Really fast x ray imaging instruments
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Really Fast X-ray Imaging Instruments. John Oertel Team Leader for Diagnostic Engineering and Operations Presented to LANL Critical Skills program June 26, 2002. Outline. Why do you need a <100 ps x-ray imager? The facilities they operate at Block diagram a gated x-ray imager

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Really fast x ray imaging instruments

Really Fast X-ray Imaging Instruments

John Oertel

Team Leader for Diagnostic Engineering and Operations

Presented to

LANL Critical Skills program

June 26, 2002


Outline

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


Really fast x ray imaging instruments

Why?

In order to minimize motional blurring and freeze material velocities of > 10 7 cm/s, spatial resolution of 5 mm 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.


The facilities

The Facilities

Nova

Omega

Trident

NIF

Others…


Block diagram

6 channel

Trigger circuit

delay circuit

Pulsers @ 6 chan.

of 4.5 kV, variable

pulsewidth,

Impedance

and 50 ohm

matching

circuit 50 Ω to

6.25 Ω

4 kV phosphor

bias

Phosphor

Film pac with

CCD camera

option

&fiberoptic

MCP module

Front-end

Filters

taper

TIM Connector

DC bias for

MCP

+/- 1000 V

Impedance

matching

circuit 6.25Ω to

50 Ω

Monitor circuit

Block Diagram

Connector includes:

1 - 10 volt trigger

3 - 15 volt DC power

3 - fiberoptics

2 - Nitrogen or water cooling lines

1 - High bandwidth monitor

1- Ground line

15 - multi-wire twisted pair


Typical specifications

Typical Specifications

40 mm MCP typical

4 Au transmission lines

16 data channels, 4 images/ strip

Variable gain

Filtering

12x, 8x, 4x and 2x magnifications

Insertable or flange mounted

Film or CCD image capture

100 eV to 10 keV sensitivity

5 mm spatial resolution

80 ps temporial resolution, some are adjustable a few ns

Film or CCD readout


Imaging x rays with pinholes has advantages and disadvantages

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


Really fast x ray imaging instruments

I/I(0)

1.0

R

q

q

L

a

kasinq

0

3.83

-3.83

Airy pattern consists of a bright central disk surrounded by a system of concentric alternately dark and bright rings. The first zero occurs at kasinq = 3.83

kasinq = 3.83

2p/l asinq = 3.83, sinq = q/R, k = 2p/l, 2a = d

q = 1.22 Rl/d


Geometric optics

Geometric Optics

image plane

object plane

r

q

d/2

q

L2

L1

tany = q/ L1+L2 = d/2L2

q = d/2(L1 + L2/L2)

q

y

The geometric part

d/2

L2

L1

Putting the diffraction and geometric parts together

setting S q = 0 and taking derivative with respect to d gives:

The optimum pinhole diameter is therefore:

0 = (L1/L2+1)1/2 - 1/d^2(1.22 l L1)

d = 2.44 l L1 (M/M+1)


Spatial resolution depends upon diffraction and geometric factors

Spatial Resolution Depends Upon Diffraction and Geometric Factors

Far field (Fraunhofer) D>>l vs. Near field (Fresnel) D~l

l = 1.54 x 10 -10 m, D = 5 x 10-6 m

q1 = 1.22lL1/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 = 2.44lL1(M/M+1)


Really fast x ray imaging instruments

Most x-ray imagers are designed to get the MCP as close as possible to TCC without clipping beams


Really fast x ray imaging instruments

Micro Channel Plate Module

fiberoptic faceplate

with P-11 phosphor

and vacuum seal or

fiberoptic w/ P-20 for CCD

All components are off-the-shelf

and interchangeable.

Be light seal

50Ω to 6.25Ω tapered

transmission lines

MCPs 3 - 105mmX35mm

6 - strips @ 13 mm wide


Really fast x ray imaging instruments

c

e

e = 3.7

Vp =

Rout (Vin)^2 E

Vout =

Rin

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.

Vp =1.5 cm/100 ps

1000 A Gold

5000 A Copper

50 A Chromium

6.6 mm

Pin E = Pout

25 W

50 W

25 W

With E = 90%

V in = 2500 V

R in = 50 W

Rout = 12.5 W

V out = 1185 volts

DC Bias

12.5 W

0 to -300 VDC

- 2500 Volts, < 200 ps FWHM


Temporal gate limited by electron transit time

Electron Gain in a MCP is very non-linear

G ~ Vg

g = kn

Electron transit time in a MCP channel

t tr = m L L

D

eV

t tr ~ 250 ps w/ V = 1 kV and L/D = 40

Temporal Gate Limited by Electron Transit Time

Fiberoptic Faceplate with

500 W/cm2 InSnO2 and

0.7 mg/cm2 P-11 phosphor

MCP

L/D = 40

Kodak

2484 35 mm

film

n = # of dynodes (26)

k = 0.5

g = 13

500 mm

e -

x-ray

e -

e -

Minimum temporal gate limited by electron transit time.

If applied voltage pulse begins to compare in width to t tr

it 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.

8o

10 mm

3 kV

-300 V


To drive a mcp stripline we use fast high voltage pulsers

To drive a MCP stripline we use fast high-voltage pulsers

4.04 kV

149.82 ps FWHM

tF = 87.75 ps


High voltage pulser similar to a marx bank

High Voltage Pulser similar to a Marx bank

DC blocking cap

  • From 2 kV, 200 ps to 4 kV, 150 ps

    • better differentiation techniques

    • better interstage capacitors

    • improved surface conditions

  • More reliable than previous pulsers

    • better interstage caps saves transistors

  • Improved pulse shape consistency

    • Off-board differentiation simplifies fab

    • and allows for variable pulse lengths

  • Reduced pulser drift

    • 1% zeners

8.2 pF

4 kV, < 200 ps Output

shorted stub reverses polarity

and reflected signal adds into

original resulting in FWHM < 200 ps

interstage cap

50 pF

other stages and

trigger

2.2 kVDC


Gxi 3 resolution grid shot trident shot t3040704

GXI-3 Resolution Grid ShotTrident Shot T3040704

50 J, 2w, 1 ns square

7 mm wire dia. 25 mm spacing

12x mag. 5 mm pinholes

10 mils Be filtering

- 200 VDC bias


Gxi 2 flatfield data for nova shot 24042613

GXI-2 Flatfield Data for NOVA shot # 24042613


Linearity plot

Linearity plot

Saturation

LLNL


2 ns electrical pulse provides a 450 ps fwhm optical gate

2 ns electrical pulse provides a 450 ps FWHM optical gate

LLNL


Optical vs electrical fwhm

Optical vs Electrical FWHM

LLNL


Gain vs bias 2 ns pfm

Gain vs Bias, 2 ns PFM

LLNL


Really fast x ray imaging instruments

1000Å

1250Å

1500Å

1750Å

Detector cathode optimization requires further study

What is the optimum cathode coating for a MCP?

3 MCP’s all from same boule

All coating were Au 250Å to 2500Å

Aluminum - DC source @ 1.6 keV

Preliminary results suggest we have not peaked!

Does it act the same for a different wavelength?


Really fast x ray imaging instruments

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?


Applications

25563

Applications


Really fast x ray imaging instruments

Rayleigh-Taylor instability growth studied in cylindrical convergent geometry using “indirect-drive” on the NOVA laser


The future gxd for the national ignition facility

The Future… GXD for the National Ignition Facility


Gxd electronic block diagram

GXD Electronic Block Diagram

28VDC

Trigger in

Imp. Mis-match

Ethernet

MCP

Module

pfn

Pulser

Cards

& Power supplies

Delay

Circuits

Trig

Circuits

PC104

computer

CCD

P.S.

Housekeeping

sensors

CCD

phos

DC bias

Cooling

Monitor

Imp. matching

Adder circuit

pcd


Gated x ray imager for the nif

Gated X-ray Imager for the NIF

Ethernet unit

4”

Embedded Computer

30” - 36”

52” - 58”

  • Kentech Electronics

  • HV pulser units (3.5 kV - 4 kV)

  • Power supplies

  • Delay generators (50 nsmax.)

  • Triggering

  • Monitor

  • Command/Control

10-12”

CCD power supply

2x2x3”, 2 ea.

CCD

Cooling in external base of airbox

MCP Module


Mcp module

MCP Module

CCD Cooling lines

Phosphor HV

SMA Connectors

MCP Striplines

Terminator Circuit Wing

Intensifier Block


Spectral instruments ccd camera

Spectral Instruments CCD Camera

Power

Readout

TE

Cooling Lines

Cooling Block

Fiber Optically coupled

Pump Out

Vacuum Enclosure


Kentech electronics

Kentech Electronics

Pulse Out

Dimension based on performance requirements

Pulse In

MCP Bias +1kV/ -500V

30” - 36”

PCD +400V

Phosphor Bias +4kV

Trigger In

Monitor Out

+28VDC

Computer Interface

Pulser Units

4 each

1 1/8” W x 4.92” H


Pc 104 embedded computer

PC 104+ Embedded Computer

Embedded Computer

PC104/PC104+

Support Cards:

Frame Grabber

Kentech Interface

Housekeeping

Ethernet:

Electrical/Fiber optic

Fiber/Fiber

CCD Power Supply

2x2x3”, 2 each


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