Dear all, I'm very interesting what is the beam intensity enjected from the internal ion source in the medical proton cyclotrons like IBA C235 or VARIAN/ACCEL 250 MeV. I need approximate value. If we know that the beam transmission from the ion source to the outlet window is ~5 % and extracted current is 300-500nA it means injected current is ~10 microA. But we know that in the PET cyclotrons ion source intensity is more then 100 microA. Where am I wrong?
Dear victor,
When one uses a internal ion source , It provides a CW ion beam , but cyclotron accepts typically only in 30 (deg) of every RF cycle , Therefore 1/12th of beam is only accepted. So, if you multiply (10 *12) you get 120 which is near to the value of 100 uA which you are talking about.
@Victor; you are comparing positive ion accelerators (proton therapy) with negative ion accelerators (PET cyclotrons) - ion sources and extraction from them is quite different (in performance)
@Anuraag : your assumption is only correct for the first harmonic order
@Christian; very good points! - an internal PIG ion source cannot be compared on the same day with an external multi-cusp ion source with an inflector; where the latter can handle up mA of current.
Thanks all for your answers... I was talking about internal positive PIG ion sources. May be my explanation is not full. For example, if I will estimate the ion source intensity in the VARIAN/ACCEL 250 cyclotron, I know (from papers), that they have 20 RF degree bunch after phase slit in the central region with mean RF phase -56 degree RF (if we have cosine dependence RF voltage from time, maximum of the voltage amplitude is on the 0 degree). In this case I can calculate from Child’s low beam intensity in this RF region, it is ~2.4 % from full 360 degree DC bunch. Next I assume that transmission such 20 degree bunch from ion source to the final radius is ~70 %, and we know that extraction efficiency is 80 % and extracted current is 500 nA. I can estimate initial current from ion source: 500 nA / ( 2.4%*70%*80%) = 37 microA ( it is DC current). In the PET cyclotrons DC is more than 100 microA.
Dr baumgarten and Dr jacek highlighted key issues here , thnks to both of them.
Victor: You also need to care and measure the beam emittance of the beam exiting from the ion source. it may so happen that you got a good beam current but due non-optimum settings of the ion source you have a larger beam emittance, basically you need to optimize beam emittance keeping the minimum beam current which you require. Generally the beam emittance is better for PIG ion sources compared to ECR ion sources.
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