My question: What happens if one inject beam bunch of 2ns into RFQ where design guidelines says, the bunch width must be three times in synchronous phase (-48 deg @ 48.5 MHz RFQ)? which means 8.2 ns as ideal bunch width injection.
My comments: If I inject a 2 ns beam bunch into an RFQ (Radio Frequency Quadrupole) where the design guideline suggests that the bunch width should be three times the synchronous phase, several issues may arise, depending on how the bunch width compares to the RFQ's acceptance and capture capabilities:
Reduced Capture Efficiency: The RFQ is designed to capture particles within a certain longitudinal phase space. If the injected bunch is narrower than the designed acceptance (which might be based on a larger bunch width), the RFQ may not efficiently capture and accelerate the beam. This could lead to a significant portion of the beam being lost or not properly accelerated. Do you agree with it?
Increased Losses: A narrower bunch width than what the RFQ is designed to handle could result in higher particle losses at the RFQ entrance. The particles might not be properly synchronized with the RF fields, leading to inefficient acceleration or beam loss. Do you agree with it?
Beam Dynamics Issues: The longitudinal dynamics of the beam may be disrupted. If the bunch width is too small, the beam might experience issues such as longitudinal emittance growth, resulting in a broader energy spread and potentially degraded beam quality. Do you agree with it?
Modifications Required: To accommodate a 2 ns beam bunch, you might need to modify the RFQ's operational parameters, such as adjusting the RF power or tuning the synchronous phase settings, to match the narrower bunch width. This adjustment would involve recalibrating the RFQ to ensure proper beam capture and acceleration. Do you agree with it?
In summary, injecting a 2 ns beam bunch into an RFQ designed for a larger bunch width could lead to inefficiencies and increased losses. The RFQ might need to be adjusted or optimized to handle the narrower bunch, or alternatively, the beam bunch width might need to be increased to better match the RFQ’s design specifications. Do you agree with it? Do i need to change design guidelines of RFQ for 2ns beam bunch injection? Please give your detailed opinion also on this query. I just wrote whatever I know about it.
RFQ longitudinal Acceptance query
-
RomualdDuperrier - Global moderators
- Posts: 80
- Joined: Fri 28 Aug 2020 14:59
- Location: Paris-Saclay
- Country:
France (fr)
Re: RFQ longitudinal Acceptance query
Post
by RomualdDuperrier »
Dear Sarvesh,
please find my replies in between your lines below with the prefix RD=.
My question: What happens if one inject beam bunch of 2ns into RFQ where design guidelines says, the bunch width must be three times in synchronous phase (-48 deg @ 48.5 MHz RFQ)? which means 8.2 ns as ideal bunch width injection.
RD= I am not sure about the guidelines you are referring to. Here is my understanding: when the synchronous phase approaches to the peak, meaning pure acceleration and no bunch focusing, the phase acceptance tends to a size equal to 3 times the sync phase. Then, your bunch width must be lower than this if you want to limit losses. Thus, from the phase dimension point of view, injecting a 2 ns bunch into a 8.2 ns acceptance should be safe. By the way, I have designed several RFQs with an acceptance larger than the bunch width and did not meet any particular problem.
My comments: If I inject a 2 ns beam bunch into an RFQ (Radio Frequency Quadrupole) where the design guideline suggests that the bunch width should be three times the synchronous phase, several issues may arise, depending on how the bunch width compares to the RFQ's acceptance and capture capabilities:
Reduced Capture Efficiency: The RFQ is designed to capture particles within a certain longitudinal phase space. If the injected bunch is narrower than the designed acceptance (which might be based on a larger bunch width), the RFQ may not efficiently capture and accelerate the beam. This could lead to a significant portion of the beam being lost or not properly accelerated. Do you agree with it?
RD = No, I don't. See my comment above. If you inject into your acceptance, you must be safe. That is the principle of an acceptance.
Increased Losses: A narrower bunch width than what the RFQ is designed to handle could result in higher particle losses at the RFQ entrance. The particles might not be properly synchronized with the RF fields, leading to inefficient acceleration or beam loss. Do you agree with it?
RD= No, I don't for the same reason than before. However, one point of attention could be considered. If space charge matters, a narrower bunch could be denser than the reference bunch used for defining the acceptance. This could result into a too weak focusing for the core and possibly an emittance growth, but I doubt that you would eject particles outside the acceptance in many cases.
Beam Dynamics Issues: The longitudinal dynamics of the beam may be disrupted. If the bunch width is too small, the beam might experience issues such as longitudinal emittance growth, resulting in a broader energy spread and potentially degraded beam quality. Do you agree with it?
RD= Yes, this is possible as mentioned just above.
Modifications Required: To accommodate a 2 ns beam bunch, you might need to modify the RFQ's operational parameters, such as adjusting the RF power or tuning the synchronous phase settings, to match the narrower bunch width. This adjustment would involve recalibrating the RFQ to ensure proper beam capture and acceleration. Do you agree with it?
RD = The beta profile being frozen into the copper, changing the RF power will change the sync phase profile and then could be used to tune the acceptance. This is done for example at Los Alamos with the first DTL tank if I am correct in order to longitudinally collimate (reduced power) and limit losses at higher energy. The RF source phase must be tuned to ensure that the bunch is as far as possible to the limits of the acceptance. All of this is true, no matters if the bunch is narrower or larger than planned.
In summary, injecting a 2 ns beam bunch into an RFQ designed for a larger bunch width could lead to inefficiencies and increased losses.
RD = Not necessarily. It could actually be an advantage as you get a larger margin (distance between bunch and separatrix).
The RFQ might need to be adjusted or optimized to handle the narrower bunch, or alternatively, the beam bunch width might need to be increased to better match the RFQ’s design specifications. Do you agree with it? Do i need to change design guidelines of RFQ for 2ns beam bunch injection? Please give your detailed opinion also on this query. I just wrote whatever I know about it.
RD = First, you need to ensure that the phase is properly set up. If space charge matters, this should correspond to a lower long. emittance while the losses are kept constant. If you are not happy with losses into the RFQ or at higher energy, then you might consider long. collimation or the opposite by adjusting your RF power. I hope it helps. Best.
please find my replies in between your lines below with the prefix RD=.
My question: What happens if one inject beam bunch of 2ns into RFQ where design guidelines says, the bunch width must be three times in synchronous phase (-48 deg @ 48.5 MHz RFQ)? which means 8.2 ns as ideal bunch width injection.
RD= I am not sure about the guidelines you are referring to. Here is my understanding: when the synchronous phase approaches to the peak, meaning pure acceleration and no bunch focusing, the phase acceptance tends to a size equal to 3 times the sync phase. Then, your bunch width must be lower than this if you want to limit losses. Thus, from the phase dimension point of view, injecting a 2 ns bunch into a 8.2 ns acceptance should be safe. By the way, I have designed several RFQs with an acceptance larger than the bunch width and did not meet any particular problem.
My comments: If I inject a 2 ns beam bunch into an RFQ (Radio Frequency Quadrupole) where the design guideline suggests that the bunch width should be three times the synchronous phase, several issues may arise, depending on how the bunch width compares to the RFQ's acceptance and capture capabilities:
Reduced Capture Efficiency: The RFQ is designed to capture particles within a certain longitudinal phase space. If the injected bunch is narrower than the designed acceptance (which might be based on a larger bunch width), the RFQ may not efficiently capture and accelerate the beam. This could lead to a significant portion of the beam being lost or not properly accelerated. Do you agree with it?
RD = No, I don't. See my comment above. If you inject into your acceptance, you must be safe. That is the principle of an acceptance.
Increased Losses: A narrower bunch width than what the RFQ is designed to handle could result in higher particle losses at the RFQ entrance. The particles might not be properly synchronized with the RF fields, leading to inefficient acceleration or beam loss. Do you agree with it?
RD= No, I don't for the same reason than before. However, one point of attention could be considered. If space charge matters, a narrower bunch could be denser than the reference bunch used for defining the acceptance. This could result into a too weak focusing for the core and possibly an emittance growth, but I doubt that you would eject particles outside the acceptance in many cases.
Beam Dynamics Issues: The longitudinal dynamics of the beam may be disrupted. If the bunch width is too small, the beam might experience issues such as longitudinal emittance growth, resulting in a broader energy spread and potentially degraded beam quality. Do you agree with it?
RD= Yes, this is possible as mentioned just above.
Modifications Required: To accommodate a 2 ns beam bunch, you might need to modify the RFQ's operational parameters, such as adjusting the RF power or tuning the synchronous phase settings, to match the narrower bunch width. This adjustment would involve recalibrating the RFQ to ensure proper beam capture and acceleration. Do you agree with it?
RD = The beta profile being frozen into the copper, changing the RF power will change the sync phase profile and then could be used to tune the acceptance. This is done for example at Los Alamos with the first DTL tank if I am correct in order to longitudinally collimate (reduced power) and limit losses at higher energy. The RF source phase must be tuned to ensure that the bunch is as far as possible to the limits of the acceptance. All of this is true, no matters if the bunch is narrower or larger than planned.
In summary, injecting a 2 ns beam bunch into an RFQ designed for a larger bunch width could lead to inefficiencies and increased losses.
RD = Not necessarily. It could actually be an advantage as you get a larger margin (distance between bunch and separatrix).
The RFQ might need to be adjusted or optimized to handle the narrower bunch, or alternatively, the beam bunch width might need to be increased to better match the RFQ’s design specifications. Do you agree with it? Do i need to change design guidelines of RFQ for 2ns beam bunch injection? Please give your detailed opinion also on this query. I just wrote whatever I know about it.
RD = First, you need to ensure that the phase is properly set up. If space charge matters, this should correspond to a lower long. emittance while the losses are kept constant. If you are not happy with losses into the RFQ or at higher energy, then you might consider long. collimation or the opposite by adjusting your RF power. I hope it helps. Best.