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IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 48, NO. 1, JANUARY 2001
Transient Ion Disturbances in Traveling Wave Tubes
William Tighe, Dan M. Goebel, Fellow, IEEE, and Charles B. Thorington
Abstract—It is well known that the presence of ions in the electron beam of a traveling wave tube (TWT) can lead to periodic
variations in the output power, phase and the body (or helix) current. This has been referred to as ion noise or jitter. Recently, we
have observed a different form of jitter, and while it is still observed as a small variation in the TWT output (typically 0.5 dB in
power and 2 in phase), it is not periodic. We refer to this phenomenon as random jitter, since its random nature in time is a defining
characteristic. Other characteristics include a relatively fast onset
( 1 ms) and slow ( 500 ms) recovery. It was found that random
jitter was due to the spurious release of extremely small amounts
of trapped gas inside the TWT. The source of the gas was identified
and the problem was resolved. The observed level of fluctuations in
power and phase had no effect on digital traffic and the small quantity of gas was found to have no measurable impact on cathode life.
Index Terms—Communication systems, electron tubes, ions,
noise.
I. INTRODUCTION
E
FFECTS due to ions in vacuum electron devices (VEDs)
have been observed from their early history [1]–[3]. In
spite of the quality of the vacuum in the device, some level
of background neutral gas will exist and with the interaction
of the electron beam, a population of ions will be created. In
some cases, these ions may be lost rapidly or be small enough in
number that they do not significantly influence the performance
of the device. In traveling wave tubes (TWTs), however, electrostatic traps allow a build-up of the ion population resulting in
an observable interaction with the electron beam. For example,
the trapping of ions in the central potential depression of the
beam is known to lead to “ion focusing” of the electron beam
[4], [16], [17].
In the mid-1950s, Cutler [5] described noiselike modulations
of the electron beam that were explained by the presence of
ions in the beam. Higher frequency phenomena were caused
by ion plasma oscillations and identified through the presence
of ion sidebands to the driving radio frequency (RF). Cutler’s
mechanism for lower frequency oscillations (up to 100 kHz with
torr) was a relaxation oscillation in
a device pressure of
which ions are trapped by the space charge of the beam. When a
critical ion density is reached, the trapped ions are released. The
trap is then refilled by further ionization and the process repeats.
Shortly after Cutler, alternative mechanisms [6]–[8] were
put forward to explain the low frequency oscillations. These
involved the formation and decay of a virtual cathode or a
Manuscript received July 26, 2000; revised September 7, 2000. This work
was supported by HED management, including T. Fong, J. Porzuki, J. Dayton
and M. Patterson. The review of this paper was arranged by Editor D. Goebel.
The authors are with Boeing Electron Dynamic Devices, Inc. (formerly Hughes Electron Dynamics), Torrance, CA 90505 USA (e-mail:
william.g.tighe@boeing.com).
Publisher Item Identifier S 0018-9383(01)00307-0.
bistable behavior with the beam shifting between two operational modes. Additionally, dielectric rod charging has been
proposed as a potential mechanism. In this case, scattered electrons are assumed to collect on dielectric rods and the material
charges up until a path to ground develops. In some cases,
conductive coatings on the rods seemed to have a significant
effect on the oscillations [9].
Over the course of time, the frequency range associated with
jitter appears to be coming down as the base pressure of the
device decreases. In very early days, frequencies up to 100 kHz
were noted. In the 1970s, this was more typically limited to 1
kHz while frequencies are at present generally found to be less
than 100 Hz.
More recent investigations [4], [10]–[13], [16]–[18] tend, in
large part, to support the original proposals of Cutler. While specific details may require further study, the primary mechanism
driving these low frequency oscillations appears to be a relaxation oscillation caused by ion formation, trapping and de-trapping in the VED.
At Hughes Electron Dynamics (HED) 1 , the low frequency
oscillation is now termed periodic jitter. This is to distinguish
it from a different, recently discovered form of jitter. This latter
form is termed random or spiky jitter and is characterized by
sudden, random noiselike bursts on the helix current and the
output power and phase. Though similar in many respects to
periodic jitter, the main differences arise from the source of the
ions. For the TWTs used in our studies, it is the interaction of the
electron beam with the background gas that provides a continuous source of ions for periodic jitter. In random jitter the ions
are produced from the beam ionization of random gas bursts
from the cathode.
In this paper, the results from a detailed investigation into
random jitter will be presented. To provide some background
into ion trapping and detrapping processes involved in both
forms of jitter, a discussion of our studies of periodic jitter will
be presented in Section II. This will be followed by sections on
the characteristics of random jitter events, their effects on the
TWT, and the cause and elimination of the phenomenon.
II. CHARACTERISTICS OF PERIODIC JITTER
There is a long history and experience with periodic jitter [4],
[16], [17]. It has been observed in virtually all periodic permanent magnet (PPM) focused TWT designs and operating frequency bands, as well as in solenoidally focused TWTs [13]
and klystrons [10]. Attempts to explain it as rod charging have
not been generally successful. It has been determined that helix
jitter is a benign issue that reduces with time, presumably as the
vacuum in the tube improves with time. The general solution
1Hughes
Electron Dynamics is now Boeing Electron Dynamic Devices, Inc.
0018–9383/01$10.00 © 2001 IEEE
TIGHE et al.: TRANSIENT ION DISTURBANCES
Fig. 1. Sketch of the potential distribution in a typical TWT showing the large
space charge depression of the central potential and possible locations of axial,
electrostatic ion traps.
has been to operate the tube for extended periods of time until
the level of jitter reaches an acceptable level.
Jitter is very sensitive to focusing of the electron beam and at
various times during processing the phenomenon can be reduced
by careful focusing of the electron beam, though it may return
at a later point in processing. Placement of magnetic shunts at
various locations, apparently related to the scallops in the beam,
have been observed to strongly affect the nature (frequency and
amplitude) of the jitter. The presence of periodic jitter has also
been found to be dependent on the environmental temperature
and, while the tube pressure was not measured directly, it has
been noted that jitter appears to occur only in a limited pressure
region.
The source term for periodic jitter is the rate at which ions
are produced and made available to an ion trap. Fig. 1 shows
a sketch of the potential distribution along the axis of a TWT.
As is well known, the central potential provides a radial ion
trap, that is; ions electrostatically confined to the central part
of the electron beam are unable to move outward to the walls of
the tube. Without any other variations in the potential, the ions
would, however, be free to move axially toward the cathode and
the collector.
As indicated in Fig. 1, traps along the length of the TWT
inhibit this motion. Because the motion is prevented along the
length of the tube, these traps are called axial ion traps. Once a
trap is filled, the ions can be released axially or, if the ion number
density is sufficient to neutralize the central potential, radially
to the wall.
There can be numerous ion traps in TWTs and their number
and magnitude can vary significantly from tube to tube. In many
TWTs, a positive anode is placed near the entrance to the helix
to create an electrostatic barrier and prevent ion bombardment
of the cathode. Furthermore, in many designs the radial location
of the ground potential wall moves significantly closer to the
beam edge as it enters the helix. As illustrated in Fig. 1, this
axial variation in the radial location of ground potential coupled
with the positive anode produces a significant axial ion trap at
this location. In designs utilizing a severed helix [4], [16], [17],
a similar axial trap may exist in the sever region near the middle
of the tube.
In addition to these two large traps, a series of smaller, axial
ion traps associated with the scalloping of the electron beam
[4], [16], [17] can form along the helix region of the TWT. The
83
scallops are due to a focusing mismatch at the entrance to the
helix combined with the confining magnetic field structure. As
the beam radius changes due to scalloping there is a change in
charge density and a variation in distance to ground, leading to
the formation of axial ion traps.
In a TWT, then, there is significant potential to trap ions along
the length of the device. While scallop traps may be minimized
with careful focusing technique, and other traps might be modified by tube design considerations, complete removal of the
traps may be impossible.
Computer simulations were undertaken at HED to better understand the trapping and de-trapping of ions in a PPM focused
TWT. Here we provide a brief description of the model and
its results, the details of which are reported elsewhere [14].
The simulation is based on a two-dimensional (2-D), time-dependent, electrostatic, particle-in-cell (PIC) code. Ions can be
handled in two ways. In one case, populations of multiple ion
species can be introduced at a user specified time step and beam
location. Alternatively, ions can produced throughout the beam
from the solution of the ionization equation.
The main results from the modeling are 1) the observation
of trapped ions in electrostatic wells due to both the scalloping
of the beam and the axial variation in the radial location of the
ground potential at the entrance to the helix, and 2) a very rapid,
radial release of the trapped ions after a threshold level for the
population density is exceeded. There is no attempt to model
the time dependence of either the ion build-up time or the ion
release time within the code. Nevertheless, for the conditions
in the simulation, the build-up time due to ionization would be
expected to be several orders of magnitude longer than the ion
release time.
The ion density threshold for detrapping was determined by
the artificial injection of increasing numbers of ions until an
unstable situation developed. The threshold density was determined to be approximately half of the space charge density of
the electron beam. Neutralization of the trap and additional processes [14] such as ion–electron viscous forces and plasma oscillations then provide the ions with sufficient energy to move
rapidly radially to the wall.
The time required to produce the needed population of ions
was calculated separately from the fine-time-step beam runs
using the ionization rate equation. For the conditions expected
in present day TWTs, the estimated time required to replenish
the ion population would be in the range of 0.25 to 2.0 s [14]
yielding oscillation frequencies from 0.5 to 4.0 Hz, in good
agreement with that observed experimentally.
From the modeling, one can qualitatively describe the behavior of the tube due to the presence of ions. Initially, as the ion
population builds up in the trap, one would expect a slow change
in the beam location and/or shape. This would be followed by a
very fast return to the initial condition due to the sudden radial
release of ions once a threshold density has been reached. The
process would then repeat as a relaxation oscillation.
The precise waveform that results from the relaxation oscillation will depend on many tube parameters. The depth of the potential well will affect the number of ions trapped and released,
while the ionization rate will depend on the beam size and current and the density of background neutrals. The response of the
84
IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 48, NO. 1, JANUARY 2001
Fig. 2. Strip chart of the helix current from a TWT exhibiting simple periodic
jitter.
Fig. 3. Strip chart of the helix current showing a somewhat more complex
waveform associated with periodic jitter. Two distinct oscillation frequencies
are observed suggesting simultaneous relaxation oscillations from two different
ion traps.
tube to the presence and release of these ions is difficult to predict, since it depends on the location of the traps, the number of
traps, and the sensitivity of the tube design to the beam disturbance.
Over the years, periodic jitter has been observed for a wide
range of tube parameters. Here, we present two examples taken
from a recent study of periodic jitter in C-band space TWTs.
These tubes were typically operated with a beam current of
about 50 mA at a beam voltage 5 kV. The tubes utilized a positive anode in the gun to form an axial ion trap at the entrance,
and contained another ion trap in the sever region of the helix.
The estimated depths of the potential traps were 20 to 30 eV at
the helix entrance and 1 to 3 eV in the scallops. The actual trap
size and shape depends on the tube construction, operation and
focusing. There would be expected to be significant variation in
these characteristics from tube-to-tube. In fact, during the processing of a single tube, one would expect changes in both the
trap sizes and the ionization rates as the focusing and vacuum
conditions varied.
While the dependence of periodic jitter on beam current,
beam voltage, anode voltage, collector voltages were examined,
this data and its analysis will be the subject of a later paper.
The results generally support the model presented here, but are
not critical to the understanding of random jitter which is the
main topic of this paper.
Fig. 2 shows a strip chart of the helix current from the C-Band
TWT exhibiting periodic jitter. The sawtooth waveform in this
example is fairly typical, although more complex shapes have
been observed. In this simple example, the jitter has a frequency
of approximately 1.5 Hz. The extreme regularity of the oscillation is perhaps its most dominant characteristic. It is possible to
identify in this waveform a slow ion build-up portion of the cycle
that is followed by a relatively rapid release. Following the release, the helix current returns to its original level and the slower
build-up phase begins again, producing the sawtooth waveform.
The response of the TWT to the release of ions is occasionally
more dramatic, resulting in a significant, short-lived spike at
this point in the waveform. In such cases, the build-up phase
is often masked by the release event and the waveform form
is characterized by a regular series of ticks. Consequently, this
type of jitter is sometimes called ticking.
The waveform of periodic jitter is sometimes more complex
than that shown in Fig. 2. In some cases, two or more oscillation frequencies can exist at the same time. A series of “double
spikes” has also been observed. Fig. 3 shows an example of a
strip chart in which two frequency components can be identified. This sort of behavior suggests the presence of more than
one ion trap. One interpretation of this waveform is that the high
frequency, low amplitude oscillation arises from a shallower
ion trap while the higher amplitude, lower frequency oscillation
comes from the action of a deeper trap releasing more ions less
frequently. In these cases, the oscillators may not be “coupled”
but are likely “connected,” as ions would be expected to move
axially from one trap to the next.
Finally, it is important to note that in all TWTs exhibiting
jitter at HED, the response of the tube has been such that the disturbances have been clearly associated with the presence of ions
trapped in the beam. Extensive life testing has demonstrated that
the phenomenon is benign with respect to the life of the device,
and effectively results in only small changes to the “spurious
noise” level in the tube output.
III. CHARACTERISTICS OF RANDOM JITTER
From time to time, over periods of many years, periodic jitter
has been observed and treated in TWTs. Recently, TWTs at
HED began displaying a new type of disturbance that appeared
as random, spiky events observed in the helix current and the
output power and phase. A strip chart capturing several of these
events is presented in Fig. 4, where the power spikes were typically less than 0.1 dB in magnitude and the helix current spikes
were about 10% of the total helix current. The events were infrequent, generally occurring about once per minute to as seldom
as once per hour.
The magnitude and waveshape of these events were similar
in many ways to periodic jitter, strongly suggesting that they
were caused by the sudden release of ions in the tube. However, the random nature and extremely low occurrence rate differentiated them from periodic jitter and the phenomenon was
termed “spiky” or random jitter. A typical, single event is shown
in Fig. 5. A rapid initial excursion on the order of 1 ms, followed
TIGHE et al.: TRANSIENT ION DISTURBANCES
Fig. 4. Strip chart showing the output power and helix current of a TWT
exhibiting random jitter. Several spikes are captured here showing the random
nature of the events.
Fig. 5. Single captured random jitter event showing the response of the output
power and phase. The events are characterized by an initial sudden excursion
followed by a slow recovery to the steady-state condition.
by a slow recovery of typically 0.1 to 1 s to the steady state condition, was found to be characteristic of this phenomenon. The
isolated event appeared very similar to a single cycle of the sawtooth waveform found in periodic jitter.
In order to fully understand the cause and effects of random
jitter, a very detailed investigation was undertaken and the nature of the random jitter events was carefully examined. Within a
single model or type of TWT, the characteristics (rates, rise and
fall times) were observed to be consistent from tube to tube. For
different TWT models, however, there was significant variation.
Certain TWT designs appeared more sensitive to the beam perturbation events resulting in larger amplitude power and phase
glitches. As with periodic jitter, some dependence on focusing
and environmental conditions was also observed.
The PIC code simulation runs [14], discussed in the previous
section, showed a dramatic release of ions once a critical level of
ion density is reached. The clear difference in Fig. 4 between the
fast onset and slow recovery suggests that the random jitter event
is initiated by a sudden release of the trapped ion population on
millisecond time scales. This is followed by a slow build-up or
recovery period with 0.1 to 1 second time scales that reestablishes the population of ions in the traps to their steady-state
level. This response and the time scales involved were very suggestive of a mechanism involving the sudden release and ionization of gas in the TWT. This event would then trigger the
85
release of the body of trapped ions resulting in the initial, sharp
response of the event. Slow ionization of the background gas
then refills the traps to their steady-state level.
During operation of the tubes in the small signal regime, the
magnitude of the random jitter events ranged from 0.05 dB to
0.5 dB in the output power, while the phase could shift by several degrees. The shape of any individual event was very similar whether observed in output power, phase or helix current.
Within a single device, the direction of the initial excursion
would remain constant from event to event; however, it was
found that with different devices the amplitude or current could
either increase or decrease during the jitter event.
Since the number density of ions released in a single event
is equivalent to one-half of the beam density, an estimate of the
beam density (
) and the trap volume (0.1
)
as
for the TWTs in our study provides an estimate of
the number of ions produced per random jitter event. From the
known rates ( 1 per min), worst-case estimates of the number
of ions released over the life of the tube can be made and the impact on the cathode calculated. The calculations demonstrated
that these events would not adversely affect cathode life or performance. Life-tests with cathodes operating at an accelerated
temperature [15] with the presence of random jitter confirmed
this analysis, showing no negative impact on cathode life or
TWT performance. Life-tests with the cathode at nominal temperature were also started one to two years ago, and to date have
not shown any negative effects due to random jitter.
Questions concerning the effect of random jitter on communications performance of the TWT were addressed. The magnitude of these jitter events (from 0.1–0.5 dB in the output power
and 1 to 2 degrees in phase) was typically at or below the discrimination threshold of the communication systems. In addition, the relatively slow nature of the events allowed them to be
tracked and corrected by the communication system. It should
be pointed out, however, that the ability to control any type of
jitter or noise will become more important as the demands of
these systems continue to increase.
IV. RANDOM JITTER CAUSE
Determination of the precise cause and the ultimate elimination of random jitter were of primary importance to this investigation. Various alternatives to a gas release mechanism were
investigated. Detailed studies of every component of the TWT
to identify possible gas sources were undertaken.
Fig. 6 shows data that originally suggested to the authors
that the cathode was the component responsible for the gas
release events in the tube. It was discovered that the cathode
temperature dramatically affected the number of random jitter
events observed per minute. It was found that the rate dependence followed an Arrhenius behavior; that is, the logarithm of
the random jitter rate varied linearly with the inverse of the true
cathode temperature. This behavior is typical of gas emission
and indicated that the cathode was indeed the source of the gas
bursts responsible for random jitter. Further investigations of
the cathode behavior produced a direct observation of these
bursts of gas with a line-of-sight mass spectrometer. Furthermore, the species of the released gas was identified as argon,
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IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 48, NO. 1, JANUARY 2001
Fig. 6. Dependence of the number of random jitter events observed per minute
on the brightness temperature of the cathode, suggesting the heated component
as the source of the gas burst involved in the jitter process.
which had been embedded in the M-layer during improper
deposition of the layer.
Specific process changes were implemented that eliminated
the Ar gas from the cathode and, subsequently, random jitter
from the TWT. There have been no further incidences of random
jitter since these process changes were put in place.
V. REDUCING ALL FORMS OF JITTER
From the present understanding of the jitter phenomena, it is
clear that in order to eliminate it one must either eliminate the
gas source (as was done with random jitter) or the ion traps.
While the use of the best vacuum techniques can help to minimize the background gas level, complete removal of the gas in
TWTs is not possible. In any case, reduction of the background
gas would only be expected to reduce the frequency of this form
of jitter. The magnitude of a jitter event depends on the depth and
location of the ion traps and the sensitivity of the TWT design to
the presence and release of ions. While design modifications resulting in the complete removal of ion traps may be challenging,
if not simply impractical, this approach is needed in order to reduce the impact of jitter on TWT performance.
Such steps have been taken at HED and found to be very effective in reducing the amplitude and phase change that results
from both forms of jitter. In Fig. 7, a comparison of the jitter
level, with and without the design modifications, is made. Initially [Fig. 7(a)], the TWT displayed significant levels of both
periodic and random jitter. The TWT was then modified by removing the gun, implementing several design changes to minimize or eliminate the ion traps, reattaching the original gun (and
cathode), and then reprocessing the TWT. The subsequent level
of jitter, shown in Fig. 7(b), was dramatically reduced and is
now lost in the measurement noise.
VI. CONCLUSIONS
Our present understanding of low frequency ion disturbances,
called periodic jitter, in TWTs has been presented. The presence
of ions, ion traps and detrapping mechanisms lead to a relaxation
oscillation responsible for periodic jitter. The precise waveform
Fig. 7. Reduction of random and periodic jitter using comparable vehicles.
A) With ion traps and poor focusing—jitter is apparent. B) Design changes to
remove ion traps and improve focusing—jitter is no longer detectable and is
now in the noise. The cathode temperature in both cases was elevated resulting
in a 40x increase in random jitter occurrence rate.
that results from the oscillation has been found to be very device
dependent.
We have observed a new type of ion disturbance termed
“random jitter.” The cause and characteristics of random jitter
have been identified following a very extensive investigation.
The cause was found to be the random release of Ar gas from
the cathode. Specific changes to the cathode production process
corrected the problem and eliminated random jitter from the
TWT. Techniques employed to reduce the size of ion traps also
significantly reduced all forms of jitter.
With fluctuations in power at the level of 0.1 to 0.5 dB and
phase events at 1 to 2 degrees, random jitter had no significant
effect on digital traffic or the operation of the communications
systems. The extremely small quantity of gas released during
the random jitter event did not result in any mission life issues
related to the cathode or the traveling wave tube.
At present, HED cathodes are being produced in a new, state
of the art facility, and tests are in place to ensure quality. The
present generation of cathodes is exhibiting very good work
function and emission stability. TWTs using these cathodes do
not exhibit random jitter; it has been eliminated.
ACKNOWLEDGMENT
The authors would like to acknowledge the hard work of the
investigative team, including S. Bosma, D. Danner, W. Rubio, J.
Vaszari, F. Churchill, B. Hannon and B. Campbell. They would
also like to recognize R. Longo, D. Komm, A. S. Gilmour, and
E. A. Adler, for their helpful discussions and contributions to
the work presented here.
TIGHE et al.: TRANSIENT ION DISTURBANCES
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[9] D. W. Maurer, E. E. Francois, and A. Zacharias, “A solution to the
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[10] E. W. McCune, “Ion oscillations for pulsed klystron amplifiers,” in
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[11] Y. Y. Lau, D. Chernin, and W. Manheimer, “A note on noise in linear
beam microwave tubes,” in APS Conf. Plasma Physics, 1998.
[12] D. Thelan, “Experimental observations of ion noise,” in APS Conf.
Plasma Physics, 1998.
[13] W. M. Manheimer, “On the theory of ion noise in microwave tubes,”
IEEE Trans. Plasma Sci., vol. 27, pp. 1146–1163, July 1999.
[14] C. B. Thorington, “Computer simulation of ion trapping and detrapping
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[15] R. T. Longo, E. A. Adler, and L. R. Falce, “Dispenser cathode life prediction model,” in IEDM Tech. Dig., 1984, pp. 318–321.
[16] A. S. Gilmour Jr., “Rev. section 7.5.3 ‘Low frequency instabilities’,”
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[17] K. G. Hernqvist, “Space charge and ion-trapping effects in tetrodes,”
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[18] Y. Y. Lau, D. Chernin, and W. Manheimer, “A note on noise in linear
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William Tighe received the B.Sc. degree from Carleton University, Ottawa, ON, Canada, and the M.Sc.
degree in physics and Ph.D. degree in electrical engineering from the University of Alberta, Edmonton,
AB, Canada, in 1980 and 1985, respectively.
In 1985, he joined the Plasma Physics Laboratory,
Princeton University, Princeton, NJ, where he
worked on X-ray lasers and spectroscopic diagnostics of fusion devices. He joined Hughes Electron
Dynamics (now Boeing Electron Dynamic Devices,
Inc.), Torrance, CA, in 1996, where he studies the
physics of thermionic emitters.
87
Dan M. Goebel (M’93–SM’96–F’99) received the
B.S. degree in physics in 1977, the M.S.degree in
electrical engineering in 1978, and the Ph.D. in electrical engineering in 1981, all from the University of
California, Los Angeles (UCLA).
He joined the research staff at UCLA in 1982,
where he invented the PISCES plasma device, which
provided the first experimental laboratory simulation
of fusion confinement-device edge and divertor
plasmas. In 1986, he co-founded PMT, Inc., a
large manufacturer of plasma-processing equipment
for the thin-film and semiconductor industries which is now called Trikon.
In 1987, he led an international fusion research program on edge-plasma
characterization and plasma-facing components in the TEXTOR tokamak at
KFA-Jülich in Germany. In 1989, he invented the APS plasma source, which is
used extensively by Leybold, Germany, in their optical coating and ion-assisted
deposition systems. In 1988, he joined Hughes Research Laboratories where
he led research and development programs on novel high-power plasma-filled
microwave sources, plasma-cathode E-guns, and pulsed-power plasma
switching devices. In 1997, he moved to Hughes Electron Dynamics (now
Boeing Electron Dynamic Devices, Inc.), Torrance, CA, to work on novel
microwave sources for communications applications and investigate the role of
plasma in various types of microwave devices. He has won several outstanding
technical publication and patent awards while at Hughes. He is the author
or co-author of 70 technical journal papers, over 50 conference papers and
reports, two book chapters, and holds 32 patents with five patents pending.
Dr. Goebel received the IEEE Nuclear and Plasma Sciences Graduate Student Award in 1979, and was named the Outstanding Ph.D. Candidate in Engineering at UCLA in 1981. He is a life member of the American Physical Society and a member of Sigma Xi Research Society. He is an Editor for the IEEE
TRANSACTIONS ON ELECTRON DEVICES, and has acted as Chairman and Program Chairman for several technical conferences and workshops.
Charles B. Thorington joined Hughes Aircraft
Company in 1981, working at various times for
Hughes Electon Dynamics Division, Hughes
Research Laboratory, and Hughes Radar Systems.
While at Hughes Radar Systems, he rewrote Hughes’
code for processing ISAR data in real-time air-to-air
imaging, and developed an advanced ray-tracing
program in which the electric fields and the principal
radii of curvature of astigmatic ray-tubes could vary
across the cross sections of the ray-tubes. At HED,
he has written both steady state and time-dependent
electron gun and depressed collector design codes, and is currently working on
a completely 3-D signal code for helix traveling wave tubes. He is currently
with Boeing Electron Dynamic Devices (formerly Hughes Electron Dynamics),
Torrance, CA.