The X-pinch, a Remarkable X-ray Sourceand High Energy Density Plasma

David HammerLaboratory of Plasma Studies

Electrical and Computer EngineeringCornell University

Cornell University

Presenting the Work ofSergei Pikuz, Tania Shelkovenko, Dan Sinars,

Byungmoo Song, Kathy Chandler, Marc Mitchell, Jon

Douglass, John Greenly and Ryan McBride

With Thanks to The P.N. Lebedev Institute group (Zakharov, Pikuz et al. plus Jiri Ullshmeid)

that conceived of the X pinch (1981)

Maxwell Laboratories, Inc., for introducing the X pinch to the U.S. (1984)

Nian-Sheng Qi, who helped start X pinch (“x-ray laser”) at Cornell (1987)

Dan Kalantar, who investigated X pinches for x-ray lithography (1989)

- and demonstrated x-ray backlighting is useful (Ph.D. 1993)

And Andrey Lebedev, who convinced me to invite Sergei Pikuz (1992)

Outline

1. Introduction to X pinches(what and how, why, where)

2. X-pinch x-ray sourceDurationSize

3. Conclusions

What and how …

Experimental Schematic DiagramX pinch

Two-wire Multi-wire Double

XP pulser diode

Anode

Cathode

Rog.1

Rog.2

Vacuum chamber

Insulator PFL

X-pinch

Water gaps

Start with crossed fine metalwires as the load of the 450kA, 100 ns (fwhm) XPpulsed-power generator.Two X pinches in parallelalso works.

Experimental Arrangement

Start by exploding 2 or more 10-50 µm metal wires in the form of an Xusing 250-450 kA, 100 ns pulse, generating X-shaped plasma. A 300-400 µm long Z-pinch forms in the middle, implodes toward theaxis, goes unstable, develops hot, dense plasma spots that emit an x-rayburst, and then opens up.The time from the start of the current can be reproducible to ± 1-2 ns.

Schleiren Images (<0.2 ns)

Why ….

Not to pump an x-ray laser

Not for x-ray lithography

Atomic physics/x-ray spectroscopy of dense high-Z plasmasDynamics of current-driven dense plasmasIntense, short pulse x-ray sourceMany materials have been studied (Mo, W, Nb, Al, Ti, NiCr,Conichrome, Alloy 188, etc.).Intense x-ray bursts last 10-1000 ps (x-ray streak camera),and have energies of up to ~ 1 J in > 1.5 keV x-rays at 400 kA.

These numbers imply a source volume power density up to 1022

W/cm3 and a surface flux up to 1016 W/cm2.Time resolved x-ray spectroscopy -->, for example, Te as high as 2.5keV and ne > 3x1023 cm-3 in Ti X-pinches (Sinars et al, JSQRT, 2003).

It is a really interesting HighEnergy Density Plasma

And they are good for imaging (forbusiness and for fun)

Point-projection radiographs have µm-scale resolution, implying source sizes of~1 µm or less. The resolution was “toogood to be true.” Also, the pulse is short.

Where?

Those Represented at DZP2005• Lebedev Institute• Cornell• Imperial College• University of Nevada, Reno• Pontificia Universidad Catolica de Chile• Ecole Polytechnique• Florida A&M University• University of California, San Diego

Pulse DurationOriginally, we used 400 MHz oscilloscopesThen an X-ray streak camera with Al (D. Kalantar)

- SubnanosecondThen a 1-2 GHz digitizer with Mo

- Sub-half nanoscecondRecently, streak camera with ~ 10 ps resolution

- Pulses as short as 10 ps (above 4 keV)

An x-ray streak camera was used to recordenlarged radiographic images of fineopaque and semitransparent objects (wires,fibers, fibers with a metal core) through anentrance slit placed in front of thephotocathode. Variation in the intensitydistribution of the images through thevarious objects provides time dependentinformation on the source size and spectralcharacteristics.

Experimental setup for time resolvedX pinch x-ray source size measurements

Anode

Catode

X pinch

Wiregrid

FilterSlit

X-ray streakcamera

Glass fibersB+W fibers

Photocathode

The image of a 1 ns x-ray streak4-wire NiCr X pinch (geometric distortion corrected)A portion of the image is shown enlarged to show thedecreasing pulse width with increasing photon energy.The x-rays reaching the photocathode through the 100µm glass core of the optical fiber (> 4 keV) have a pulsewidth of about 10 ps (resolution limit).The 20 µm W core of the B fiber does not becometransparent, which means there is not intense emissionat or above 15 keV from this X pinch.

Streaked image of the wire grid in x-rayradiation of 4 x 20 µm NiCr X pinch

1 ns

1 m

m

0

1

2

0 50 100 150Time (ns)

X-ra

y In

tens

ity (A

rb.u

nits

)

50

100

150

0 1/3

Curre

nt (k

A)

PCD

Rogowski

T (ps)0

100 µm

W coreB shell

Plastic shellGlass core

Pulse 3626

100 200 300

(1)

(2)

(3)(4)

(5)

Radial Size of the Source Vs Time

• The radial size of the first source is 10 µm orless for more than 100 ps even as the photonenergy of the radiation increases from thebeginning of the burst to the intensitymaximum. At the moment of maximumradiation intensity, this source seems to reachits minimum diameter, after which theradiation appears to drop very rapidly (withno visible expansion of the source size).

Time integrated and streaked images of W wire inB shell in x-ray radiation of 4 x 20 µm NiCr X pinch

0

100

200

T (ps)

100 µm

17 µm

B shell

W core

Source 1 Source 2

1

234

Pulse 3626

10 µm

1

2

3

45

5

Planetime integrated

radiographimage

Streakedimage

Outline of plane

radiograph image

Outlines of streaked

image

Source Size

Source sizes for variousmaterials are measured by

imaging known finefibers/wires or slits

Wave-Optics-Enhanced Point-ProjectionRadiography Requires a Small Source

(Actual Wave-Optics Calculations for 8 µm B and 3 Å)

Wavelength Spread

Finite source size &Wavelength spread

Experimental Arrangement

Source size using a wire and fiber

8 µm Glass fiber image

Computed image for 1 ± 0.2 µm size Computed image for 1 ± 0.2 µm size

7.5 µm W wire image

Nb X pinch; 93:1 Experimentalmagnification Calculations include sourcebandwidth

The Middle of an X pinch“Thermal x-rays” come from necks (bytriangulation using images of a mesh).

Electron-beams generate > 10 keV x-rays 100-500µm away on the anode side, adding “background.”

The X pinch is a very interesting high energy density plasma

Pulse is a function of energy; can be < 100 ps

Refraction is responsible for a majority of the edge-enhancement in

radiographic images from X pinches

Direct Determination of Source Size

- 1. Agreement between fine objects in point projection and Fresnel-Kirchhoff

integral- 2. In 3-5 keV, Nb: 1 µm, Mo: 1.2 µm, W: 1.6 µm, NiCr: 2.8 µm, Ti: 14 µm

- 3. 1-2 µm source size up to 12 keV

High-Quality Coherence-Enhanced Imaging requires controlling X pinches to

produce one, intense micropinch with reduced E-beam radiation

Smaller drivers are more convenient … (UCSD, Ecole Polytechnique)

Conclusions

Just when we thought we had moved beyond our past ….

Dr. Claudio Alonso, University Lecturer in Cell BiologyDepartment of Zoology, University of CambridgeDowning Street, Cambridge CB2 3EJUnited Kingdom

“I have an article just been accepted in Nature ReviewsGenetics (NRG) … about the … elements that controlanimal development and their potential for evolutionarychange - a subject area rather distant from your field ofresearch, I would imagine.”

He asked if they could use our image for the cover …