JAO 6/26/02 1 Really Fast X-ray Imaging Instruments John Oertel Team Leader for Diagnostic Engineering and Operations Presented to LANL Critical Skills program June 26, 2002
JAO 6/26/02 1
Really Fast X-ray Imaging Instruments
John OertelTeam Leader for Diagnostic Engineering and Operations
Presented toLANL Critical Skills program
June 26, 2002
JAO 6/26/02 2
Outline
• Why do you need a <100 ps x-ray imager?• The facilities they operate at• Block diagram a gated x-ray imager• Some specifications• X-ray imaging basics• X-ray gating basics• Characteristics• Developments• Applications• The future
JAO 6/26/02 3
Why?
In order to minimize motional blurring and freeze material velocities of > 10 7 cm/s, spatial resolution of 5 m and gate times of 50 ps are required.
One way to gate images from an x-ray pinhole camera is to propagate a high-voltage gate pulse across a microwave transmission deposited on the front surface of a Microchannel Plate.
JAO 6/26/02 4
The Facilities
NovaOmegaTridentNIFOthers…
JAO 6/26/02 5
Block Diagram
Connector includes:1 - 10 volt trigger3 - 15 volt DC power3 - fiberoptics2 - Nitrogen or water cooling lines1 - High bandwidth monitor1- Ground line15 - multi-wire twisted pair
Film pac withCCD camera option
4 kV phosphorbias
Impedancematchingcircuit 50 Ω to6.25 Ω
Pulsers @ 6 chan.of 4.5 kV, variable pulsewidth,and 50 ohm
6 channeldelay circuitTrigger circuit
Monitor circuit
DC bias forMCP+/- 1000 V
TIM
Connector
Impedancematchingcircuit 6.25Ω to50 Ω
Front-endFiltersMCP modulePhosphor& fiberoptictaper
JAO 6/26/02 6
Typical Specifications
40 mm MCP typical4 Au transmission lines16 data channels, 4 images/ stripVariable gainFiltering12x, 8x, 4x and 2x magnificationsInsertable or flange mountedFilm or CCD image capture100 eV to 10 keV sensitivity5 m spatial resolution80 ps temporial resolution, some are adjustable a few nsFilm or CCD readout
JAO 6/26/02 7
Imaging X-rays with Pinholes has Advantages and Disadvantages
• Pros: – Simple
– Good signal to noise ratio– Broadband energy transmission– Inexpensive technology for multiple channels
• Cons:– Low flux due to small solid angles– Have to get pinhole close to TCC for best
resolution
JAO 6/26/02 8
Airy pattern consists of a bright central disk surrounded by a system of concentric alternately dark and bright rings. The
first zero occurs at kasin = 3.83
1.0
kasin
3.83
-3.8
3 0
I/I(0)
a
qR
L
kasin= 3.832asin = 3.83, sin = q/R, k = 2 2a = d
q = 1.22 R/d
JAO 6/26/02 9
Geometric Optics
L1 L2
r
L1 L2
object plane image plane
d/2
d/2q
q
tanq/ L1+L2 = d/2L2
q = d/2(L1 + L2/L2)
Putting the diffraction and geometric parts togethersetting q = 0 and taking derivative with respect to d gives:
The geometric part
0 = (L1/L2+1)1/2 - 1/d^2(1.22 L1)
The optimum pinhole diameter is therefore:
d = 2.44L1 (M/M+1)
JAO 6/26/02 10
Spatial Resolution Depends Upon Diffraction and Geometric Factors
Far field (Fraunhofer) D>> vs. Near field (Fresnel) D~= 1.54 x 10 -10 m, D = 5 x 10-6 m
q1 = 1.22L1/d, diffraction of circular aperture
q2 = d/2(L1/L2+1) geometric optics
Minimized source produces a optimum aperture for given E
Q(d) = q1 + q2
d = 2.44L1(M/M+1)
JAO 6/26/02 11
Pinhole Resolution vs X-ray Energy
0
5
10
15
20
25
30
35
40
45
50
0 2 4 6 8 10
X-ray Energy (keV)
Pin
hole
resolu
tion
(u
m)
12X, 1.38"
8X, 2.00"
4x, 3.60"
2x, 6.00"
Most x-ray imagers are designed to get the MCP as close as possible to TCC without clipping beams
OPHD 2.44LM /M 1
Re solution OPHD 2
JAO 6/26/02 12
Be light seal
MCPs 3 - 105mmX35mm6 - strips @ 13 mm wide
50Ω to 6.25Ω taperedtransmission lines
fiberoptic faceplatewith P-11 phosphorand vacuum seal orfiberoptic w/ P-20 for CCD
Micro Channel Plate Module
All components are off-the-shelfand interchangeable.
JAO 6/26/02 13
Gating is provided by launching a short (<200 ps) ~1kV voltage pulse across a microstrip transmission line coated on the MCP. A photoelectron signal produced at the front surface of the MCP is then only amplified during the transit time of the voltage pulse across a given point on the microstrip.
50
25
25
12.5 DC Bias
- 2500 Volts, < 200 ps FWHM
6.6 mm
1000 Gold5000 Copper50 Chromium
Pin E = Pout
Rout (Vin)^2 E
Rin
Vout =
0 to -300 VDC
With E = 90%V in = 2500 VR in = 50 Rout = 12.5
V out = 1185 volts
Vp =c
Vp = 1.5 cm/100 ps
JAO 6/26/02 14
Temporal Gate Limited by Electron Transit Time
MCP L/D = 40
Fiberoptic Faceplate with500 /cm2 InSnO2 and0.7 mg/cm2 P-11 phosphor
Kodak2484 35 mmfilm
x-ray
3 kV-300 V
10 m
500 m
8o
e -
e -
e -
t tr = m L LeV D
Electron transit time in a MCP channel
t tr ~ 250 ps w/ V = 1 kV and L/D = 40
G ~ V
Electron Gain in a MCP is very non-linear
kn n = # of dynodes (26)k = 0.5
Minimum temporal gate limited by electron transit time.
If applied voltage pulse begins to compare in width to t trit is no longer possible to extract the full gain from a channel.
For usable output gains minimum optical gate time tends to be 1/3 t tr.
JAO 6/26/02 15
To drive a MCP stripline we use fast high-voltage pulsers
4.04 kV149.82 ps FWHMtF = 87.75 ps
JAO 6/26/02 16
High Voltage Pulser similar to a Marx bank
4 kV, < 200 ps Output
2.2 kVDC
• From 2 kV, 200 ps to 4 kV, 150 ps better differentiation techniques better interstage capacitors improved surface conditions
• More reliable than previous pulsersbetter interstage caps saves transistors
• Improved pulse shape consistencyOff-board differentiation simplifies faband allows for variable pulse lengths
• Reduced pulser drift1% zeners
other stages andtrigger
50 pF
8.2 pF
interstage cap
DC blocking cap
shorted stub reverses polarityand reflected signal adds into original resulting in FWHM < 200 ps
JAO 6/26/02 17
GXI-3 Resolution Grid ShotTrident Shot T3040704
7 m wire dia. 25 m spacing12x mag. 5 m pinholes10 mils Be filtering- 200 VDC bias
50 J, 2, 1 ns square
JAO 6/26/02 18
GXI-2 Flatfield Data for NOVA shot # 24042613
GXI-2 Flatfield Data Shot#24042614
0.00E+00
5.00E-02
1.00E-01
1.50E-01
2.00E-01
2.50E-01
3.00E-01
3.50E-01
0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00
Position (mm)
Expo
sure
(erg
s/cm
2)
Stripline 1Stripline 2Stripline 3Stripline 4
Time
JAO 6/26/02 19
Linearity plot
Saturation
LLNL
JAO 6/26/02 20
2 ns electrical pulse provides a 450 ps FWHM optical gate
LLNL
JAO 6/26/02 21
Optical vs Electrical FWHM
LLNL
JAO 6/26/02 22
Gain vs Bias, 2 ns PFM
LLNL
JAO 6/26/02 23
MCP Output vs Coating
250
1250
2250
3250
4250
5250
6250
7250
8250
9250
10250
11250
12250
13250
14250
15250
16250
17250
0 500 1000 1500 2000 2500 3000
Coating thickness (Å)
500 V
600 V
700 V
800 V
900 V
MCP A
MCP B
MCP C
1000Å
1250Å
1500Å
1750Å
3 MCP’s all from same bouleAll coating were Au 250Å to 2500ÅAluminum - DC source @ 1.6 keVPreliminary results suggest we have not peaked!
Does it act the same for a different wavelength?
Detector cathode optimization requires further study
What is the optimum cathode coating for a MCP?
JAO 6/26/02 24
P-11 Phosphor Areal Density vs Intensity
y = -107.36x6 + 1442.3x5 - 7601.8x4 + 19722x3 - 25595x2 + 14205x
0
500
1000
1500
2000
2500
3000
3500
0 0.5 1 1.5 2 2.5 3 3.5 4
Areal Density (mg/cm2)
Resolution vs. Phosphor Areal Density
y = 2.9769x + 74.032
60
65
70
75
80
85
90
95
0 0.5 1 1.5 2 2.5 3 3.5 4
Areal Density (mg/cm2)
P-11 Phosphor optimization
What phosphor coating density yields the greatest flux? 0.6 mg/cm2
What phosphor coating density yields the best spatial resolution?
JAO 6/26/02 25
Applications
25563
JAO 6/26/02 26
Rayleigh-Taylor instability growth studied in cylindrical convergent geometry using “indirect-drive” on the NOVA laser
JAO 6/26/02 27
The Future… GXD for the National Ignition Facility
JAO 6/26/02 28
GXD Electronic Block Diagram
MCPModule CCD CCD
P.S.
PC104computer
Housekeepingsensors
PulserCards
& Power suppliespfn
DelayCircuits
TrigCircuits
Imp. Mis-match
Trigger in
Imp. matching
Cooling
28VDC
Ethernet
DC bias
Monitor
phos
Adder circuit
pcd
JAO 6/26/02 29
Gated X-ray Imager for the NIF
52” - 58”
Ethernet unit
CCD power supply2x2x3”, 2 ea.
Kentech Electronics•HV pulser units (3.5 kV - 4 kV)•Power supplies•Delay generators (50 nsmax.)•Triggering•Monitor•Command/Control
CCDMCP Module
4”
10-12”
30” - 36”
Cooling in external base of airbox
Embedded Computer
JAO 6/26/02 30
MCP Module
Phosphor HV
MCP Striplines
Intensifier Block Terminator Circuit Wing
CCD Cooling lines
SMA Connectors
JAO 6/26/02 31
Fiber Optically coupled
Vacuum Enclosure
Pump Out
Cooling Block
PowerReadoutTE
Cooling Lines
Spectral Instruments CCD Camera
JAO 6/26/02 32
Kentech ElectronicsPulse Out
Pulse In
MCP Bias +1kV/ -500V
Phosphor Bias +4kV
PCD +400V
Trigger In
Monitor Out
+28VDC
Computer Interface
30” - 36”
Dimension based on performance requirements
Pulser Units4 each1 1/8” W x 4.92” H
JAO 6/26/02 33
PC 104+ Embedded Computer
CCD Power Supply2x2x3”, 2 each
Embedded ComputerPC104/PC104+Support Cards:Frame GrabberKentech InterfaceHousekeeping
Ethernet:Electrical/Fiber opticFiber/Fiber