Plan for Beam Extraction using strip-line kicker with pulse bump orbit •Present extraction kicker system •Strip-line kicker system for ILC •Beam extraction using strip-line kicker at ATF • Preliminary test •Magnets and power supplies for pulse bump •Experiment plan T.Naito
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Plan for Beam Extraction using strip-line kicker with pulse bump orbit Present extraction kicker system Strip-line kicker system for ILC Beam extraction.
Strip-line kicker system for ILC ~20 units for 0.6mrad kick angle
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Plan for Beam Extraction using strip-line kicker with pulse bump orbit
The shape of the electrode is designed to keep good uniformity of the deflecting field. The calculated flatness is 0.07% in the area of +/-1.8mm from the center.
The kick effect of the single strip-line kicker was measured by measuring the amplitude of the betatron oscillation in the ring. A turn-by-turn BPM system was used for the measurement of the betatron oscillation.
Timing scan of the kick pulse
Rise time = 3.2ns(1%~100%)Fall time = 4.0ns(100%~1%)
Beam kick profile measurementThe timing of the kick pulse is scanned for the timing of the beam with 200ps steps.
The kick angle is estimated from the amplitude of the betatron frequency of the FFT signal.
The bunch spacing in extraction line does not completely the same interval. A 2.8ns( or 5.6 ns) is added at every three bunches, for example, 154ns, 154ns, 154ns, 156.8ns, 154ns . . . .
The extraction pulse magnet is replaced by two units of strip-line kickers. Three cycles of the injected beam, which include up to 60 bunches, are extracted bunch-by-bunch with 154ns (or 308ns) spacing.
Strip-line electrode and pulser for ATF beam extraction
Electrode distance:12mmChamber diameter : 24mmImpedance :50ohmMax field at 10kV : 4.7MV/m
A 60cm long kicker magnet makes a 4.6mrad kick angle. Two strip-line kickers can make only1.3mrad kick angle. It is not enough for the kick angle to extract the beam.
Replacement plan from kicker magnet to strip-line kicker
Beam extraction design with two strip-line kicker
The kick angle of the strip-line kicker is not enough to make the beam extraction orbit. A design uses pulse bump magnets and an auxiliary septum magnet, which has thin separator, to help in making the extraction orbit. This design makes a bump orbit after the beam damping, then the selected beam is extracted bunch-by-bunch by the strip-line kicker.
Timing chart of 60(30) bunches beam extractionThe bump orbit is gradually increased after all of the bunches have been damped. The strip-line kicker kicks out the beams at the timing of the flat-top of the bump orbit. The beams are extracted as one long bunch train, which is a 10micro-sec long with 154ns (or 308 ns) spacing.
Local bump test by using present magnets and DC power supplies(1)
The aperture survey was carried out by using present magnets and DC power supplies. The required bump height is 5mm to separate the extraction beam and the circular beam. However, the local bump could make only +4mm and -2mm height.
Local bump test by using present magnets and DC power supplies(2)
Bump height
The measurement has agreed with the optics settings. The aperture limit at +4mm and -2mm are assumed that the limits show the miss-alignment of the septum or a large orbit distortion at the location.
Beam extraction design with two strip-line
The bump orbit is optimized to eliminate the aperture limit at the septum area. This design has no orbit change at the septum area, however the bending angle of the bump magnets is increased.