Compact LAser Plasma Accelerator (CLAPA) Lab at Peking University
Xueqing Yan, ChenLin, H.Y.Lu, K.Zhu,WenjunMa,Y.Y.Zhao, C.E.Chen et al.,
Peking University
The world firstcompact laser plasma accelerator of protons (CLAPA)(Fig. 1) based on 200 TW laser system has been designed and builtrecently at Peking University. The Compact LAserPlasma Accelerator (CLAPA) of ten MeV proton with reliability, availability, maintainability and inspectability (RAMI)was demonstrated for the first time. Our approachuses laser driven ion acceleration to produce and transport proton ions with <1% energy spread, tens pC charge and different energiesbelow 10MeV through beam lattice line using combination of quadrupole and bending electromagnets. The high current proton beam with a large divergence angle is generated by using a high contrast laser and thin plastic foils from tens nm to 1 micron, later it is collected, analyzed and refocused by the electromagnetlattice.
Fig. 1 The layout of the CLAPA
Fig. 2 The devices of fabrication of free-stand foils and the home-made free-stand foils
In 2017, by using thehigh contrast high intensity laser pulse and micrometer thickness targets, CLAPA successfully generated proton beams with 1-15 MeV energy and the 10^6-8 particles per flux. In the experiment, the proton beam was measured by both a Thomson Parabola energy spectrometer and a radiochromic film (RCF) stack positioned behind the target in the experiments. The results are shown in Fig. 3. Thanks to the remote precise control of theacceleration system and the high quality home-made target, the stability of the proton cut-off energy was better than 3% for five continuous shots, as shown in Fig.3(c), whichis best performance in laser driven accelerator of ions.
Fig. 3(a-d) The RCF stack track of proton beams. (e) was thepicture of etched CR-39 imaged by the microscope and theinset was the region of interest. (f) The black line is the typically proton spectrum recorded with the magnetic spectrometer and the pink dot shows the proton measured by RCF stack. (g) Proton cutoff energy detected by the TPS fordifferent target thickness and the error bars were determinedby the variation in maximum energy over five shots. (h)Thestatistical proton spectrum of 1.2um plastic foils for sevenshots measured by the TPS. The blue line presents the averageproton spectra and the gray zone corresponds to standarddeviation.
Fig.4 (a) Layout of Compact Laser Plasma Accelerator based on a high power laser. (b) Proton beam distributions on the RCF stack positioned 4 cm behind the target. (c) Simulated envelope evolution of the proton beam with central energy 15 MeV, initial spot 5 um and 100 mrad divergence angle inside the beam line. (d) Scaling of the proton charge with central energy on theirradiationplatform. (e)Repeatability of proton beams on the irradiation platform with 7 MeV central energy and 1% energy spread for nine shots in series.
A beam lattice line using combination of quadrupole and bending electromagnets is employed to transport proton ions with <1% energy spread, several to tens of pC charge and 3 MeV to 9 MeV (Fig. 4). For the first time in the world, the laser accelerated proton beam can be precisely manipulated in terms of energy, charge, uniformity, anddiameter with repeatability and availability. It raises the “laser acceleration” to “laser accelerator” of ~10 MeV protons through beam control since the invention of laser acceleration in 1979. The setup of bendingmagnetproperly integrated with triplet and doublet quadruplelenses can overcome inherent drawbacks of the laser driven beams, and paves the way for laser accelerator in a wide range of applications. With the uniform mono-energetic pencil beamsdemonstrated at CLAPA, primary biomedical cell irradiation experiments and material irradiation experiments to emulate the spaceconditions are under way. Moreover, this technology can be easily applied to the high energy protons, such as 200 MeV, resorting to pulsed magnets or superconducting magnets. With the development of high-rep rate PW laser technology,the proton energy and current will be soon available for the applications such as cancer therapy; we can envision a compact beam therapeutic machine of cancer treatment in the near future.
Fig.5 laser acceleration to laser proton accelerator