 
extends from the electrical lead 43 on the sense cone 
shaft 27 through a shielded cable 51 to a standard cur- 
rent measurement device 15 such as Keithley Model 610 
60 BR Electrometer. The cable 51 should be shielded by 
multiple layers of metallic braiding or for superior per- 
formance by placing it inside a flexible metal tubing 
which has been grounded. 
The outer case 21 should be grounded by being 
15 Teflon. 
25 
45 from the outer case. 
FIG. 1 is a partial sectional view of an embodiment of 65 mounted on a support which is grounded or having a i  
electrical wire 53 fastened thereto to ground. Other- 
FIG. 2 is pictorial view of the forward end of the wise, a charge buildup will occur in the insulation divid- 
ers 23 used which will periodically discharge and cause 
the invention. 
sense cone. 
4,455, 
3 
inaccurate readings. The outer case 21 also serves as a 
shield against incident radiation reaching the sense cup 
and cone except through the entry aperture or passage- 
way. 
5 We claim: 
1. An apparatus for measuring incident charge parti- 
a sense cup adapted to absorb and conduct incident 
said sense cup having a cylindrical interior chamber 
with a closed bottom and a front entry passageway 
for said charged particle beam to enter the interior 
cle beam flux, comprising: 
charge particles of the beam flux; 10 
532 
4 
passageway is axially aligned with the entry pas- 
sageway of said sense cup; and 
electrical insulation between said outer case and said 
sense cup. 
2. An apparatus according to claim 1, wherein: 
said sense cone is fitted to the bottom of said sense 
cup by an integral cylindrical base portion having a 
diameter greater than the bottom diameter of the 
cone so as to have contact with the cylindrical side 
wall of said sense cup and forming a part of the 
bottom well of said sense cup; 
said base portion having a shaft extending rear- 
wardlv: 
chamber; 
said sense cup having a sense cone forming the bot- 15 
tom of the interior chamber which is opposite the 
entry passageway and extending forward with its 
cone apex toward and adjacent said entry passage- 
way, the bottom diameter of the Sense cone come- 
sponding to the diameter of the interior cylindrical 20 
chamber so the forms the entire bottom sur- 
face of the interior chamber, said sense cup and 
between the absorbed charged particles from said 
incident charge particle beam flux; 
the absorbed charged particles of said sense cup 
and said sense cone; 
said outer case having a bore in its real wall through 
which said shaft extends rearwardly; 
said shaft having a smaller diameter than said bore in 
said outer case whereby an insulating air gap is 
formed; 
insulating means for Clamping said shaft relative to 
Said outer case; and 
said electrical current measuring means includes an 
electrical conductor secured to said shaft. 
cone contacting each other so as to conduct there- 3* An apparatus according to wherein said outer case is electrically grounded to prevent an electri- 
4. An apparatus according to claim 1 wherein said 
25 cal charge buildup in said electrical insulator. 
an current measuring for measuring cone has an interior planar apex angle of approximately 
40 degrees. 
5. An apparatus according to claim 2 including a 
30 protective metallic cup secured to the rear of said outer 
case to shield the shaft from radiation. 
6. An apparatus according to claim 5 including cable 
means to shield said electrical conductor from radiation. 
an outer case with an interior chamber; 
said sense CUP fitted within the interior chamber of 
said outer case having an entry passageway for the 
said outer case; 
charged particle beam to be measured which entry * * * * *  
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45 
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55 
60 
65 


Apparatus for measuring charged particle beam

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