The techniques and procedures for producing very-large-format pulse-counting array detector systems for use in forthcoming high-energy astrophysics facilities were defined, and the structures and performance characteristics of high-sensitivity photocathodes for use at soft X-ray wavelengths between 100 and 1 A were determined. The progress made to date in each of these areas are described and the tasks that will be undertaken when the program is continued are summarized

Timothy, J. G.

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=19840008389 2020-03-20T23:34:39+00:00Z
i
—T
THE DEVELOPMENT AND TEST OF
MULTI-ANODE MICP.00HANNEL ARRAY DETECTOR SYSTEMS
II. SOFT X-FAY DETECTORS
Final report for NASA grant NAG5-211
For the Period trough 30 November 1983
t
s
(NASA-CR-173145) THE DEVELOPMENT AND TEST
	 N84-16457
U? MULTI-ANUDE MICROCHANNEL ARRAY DETECTOR
SYSTEMS. 2: SOFT X-RAY DETECTORS Final
Feport (Colorado Univ.) 8 p HC A02/MF A01
	 Unclas	 r`^
CSCL 09C G3/33 OU508
AY
J. Gethyn Timothy
Principal Investigator
Department of Astro-Geophysics
University of Colorado
Boulder, Colorado 80309
i
I. INTRODUCTION
The objectives of the development pro g ram supported by this grant are,
first, to define the techniques and procedures for p oducing very-large-format
i
pulse-countin g array detector systems for use in forthcoming high-energy
astrophysics facilities and, second to determine the structures and performance
characteristics of high-sensitivity photocathodes for use at so`t x-ra,
wavelengths between 100 and 1 A. This final report describes the progress
made to date in each of these areas and surmarizes the tasks that will be
undertaken when the program is continued at Stanford University.
II. CURVED-CHANNEL MICROCHANNEL PLATES
The key component of the Multi-anode Microchannel Array (MAMA) detector
system is t l e high-gain curved-channel Microchannel Plate WCP). Accordingly
during the first period of this grant, a significant amount of effort was
expended at Galileo Ele , :tro-Optics Corp. in developing the engineering
proc-, dur,s reouired for the fabrication of curve-channel MCPs with active
areas 15 mm in diameter and larder. On the base= of the results of the initial
fabrications of the first-generation curved-channel MCPs with active areas 27
mrm in diameter, Lhere was considerable concern that there would be a problem in
maintainin g the uniformity of curvature of the channels across the active area
r	 of a large diameter MCP. During the period of this grant these efforts have
paid off and the first units of the curved-channel MCPs have been fabricated
with active areas 40 mm in diameter as shown in Fig. 1. The initial test data
for these MCPs indicate that the curvature of the channels across the active
area is extremely uniform.
A second area of concern is the flatness of the MCP since the distance
between the output face of the MCP and the multi-anode array must be less than
50 microns if a spatial resolution of 25 microns or better is to he obtained.
f:z)
-1-
111 rrrrm rrt^rt mrrttrr Sri ^
C
ORIGINAL PAGE 19
OF POOR QUALITY
The output faces of the first two 40 mm M'CPs are flat to t-tier than 15 microns
meeting this requirement.
Figure 1. 27 mm and 40 mm curved-channel MCPs.
The internal surface area of a curved-channe) KP is extremely large, of
1
the order of 1400 cm 2 for a 27-mm diameter MCP with 12-micron-diameter channe-
ls. In order to facilitate the outgassing of the channels prior to operation of
the MCP and to reduce the overall dark count rate it is hi g hly desirable to
reduce the active area of the channeis to match that of the readout array.
Under a separate grant from the NASA Astrophysics office we have procured
27-mm-diameter curved-channel WCPs with rectangular active areas of 7 x 27 mm2
to match the (256 . 1024)-pixel MAMA anode array (see Fig. 2). As the next step
in this fabrication program vie have just received the first 40-mm curved-
charnel r 1CP w it h a square active area of 27 x 27 mm 2 . This format will be used
-2-
CIP)
C*Q
UHIGINAL PAGE Q
OF POOR QUALITY
for the (1024 x 1024)-pixel x-ray detector to be fabricated during the next
i
phase of this development program.
i
Figure 2. 27-mm-diameter curved-channel MC s with circular
and rectangular active areas.
In order to facilitate the fabrication of high-gain MICPs with very large
active areas it is important to increase the length-to-diameter ratios of the
channels above the current value of 100:1. Several units of the recently del-
ivered MCPs have channel length-to-diameter rat i os of 140:1 and the fabrication
of an MCP with channel length-to diameter ratios of 200:1 has just been com-
pleted succesfully. These thicker MCPs will be significantly more rugged and
mechanically stable. In addition it will be possible to fabricate a curved-
I channel MCP with a curved input --urfacc to match the focal surface of a Wolter
crazing-incidence telescope system and a planar output surface which can be
t	 mounted in proximity focus with a high-resolution multi-anode readout array. A
-3-
27-mm-diameter curved-channel MCP with the input face ground to a radius-of-
curvature of 0.25 m has just been delivered and will be tested during the next
phase of this pro g ram. An alternative technique for curving the MCP, namely
"slumping" the MCP, will be investigated at a future date.
As the result of these development efforts we now have the high gain MCPs
required for high-resolution x-ray detectors with formats of (1024 x 1024)
pixels. Further, the fabrication procedures developed at Galileo Electro-Optics
will permit the fabrication of curved-channel MCPs with diameters of 75 mm and
larger. These large diameter MCPs will enable us to fabricate the very-large-
format (4096 x 4096 pixels and lar g er) high-resolution detectors required for
the high energy astrophysics missions of the next decade.
III. HIGH-SEIlSITIVITY X-RAY PHOTOCATHODES
We have determined from earlier tests that CsI has potentially very high
quantum efficiencies at Extreme Ultraviolet (EUV) and soft x-ray wavelengths.
It is also 7lear from preliminary data obtained by other investigators that the
high quantum efficiencies extend to x-ray wavelengths as short as 1 A. However,
it is also clear that a severe degradation of the quantum efficiency will
result if the cathode is exposed to the ambient atmosphere. Accordingly, in
s
order to process and evaluate CsI photocathodes under high vacuum, we have
assembled a discrete-anode MAMA detector tube with a high-vacuum gate valve and
a F1gF 2 window as shown in Fig. 3.
Two di°ferent types of CsI photocathodes need to be studied namely,
,jpaque CsI deposited directly on the front face of the MCP and illuminated at
grazing incidence, and low-density "flu f fy" t,	 mou-nted in proximity `ocus with
the front face of the IICP.The first evaliations will be of opaque CsI photo-
cathodes. with the gate valve open and the tube sealed by the MgF 2 window
assembly , it will be possible to process the CsI photocathode using estab-
-4-
'Mow
	 .^
'i
C
r°1
ORIGINAL rA(;r ;3
OF POOR QUALIrf
lished visual and photoelectric monitoring procedures to determine the optimum
thickness for a high quantum yield at EUV and soft x-ray wavelengths.
Figure 3. Demountable MAMA detector tube with a high-vacuum gate-valve
assembly.
The quantum efficiency of the photocathode will be measured through the MgF2
window down to wavelengths as short as 1160 A. The gate valve will then be
closed, the MgF 2 window removed, and the detector tube attached to a high-v-
acuum x-ray calibration facility for quantum efficiency measurements in the
open-structure mode at wavelengths down to 1 A.
Pro9 ress with this aspect of the development program has been much slower
than expected because of* the inordinate delay in the delvery of the high-vacuum
gate-valve. However the assembly of the gate-valve tube was finally completed
late last summer. Prior to assembly, the curved-channel MCP was baked out at a
temperature in excess of 350% and "burned-ire" with ultraviolet light. until
gain stability was achieved. The accumulated signal required to fully clean up
the MCP was in excess of 4 x 10 10 counts mm- 2
 with a total charge throughput of
-5-
W.
the order of 0.5 C cm- 2 . These count levels are a Factor of 100 higher than the
maximum count rate capabilities reported for the high gain MCPs used in the
Einstein High-Resolution Imager (HR1). The fact that signal lzvels of this
magnitude are required to clean up a curved-channel t1CP and reach a plateau of
gain stability should dispel any concerns regarding the lifetimes of the cur-
rent generation of high gain MCPs.
During bakeout and "burn-;n", residual gas analyses were recorded to
provide quantitative measurements of the constituent gases present inside the
vacuum system. As a further test, prior to assembly of the gate- s alve detector
tube, the MCP was briefly exposed to dry nitrogen at atmospheric pressure and
then re-evacuated for fu r ther operation without an additional bakeout. This was
carried out in order to determine the effects of exposure to ambient atmosphere
as might happen, for example, in an open-structure flight detector system
during environmental testing and spacecraft integration. It was found that the
nominal gain value was obtained at an applied potential about 50 V lower than
that required prior to exposure to dry nitrogen, i.e. a slight gair recovery
was observed. This behavior is identical to that observed with open-struc:(ire
channel electron multipliers used in earlier space missions. Subseouent oper-
ation has eliminated this slight gain recovery and the MCP has returned to a
stable operating plateau. However, it does appear desirable for maxinum photo-
metric stability to maintain the 11CF in a hiqh vacuum environment at all times
prior to operation in orbit. This fact, together with the need to protect the
CsI photocathode, underlines the need for a high-vacuum gate-valve assembly as
an essential part of a high-sensitivity x-ray detector. At this time, we are
completing the final characterisation of the MCP in preparation for CsI photo-
cathode deposition.
s^	 -6-
I 
RT `
IV. SUMMARY OF FUTURE PROGRAM TASKS
Following the transfer of the program to Stanford University the following
tasks will be undertaken:
1) Determine in detail the performance characteristics of the 40-mm-
diameter curved-channel MCPs.
2) Determine the performance characteristics of the 27-mm-diameter curved-
channel MCP with the curved input face.
3) Complete the initial program of measurements of the quantum efficien-
cies of opaque CsI photocathodes at soft x-ray wavelengths down to I A.
4) Attempt a quantitative comparative evaluation between an opaque and a
"fluffy" CsI photocathode.
5) Define the procedures required for the fabrication of 75-mm-diameter
curved-channel 14CPs .
6) Determine the performance character i stics of a high-resolution (1024 x
1024)-pixel detector at x-ray wavelengths.
V. REFERENCE
"Multi-Anode Microchannel Arrays: New detectors for imaging and spectro-
scopy in space" by J. G. Timothy and R. L. Bybee (attached).
-7-	 I


The development and test of multi-anode microchannel array detector systems. 2: Soft X-ray detectors

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server