56 / 2020-02-25 17:04:23

Flux control of a MeV proton beam driven by ultra-intense lasers

Flux control,proton,laser

全体主题 > 高能量密度物理

Since the first ruby laser was invented by Dr Maiman in 1960, the laser technology has attained intensive progress. The development of Q-switching, mode-locking and CPA (Chirped Pulse Amplification) techniques reduced the pulse width of the laser to femtosecond scale and increased its power to petawatt scale . Such a high-power laser will produce many interesting physics phenomena while interacting with targets. Among them, laser driven ion acceleration has aroused great interest because of its potential for many groundbreaking applications, such as cancer therapy, proton imaging, generating warm dense matter (WDM), ion fast ignition, etc.
Laser driven ion acceleration studies have been focusing on improving the cut-off energy of the ion beam, and protons up to 94 MeV have been demonstrated with a PW laser system . However, for some application scenarios, people are more concerned about the high flux of the ion beam instead of the cut-off energy. For example, to measure the cross section of the P-(_ ^11)B reaction (which is a candidate for neutron free fusion), protons with 100KeV-10MeV energy and 〖10〗^(8~10) per shot are required [4]. The former is relatively easy to achieve, but the latter is hard to realize. In recent experiments on Compact Laser Plasma Accelerator (CLAPA) platform at Peking University, we have found that the charge of the proton beam can be manipulated by changing the coupling condition between the laser focal spot and the target position. The protons with central energy from 200 keV to 4.5 MeV were collected by a quadrupole magnet triplet and measured by scintillator and RCF detectors. At certain defocusing distance, the proton cut-off energy is decreased, but there is a nearly tenfold increase in its quantity. This experiment result provides a possible method to acquire a laser driven proton beam with high quantity, which will be helpful to applications such as cross section measurement, nuclear reaction analysis and laboratory warm dense matter producing.