1. Critical Density Target Design for Ion Acceleration on the T-Cubed Laser
Peter Kordell1, Paul Campbell1, Anatoly Maksimchuk1, Louise Willingale2, Karl Krushelnick1 1. University of Michigan, Center for Ultrafast Optical Science 2. Lancaster University Physics

2. Electrostatic Shock Wave
We are attempting to reproduce a successful experiment at UCLA which generated a quasi-monoenergetic proton beam from a Hydrogen gas jet.* Our use of the with the T Cubed Laser presents target fabrication challenges.
Energy = 8 J
Pulse Length = 400 fs
λ = 1.053μm
Without the target shaping pulse train and the low critical density of a C02 laser system, we must construct a high density jet with density shaping capabilities.
*D. Haberberger et al. Nature Physics, vol. 8, pp. 95–99, JAN 2012

3. Laser Induced Shock - Front Length Scale
Counts
103
102 10 1
0.1
Laser Induced Shock - Front Length Scale
p1 (mec)
x (c/ω0)
Ion phase space
50λ0 Scalelength
Ion phase space
10λ0 Scalelength
x (c/ω0)

4. Sheath Field and Shock Depletion Rear Length Scale
The rear length scale of the target is doubly constrained for our system. The lengthscale must be long enough to suppress a rear sheath field. *
It must also be as short as possible to prevent the shock wave from fully decelerating in an overlong plasma.
* T. Grismayer and P. Mora, Phys. Plasmas 13, (2006).

5. Methane Backed Parker Valve Setup
Target Specifications
Parker Series 99 micro dispensing valve
Liquid Nitrogen Cooled
Max Pressure P = 8.6 MPa
Min Temperature T =120 K
Backing Gas Choice
CH4 gives a 5x increase in electrons per molecule over H2
CH4 is thermodynamically active within our T and P range, providing subsonic and supersonic gas flow, clustered media* and liquid jets.
*K. Y. Kim Appl. Phys. Lett. 83, 3210 (2003)

6. Density Measurements
We performed a density and lengthscale characterization with a green HeNe Mach-Zhender interferometer
At 6.8MPa and -60oC we reach critical density 200μm above the nozzle tip.
The density profile from a 200μm ID needle matches our desired 40μm exponential lengthscale at this height.

7. Phase Dependent Front Lengthscale
As the nozzle cools, the flow transitions from supersonic to clustered.
The shadow cast by the high density gas allows us to estimate the front lengthscale of our target to be a 40μm total rise.