JED - March 2018 - 30

The Journal of Electronic Defense | March 2018

30

new, more-advanced manufacturing approaches, such as "additive manufacturing." (Additive manufacturing refers
to a process by which digital 3D design
data is used to build up a component in
layers by depositing material.) For example, says Palmer, "What if you could
take an engineering drawing of a tube
and ship it to a 3D printer and have the
printer just print the entire vacuum
tube structure and take care of the precision and alignment at the same time.
Indeed, an ultimate and most welcome
outcome would be to transform the new
scientific understanding and engineering know-how that emerges from the
INVEST program into novel tools for
analyzing, synthesizing and optimizing new VED designs and then
deploying innovative advanced manufacturing
methods, including 3-D
printing, to actually
produce the devices.
That is a beautiful
vision."
DARPA MTO released a
BAA for the INVEST program in August
of 2015, and has since awarded a number
of contracts to industry and academia to
research techniques and technologies.
Among these is a program at the University of California, Berkeley (Berkeley,
CA) which is looking at additive manufacturing in pure copper.
Palmer also points to multiple projects
underway examining ways to improve
basic thermionic cathodes. "Thermionic
cathodes have been the workhorse that
we've been using in electron tubes ever
since the Fleming valve," (From Wikipedia - the Fleming valve, also called the
Fleming oscillation valve, was a vacuum
tube, or 'thermionic valve,' invented
in 1904 by John Ambrose Fleming as a
detector for early radio receivers used
in wireless telegraphy. It was the first
practical vacuum tube.), but people still
don't really have a thorough quantitative understanding of how and why they
work the way they do."
To address this area, INVEST includes
a broad team of universities and US
cathode manufacturers looking at the
chemistry and material science behind
thermionic cathodes and trying to relate
this to the manufacturing process and

Perhaps one of the most
promising technologies
being explored through
INVEST is the science
of cold-cathode
technology.
ultimately to performance. Among these
are Ohio University (Athens, OH), which
is looking at barium-oxide scandiumoxide cathode science and technology,
and the University of Kentucky Research Foundation, which is conducting
a theoretical and experimental investigation of scandate cathode composition.
On the industry side, Ceradyne Inc.
(Costa Mesa, CA), is working on
fast warm-up scandate
cathodes using additive manufac-

DARPA's INVEST Program
aims to develop the science
and technology base for a
new generation of more capable
vacuum electronic devices. DARPA

turing, and Leidos (Reston, VA), is
modeling the effect of manufacturing
tolerance on device performance and
yield. Says Palmer, "At some point, maybe we can actually have an a-priori design of a thermal cathode that operates
exactly the way we expect it to."
Another INVEST team from the University of Wisconsin-Madison (Madison,
WI) is looking at other compounds besides the common oxides used in cathodes or even some of the newer scandium
oxide cathodes to see if there are any
other material combinations that might
provide better performance. To do this,
they're using a computer modeling technique called "density functional theory" (DFT) to scan the periodic table for
compounds that have the lowest "work

function" - a critical parameter of a
thermionic cathode, in that it defines
the temperature required for the thermionic material to emit electrons.
Other researchers are exploring new
and different beam-wave interaction
structures where the actual amplification occurs through the exchange of
energy between the electron beam and
the electromagnetic signal. "We're looking at some new and different ideas for
how to build this interaction structure
that may not be quite as limited by the
geometry," says Palmer. Among these
are the Massachusetts Institute of Technology (MIT) (Cambridge, MA), which is
examining the photonic bandgap structure for an oversized and overmoded
vacuum electron device.
A wide and disparate list of other
activities are being sponsored to pursue
other critical VED technology objectives.
Among these are work at Teraphysics
(Cleveland, OH) on an ultra-compact Eband TWT; RTI International (Research
Triangle Park, NC) on a nano-gated
emitter array; eBeam Inc. (Beaverton, OR) on an ultracompact electron gun
for oxide cathodes;
and the University
of New Mexico
(Al buq ue rq ue,
NM) on a clamp
clystron for simple
construction at high
frequency.

COLD-CATHODE TWTS
Perhaps one of the most promising
technologies being explored through INVEST is the science of cold-cathode technology. The cathode is the thermionic
emitter of the electron beam that flows
through the vacuum tube when it is
heated to extremely high temperatures
(approximately 1,000°C.) The lower the
temperature that the cathode material
will emit is reflected in its work function which, as described above, is dependent on the material used.
Obviously the lower the cathode temperature requirement, the more efficient and reliable will be the tube, with
the "Holy Grail" being a cathode that
operates at ambient temperature. This
would not only eliminate the need for



JED - March 2018

Table of Contents for the Digital Edition of JED - March 2018

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor - DOD Rolls Out $686 Billion FY2019 Budget
World Report - Russia Developing More Sophisticated Approach to EW
The Domain of the Tube – Millimeter Wave and Beyond
A Wild Weasel EWO Kills a SAM – from an AC-130E Gunship
Resilient and Ready: NATO JEWCS in Transition
EW 101
2018 AOC Industry & Institute/ University Member Guide
AOC News
Index of Advertisers
JED Quick Look
JED - March 2018 - intro
JED - March 2018 - cover1
JED - March 2018 - cover2
JED - March 2018 - 3
JED - March 2018 - 4
JED - March 2018 - 5
JED - March 2018 - The View From Here
JED - March 2018 - 7
JED - March 2018 - Conferences Calendar
JED - March 2018 - 9
JED - March 2018 - Courses Calendar
JED - March 2018 - 11
JED - March 2018 - From the President
JED - March 2018 - 13
JED - March 2018 - 14
JED - March 2018 - The Monitor - DOD Rolls Out $686 Billion FY2019 Budget
JED - March 2018 - 16
JED - March 2018 - 17
JED - March 2018 - 18
JED - March 2018 - 19
JED - March 2018 - 20
JED - March 2018 - 21
JED - March 2018 - World Report - Russia Developing More Sophisticated Approach to EW
JED - March 2018 - insert1
JED - March 2018 - insert2
JED - March 2018 - 23
JED - March 2018 - The Domain of the Tube – Millimeter Wave and Beyond
JED - March 2018 - 25
JED - March 2018 - 26
JED - March 2018 - A Wild Weasel EWO Kills a SAM – from an AC-130E Gunship
JED - March 2018 - 28
JED - March 2018 - 29
JED - March 2018 - 30
JED - March 2018 - 31
JED - March 2018 - Resilient and Ready: NATO JEWCS in Transition
JED - March 2018 - 33
JED - March 2018 - 34
JED - March 2018 - 35
JED - March 2018 - 36
JED - March 2018 - 37
JED - March 2018 - 38
JED - March 2018 - 39
JED - March 2018 - 40
JED - March 2018 - 41
JED - March 2018 - EW 101
JED - March 2018 - 43
JED - March 2018 - 44
JED - March 2018 - 45
JED - March 2018 - 2018 AOC Industry & Institute/ University Member Guide
JED - March 2018 - 47
JED - March 2018 - 48
JED - March 2018 - 49
JED - March 2018 - 50
JED - March 2018 - 51
JED - March 2018 - 52
JED - March 2018 - 53
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JED - March 2018 - 68
JED - March 2018 - 69
JED - March 2018 - 70
JED - March 2018 - AOC News
JED - March 2018 - 72
JED - March 2018 - Index of Advertisers
JED - March 2018 - JED Quick Look
JED - March 2018 - cover3
JED - March 2018 - cover4
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