Minutes of the 3rd Meeting of the Working Group
on the High Bandwidth Transverse Damper
August 2, 2012, 10:00
Present: H. Bartosik, W. Hofle, G. Iadarola, G. Rumolo, Y. Papaphilippou
The minutes of the Meeting of July 26, 2012 were approved.
Aperture Constraints in LSS3 for the HBTD
Hannes presented the aperture constraints for the new pick-up (close to QD319)
and kickers (close to MBB321) for the new devices for the high bandwidth
feedback1. This analysis is a refined assessment of the previous results which
asked for a vertical stay clear (half) aperture of 20 mm next to the MBB321 at the
place of the missing MBA magnet. In the horizontal plane the previous analysis
yielded 40 mm which can be considered as extremely aggressive as pointed out
by Hannes. There is a conservative approach which is to stay always in the
shadow of other existing standard machine elements and the aggressive “local”
approach which is riskier but opens the possibility to go slightly closer to the
beam. The most critical beam is the CNGS beam at injection concerning the
vertical plane and the CNGS beam with Q20 optics for the horizontal plane
(larger dispersion for Q20 than for the standard Q26 optics). Currently Q20 is
not used for the CNGS beam, but it is an option for the future to be taken into
consideration for the aperture. Karel (by phone) pointed out the ZS restriction in
LSS2 and the associated aperture needed in the horizontal plane for the slow
extraction.
Kicker Vertical Aperture
The machine aperture restriction by the TIDV (19 mm at y= 72 m for
Q26/CNGS) is only slightly tighter than the 20 mm of the present proposal next
to the MBB321. Hannes confirmed the 20 mm, however this aperture in the
vertical plane is needed over the entire horizontal space with no parts of
equipment like electrodes sticking in closer than 20 mm horizontally off-axis.
Kicker Horizontal Aperture
The analysis is more elaborate (different optics, dispersion, larger injection
oscillations both longitudinal and transverse). The conservative approach yields
65 mm half aperture next to the MBB and 75 mm at the missing MBA next to the
QF, which corresponds to the linear interpolation of existing apertures close by.
This is considerably more than the 40 mm quoted previously. Wolfgang pointed
out that for the maximum frequency reach of the kicker (TE10 mode cut-off) it
would be important to know if 65 mm is a hard limit. Hannes will investigate
how close the hard limit from the ZS aperture in LSS2 is considering the 3rd order
Due to symmetry the same aperture restrictions apply on both sides of LSS3, position 3.21 and
3.14; plots were shown for 3.14.
1
resonant extraction which requires a large horizontal aperture. Wolfgang will
assess any potential gain in frequency going from 65 mm closer to the 40 mm
specified earlier. Input from Karel and Brennan will be sought for formal
approval at one of the next LIU Coordination Meetings (August 15 or later).
Pick-up next to QD319
The analysis showed that a circular aperture of 83 mm close to the geometry of
the QD is acceptable using the conservative approach. Wolfgang commented that
the case of the pick-up is easier as 83 mm will in any case define a frequency
reach of the pick-up higher than what can be achieved for the kicker.
Kicker Design
If a bandwidth for the kicker is required that would be higher than what can be
achieved in the aperture of at position 321, then this would probably mean to
move with a kicker closer to a QD which is not possible in LSS3, hence would
require to have the system in LSS5. Wolfgang will nonetheless check with
F. Caspers damping of propagating modes when a large chamber is used.
Eric Montesinos has been asked to give input concerning the possibilities of
manufacturing chambers with some of the more exotic (elliptical cross-sections)
under discussion. Based on the aperture studies and the input from Eric a
proposal will be made to LARP by Wolfgang for realistic cross sections.
Beam Parameter List for ecloud feedback simulations
In the discussion of the beam parameter list agreement was reached that both
cases the Q20 and the Q26 parameters should be studied. Two sets of
parameters for the injection plateau, three during the ramp and two at flat-top
shall be given. At injection and flat top the sets cover two different bunch lengths
and during the ramp the most critical energy is thought to when we have the
shortest bunch length, just before the longitudinal blow-up is switched on.
Gianni emphasized that while shorter bunches are more critical the most critical
situation is probably at flat bottom where we stay a long time with the beam.
Wolfgang will assemble a prototype table, discuss parameters with Thomas and
Elena and send it to Giovanni for completion and checking. This list will then be
used by Claudio and Kevin for the simulations. Concerning the question on
injection transients Wolfgang will communicate to the LARP team the conclusion
that the vertical oscillations at injection can be kept to below under 1 mm in
amplitude (at =102 m).
A.o.B.
LIU Day, 28 August 2012
Concerning the planned LIU 1 day meeting on August 28, Giovanni asked if
Wolfgang was available to present. In the discussion the need for a back-up plan
was agreed and the proposed speaker will be contacted. Material will be
provided by John Fox and our Working Group. MD needs also for 2013 can be
proposed at the LIU day.
Next Meetings:
The next meeting will take place next week at 17:45, conference room in the CCC
glass box. There will be no meeting on 16.08.2012 (LHC MAC week) and
23.08.2012 (ICAP conference). The meeting on 30.08.2012 (18:00 joint meeting
with LARP) could concentrate on the simulation effort and the hardware
developments.
Adjournment: 09.08.2012, 17:45 (CCC glass box); Agenda: C. Zannini (SPS
impedance), SLAC Team (MD results - Review)
WH, 08/08/2012