1. Creation of a Novel X ray Generator
James Hostetter
Louisiana State University and
SLAC National Accelerator Laboratory

2. Why X rays?
adapted from:

3. Why short pulses?

4. Capabilities and Advantages
10’s of KeV X rays
1 picosecond pulses
100 MHz pulses
108 photons/s at 8 KeV
Compact
Relatively cheap to build
Complementary to LCLS
Always available to PULSE researchers

5. Current, Future and Past X ray Sources
Shorter pulses means studying faster processes
More photons means bigger signal
May be unnecessary
May be harmful
LCLS is by far the brightest and fastest pulse source, but runs at very low repetition rate.

6. X-ray Production Cathode creates e-
Potential difference accelerates electrons towards anode
Collision with anode causes emission of X-rays
E = q * V

7. Better X-ray Production
Laser allows for pulsed x rays
RF cavity compresses electron bunches
Shorter pulses
Brighter pulses

8. Photocathode basics GaAs Must be cesiated Must be exposed to NF3 or O2
Must have an ultra-high vacuum (UHV)
Photocurrent decays
~10% Quantum Efficiency (QE)
QE=e-/photon
QE = I*h*ν
Gate Valve
Loadlock
Laser
Cesiator
Manipulator
Heater
Ion pump
P*e

9. Photocurrent Decay
I = I0*e-t/τ ≈ I0 (1-t/τ)
Half-life=2.36 days

10. Photocurrent vs. Power

11. Conclusion Future Work
Significant Progress in the design of the x-ray generator.
Understanding the photocathode is proceeding well
Decay on the order of days
Linear dependence of QE on power
Future Work
Scaling to short laser pulse and higher average current (1mA)
Finish Electron gun design and sample hand-off

12. Acknowledgements David Reis Shambhu Ghimire Takashi Maruyama
SULI program