Plasma devices to guide and collimate a high density of MeV electrons

Abstract

The development of ultra-intense lasers has facilitated new studies in laboratory astrophysics and high-density nuclear science, including laser fusion. Such research relies on the efficient generation of enormous numbers of high-energy charged particles. For example, laser-matter interactions at petawatt (10(15) W) power levels can create pulses of MeV electrons with current densities as large as 10(12) A cm(-2). However, the divergence of these particle beams usually reduces the current density to a few times 10(6) A cm(-2) at distances of the order of centimetres from the source. The invention of devices that can direct such intense, pulsed energetic beams will revolutionize their applications. Here we report high-conductivity devices consisting of transient plasmas that increase the energy density of MeV electrons generated in laser-matter interactions by more than one order of magnitude. A plasma fibre created on a hollow-cone target guides and collimates electrons in a manner akin to the control of light by an optical fibre and collimator. Such plasma devices hold promise for applications using high energy-density particles and should trigger growth in charged particle optics.

Fast-electron self-collimation in a plasma density gradient

“…IV and V. The transverse absorption profile into fast electrons is determined by I ¼ aI 0 exp(À(r/r spot ) 8 ), where a ¼ 0.5 is the laser absorption efficiency, I 0 ¼ 2 Â 10 20 W=cm 2 is the laser maximum intensity, r is the radial distance from y ¼ z ¼ 100 lm, and r spot ¼ 20 lm is the laser focal spot radius. The wavelengh of the laser is set to 0.351 lm.…”

“…This has motivated a number of theoretical and experimental studies on the collimation of fast electrons. [7][8][9][10] A possible route to fast electron collimation is via the magnetic field generated by the resistivity of the cold target as the fast electrons propagate into the target. The amplitude of the self-generated magnetic field can reach hundreds of Tesla, which is enough to collimate the fast electrons.…”

Collimation of Fast Electrons in Critical Density Plasma Channel

“…Therefore, we conclude the narrow electron beam divergence is caused by the strength and structure of the magnetic field in the plasma. Similar collimation mechanisms have been reported in cone wire target [18], target surface coiling [24], resistivity controlled target [19] and preformed magnetic field structure [20]. But the difference in our case, the strong magnetic field for the collimation is generated along the plasma channel in critical or over dense plasma.…”

“…Assuming the conversion efficiency from laser to proton energy of 1% and using proton sensitivity for IP [16], signal intensity on the IP from protons are 20 times smaller than that from electrons [17]. Since the simulation result reproduces the experimental results qualitatively, we proceed to find the collimation mechanism using the magnetic field in the simulation that is well known to function as an electron collimator [18][19][20] or scatterer [21,22]. Figures 4 (a) and (b) show typical magnetic field structure taken at the timing of 600 fs as calculated by the PIC code.…”

An ultracompact X-ray source based on a laser-plasma undulator

“…Indeed, as an ionized medium, plasma can withstand much higher fields than the cavity walls in conventional accelerators, which are subject to electrical breakdown. Besides particle acceleration, laser-plasma technology can be used, for instance, in plasma mirrors 9 , to manipulate high-intensity laser pulses 10 , or to collimate relativistic electrons 11 .…”