# Presentation: 264906

## 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
- Some specifications
- X-ray imaging basics
- X-ray gating basics
- Characteristics
- Developments
- Applications
- The future

## 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.

## The Facilities

- Nova
- Omega
- Trident
- NIF
- Others...

## 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

- 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 m 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

- 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

## 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 

- kasin= 3.83
- 2asin = 3.83,              sin = q/R,     k = 2 2a = d
**q = 1.22 R********/d**

## Geometric Optics

- L1

- L2

- r

- L1

- L2

- 

- object plane

- image plane

- d/2

- d/2

- q

- q

- 

- tanq/ L1+L2 = d/2L2

**q = d/2(L****1**** + L****2****/L****2****)**

- Putting the diffraction and geometric parts together
- setting 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 = 2.44********L****1**** (M/M+1)**

## 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 = 1.22L1/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 = 2.44L1(M/M+1)

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

## Micro Channel Plate Module

**Be light seal**

**MCPs    3 - 105mmX35mm**
**6 - strips @ 13 mm wide**

**50Ω to 6.25Ω tapered**
**transmission lines**

**fiberoptic faceplate**
**with P-11 phosphor**
**and vacuum seal or**
**fiberoptic w/ P-20 for CCD**

**Micro Channel Plate Module**

**All components are off-the-shelf**
**and interchangeable.**

## 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  Gold
- 5000  Copper
- 50  Chromium

- Pin E = Pout

- 0 to -300 VDC

- With E = 90%
- V in = 2500 V
- R in = 50 
- Rout = 12.5 
**V ****out**** = 1185 volts**

- Vp = 1.5 cm/100 ps

## Temporal Gate Limited by Electron Transit Time

- MCP
- L/D = 40

- Fiberoptic Faceplate with
- 500 /cm2 InSnO2 and
- 0.7 mg/cm2  P-11 phosphor

- Kodak
- 2484 35 mm
- film

- x-ray

- 3 kV

- -300 V

- 10 m

- 500 m

- 8o

- e -

- e -

- e -

- 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 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.

## 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

- 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 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**

- other stages and
- trigger

- 50 pF

- 8.2 pF

- interstage cap

- DC blocking cap

- shorted stub reverses polarity
- and reflected signal adds into
- original resulting in FWHM < 200 ps

## GXI-3 Resolution Grid ShotTrident Shot T3040704

- 7 m wire dia. 25 m spacing
- 12x mag.  5 m pinholes
- 10 mils Be filtering
- - 200 VDC bias

- 50 J, 2, 1 ns square

##  GXI-2 Flatfield Data for NOVA shot # 24042613

## Linearity plot

**Saturation**

_***LLNL***_

## 2 ns electrical pulse provides a  450 ps FWHM optical gate

_***LLNL***_

## Optical vs Electrical FWHM

_***LLNL***_

## Gain vs Bias, 2 ns PFM

_***LLNL***_

## Detector cathode optimization requires further study

- 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?*

**Detector cathode optimization requires further study**

- What is the optimum cathode coating for a MCP?

## 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

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

## The Future...  GXD for the National Ignition Facility

## GXD Electronic Block Diagram

- MCP
- Module

- CCD

- CCD
- P.S.

- PC104
- computer

- Housekeeping
- sensors

- Pulser
- Cards
- & Power supplies

- pfn

- Delay
- Circuits

- Trig
- Circuits

- Imp. Mis-match

- Trigger in

- Imp. matching

- Cooling

- 28VDC

- Ethernet

- DC bias

- Monitor

- phos

- Adder circuit

- pcd

## Gated X-ray Imager for the NIF

- 52” - 58”

- Ethernet unit

- CCD power supply
- 2x2x3”, 2 ea.

- Kentech Electronics
- HV pulser units (3.5 kV - 4 kV)
- Power supplies
- Delay generators (50 nsmax.)
- Triggering
- Monitor
- Command/Control

- CCD

- MCP Module

- 4”

- 10-12”

- 30” - 36”

- Cooling in external base of airbox

- Embedded Computer

## MCP Module

**Phosphor HV**

**MCP Striplines**

**Intensifier Block**

**Terminator Circuit Wing**

**CCD Cooling lines**

**SMA Connectors**

## Spectral Instruments CCD Camera

**Fiber Optically coupled**

**Vacuum Enclosure**

**Pump Out**

**Cooling Block**

**Power**
**Readout**
**TE**

**Cooling Lines**

## Kentech Electronics

**Pulse 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 Units**
**4 each**
**1 1/8” W x 4.92” H**** **

## PC 104+ Embedded Computer

**CCD Power Supply**
**2x2x3”, 2 each**

**Embedded Computer**
**PC104/PC104+**
**Support Cards:**
**Frame Grabber**
**Kentech Interface**
**Housekeeping**

**Ethernet:**
**Electrical/Fiber optic**
**Fiber/Fiber**