# 17th Advanced Accelerator Concepts Workshop

31 July 2016 to 5 August 2016
Gaylord Hotel and Conference Center
US/Eastern timezone

## MeV electron acceleration at 1 kHz with <10 mJ laser pulses

4 Aug 2016, 10:50
20m
Woodrow Wilson CD (Gaylord Hotel)

### Woodrow Wilson CD

#### Gaylord Hotel

Oral Working Group 1

### Speaker

Fatholah Salehi (University of Maryland)

### Abstract

We demonstrate laser driven acceleration of electrons to MeV scale energies at 1 kHz repetition rate using <10 mJ pulse energies focused on a near-critical density He or H$_2$ gas jet. Using the H$_2$ gas jet, electron acceleration to ~0.5 MeV is observed with laser pulse energy as low as 1.3 mJ.

### Summary

Typical laser wakefield acceleration (LWFA) experiments demand high laser pulse energies (more than ~0.5 J), and consequently they are limited to low repetition rates ($\leq$ 10 Hz) using existing laser technology. LWFA is initiated by relativistic self-focusing of the laser pulse in the plasma, which has a critical power of $P_{cr}=17(N_{cr}/N_{e}) GW$, where $N_{e}$ is the plasma density and $N_{cr}$ is the critical density. Here, we show that using a near critical density gas jet lowers $P_{cr}$ sufficiently to enable relativistic self-focusing and MeV-scale electron acceleration for laser pulses as low in energy as 1.3 mJ, demonstrating acceleration of relativistic beams using a high repetition rate laser system.

Pulses from the laser (1 kHz, $\lambda$=800nm, 30fs, < 12 mJ) are tightly focused with an f/8.5 off-axis paraboloid to a ~ 9 µm intensity FWHM in the jet. The high density thin (~150 µm) jet was produced by cooling He, or H$_2$ gas to -150 C while under up to 1000 psi in backing pressure. Accelerated electron spectra were collected by a magnetic spectrometer. Electron acceleration up to 0.5 MeV was observed in the H$_2$ jet with pulse energy as low as 1.3 mJ. Increasing the pulse energy increases both the electron energy and bunch charge such that 10 mJ laser pulses accelerate ~ 1 pC of charge to 1-2 MeV.

Such a high repetition rate, high flux ultrafast source has immediate application to time resolved electron probing of matter. Using a high Z-foil converter, one also has a high rep. rate $\gamma$-ray source for applications such as ultrafast radiography for scientific or medical applications.

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### Primary author

Fatholah Salehi (University of Maryland)

### Co-authors

Dr. Andy Goers (University of Maryland, College Park) Dr. Donghoon Kuk (University of Maryland, College Park) Mr. George Hine (University of Maryland College Park) Prof. Howard Milchberg (University of Maryland) Prof. Ki-Yong Kim (University of Maryland, College Park) Mr. Linus Feder (Universityof Maryland, College Park)

### Presentation Materials

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