I'm looking for the way of measuring emittance of the electron beam.
The beam is generated by the laser incident on the copper and it is accelerated up to 20 keV or little higher in D.C E-field.
Some paper shows that the multi-slit method can be applied for emittance measurement. In this method, electron beam should be imaged in some way.
I believe the typical method for beam imaging is by using a scintillating plate like Lanex flim etc. But most of the beam imaging is done for a high energy electron beam, not keV class.
Could you give me a way to image a low energy electron beam of keV order?
What about using ICCD to the plate to amplify signal? In order for this method to applicable, the beam energy must be higher than threshold of the plate but I don't know typical threshold value of the scintillation plate.
Data Multi-slit emittance measurement study for BNL ERL BNL-98657...
Multislit emittance measurements, or its variation is indeed the first technique to consider. However, first of all one need to know if the beam is emittance dominated or space charge dominated, i.e., dependent on the peak current of the beam if the space charge contributes to the evolution of the transverse beam size or not. Multislit-like techniques is used for space charge dominated beams, if the defocusing effect of the space charge of the beam is negligible then there is no need to use the multislit and emittance measurements can be made using quadrupole scan technique.
In both cases transverse beam profile needs to be measured. For such low beam energies thin scintillator screen would be a good way to do that. For example YAG:Ce, which is one of the most efficient scintillators. On need to know the average beam current available to calculate the amount of light produced by a scintillator. On the other hand dependent on the average beam current, one have to consider if such average current is acceptable for the scintillator screen, or if its duty cycle needs to be reduced.
The scintillator can be used in a form of single free standing crystals, which I believe can be made as thin as 30 microns now. Another option is to use a conducting substrate with phosphor coating, as they are used for x-ray imaging and also available commercially just as single crystal YAG:Ce.
I would be concerned with the beam energy being so low, all the electrons will be stopped in a scintillator, which is also an electrical insulator. If this happens the charge will accumulate in the scintillator up to very high voltages when it a break down will occur eventually destroying the scintillator. From this point of view conducting substrate with phosphor coating might be better, but one needs to make sure that they resolution of the transverse beam size measurements will be sufficient, which again depends on the emittance you are expecting to measure.
Hello! I really appreciate your comments. Thanks people!
I'm actually new in this field and I have two question regarding your comments.
For obtaining thin scintillator, Is it normally made with lab fabrication or commercially available? If I can purchase, could you provide me important names of vendor?
And I don't understand phosphor coating on the conducting substrate. The phosphor coating emits light when the electron hit it but the light emitted should be blocked by conducting substrate (normally metal right?) thus backside observation of light is not possible. Is it operated in opposite way such that the electron penetrate the conducting substrate and hit the phosphor screen at last?
Everybody who uses YAG:Ce for beam diagnostics, as far as I know, obtain them from a Czech company: www.crytur.com they are doing a very good job.
A phosphor coated viewer would be a conducting substrate with the coating on one side. The coated side is facing the beam, that side still can be observed. If the setup does not allow to view viewer oriented normal to the beam direction, setup the viewer 45 degree to the beam and look at it perpendicular to the beam direction.
How much current do you intend to use and now small beam size to you anticipate to measure?
I'm out of this field since about 20 years now, and I used much higher MeV energies at that time. Optical Transition Radiation (OTR) was very interesting because it allowed to see the beam size and have a go at estimating emittance (OTR is directionally emitted especially at high energies).
Other advantage: with thin foils and sufficiently high energies: it is not much disturbing the beam. Setting the foil at 45 degrees will nicely extract the light perpendicular to the beam pipe. With an appropriate optical system you can both measure the angular distribution and the beam size. I'm just afraid you will not have enough intensity at such low energy, and also you may get background light coming of the cathode.
You may want to read this recent paper: https://doi.org/10.1364/JOSAB.31.002438 and follow up with it's authors as they mentioned planned experiments.
Another option would be wire scanners? These have been widely used for emittance measurements in the past.
Best,
Peter