Speaker: Shinji Machida
Abstract: vFFA concept can be used almost all the area of muon collider complex. I will give a design example of muon accelerator and arc optics of collider ring.
Categories
FFA'20
International Workshop on Fixed Field alternating gradient Accelerators
15 replies on “vFFA for muon collider complex”
What is the advantage of using an FFA for the collider ring? I don’t see a need for particularly large energy acceptance, and in any case your energy acceptance is generally dominated by what is happening at the IR anyhow.
What was it about the accelerator design that led you to start with a design with a reverse bend? I guess I thought of the vFFA as generally being able to avoid the reverse bend (flipping the sign of m for F/D), but I guess there is some sense in which that is not a free variable.
Do your acceleration cells have space in each cell for an RF cavity?
Hi Scott, thank you for watching the video! Actually I tried not to say FFA for the collider arc. My design with skew quadrupoles will satisfy 1) small momentum compaction factor and 2) combined function arc. I thought the former is necessary for keeping high luminosity and the latter for spreading out neutrino. IR has not been designed yet, but it is most likely just 45 rotated one to match skew quadrupole arc.
Maybe I was too naive to assume that we cannot flip the sign of m for F/D. Do you think the it is possible to make a lattice zero chromaticity with flipped m? It will then look like the lattices on page 13. Assuming that the sign of m should be the same, I cannot avoid the reverse bend. The lattice works as expected.
RF cavity should be put in longer drift section which will come in one after a normal FODO cell. I understand that bending per FODO has to be doubled in that case.
For the ancient “Study II” neutrino factory design, we had a similar idea for the decay ring. The logic was that you could create a very compact arc with superconducting pancake coils above and below the midplane. The idea was that your dipole regions would have pancake coils above and below, and you would create a skew region by stopping the dipole coil on the top or bottom (depending on the sign of your focusing strength) and replacing it with a pancake coil in the reverse direction. It also had the advantage of a an open midplane while having a superconducting magnet. There was no real goal for isochronicity, etc., it was an otherwise fairly conventional lattice.
Yes, I see what you are saying, I just wasn’t thinking, you’re right, you probably need to keep all the m with the same sign.
Hi Scott, thank you for watching the video! Actually I tried not to say FFA for the collider arc. My design with skew quadrupoles will satisfy 1) small momentum compaction factor and 2) combined function arc. I thought the former is necessary for keeping high luminosity and the latter for spreading out neutrino. IR has not been designed yet, but it is most likely just 45 rotated one to match skew quadrupole arc.
Maybe I’m not following completely. When we did radial linear FFAs, generally we had simple, identical cells, and inserted a drift long enough for an RF cavity in each cell, even if it was not necessarily occupied in each cell. The high periodicity was necessary to avoid resonance conditions, and distributed cavities were necessary to minimize the closed orbit jumps across cavities (essentially to track the closed orbit adiabatically). The former is not as much of an issue for scaling FFAs, but the latter is still important. If all cells are not identical, you need matching between different types of cells, which will need to occur frequently; right now, if I understand correctly, you have a periodic cell assuming no drift for a cavity. You can’t simply add a drift because that will effectively mean that you have a longer cell, so you’ll have to re-match for that longer cell, resulting in a higher tune (probably unstable here) and larger orbit excursion. Unless I’m getting things wrong. You could also match into another cell with RF, but it has to happen pretty frequently. So I’m trying to understand how you’re getting the RF in here.
I saw a design by B. Parker on the skew superconducting quadrupole. I thought it is encouraging because he mentioned it is mechanically favourable to have skew instead of normal. I believe his optics stays on a horizontal plane. How about the one you just mentioned on Study-II? My idea is to introduce vertical displacement between D and F to have another knob to control momentum compaction factor.
I hope you can tell me the scheme of RCS muon acceleration. How long the RF cavity is and how many of them is necessary? Of course the shape of RF cavity will be different because of the large aperture, but still it would he helpful to design how long space per cell I should reserve for the RF cavity. One advantage of scaling vFFA is the decoupling between shape of the ring and shape of magnetic gradient r^k. We think design of insertion, for example, is easier with vFFA as we demonstrated in the IPAC 19 paper which is doublet scaling vFFA.
Yes, the orbit in Brett’s design stays in the midplane, despite the skew focusing, though the dispersion does not.
For the RCS we use 1.3 GHz cavities; for the lower energies we have something of the order of 6 or 8, probably many more for higher energies. We use achromats between the cavities to avoid the orbit mismatch issues. You still need to try to get in as many cavities as reasonably possible to avoid mismatch between energy and the ramping magnet fields, particularly at the lower energies. This at least will not be an issue for the FFA, but the issue in the FFA is the orbit dependence on energy, which leads you to want more cavities per turn.
Thanks Scott. Sorry, another question if I may ask. Where can I find the lattice structure and functions of muon RCS accelerator?