Andrei Seryi: BDS with new betatron
- Andrei presented an updated BDS optics with optimized betatron
collimation. In comparison with the previous version (ilcff6), its bandwidth
is IP improved and the FD bandwidth is improved significantly, which should
be good for collimation performance. The BDS layout can be fixed in the
entire range up to 1TeV CM. The FD may need to be replaced in the 1TeV
energy upgrade. There is a feature, that with -5% energy error the betatron
beam size at SPE spoilers is small, however this is not an MPS issue since
the energy spread of the beam with energy error is usually also much larger
than the nominal.
Takashi Maruyama: Update on background in 20 and 2mrad cases
- Takashi presented updates on the background calculation of 20 and 2
mrad cases. In the latter, the redesigned QF1 was used, with larger gap
for the disrupted beam. This allowed to reduce losses at this magnet
from 400W to several watts. The next thing to do is to include into
consideration all the magnets of the extraction line downstream of QF1.
Lew Keller: A look at zero degree
extraction using RF kicker
- Lew presented results of a very first look into zero degree
extraction in the scheme with RF kicker. This RF kicker concept, based
on Finemet core, was presented at 2005 MDI workshop by Y.Iwashita.
- In comparison with SLC pulsed kicker, which provided head-on
collision, the kicker required for ILC has about ten times more field,
the ILC disrupted beam has 100x more power, much larger energy spread
(up to -50% dE/E), and a large vertical average deflection angle (200
microrad) under some conditions. In addition, the ILC has about 400 kW
beamstrahlung flame with non-negligible angular spread.
- In the scheme that Lew has considered, the RF kicker was assumed to
be located at 25m from IP and was conservatively assumed to have kick of
1.2mrad (at MDI workshop 2mrad was discussed). The beamstrahlung photons
with angles more than 0.16mrad and the disrupted beam with less than 80%
of the nominal energy are collimated at the protection collimator at 90m
from IP, just in front of the bends. Without such collimation it would
be very difficult to deal with divergent photon beam downstream. The
kicked beam, when it is separated by ~0.2m from an incoming beam, pass
through a dipole and receive additional 6mrad kick. This dipole is
located 200m from the IP.
- The findings from this first look are the following:
Photon power losses on the protection collimator are about 70kW when the
beams collide without offset, and reach 365kW for a worst case when the
beams collide with 200nm vertical offset. To that one need to add about
120kW of losses from the disrupted beam. Opening up the apertures of
protection collimator increases the losses on the downstream extraction
quads and makes separation of photons and incoming beam more difficult.
- In terms of the Machine Protection, the following fault examples are
possible and need to be prevented by a robust MPS:
a) Reduced kick, undisrupted bunches hit protection collimator;
b) No kick, undisrupted bunches go backward through incoming line;
c) Kicker at wrong phase so the incoming bunch gets a kick;
d) Incoming dark current bunches see non-zero kicker field and hit
elements in the IR;
The latter two have severe damage potential and potential for large
backgrounds in the detector, and have to be prevented.
Thus, to conclude on feasibility of using an RF kicker for extraction in
ILC, in addition to R&D of the kicker itself, serious design studies are
needed for the extraction beamline, for dark current suppressor, and in
particular for the MPS system.