Improvements were carried out on a TWT (traveling wave tube) for use in EMC (electronic countermeasure) systems by applying MDC (multi-stage depressed collector) and spent-beam refocusing techniques. The MDC geometric design consists of six collecting elements (electrodes) at ground and cathode potentials operating in 2 or 4 stage configuration. The refocusing system designed allows a controlled beam expansion to the point that space charge becomes negligible at the MDC entrance. Simultaneously, the standard deviation of the radial velocity (angular spread) is reduced. This system provides an analog real time readout of P(recovered). Data on all tests is obtained with an automated data acquisition system

Kosmahl, H.

Ramins, P.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19770005354 2020-03-22T12:33:49+00:00Z
PNASA TECHNICAL	 NASA TM X- 73572
MEMORANDUM
(NASA-TM-%-73572) AN 82 TO 84 PERCENT
	 M77-12297
ti EFFICIENT, SMALL SIZE, 2 AND 4 STAGE
UN DEPRESSED COLLECTOR FOR OCTAVE BANDWIDTH
ti HIGH PERFORMANCE TWT • S (NASA) 9 p HC A02/MF	 Unclas
A01	 CSCL 09A G3/33 56906
_	 ,,
d
NF;.>:
	 4
Z >LF3
i
AN 82TO 84 PERCENT EFFICIENT, SMALL SIZE,
2 AND 4 STAGE DEPRESSED COLLECTOR FOR
OCTAVE BANDWIDTH HIGH PERFORMANCE TWT'S
by H. Kosmahl and P. Ramins
Lewis Research Center
Cleveland, Ohio 44135
TECHNICAL PAPER to be presented at the
International Electron Devices Meeting
Washington, D.C. , December 6-8, 1976
AN 82 TO 84 PERCENT EFFICIENT, SMALL SIZE, 2 AND 4 STAGE DEPRESSED COLLECTOR,
FOR OCTAVE BANDWIDTH HIGH PERFORMANCE TWT'S
H. Kosmahl and P. Ramins
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio
c	 in a joint USAF-NASA program, Lewis Research Center is carrying
°i	out an efficiency improvement program on traveling wave tubes (TWT's)s=	
``'	 for use in electronic countermeasure (ECM) systems by applying multi-
stage depressed collector (MDC) and spent beam refocusing techniques
developed at Lewis.
Analytical Program
In the analytical part of the effort, three-dimensional electron
trajectories are computed throughout the slow-wave structure of the TWT
(10 to 18 percent electronic efficiency, 4.8 to 9.6 GHz bandwidth, and
330 to 550 W continuous wave power output). Trajectory computation
continues through the spent-beam refocuses and the depressed collector.
Both refocusing system and MDC designs are produced by reiterative
computations. Collector efficiency, collector losses and overall
efficiency are computed.
The refocusing system designed for this TWT allows a controlled
beam expansion to the point that space charge becomes negligible at
the MDC entrance. Simultaneously, the standard deviation of the radial
velocity (angular spiead) is reduced.
The summary of spent beam parameters before and after refocusing is
shown in figure 1. Initial and final radii, axial velocities and angles
of trajectories are shown. Three important results may be extracted
from the table: The average final beam radius is 2.7 times larger than
the radius before refocusing, secondly all negative angles disappeared
after refocusing- an y!, thirdly, the standard deviation has been reduced
by a factor of 2.4 for the exit angles. Thus, the beam became more
laminar and is much less dense due to refocusing.
The three-dimensional theory for ideal tubes with symmetric, circular,
and optimally refocused beams predicts MDC efficiencies at mid-band of
82 and 85.5 percent for the two and four stage MDC's, respectively,
designed for this TWT.
'Paper pre :lenLed December 7, 1976 at the IEDM, Washington, D.C.
STAR Cat 33
f
-I-
The application of computer programs and some experimental results
permit a pretty accurate determination and identification of collector
losses, shown in figure 2. The use of larger collector sizes and more
depressed stages than present AF constraints allow would push the collector
efficiency above 90 percent for ECM TWT's.
The Secondaries
in spite of the fact that most electrons are collected in regions
of negative fields which suppress secondaries,a small percentage of
primaries hit the unfavorable side of plates and some elastically
reflected primaries are also generated. 	 Both groups of secondaries
cause a loss in "a-- of 2-4 percent.
Experimental Pro4ram
The Teledyne-MEC TWT type No. M5897C as modified for use in this
program and its performance characteristics are shown in figure 3. A
refocusing system consisting of two coils (eventually to be replaced
by a permanent magnet) has been added, and the TWT is mounted on a
10-inch UHV flange. A matching flange exists on the vacuum system 	 =_
used for MDC tests. The UHV valve was designed to keep the TWT under
vacuum during MDC installation and changes, facilitating startup and
enabling many collector changes without cathode activation problems.
Prior to collector tests, the spent beam is analyzed for the
distribution of its angular and axial energy. Figure 4 shows the
result. Note that the computed curve did not include the.taper whose
presence and parameters were unknown to us. The taper gives rise to
the second plateau, whose presence is very beneficial to the design
of efficient collectors with only a few stages.
During an MDC test, with the TWT operating, the following are
varied to optimize performance; Individual Collector Stage Voltages;
Refocusing Coil Currents; Refocusing Coil/Polepiece Locations; Var-
iable Spike Length. A novel data acquisition system is u s ed to op-
timize MDC performance under various conditions (frequency, level of
saturation, etc.). This system provides an analog real time readout of
P(Recovered) as any of the above are varied. Maximizing P(Recovered) is
identical to maximiziag the true MDC efficiency. Data on all tests is
obtained with an automated data acquisition system. A steady state is
established and 100 scans are taken on all measurements and averaged to
improve accuracy.
An experimental program was conducted to optimize the TWT/Refocusing
System/MDC performance. This led to demonstrated MDC efficiencies (at
maximum rf output frequency of the TWT) of 82 and 84 percent for a two
-3-
any: four stage MDC, respectively. These results were obtained with
a single, rather complex, MDC geometric design consisting of six
collecting elements (electrodes), shown in figure 5. These include
electrodes at ground and cathode potentials. The number of MDC
stages is defined as the number of distinct voltages needed to
operate the TWT/MDC other than ground and cathode potentials. In
the 4 stage configuration, the four intermediate collecting elements
were operated at four different voltages; in the two stage configu-
ration, they were electrically connected as two pairs.
An experimental program aimed at simplifying the geometric design
of the two stage collector led to the design shown in figure 6.
The same collector with plots of a few equipotential lines is
shown in figure 7. Note the presence of convergent lenses in the
vicinity of the electrodes and on the axis at a normalized potential
of 0.5. These convergent lenses are useful in very small size
collectors-to prevent excessive beam spreading, but are not required
in larger size collectors for maximum efficiency.
The performance of the MDC's, optimized at 8.4GHz (the maximum
rf output point), is compared in figure 8. The TWT/MDC performance at
and below saturation is shown in figures 2 to 4. For these tests,
all MDC active collecting surfaces were coated with a secondary electron
suppression coating (soot).
Very substantial efficiency enhancement was demonstrated by each
of the MDC's. The simplified two stage design should be readily adapt-
able to practical TWT's used in systems. The size of the collector is;
5 cm diameter by 7 cm high (inside dimensions). Further small improve-
ments are possible.
f
I^
Trajectory RI VI Al RF VF AF
1 0.556E+00 0.771E+00 0.783E+01 0.600E+00 0.774E+00 0.197E-1O1
2 0.516E+00 0.796E+00 0.282E+01 0.971E+00 0.797E+00 0.395E+01
3 0.409E+00 0.801E+00 -0 . 312E+01 0 . 170E+01 0.802E+00 0.496E+01
4 0.554E+00 0.808E+00 -0.194E+01 0 . 152E+01 0.808E+00 0.582E+O1
5 0.353E+00 0.809E+00 -0.526E+01 0.203E+01 0 . 812E +00 0.442E+01
6 0.551E+00 0.816E+00 0.630E+01 0.676E+00 0.818E+00 0.159E+01
7 0.454E +00 0.828E +00 0.104E+01 0.112E +01 0.828E +00 0.397E+01
8 0.205E+00 0.837E+00 0.370E+00 0.151E +01 0.839E+00 0.300E+01
9 0.541E+00 0.839E +00 0.291E+01 0.867E+00 0 . 840E+00 0.332E+01
10 0.445E+00 0:843E +00 0.267E +01 0.980E +00 0.845E+00 0.289E+01
11 0.672E+00 0.846E+00 0.585E+01 0.574E+00 0.847E+00 0.206E+01
12 0.335E+00 0.855E +1J0 -0.392E+01 0.183E +01 0.857E +00 0.471E+01
13 0.249E+00 0.859E +00 -0.199E+01 0.166E+01 0.861E+00 0.397E+01
14 0.328E +00 0.864E +00 0.140E+01 0.122E+01 0.866E+00 0.301E101
15 0.744E+00 0.866E +00 0.445E +01 0.596E +00 0.866E +00 0.326E+01
16 0.381E +00 0.866E+00 0.247E+01 0.197E+01 0.868E+00 0.261E+0l
17 0.164E+00 0.883E+00 0.124E+00 0.162E+01 0.886E+00 0.306E+01
18 0.550E +00 0.897E +00 0.399E +01 0.775E+00 0.899E+00 0.182E+01
19 0.266E +00 0.898E+00 0.395E+00 0.138E+01 0.900E+00 0.330E+01
20 0.271E+00 0.915E+00 0.452E+00 0.143E+01 0.916E+00 0.367E+01
21 0.322E+00 0.921E+00 0.104E+01 0.123E+01 0.922E+00 0.307E+01
22 0.392E +00 0.928E+00 -0.390E+01 0.175E +01 0.929E+00 0.519E+01
23 0.517E +00 0.932E +00 -0.994E+00 0.116E+01 0 . 932E +00 0.471E+01
24 0.418E+00 0.938E+00 -0. ,' 52E+01 0.145E+01 0.939E+00 0.497E+01
25 0.525E+00 0.952E+00 0.483E+01 0.873E +00 0.954E+00 0.806E-100
26 0.256E-:00 0.954E +00 -0.905E+00 0.147E +01 0.955E+00 0.383E+01
27 0.33d7+00 0.982E+00 0.883E+00 0.114E+01 0.893E+00 0.303E-1O1
28 0.574E+00 0.101E+01 0.245E+01 0.772E +00 0.101E+01 0.191E401
29 0.350E +00 0.101E+01 0.592E +00 0.116E +01 0.101E+01 0.314E+01
30 0.569E+00 0.103E+01 0.282E+01 0.793E+00 0.103E+01 0.152E+01
31 0.559E+00 0.109E +01 0.304E+01 0.861E+00 0.109E+01 0.114E+01
32 0.563E+00 0.111E+01 0.232E+01 0.815E-+00 0.111E+01 0.143E+01
Average = 0.435E+00 0.898E +00 0.111E+01 0.118E +0i 0.900E+00 0.319E+01
Standard deviation = 0.139E+00 I 0.835E-01 I	 0.307E +01 0.394E+00 0.832E-01 1 0. 126E-4Ul
CS-79032
Figure 1. - Electron spectrum before and after refocusing.
PRECEDUG PAGE BLANK NOT FU"
I'	 f
LOSS,
3	 1. FINITE NO. OF ELECTRODES 2-4 COMPARED WITH IIFMNTE 	 10-5
NO.
2. RADIAL VELOCITY SORTING 	 3
3. VERY LARGE ANGLES 00) & VERY SMALL ANGLES fm 29) 	 2-4
4. SECONDARIES ON CONE & ELSEWHERE 	 2.648
5. ASYMMETRY & NONCIRCULARiTY OF THE BEAM*
6. NONIDEAL TUBES*
7. NO REFOCUSING AT All	 9
CS-79026
*LOSSES DUE TO THIS CAN VARY WIDELY.
Figure 2. - Identification of collector losses.
FRS aRm+.^aa
►^	 ^m^ewclR
vR 	s.4 w
aNA
VRIR N® •
Iti IFNUT	 wt	 It m IiF
mmwm SEFS
RF OUTPUT	
MM
FOCUSING
IMUS cas
IAN GALE
uN v LA	
ACTUATOR
vACUM
FIIYIOE
"f cw m MK
	
' VARIMtE	 CS-79025
IENCTN SPIRE
Figure 3. - MEC TWT typ. no. M07C schenrtic.
^F
r COMPUTED 3-D
WITHOUT TAPER
cv •
1
E
1
1.0
.B
?	
.6
I1"10 4 MEASURED ON AXIS
1S OF BEAM ACTUAL
TUBE WITH TAPER
.2
CS- 79027	 +0	 .2	 .4	 .6	 8	 1.0	 1.2
VNo — 6^
Figure 4 - Computed and measured energy distribution
curve for the 4. 8 - 9.6 GHz NEC 500 watt CW TWT.
CS-79029
i
Figure 5. - Experimental 2- and 4
-std collector.
6-VO
1.0
.71
L U In.	
.52
0
C.---^Cs- 79022
Figure 6. - Si mple goometry, 2-stage col lector.
a,
.6
oml 	CS-79031
Figure 7. - Sln*lo goometry. 2-stage collector.
A^
Ki
-v 
ff(3
OVERALL OVERALL COLLECTOR
EFF, EFF, EFF,
NO MDC, M714 MDC, #.
SIMPLE TWO STAGE MDC 12.7 37.6 K 6
COMPLEX TWO STAGE MDC 12.7 39.0 62,
FOUR STAGE MDC 1Z.6 41.6 U.2
"MDC EFF OPTIMIZED AT 8.4 GHz tAATURATION). 	 CS- 7902a
Figure fL - TWTIMOC performance.
FREQUENCY,
Wiz
OVERALL EFF"-
NO MDC,
OVERALL EFF
WITH MDC,
COLLECTOR EFF,
s
ILk
SATURATION 6.9 23.2 81.1
-3 A IIOM INAL) 4.2 17.5 1& 1
-6N 2.0 10.1 K1
LAI:
SATURATION 12.7 39.0 82,1
-3 d8 IIOMINAL) 6.3 21.5 M.5
-6 65 IIOM INAL) 12 16.9 85.1
R&
SATURATION 11.5 30.7 813
-3 N
	
tAL) 4.3 20.4 K 9
-6 dB IIDMMU) 2.2 12.1 85.3
K44 941
'IASED ON rf OUTPUT POWER AT THE FUNDAMENTAL FREQUENCY. cs-?tots
F*un 9. - TWT12-stsge MDC performance. (Optimized at 8.4 GHz Esstt?rMianL )
r
FREQUENCY OVERALL EFF*-
NO MDC,
7^
Ob -RALL EFF*
V. TH MDC,
9,
COLLECTOR EFF,
x
4.8:
SATURATION 669 ?a B 812
-3 d8 (NOMINAL) 3.4 19.0 87.2
-6 dB (NOMINAL) L 8 14 9 88.0
-9 dB 010MINAL) .9 6.5 B9.4
8.4:
SATURATION 12.6 41.6 114.2
-3 dB (NOMINAL) 6.4 341 B6.4
-6 dB (NOMINAL) 3.1 16.6 87.4
-9 (18 WOMINAL) L 6 14 9 88.1
9.6:
SATURATION 8.5 32.9 85.2
-3 d8 (NOMINAL) 4.3 23.9 V.2
-6 dB (NOMINAL) 2.1 13.9 07.8
-9 dB (NOMINAL) L 1 8 1 a. 7
DC BEAM 90.8
do-^
'BASED ON rf OUTPUT POWER AT THE FUNDAMENTAL FREQUENCY, 	 CS-74429
Figure 14 - TWT14-stage MDC performance. (Optimized at 8.4 GHz (saturation). )
FREQUENCY,
GHz
OVERALL EFF*-
NO MDC,
x
OVERALL EFF"
WITH MDC,
^
COLLECTOR EFF,
4.11:
SATURATION 7.2 216 80.5
-3 dB NOMINAL) 4.2 17.8 84.8
-6 dB D)OMINAL) 1.9 1115 85.8
-9 dB WOMINAL) .9 62 87.8
8.4:
SATURATION 12.7 37. S 8L 5
-3 dB fROMINAL) 6.4 :6.5 83.2
-6 (19 NOMINAL) 3.1 16.1 84.7
-9 dB	 AINAL) 1.6 9.4 8b. 2
9.6:
SATURATION 8.1 28.8 82.0
-3 dB NOYHNALi 4.1 19.8 84.7
-6 dB NOMINAL) 2.0 1L4 85.2
-9 dB NOMINAL) 1.0 6 4 86.8
DC BEAM 89.4
*BASED ON rf OUTPUT POWER AT TIC FUNDAMENTAL FREQUENCY. Cs -79039
Figure 1L - TWTl2-stage MDC performance. Simplified MDC design.,
optimized tar 8.4 GHz (satu ration ►.
pAGE L5
Q^


An 82 to 84 percent efficient, small size, 2 and 4 stage depressed collector for octave bandwidth high performance TWT's

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server