Fusion: It’s Time to Color outside the Lines

There has been some good news, and some bad news in the controlled fusion community recently. The good news is that the Lawrence Livermore National Laboratory (LLNL) has recently produced a burning plasma. It succeeded on several of its shots where ~1.5 - 2 megajoules from its laser (National Ignition Facility, or NIF) has generated ~1.3 - 3 megajoules of fusion products. The highest ratio of fusion energy to laser energy it achieved, defined as its Q, was 1.5 at the time of this writing. While LLNL is sponsored by nuclear stockpile stewardship, this author sees a likely path from their result to fusion for energy for the world, a path using a very different laser and a very different target configuration. The bad news is that the International Tokamak Experimental Reactor (ITER) has continued to stumble on more and more delays and cost overruns, as its capital cost has mushroomed from ~$5 billion to ~ $25 B. This paper argues that the American fusion effort, for energy for the civilian economy, should switch its emphasis not only from magnetic fusion to inertial fusion but should also take much more seriously fusion breeding. Over the next few decades, the world might well be setting up more and more thermal nuclear reactors, and these might need fuel which only fusion breeders can supply. In other words, fusion should begin to color outside the lines.

Drive laser system for the DC-SRF photoinjector at Peking University

Photoinjectors are widely used for linear accelerators as electron sources to generate high-brightness electron beams. The drive laser, which determines the timing structure and quality of the electron beam, is a crucial component of a photoinjector. A new drive laser system has been designed and constructed for the upgraded 3.5-cell DC-SRF photoinjector at Peking University. The drive laser system consists of a 1064 nm laser oscillator, a four-stage amplifier, second and fourth harmonic generators, an optical system to transfer the UV pulses to the photocathode, and a synchronization system. The drive laser system has been successfully applied during stable operation of the DC-SRF photoinjector and its performance meets requirements. A 266 nm laser with an average power close to 1 W can be delivered to illuminate the Cs2Te photocathode and the instability is less than 5% for long time operation. The design considerations for improving the UV laser quality, a detailed description of the laser system, and its performance are presented in this paper.

Manipulation of Micro Solid Particles and Induced Flows in Water by Laser Irradiation

Q-switch for pulsing laser beam and Galvano scanner for rapid scanning laser beam were adapted to manipulate micro solid particles in a water droplet. The trapping of fine particles at micron-sized diameters by a YAG laser system, induced flows, and the induced motion of the particles by laser beam irradiations are discussed. Particle rotations are observed by using anisotropic micro objects, and moreover the rotational rate with clockwise direction is 22 r/min. The fragments of a cover glass were mixed in a water droplet, and their size and shape are uneven. The rotation of that non-spheres without scanning by the Galvano scanner is also observed in water.

Photoinjector beam quality improvementby shaping the wavefront of a drive laser with oblique incidence

To increase the quantum efficiency （QE） of a copper photocathode and reduce the thermal emit- tance of an electron beam, a drive laser with oblique incidence was adopted in a BNL type photocathode rf gun. The disadvantageous effects on the beam quality caused by oblique incidence were analyzed qualitatively. A simple way to solve the problems through wavefront shaping was introduced and the beam quality was improved.

Beam dynamics study of the photoinjector at Wuhan advanced light source

Background A full-energy LINAC is under development at Wuhan Advanced Light Source(WALS)to provide beams for the 1.5 GeV storage ring proposed as a fourth-generation synchrotron radiation light source and a future free electron laser(FEL)facility.The LINAC starts from a photoinjector that is able to produce electron beams with low emittance(<1 mm·mrad),small relative energy spread(<0.5%),and high bunch charge(~1 nC).Purpose and methods To minimize the output emittance and RMS bunch length for the purpose of improving the photoinjector brightness,the influence of different laser pulse profiles on the slice emittance is investigated,and the beam dynamics simulation is performed with non-dominated sorting genetic algorithm-II(NSGA-II)combining with ASTRA code to find the optimal solution at a bunch charge of 1 nC.Results and conclusion In this paper,the beam dynamics optimization of the photoinjector is presented in detail;the simulation results imply that the laser pulse profile with 1σtruncated Gaussian distribution in transverse and flat-top-like temporal distribution is beneficial to the improvement of beam brightness of the photoinjector,which shows an output emittance of 0.63 mm·mrad in the case of intrinsic thermal emittance of 0.43 mm·mrad.