Novel ultrafast electron diffraction system streaked ued
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Novel Ultrafast Electron Diffraction System (“streaked”-UED). Luigi Faillace. Ultrafast Electron Sources for Diffraction and Microscopy Workshop December 12 th - 14 th 2012, California NanoScience Institute at UCLA . ABOUT RADIABEAM.

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Novel Ultrafast Electron Diffraction System (“streaked”-UED)

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Novel ultrafast electron diffraction system streaked ued

Novel Ultrafast Electron Diffraction System (“streaked”-UED)

Luigi Faillace

Ultrafast Electron Sources for Diffraction and Microscopy Workshop

December 12th - 14th 2012, California NanoScience Institute at UCLA


Novel ultrafast electron diffraction system streaked ued

ABOUT RADIABEAM

RadiaBeam Technologies, LLC. is a small business with core expertise in accelerator physics.

Spin-off from UCLA (2004)

Extensive R&D Program (DOE, DOD, DHS, NSF)

Growing products line for research laboratories and industrial customers (magnets, diagnostics, RF structures, complete systems)

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Customers

Customers

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Ultrafast electron diffraction

Ultrafast Electron Diffraction

Ultrafast electron diffraction (UED) has the potential for real-time imaging of structural changes on atomic length scales, thus promising to make a profound impact on a large area of science including biology, chemistry, nano and material sciences [*]

x

x

x

x

x

x

Pegasus pump and probe setup

o

o

RF gun UCLA/BNL/SLAC

6 MW 2.856 GHz

o

o

o

Two axes x-y

sample-holder movement

o

Probing electron beam

~200 fs rms long

1 pC 3.5 MeV

e- beam

12 bit camera

f/0.95 lens coupling

Lanex screen or

MCP detector

IR laser pulse

1-10 mJ 40 fs rms

Collimating hole

1mm diameter

Pump pulse

0.5 mJ 800 nm

0.1 mJ 400 nm 40 fsrms

*P. Musumeci et al., Relativistic electron diffraction at the UCLA Pegasus photoinjectorlaboratory,

Ultramicroscopy108 (2008) 1450– 1453

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Conventional vs relativistic electron diffraction

Conventional vs. Relativistic Electron Diffraction

Relativistic

Conventional

  • Low-energy electrons (conventional electron gun)

  • Compact system due to larger diffraction angle

  • Low SNR (few electrons per bunch in order to reduce space charge >>> pulse broadening)

  • Thousands of pulses to obtain a good diffraction pattern

  • Need of a relativistic electron Gun

  • Longer diffraction camera length

  • More intense electron bunches possible due to weaker space charge effects

  • Single-shot measurement

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Novel ultrafast electron diffraction system streaked ued

Streaked UED System

Diffracted

e- bunch

Originally proposed by P. Musumeci et al., P. Musumeci et al. RF streak camera based ultrafast relativistic electron diffraction. Review of Scientific Instruments (2009) vol. 80 pp. 013302

Main Parameters

Pump laser

pulse

  • Innovations

  • Compromise between Conventional and Relativistic UED systems

  • Same physics of current UED systems but cheaper and more compact

  • UED measurements in small laboratories

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Novel ultrafast electron diffraction system streaked ued

SUED System Block Diagram

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Photoelectron gun electrostatic design

Photoelectron gun(electrostatic design)

  • 2D simulations with code (approach from Eindhoven University of Technology**)

  • The replaceable cathode sample is held by a hollow cylindrical body made out of aluminum while the vacuum vessel, that the anode electrode is attached to, is stainless steel.

  • The isolation between cathode anode is realized by using an insulating cone

SuperFish

9.8 MV/m

Surface electric field distribution along gun surfaces (start: from and back to cathode center in a counterclockwise path)

E (V/cm)

Breakdown risks are present inside the gun itself, but 100 kV is considered a safe value below the 250kV threshold (empirically determined*) that is actually the limit inside a gap (cathode-anode) of about 1cm .

  • *L. L. Alston, High Voltage Technology, Oxford University Press, 1968.

  • **T. van Oudheusden. Electron source for sub-relativistic single-shot femtosecond diffraction. Ph.D. Thesis Dissertation (2010), Eindhoven University of Technology.

3D model rendering

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Photoelectron gun beam dynamics simulations

Photoelectron gun(beam dynamics simulations)

EGUN

Emittance evolution

Transverse size

e- beam

Emittance evolution

Transverse size

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Novel ultrafast electron diffraction system streaked ued

Photoelectron gun(initial engineering)

NEG pump

Stainless steel

Vacuum vessel

anode

insulator

Window for

back-illumination

Aluminum

holder

Feed-through

cathode

TMP pump

3D model of the 100 kV photo-gun, from SolidWorks

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Deflecting cavity

Deflecting Cavity

proportionality factor K between the temporal and transverse coordinate on the screen located at distance L from the cavity center.

σtis the rms pulse length and σ0is the spot size with the cavity voltage off

minimum attainable

temporal resolution

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Deflecting cavity rf design

Deflecting Cavity (RF design)

Optimized cell geometry. The use of nose cones allows the concentration of the field toward the center of the deflecting gap, which creates a stronger field and better deflection, especially in our case of slow electrons (β=0.54).

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Deflecting cavity initial enginering

Deflecting Cavity (initial enginering)

Input RF

coupler

Inter-cell

coupling slot

Side cell

Nose cone type cells

3D model of the X-Band Deflector, from SolidWorks

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Detector system

Detector System

Pictures of the the diffraction patterns will be taking by using a micro channel plate (MCP) detector that basically works as an electron amplifier in which the incoming electrons generate secondary electrons. In this case, the incoming electrons enter channels in which they are accelerated by an electric field and generate the secondary electrons.

The size of the channels is on the order of 12 μm, which is the highest attainable spatial resolution. There are four plates of which three are connected to high voltage supplies and one is grounded. The four plates are respectively at -1 kV, 0 V, +1 kV and +3 kV. The accelerated electrons hit a phosphorous screen in which photons are produced due to the electrons from the channels.

This image is recorded by a CCD camera.

Diffraction pattern from a gold foil

at Pegasus Lab

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Complete system

Complete System

beam images at the screen

Evolution of the beam size and the horizontal emittance are shown (from GPT). Emittance compensation is obtained after the solenoid (0.3μm from z=0.45m to z=1m). .

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Synchronization

Synchronization

Electron beam, laser and RF cavity synchronized by locking 80 MHz laser oscillator cavity with sub-harmonic of the RF frequency by commercial active phase lock loop.

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Complete system initial engineering

NEG pump

RF deflector

Complete System (initial engineering)

Solenoid

CCD camera

Photo-gun

MCP

Steering magnets

Laser-sample

Interaction chamber

HV feed-through

3D model of the SUED system, from SolidWorks

Tasks to be performed at UCLA

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Conclusions

Conclusions

  • The SUED system will fabricated and tested at the Pegasus Laboratory at UCLA. The major components of the system are:

  • 100 kV photo-gun for 20 ps, 80 mA electron bunch generation;

  • Sample holder

  • RF deflector (20 kV voltage) for electron bunch streaking. Allowing ;

  • MCP detector

  • Synchronization System

  • Data acquisition/analysis system

  • We would love to hear feedback about what you like (or don’t like) about this system and anything we can do to improve it. You will hopefully be our customers!

Ultrafast Electron Sources for Diffraction and Microscopy Workshop


Novel ultrafast electron diffraction system streaked ued

Thank you !


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