In order to achieve a high-quality, i.e., monoenergetic, intense ion beam, we propose the use of a double-layer target. The first layer, at the target front, consists of high-Z atoms, while the second (rear) layer is a thin coating of low-Z atoms. The generation of high-quality proton beams from the double-layer target, irradiated by an ultraintense laser pulse, is demonstrated with three-dimensional particle-in-cell simulations.
Arguments in support of any particular superconducting coating must be framed in terms
of its fundamental thermodynamic properties. The superconducting transition temperature,
Tc, determines the surface resistance, and thus the
Q
of the cavity. This must remain sufficiently high that the system can be driven at the required
field gradients and frequencies without leading to excessive power loss. In this regard the 39 K
Tc of
MgB2
is advantageous. With an anticipated maximum accelerating field,
EaccMAX, of
77 MV m−1 and a BCS surface
resistance, RsBCS (4 K,
500 MHz), of 2.5 n Ω as
discussed later, MgB2
represents an interesting possibility as a coating for SRF cavities. In addition, the higher
Hc2 of
MgB2
than Nb results in a slightly lower estimated trapped flux sensitivity. Recent measurements of an
MgB2
film at the Los Alamos National Laboratory (LANL) have shown an RF surface resistance
lower than that of Nb at 4 K, which is proof-of-principle evidence of the attractiveness of
MgB2. Our calculations are based conservatively on 4 K operation at 500 MHz. However, with a
Tc of
39 K, MgB2-coated cavities should be less susceptible to thermal breakdown than
low-Tc
ones. Superconducting materials for use at GHz frequencies at voltage gradients
>40 MV m−1, a recently cited target, will require both low
Rs (high
Tc) and high
Hsh values. With
a Tc of 39 K,
MgB2 clearly has the
potential to reduce RsBCS
if the films are well prepared and free from defects and particles. Additionally, while the
Hc1
for MgB2
is relatively low, the superheating critical field,
Hsh, is higher than that of Nb. Currently, there is some debate about the exact roles of
Hc1 and
Hsh in the determination
of Eacc limits. However,
the higher values of Hsh
for MgB2 do suggest the
possibility of enhanced Eacc
values. The exact roles of Hc1
and Hsh
should be further investigated. Techniques exist that may enable cavity-like structures to be internally coated
with a MgB2
film.
The synthesis of pure δ-MoN with desired superconducting properties usually requires extreme conditions, such as high temperature and high pressure, which hinders its fundamental studies and applications. Herein, by using a chemical solution method, epitaxial δ-MoN thin films have been grown on c-cut Al(2)O(3) substrates at a temperature lower than 900 °C and an ambient pressure. The films are phase pure and show a T(c) of 13.0 K with a sharp transition. In addition, the films show a high critical field and excellent current carrying capabilities, which further prove the superior quality of these chemically prepared epitaxial thin films.
Experimental data from the Trident Laser facility is presented showing quasimonoenergetic carbon ions from nm-scaled foil targets with an energy spread of as low as ±15% at 35 MeV. These results and high-resolution kinetic simulations show laser acceleration of quasimonoenergetic ion beams by the generation of ion solitons with circularly polarized laser pulses (500 fs, λ=1054 nm). The conversion efficiency into monoenergetic ions is increased by an order of magnitude compared with previous experimental results, representing an important step towards applications such as ion fast ignition.
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