Based On The Principle Of Anti-magnetic Loop, Online Diagnosing The Emittance Of Strong Current Beam

High current linear induction accelerator(LIA)plays an important role in the field of national defense,and beam quality is one of the important indicators of high current linear induction accelerator.To a certain extent,the radius and emittance of the beam directly determine the quality of the beam.It is very necessary to diagnose the beam radius and emittance accurately and quickly.At present,the beam diagnostics technology applied to high current linear induction accelerator is mostly based on optical principle,and is truncated,and the diagnostic efficiency is not very high.In this paper,based on the dynamic characteristics of the electron beam in the solenoid magnetic field,by measuring the electromagnetic field of the beam,a double loop beam diagnostic structure(antimagnetic loop flow diagnosis structure)is proposed for the first time.This diagnostic method can achieve strict beam diagnosis,that is,without destroying the vacuum environment and not destroying the beam.This work confirms the feasibility of the idea from three perspectives:principle,finite element simulation and experiment.When the electron beam is transmitted through the magnetic field of a solenoid coil,the rotation will occur due to the existence of a certain transverse velocity component,which will introduce an axial magnetic field.The introduction of the axial magnetic field will produce an induced EMF signal(differential mode signal)in the antimagnetic coil.The size of the signal is directly related to the beam radius and density distribution.At the same time,the electric field of the electron beam will also induce signals(common mode signals)in the diamagnetic coil.When the ground direction of the two diamagnetic coils is opposite,the induction electromotive force of the axis magnetic field reverses,and the direction of the signal induced by the electric field remains unchanged.Therefore,the signal difference between the two coils reflects the axial magnetic field information,and the signals of the two coils and the electric field information are reflected.From the axial magnetic field information,the beam radius and even the density distribution of the beam can be reversed,and the beam intensity can be deduced from the electric field information.The finite element simulation part mainly simulates the diamagnetic loop probe in frequency domain.A plane wave is used to simulate the axial electromagnetic field passing through the beam.Each port is a coaxial port and an electric boundary condition.The ideal conductor helix under different radii conditions is used to simulate the beam in different circumstances.Through analysis,it is found that under low frequency conditions,the differential mode signal is linear with frequency,and has self integration with the increase of frequency;the common mode signal has two square relations with the frequency,and the common mode signal is one order of magnitude larger than the differential mode signal.At the same time,the sensitivity factor of the anti magnetic loop probe at 10MHz is calculated under different conditions.Using the same platform as the axial B-dot,a spiral rod with different diameters and pitch is used to simulate the beam of different state lines.The spiral rod is composed of eight 2mm wires.The two opposite grounding coils of the reverse magnetic loop probe are placed on the PCB board of 6mm thickness,and the i-pex coaxial connector is used.An equivalent circuit which is similar to the axial B-dot probe is proposed in the experiment.The vector network analyzer and oscilloscope are used to measure the frequency and time domain of each case.The results show that the results obtained in the frequency domain are in good agreement with the results of the finite element simulation,and the electrical parameters in the equivalent circuit are obtained by the phase fitting method.In the time domain,the signal consistency problem is analyzed under the condition of the straight rod,and the original structure of the probe is optimized.The consistency of the signal is increased from 94%to 99%;the inverse is introduced.The radius of the analogue rod is within lmm.Finally,the measurement scheme and measurement results of the beam radius on the "Dragon II" are given,as well as the experimental scheme and results using the modified three gradient method.The results show that the detection structure of diamagnetic loop is feasible in beam diagnostics of high current linear induction accelerator,and the measurement is simple and efficient.The innovation of this paper is to put forward the detection structure of double loops anti magnetic circuit and make a full study on the three angles of the structure from theory,simulation and experiment,and make clear the application value of the structure in the diagnosis of beam flow.