Development Of An ECR Ion Source For Mass Spectrometry

Mass spectrometer is an instrument that ionizes substances and measures the mass-charge ratio of charged particles generated,it can be used to analyze the structure and composition of substances,it is widely used in the fields of environmental monitoring,medical and health care,food safety,industrial analysis,life science and national defense security.The ion source is the core component of the mass spectrometer,and its function is to ionize the sample to produce charged ions.Ion source is one of the most important factors affecting the performance of mass spectrometer and is the key technology to promote the development of mass spectrometer.ECR ion source has the advantages of high ionization rate,can ionize most of the elements,strong beam current,no cathode and long service life,etc.it has been widely used in accelerator,nuclear physics,materials research and semiconductor industry,however,the application of ECR ion source in mass spectrometry is still only in the scientific stageIn this paper,a 2.45GHz ECR ion source used in the mass spectrometer was built,the liquid phase sampling system of ECR ion source was designed and tested;the ECR ion source was debugged,the ignition problem of electrode was solved,the factors affecting the extraction beam intensity of the ion source were studied;some performance indexes of the mass spectrometer ECR-MS based on the ion source were tested,and the feasibility of ECR-MS was preliminarily verified.Simultaneously,the beam transport section from the ECR ion source to the quadrupole mass analyzer was simulated and optimized.The main work of this paper is as follows:（1）A series of designs and experiments are carried out on the ECR ion source liquid phase sampling system.After continuous experiments and conclusions,the ECR ion source was redesigned.Firstly,the way of feeding the microwave into the discharge cavity was changed,from the combined feeding of the ridge waveguide and the microwave window to the coaxial antenna feeding,which created conditions for the redesign of the discharge cavity.Afterwards,a furnace wire heating device that runs through the end cover of one side of the discharge chamber was designed,the method of heating the liquid phase sample inside the discharge chamber was adopted,and finally realized the liquid phase sampling of the ECR ion source.（2）A 2.45GHz ECR ion source was built,which was grounded and a negative extraction system was used,can provide 1m A ion beam current for mass spectrometer.The commissioning of the ECR ion source was completed,and the ignition problem of electrode occurred during the working process of the ion source was solved.The effects of extraction voltage,working vacuum,microwave power and impedance matching on the extraction beam intensity of the ion source were studied.The extracted beam current increases with the voltage of the suppressing electrode,increases first and then remains unchanged with the third electrode voltage,the commonly used working voltages are-5 k V and-1 k V respectively;as the working vacuum increases,it first increases and then decreases,and reaches the maximum value in the range of 8×10^-4Pa～1×10^-3Pa;in the range of 200W～800W,it increases with the increase of microwave power and the improvement of impedance matching.The feasibility,sensitivity,detection efficiency,stability and precision of ECR-MS were tested,which proves the feasibility of mass spectrometry based on ECR ion source.The gas sensitivity of ECR-MS is much higher than that of ICP-MS,and the detection efficiency is two orders of magnitude higher than that of ICP-MS,under the condition of 0.2 sccm Kr gas injection,the response value of ⁷⁸Kr reaches 600 Wcps;under the condition of 0.2 sccm Ar gas injection,the response value of ³⁶Ar is 153 Wcps;the detection efficiency is two orders of magnitude higher than that of ICP-MS;the stability and precision can be stabilized within 3%,which can meet the requirements.（3）Aiming at the problem of excessive loss of ions in the beam transmission process after being extracted from the ion source,the beam transmission model was reconstructed using IBSIMU particle optics simulation software,the beam transmission process was simulated,and the position of the beam loss was determined,a corresponding transmission optimization scheme is proposed.The beam transmission line is optimized,the radius of the deceleration electrode extraction hole is enlarged from 5mm to 10mm;the positions of the two sets of focusing lenses and the deceleration electrode in the transmission line are moved;and the voltage applied to each electrode is changed.After simulation,it is found that the loss of the optimized beam during transmission is significantly reduced,and the beam emittance is also significantly reduced.