I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October Damping ring kickers George Gollin University of Illinois at Urbana-Champaign and Fermi National Accelerator Laboratory

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October Outline The problem The specs Current ideas Opinions from the speaker Illinois/Fermilab efforts ILC-America + ILC-global near term goals

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October The problem Linac beam (TESLA TDR): 2820 bunches, 340 nsec spacing (~ 300 kilometers) Cool an entire pulse in the damping rings before linac injection ILC damping ring beam: 2820 bunches, closely spaced Eject every n th bunch into linac (leave adjacent bunches undisturbed) Minimum damping ring circumference depends on minimum realizable bunch spacing (kicker speed and instability issues) Kicker: 20 ns kicker  17 km circumference (TESLA dog bone) 6 ns kicker  6 km circumference (Fermilab small ring)

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October What an interesting problem! There’s significant global interest in tackling the challenges posed by the damping ring and kicker. We have already started an informal, global “conversation”: see Andy Wolski’s site at for a partial list of who has made contact. There are physicists from ANL, CERN, Cornell, Daresbury, DESY. Fermilab, Frascati, Harvard, Illinois, KEK, LBNL, Minnesota, SLAC, Tokyo so far.

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October What we have to work with Injection: already-orbiting bunches have not damped appreciably, have large transverse sizes (~2 cm); kicker must inject new bunches into damping ring acceptance without losing already-orbiting bunches. Extraction: damping is finished, bunches are small (a few microns in diameter) ; kicker must preserve beam emittance for still-orbiting bunches as well as the kicked bunch. Performance demands on kicker are different for injection/extraction. Should we consider separate designs for injection and extraction?

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October The specs Kicker specs depend, in part, on beam dynamics: phase space volume occupied by a just-kicked bunch must be well separated from that of an unkicked bunch. Dog bone (TESLA TDR) kicker specs: impulse: 100 G-m (3 MeV/c) ± 0.07 G-m (2 keV/c) residual (off) impulse: 0 ± 0.07 G-m (2 keV/c) rise/fall time: < 20 ns Perhaps larger (but less precise) impulse at injection, smaller (but more precise) impulse at extraction will be desirable. Small ring kicker rise, fall times can be asymmetric: leading edge < 6 ns, trailing edge < 60 ns

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October The ideas (1): strip line kicker modules Fast switches dump high voltage pulses into a series of strip line structures. Electromagnetic pulse applies transverse kick to one bunch, but is absorbed in a load in each strip line module before next bunch arrives. switch speed, on-resistance, and stability are concerns adequate precision of strip line termination is challenging TESLA and SLAC are thinking about this

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October The ideas (2): longitudinal kick + dispersion Separate the beam so that it travels along multiple paths. Demands on kicker are less severe: it only sees every 4 th bunch. The system needs to be studied in detail: how to do it, what happens when it is installed in a damping ring. Cornell, Frascati are thinking along these lines.

I PhysicsP I llinois 9 The ideas (3): Fourier engineering Instead of a pulsed kicker, construct a kicking pulse from a sum of its Fourier components. Most interesting (to me) idea now: combine this with a pulse compression system to drive a small number of low-Q cavities. what are stability requirements on RF components? how robust to bunch arrival time errors can the system be made? Illinois, Fermilab, Cornell are involved.

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October The speaker’s opinions (1) The kicker has the potential to be a “show-stopper.” Damping ring architecture (bunch timing structure, injection/extraction optics, etc.) is strongly tied to details of the kicker. A fast pulsed kicker might be simplest to operate BUT switch speed and stability are challenging issues. Significant proof of the feasibility of at least one design is needed before a choice of damping ring design (big ring vs. small ring) will be possible.

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October The speaker’s opinions (2) Fermilab small ring studies incorporate: damping ring bunch trains with ~60 ns inter-train gaps long straight section to allow installation of as-yet unspecified kicker Perhaps these features should be included in all damping ring designs? There are three distinct stages in damping process: injection and assembly of bunch trains damping disassembly of bunch trains and extraction Beam is very different in each of these stages. Should there be distinct subsystems (including different kickers) for each of them?

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October Separating injection, damping, extraction functions Large acceptance injection ring: (340 – 6) = 334 ns circumference assemble a single bunch train by injecting successive bunches into this ring at the tail of the train already orbiting the injection ring transfer entire bunch train into the damping ring in one orbit Large acceptance damping ring (6 ns bunch spacing) Small acceptance extraction ring: ( ) = 346 ns circumference transfer one entire bunch train from the damping ring extract by kicking the last bunch in the train on successive orbits

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October Separating injection, damping, extraction functions Injection and extraction rings differ in circumference by two bunch spacings to allow injection/extraction to/from tail of bunch train.

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October Fermilab/Illinois activities Initial studies: use Fermilab A0 photoinjector beam (16 MeV electrons) for studies: 1.build a fast, simple strip line kicker 2.use the kicker to study the timing/stability properties of the A0 beam 3.build a single-module pulse compression kicker 4.study its behavior at A0 5.perform more detailed studies in a higher energy, low emittance beam (ATF??)

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October A0 photoinjector beam 16 MeV electron beam, good spot size, emittance. EOI submitted to A0 group last spring. Space in beamline will be available ~January 2005

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October Simple kicker for initial tests Start with a simple kicker whose properties are calculable and can be measured independently of its effects on the A0 electron beam. Most important: how well can we measure a device’s amplitude and timing stability with the A0 beam? Fermilab is currently designing this. Probably ready by January 2005.

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October UIUC/FNAL, longer term plans Design, then build one module using existing components. Fermilab RF group is involved UIUC HEP electronics design group’s chief is too. So we’re starting to make progress. Goals: install strip line kicker in A0 by January, 2005 understand A0 by spring, 2005 install small pulse compression kicker at A0 by summer, 2005

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October ILC-America + ILC-global near-term goals Possible goals and timelines: pre-KEK: discuss tentative plans for kicker R&D with our colleagues in America, Asia, and Europe to have a sense of who would like to do what. at KEK: rough-out an R&D plan aimed at choosing a kicker technology in ~2 years at Snowmass (August, 2005): kicker workshop with international participation to assess how well we’ve gotten started, and what we have learned

I PhysicsP I llinois George Gollin, Damping ring kickers, SLAC ILC-America, October End notes The kicker and damping ring scare the daylights out of me. We must build one and make it work before the ILC main linac is completed. More information: Studies Pertaining to a Small Damping Ring for the International Linear Collider, FERMILAB-TM-2272-AD-TDFERMILAB-TM-2272-AD-TD ILC Damping Rings web site: