Jangho Park

Quantitative evaluation of single-shot inline phase contrast imaging using an inverse compton x-ray source

Inverse compton scattering (ICS) x-ray sources are of current interest in biomedical imaging. We present an experimental demonstration of inline phase contrast imaging using a single picosecond pulse of the ICS source located at the BNL Accelerator Test Facility. The phase contrast effect is clearly observed. Its qualities are shown to be in agreement with the predictions of theoretical models through comparison of experimental and simulated images of a set of plastic wires of differing composition and size. Finally, we display an application of the technique to a biological sample, confirming the possibility of time-resolved imaging on the picosecond scale.

Simulations of a High‐Transformer‐Ratio Plasma Wakefield Accelerator Using Multiple Electron Bunches

Particle‐in‐cell simulations of a plasma wakefield accelerator in the linear regime are presented, consisting of four electron bunches that are fed into a high‐density plasma. It is found that a high transformer ratio can be maintained over 43 cm of plasma if the charge in each bunch is increased linearly, the bunches are placed 1.5 plasma wavelengths apart and the bunch emmitances are adjusted to compensate for the nonlinear focusing forces. The generated wakefield is sampled by a test witness bunch whose energy gain after the plasma is six times the energy loss of the drive bunches.

Vacuum laser acceleration in proof of principle at BNLATF

The novel and revolutionary concept of real Vacuum Laser A acceleration proof of principle is described in this paper. The simulation with the current BNL-ATF parameter shows that electron beam can get net energy from intense laser beam. The initial 20MeV electron beam with energy spread of 10−3 can get hundreds of KeV energy gain with energy spread of 10−2 by interacting with a laser a0 = 1. The proposal has been presented and approved by BNL-ATF. The experiment for this proof of principle is going to be scheduled.

A multibunch plasma wakefield acceleration experiment at the Brookhaven National Laboratory

Plasma-based particle accelerators have made remarkable progress in the recent years. In particular the doubling of the energy of 42 GeV trailing electrons has been demonstrated in a bean-driven plasma wakefield accelerator (PWFA) at the SLAC National Accelerator Laboratory [I. Blumenfeld et al., Nature 445, 741–744 (15 February 2007)]. The next significant step for a PWFA is to demonstrate the acceleration of a witness bunch with a narrow energy spread. We have recently demonstrated experimentally a simple mask method to generate a train of drive bunches followed by a witness bunch with variable spacing in the picosecond range [P. Muggli et al., Phys. Rev. Lett. 101, 054801 (2008)]. The train of drive bunches resonantly drives the wakefield, while the witness bunch is accelerated. The number of drive bunches, and therefore the accelerating wakefield amplitude can be selected. In a multi-drive-bunch configuration the witness bunch energy can be multiplied by a factor larger than two, and the transformer ratio and the transfer efficiency can in principle be maximized. The plasma is generated by a H2-filled capillary discharge. The plasma density measured and time-resolved using Stark broadening of the Hα atomic line. It is adjusted to the resonance by varying the delay between the capillary discharge time and the arrival time of the electron train.

Contrast of Subpicosecond Microelectron Bunch Trains

We recently demonstrated that electron bunch trains with a controllable number of bunches and adjustable subpicosecond spacing can be produced using a mask technique. In this paper we calculate the bunch train contrast as a function of the beam betatron size at the mask σβ and of the diameter d of the mask wires separated by a period D. As expected, when σβ/(d/2) the contrast is high and decreases with increasing σβ/(d/2).