Emittance diagnosis based on energy-dispersed measurement method

We have developed a single-shot emittance measurement scheme suitable for laser wakefield accelerators, which corrects the phase advance related to the energy introduced by the Betatron oscillation of electrons in the bubble.Electrons oscillate in the vacuole under the action of the transverse focusing field, and the oscillation frequency is related to the energy, which leads to an additional phase advance in the transverse phase space of the electron beam with energy spread.Combined with the electron transverse oscillation trajectory, phase compensation can be achieved through the matrix. The compensated electron beam has the same transverse phase. At this time, the global emittance is equivalent to the slice emittance.We use the measurement method of energy spectrum resolution in the experiment. This method constructs a focused beam line that matches the center energy of the electron beam by adjusting the position and focusing intensity of the quadrupole magnet. The size envelope of the focused electron beam is energy-related. Combined with the electron beam phase compensation technology, the emittance diagnosis of the electron beam slice can be realized.The optimized emittance of the electron beam slice is stable within 0.4mm mrad, of which the minimum emittance is 0.27mm mrad, which is consistent with the simulation.