Emittance reduction by a SC wiggler in the ATF-DR September 16 th, 2009 Yannis PAPAPHILIPPOU and Rogelio TOMAS ATF2 weekly meeting

One of the main ATF2 goals is the creation of very low emittance beams High-field damping wigglers can be used for further emittance and also damping time reduction in the damping ring Super-conducting wigglers are considered in the design of the CLIC damping rings Short prototypes are being constructed and magnetically measured Final magnet should be tested with beam Motivation ATF2 meeting2 16/09/2009

CLIC DR design goals In order to reach ultra-low emittance, CLIC DR design is based on the inclusion super-conducting wigglers Output emittance is dominated by Intrabeam Scattering (IBS) due to high bunch charge density and instabilities may be triggered due to a number of collective effects (e.g. e - -cloud, fast ion instability) PARAMETERNLC CLI C bunch population (10 9 ) bunch spacing [ns] number of bunches/train number of trains31 Repetition rate [Hz]12050 Extracted hor. normalized emittance [nm]2370<500 Extracted ver. normalized emittance [nm]<30<5<5 Extracted long. normalized emittance [keV.m]10.9<5<5 Injected hor. normalized emittance [μm]15063 Injected ver. normalized emittance [μm] Injected long. normalized emittance [keV.m]

4 DR layout 125m 39m 16/09/2009 ATF2 meeting

CLIC DR parameters Energy [GeV]2.86 Circumference [m] Coupling Energy loss/turn [Me]5.04 RF voltage [MV]6.5 Natural chromaticity x / y-149 / -79 Compaction factor6e-5 Damping time x / s [ms]1.87 / 0.94 Dynamic aperture x / y [σ inj ]  12 / 50 Number of arc cells100 Number of wigglers76 Wiggler field [T]2.5 Wiggler period [m]0.05 Cell /dipole length [m]2.30 / 0.4 Bend field [T]1.27 Bend gradient [1/m 2 ]-1.10 Max. Quad. gradient [T/m]60.3 Max. Sext. strength [T/m ]6.6 Bunch population, [10 9 ]4.1 IBS growth factor2.0 Hor. Norm. Emittance [nm.rad]480 Ver. Norm. Emittance [nm.rad]4.7 Bunch length [mm]1.4 Longitudinal emittance [eVm]3700 Race-track shape with TME arc cells (dipoles with gradient) and long straight sections with FODO cells filled with super- conducting wigglers for achieving ultra-low emittance and fast damping Optics modified in order to reduce impact of IBS (growth factor of 2 with respect to zero- current emittance, as compared to 5 with previous ring version) Comfortable dynamic aperture

Nb 3 Sn SC wiggler NbTi SC wiggler BINP PM wiggler Wigglers’ effect with IBS Stronger wiggler fields and shorter wavelengths necessary to reach target emittance due to strong IBS effect Two wiggler prototypes  2.5T, 5cm period, built and currently tested by BINP  2.8T, 4cm period, designed by CERN/Un. Karlsruhe Current density can be increased by using different conductor type Prototypes built and magnetically tested Installed in a storage ring (ANKA, CESR-TA, ATF) for beam measurements (IBS and wiggler dominated regime) Major DR performance item Parameters BIN P CER N B peak [T] λ W [mm]5040 Beam aperture full gap [mm] 13 Conductor typeNbTiNbSn 3 Operating temperature [K]4.2

Present design uses NbTi wet wire in separate poles clamped together (2.5T, 5cm period) Wire wound and impregnated with resin in March Short prototype (0.8m) assembled including corrector coil and quench protection system by end of April Field measurements started at in June showing poor performance due to mechanical stability problems Presently wiggler delivered at CERN for additional beam measurements and further design optimization NbTi Wiggler Design Iron yoke Regular coil End coils to compensate the first and the second integral Corrector coils with individual PS P. Vobly, et al., 2008

Nb 3 Sn Wiggler Design R. Maccaferri and S. Bettoni, 2009 Two models (2.8T, 40mm period)  Vertical racetrack (VR)  Double helix (WH), can reach 3.2T with Holmium pole tips Nb3Sn can sustain higher heat load (10W/m) than NbTi (1W/m) Between , 2 short prototypes will be built, tested at CERN and measured at ANKA Higher wiggler field for lower gap

ATF2 parameters Wiggler effect is calculated for typical ATF2 parameters, excluding the effect of coupling and IBS The emittance can be evaluated as and the horizontal damping time with and Energy [GeV]1.3 Circumference [m]138 Hor. damping partition number1.84 Number of arc cells36 Bend field [T]0.69 Wiggler length [m]2 Beta function on wiggler [m]2 Hor. Norm. Emittance [ μ m.rad]6

Wiggler effect in emittance Important emittance reduction for a few wigglers, saturating as number of wigglers grows Strong dependence on the the wiggler peak field Weaker dependence on the period length

Wiggler effect in emittance With a 4T wiggler field and 1 wiggler, more than 30% emittance reduction Emittance reduced by a factor of 2 for two 4T wigglers This field can be achieved for small gaps of around 5mm  Is this compatible with ATF2 operation, i.e. geometrical acceptance, lifetime

Effect in damping time Similar dependence of damping times to number of wigglers and peak field Reduced by almost a factor of 2 for two 4T wigglers

Next steps Important emittance reduction with the inclusion of SC wigglers Reduction should be re-estimated when including the effect of IBS and coupling Effect of wigglers to dynamic aperture  Pending specifications for the CLIC damping rings and measurements Evaluation of technical aspects, i.e. available space, radiation absorption, associated cryogenic system