Focusing and transport of high-intensity multi-MeV proton bunches from a compact laser-driven source

Abstract

Laser ion acceleration provides for compact, high-intensity ion sources in the multi-MeV range. Using a pulsed high-field solenoid, for the first time high-intensity laser-accelerated proton bunches could be selected from the continuous exponential spectrum and delivered to large distances, containing more than 109 particles in a narrow energy interval around a central energy of 9.4 MeV and showing 30 mrad envelope divergence. The bunches of only a few nanoseconds bunch duration were characterized 2.2 m behind the laser-plasma source with respect to arrival time, energy width, and intensity as well as spatial and temporal bunch profile

Commissioning of a compact laser-based proton beam line for high intensity bunches around 10 MeV

“…A pulsed high-field solenoid is used for collimation and transport of the bunch. A detailed description of this first stage of the beam line including a full characterization of the proton bunch can be found in a previous publication [22]. Similar targets (5 and 10 μm thin flat gold foils) and laser parameters (laser pulse duration τ ¼ 650 fs, focal spot size 3.5 × 3.5 μm 2 (at FWHM) and 10-15 J of laser energy on target, thus laser intensities exceeding 10 19 W=cm 2 ) were used.…”

“…In the experiments at hand, the proton numbers in the central region are in excess of 10 9 and the transverse beam dimensions are 15 × 15 mm 2 . This is because of the very smooth focusing of the solenoid, its field aberrations, and the beam profile modulation caused by comoving electrons within the solenoid (compare [22]) as well as the fact that the bunch has a large energy spread and the focal spot size at one detection position is different for every energy. A reduction in beam size could be achieved by adding an additional focusing element (e.g., second solenoid or quadrupole doublet) to the beam line.…”

“…First, a diamond detector is used for time-of-flight (ToF) measurements to determine the reference energy spectrum of the proton bunch without applied rf. Its description can be found in [22]. Figure 2 shows the recorded ToF signal and the resulting proton spectrum when focusing 8.8 MeV at the detection position of 3 m behind the laser target (i.e., B z;max ¼ 7.3 T).…”

Proton probing of laser-driven EM pulses travelling in helical coils

“…Although the two latter properties are advantageous in plasma radiography applications [2][3][4][5][6] , these are generally undesirable in view of many other potential applications [7,8] . Therefore controlling and optimising the laser driven ion beam parameters has been one of the intensively studied research topic over the past decade [8][9][10][11][12][13] .…”

Tc-99m production with ultrashort intense laser pulses

“…For example, if an angular spreading of the accelerated multi-MeV protons is 10°, that is the case of our simulations, almost all accelerated energetic protons will interact with the 15-30 μm radius catcher which is placed at the distance of 100-200 mm. Because low-energy protons (with energy < 8 MeV) considerably contribute to the total power flux density but are useless for technetium production these protons can be excluded with magnetic selection (Busold et al, 2013) before they reach the catcher. If necessary (when the distance between the pitcher and catcher is small), additional thin metal or/and plastic films with thickness less than 50 μm can be placed behind laser target .…”