ATF status

1. ATF status M. Ross October 15, 2004 • The ATF is the largest test facility built exclusively for linear collider RD • Utility not reduced by the selection of SCRF technology • Parameters: linac is 100 m long, 140m circumference ring and 30 m long extraction line. • Comparable in size to the TTF2-VUV FEL, 250m long linac / undulator system. • The ATF collaboration (includes KEK, SLAC, CERN, DESY, etc.) is headed by Junji Urakawa. • Since the system is intended for LC work, ATF program will be directed through GD organization.

2. Achievements • Generation of nominal LC beams • Demonstration of critical technology • Instrumentation to validate performance • Operation • The ATF operates approximately 2000 hours per year in short 4 day (M-F) blocks. There are about 6 KEK FTE’s assigned to ATF operation, a dozen students at any given time and several contractors who provide various kinds of support. In addition, the lab provides safety-watch shift leaders. • even though the total number of operation hours is limited, we have complete control over the configuration • Cost of operation is difficult to judge directly because Japanese accounting is different than either US/Europe.

3. General Status – Fall 2004 • Typical extracted (damped) beam operation is at 3Hz, single bunch, 1.3e10 electrons/bunch, 1.28GeV. Up to 200 mA has been stored in the ring (about 10e10 in each of 60 bunches) 1.7e10 is the max achieved single bunch intensity. Typical extracted emittance is 2 nm (x) by 20 pm (y) 5 um x 50nm normalized. The vertical emittance in the ring is 5 x lower than extracted ε(0.3% coupling), there remains a source of coupling in the extraction channel we have been unable to fix. • The injection system is capable of injecting 3 20-bunch trains, with 2.8ns inter-bunch spacing. At nominal emittance and train intensity, the last few bunches in the train are unstable. We think this is due, in part, to poor ring vacuum. The average ring pressure is about 6nTorr (design 10nTorr). There is a high pressure section inside the extraction kicker. • The ring wiggler magnets have been modified and adapted in the last two months. Studies with them will begin this year.

4. The ATF (near term) program has 3 parts: • ring beam dynamics • instrumentation (many) & supporting technology development • Kicker  • Alignment • source development • compton e+ • S-band photocathode guns • Ideal facility for instrumentation studies • stable extracted beam; controlled environment

5. Beam Dynamics • includes single particle effects such as coupling and dispersion correction, with supporting beam based alignment and optical error analysis tools • rms residual dispersion: 2mm • coupling: 0.3% • extraction x-y coupling (as at SLC)  5x εy blowup • Collective effects associated with fast ion instability (FBII) and coupled bunch instabilities. FBII has emittance dependent threshold  must be studied at ATF • clearly seen at ATF for 2.8 ns bunch spacing, 3e9 ppb, avg P 6 nT, εy ~ 6pm (beam size in arc cell: 2.5 to 5 um). • work on modeling, diagnostic strategies and measurements needed this year • Wiggler • 12 m wiggler prepared 2004.10 (9% circumference)

6. Instrumentation / subsystem • Key instrumentation issues: position & size • state of the art exceeded at ILC for many aspects; reliance/trust also beyond present level • secondary, more specialized, monitors also critical • BPM is the dominant instrumentation cost (10% of total instrumentation/controls cost) and dominant importance • ATF RD on cavity BPM will be a key element for next few years (small, stable beams enable RD) • applications across ILC complex (DR, linac, BD, MDI) • present status: 2 triplets of copper cavity BPM’s with movers; expected performance should enable studies of offsets, stability, coupling. demonstrated resolution ~ 0.5um equivalent for 70mm BPM diameter • Beam size monitor • ATF ‘in the ring’ laserwire is the best ‘resolution’ precision beam size monitor  1% reproducibility @ 5um (typ ‘best’ SLC 5%; typ. usual 10%) • many issues: dynamic range, linearity, correction algorithms, aspect ratio, operational • present status: strong RD for ‘in the ring’ monitor; UK (with KEK/SLAC) monitor to be installed 2005

7. Kicker • Demonstrated ‘kicker achromat’ jitter suppression (3x) • existing layout accomodates 3MHz, single bunch extraction but … pulser requirements beyond what is described in TDR • long pulse extraction / single bunch fill sequence allows generation of 2-3 bunch TESLA train in extraction line • 2005.10 • short pulse kicker one year later – 20 extracted bunches with ILC emittance and spacing

8. Sources • e+ Compton γyield demonstrated; preliminary positron polarization measurement done • S-band RF gun performance excellent; 1) online and in use for damping ring studies 2) complete test stand for laser studies

9. Long term program • emittance ~ 1pm-rad • creation of ILC damped beam • final focus optics tests

10. Summary • ‘Controversial’ (i.e. important to pursue): • Kicker development (SLAC group – conventional pulser/stripline; KEK novel approaches) • Beam optics and collective effects (FBII) • Beam Position monitoring • Beam size monitors • ATF is a proven tool for the development of international collaboration