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MTE workshop 2011
Description
- Review current beam status and issues
- Review possible mitigation measures
- Define a strategy to have an operational MTE
Workshop secretary
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14:00
→
18:25
Convener: Roland Garoby (CERN)Status of commissioning with beam (S. Gilardoni)
Roland asked if the fluctuations could come from POPS or if POPS had made the situation worse. Simone replied that the data were taken when POPS was not optimized but can’t comment more. Jean-Paul commented that the feedback system is the same (for POPS and for the rotating MPS) so no difference should be seen between the two. The only difference might come from the noise, the MPS has a 50 Hz noise whereas the POPS has noise line at some kHz.
Oliver asked about the remnant field that could be present at injection. Simone confirmed that a remnant field is present at injection both of dipolar and quadrupolar type. However, no measurable difference could be observed from super-cycle to super-cycle. In any case, the sextupolar and octupolar components cannot be measured, yet. An improved magnetic measurement system is foreseen for the coming winter technical stop.
Gianluigi suggested performing measurements with an MTE user located after a 26 GeV/c cycle in order to go to have the maximum hysteresis effect from the saturation of the MMU. Simone answered that an idea was to cycle the figure-of-eight loop before the MTE cycle.
Roland commented that the capture process should be very sensitive to perturbation at the beginning of the process. Simone confirmed that indeed the beginning of the capture process is crucial. This was confirmed also by wire scanner measurements performed right after resonance crossing: from the shape of the profile it was possible to infer whether the trapping was good or bad.
Olivier asked if an energy error is seen at injection due to the remnant field. Simone replied that due to the radial loop we are put back in the center of the pipe. However, it was checked that no particular activity was on-going on the RF loops at 14 GeV/c significantly different from cycle-to-cycle, thus indicating that no energy error is present at 14 GeV/c.
Massimo commented that 2 GeV/c tests were proposed to have an even simpler situation, for example at that energy we don’t need to use the pole-face-windings and were the machine is very linear.
Measurements’ analysis (A. Lachaize)
Jean-Paul argued that the MTE sextupoles are assumed to be stable in current, but that maybe they are not in remnant field. Simone answered that it is the reason why the chromaticity measurements (scans in energy) are not “centered”, but are done with an offset to probe the sextupolar component (in any case, these magnets are used only by MTE and hence, they are always on the same hysteris cycle. Therefore, they should provide a very reproducible field).
Massimo commented that next to the origin the measurement of the higher-order field components is rather difficult. This is why the beam is indeed displaced to rather large amplitudes (up to ±20 mm) to enhance the sensitivity of the measurement to the high-order components. Around these points the energy scan is then performed to measure the non-linear chromaticity.
Jean-Paul commented that the 24 kHz structures seen by Antoine are at a multiple of the 6 kHz frequencies of switch power converters used by the pole-face-windings. This should be looked at in more details.
Simone mentioned that tests in three-current mode are planned. However it is commented that due to power converter changes that will not restore exactly the same situation back to when the three-current mode was the only one in operation.
Roland asked if it is possible to close the bump for the core and for the islands. Antoine replied that we can try as there are six independent bumpers.
Gianluigi asked what is the nominal amplitude of the islands at extraction (as it was showed that the fluctuations are more important for the outer islands, the fluctuations then being amplitude dependent). Massimo answered that the parameters used during the measurements are realistic, except for the tune ramp that is slower in the nominal MTE case.
Jeroen asked if bunch length changes were seen during the tune ramp. Antoine answered that it was not the case.
Simone commented that the extraction is done around 20 -30 mm, for a horizontal tune of 0.255-0.256. Therefore the oscillations (“resonance”) seen at 0.26 will be possibly not crossed. This would depend on the tune line and it will be investigated.
Status of instrumentation (S. B. Pedersen)
Roland asked what type of BLM are to be installed to replace the old ACEM. Stephane replied that the type is not known, yet, but that they will install the cables and the electronics.
Roland asked if the new bellows for the BWS would really allow going for 20 m/s. Stephane answered that they need to be tested. Simone asked if the current impossibility to scan at 20 m/s is due exclusively to the bellows. Ana replied that some issues at 20 m/s were found during tests in the lab and it was decided to exclude this speed from the operational ones.
Roland asked what are the advantages of the new tank. Stephane replied that it is going to allow a larger scanning amplitude (up to 30 mm). Simone and Gianluigi added that the current tank is an aperture limit for the machine and a replacement was requested by the APC.
Roland commented that the warnings about “available resources” shown in the presentation are meaningful only if they are discussed together with the prioritization of the requests. Gianluigi added that the actual conflicts with the LHC should also be mentioned and that the LHC activities should come to an end!
Simone added that MTE could not be charged for the costs of the new cables for the BLMs. The budget requested for this will be discussed between the consolidation and the upgrade projects.
Mitigation measures for extraction losses (M. Giovannozzi)
It was asked if a bunched-beam extraction is still a possibility. Massimo answered that this option should be ruled out following the numerous tests performed in the past. The barrier bucket option might remain, but it would create four gaps in the longitudinal SPS structure and that will be a problem for the fixed-target experiments (although it would not be a problem for CNGS or for neutrino experiments in general).
Roland asked what would be the impact of the dummy-septum in SS15 on the shielding that will be added in SS16 during the LS1. Massimo answered that it should be considered when investigating the dummy-septum option, but in principle it should not have any impact.
Simone added that the situation should be improved by the dummy septum but this does not imply a reduction of the foreseen shielding increase.
Roland wondered that the dummy septum in SS15 would become the hottest part of the PS. Simone answered that the dummy septum will improve the situation in SS16 and in SS15 the situation will be mitigated by the added local shielding around the dummy septum.
Massimo warned that the fluctuations in fixed point positions would certainly worsen the situation in terms of losses. In reply to a question by Brennan, Massimo stated that the average loss rate measured during the 2010 MTE run, i.e., 5 %, should be used for estimating the irradiation of the SS15 and the surroundings. Simone commented that the shielding to be added in SS16 only make the shielding in that section in conformity with the shielding in other parts of the tunnel: indeed the shielding is “depressed” in that section from the construction of the tunnel. The civil engineering interventions will be done such as in the future will be possible to increase even more the shielding by 50 cm of earth if necessary.
Laurent asked if the dummy septum would be installed during the LS1 or before. Massimo replied that it will never be ready before that. Only some beam tests could be performed before and in particular tests for the hybrid-MTE option.
Rende asked if a two-month shutdown would not be enough to install the dummy septum. Massimo answered that even if the gamma-jump quadrupoles could be moved, the construction of the dummy septum could not be finished before the LS1.
Impact of MTE on PS septa (J. Borburgh)
Massimo asked if an answer on the use of the CT septum and related elements should really be provided by the end of 2011. Jan answered that an answer on the dummy septum option should also be given by the end of the year.
Thomas asked what was the expected lifetime of the dummy septum. Jan answered that the dummy septum would be built to require a minimum amount of maintenance.
Roland asked how much time is required to replace the septum 31 that is in operation. Jan answered that only a couple of days are required. It can easily fit in the Christmas shutdown.
Simone asked if a spare dummy septum would be built. Jan answered that, as the device is simple, two dummy septa could be built.
Kicker options for MTE (L. Ducimetiere)
Roland asked what exactly is included in the hybrid solution. Laurent answered that all CT and MTE elements are included and that is would allow operation of both methods.
Simone asked what is included in the consolidation budget. Laurent answered that 260 kCHf were already included.
Electronics issues for MTE (E. Carlier)
Massimo commented that the “MTE only” option was planned in the resources and hence its cost would be a baseline. It was answered that it is the case, but that the reshuffling of building 359 was not foreseen.-
14:00
• Current status of studies • Issues encountered • Plans for the rest of 2011Speaker: Dr Simone Gilardoni (CERN)Status of commissioning with beam (S. Gilardoni) - Discussion
Roland asked if the fluctuations could come from POPS or if POPS had made the situation worse. Simone replied that the data were taken when POPS was not optimized but can’t comment more. Jean-Paul commented that the feedback system is the same (for POPS and for the rotating MPS) so no difference should be seen between the two. The only difference might come from the noise, the MPS has a 50 Hz noise whereas the POPS has noise line at some kHz.
Oliver asked about the remnant field that could be present at injection. Simone confirmed that a remnant field is present at injection both of dipolar and quadrupolar type. However, no measurable difference could be observed from super-cycle to super-cycle. In any case, the sextupolar and octupolar components cannot be measured, yet. An improved magnetic measurement system is foreseen for the coming winter technical stop.
Gianluigi suggested performing measurements with an MTE user located after a 26 GeV/c cycle in order to go to have the maximum hysteresis effect from the saturation of the MMU. Simone answered that an idea was to cycle the figure-of-eight loop before the MTE cycle.
Roland commented that the capture process should be very sensitive to perturbation at the beginning of the process. Simone confirmed that indeed the beginning of the capture process is crucial. This was confirmed also by wire scanner measurements performed right after resonance crossing: from the shape of the profile it was possible to infer whether the trapping was good or bad.
Olivier asked if an energy error is seen at injection due to the remnant field. Simone replied that due to the radial loop we are put back in the center of the pipe. However, it was checked that no particular activity was on-going on the RF loops at 14 GeV/c significantly different from cycle-to-cycle, thus indicating that no energy error is present at 14 GeV/c.
Massimo commented that 2 GeV/c tests were proposed to have an even simpler situation, for example at that energy we don’t need to use the pole-face-windings and were the machine is very linear. -
14:30
Discussion 10m
-
14:40
• Closure of slow bump • Islands' position and fluctuations. Scans performedSpeaker: Antoine Lachaize (CERN)Measurements’ analysis (A. Lachaize) - Discussion
Jean-Paul argued that the MTE sextupoles are assumed to be stable in current, but that maybe they are not in remnant field. Simone answered that it is the reason why the chromaticity measurements (scans in energy) are not “centered”, but are done with an offset to probe the sextupolar component (in any case, these magnets are used only by MTE and hence, they are always on the same hysteris cycle. Therefore, they should provide a very reproducible field).
Massimo commented that next to the origin the measurement of the higher-order field components is rather difficult. This is why the beam is indeed displaced to rather large amplitudes (up to ±20 mm) to enhance the sensitivity of the measurement to the high-order components. Around these points the energy scan is then performed to measure the non-linear chromaticity.
Jean-Paul commented that the 24 kHz structures seen by Antoine are at a multiple of the 6 kHz frequencies of switch power converters used by the pole-face-windings. This should be looked at in more details.
Simone mentioned that tests in three-current mode are planned. However it is commented that due to power converter changes that will not restore exactly the same situation back to when the three-current mode was the only one in operation.
Roland asked if it is possible to close the bump for the core and for the islands. Antoine replied that we can try as there are six independent bumpers.
Gianluigi asked what is the nominal amplitude of the islands at extraction (as it was showed that the fluctuations are more important for the outer islands, the fluctuations then being amplitude dependent). Massimo answered that the parameters used during the measurements are realistic, except for the tune ramp that is slower in the nominal MTE case.
Jeroen asked if bunch length changes were seen during the tune ramp. Antoine answered that it was not the case.
Simone commented that the extraction is done around 20 -30 mm, for a horizontal tune of 0.255-0.256. Therefore the oscillations (“resonance”) seen at 0.26 will be possibly not crossed. This would depend on the tune line and it will be investigated. -
15:10
Discussion 10m
-
15:20
• Status of orbit system (recent issues, solutions, future imrpovements) • Status and plans for FWS and BLMs • Status and plans for BCTs in TT2, pick-ups in TT2, sem-grids in TT2Speaker: Stephane Bart Pedersen (CERN)Status of instrumentation (S. B. Pedersen) - Discussion
Roland asked what type of BLM are to be installed to replace the old ACEM. Stephane replied that the type is not known, yet, but that they will install the cables and the electronics.
Roland asked if the new bellows for the BWS would really allow going for 20 m/s. Stephane answered that they need to be tested. Simone asked if the current impossibility to scan at 20 m/s is due exclusively to the bellows. Ana replied that some issues at 20 m/s were found during tests in the lab and it was decided to exclude this speed from the operational ones.
Roland asked what are the advantages of the new tank. Stephane replied that it is going to allow a larger scanning amplitude (up to 30 mm). Simone and Gianluigi added that the current tank is an aperture limit for the machine and a replacement was requested by the APC.
Roland commented that the warnings about “available resources” shown in the presentation are meaningful only if they are discussed together with the prioritization of the requests. Gianluigi added that the actual conflicts with the LHC should also be mentioned and that the LHC activities should come to an end!
Simone added that MTE could not be charged for the costs of the new cables for the BLMs. The budget requested for this will be discussed between the consolidation and the upgrade projects. -
15:50
Discussion 10m
-
16:00
Coffee Break 15m
-
16:15
Feasibility of • dummy septum in SS15 • extraction with SEH31 Performance reach of faster kicker rise timeSpeaker: Dr Massimo Giovannozzi (CERN)Mitigation measures for extraction losses (M. Giovannozzi) - Discussion
It was asked if a bunched-beam extraction is still a possibility. Massimo answered that this option should be ruled out following the numerous tests performed in the past. The barrier bucket option might remain, but it would create four gaps in the longitudinal SPS structure and that will be a problem for the fixed-target experiments (although it would not be a problem for CNGS or for neutrino experiments in general).
Roland asked what would be the impact of the dummy-septum in SS15 on the shielding that will be added in SS16 during the LS1. Massimo answered that it should be considered when investigating the dummy-septum option, but in principle it should not have any impact.
Simone added that the situation should be improved by the dummy septum but this does not imply a reduction of the foreseen shielding increase.
Roland wondered that the dummy septum in SS15 would become the hottest part of the PS. Simone answered that the dummy septum will improve the situation in SS16 and in SS15 the situation will be mitigated by the added local shielding around the dummy septum.
Massimo warned that the fluctuations in fixed point positions would certainly worsen the situation in terms of losses. In reply to a question by Brennan, Massimo stated that the average loss rate measured during the 2010 MTE run, i.e., 5 %, should be used for estimating the irradiation of the SS15 and the surroundings. Simone commented that the shielding to be added in SS16 only make the shielding in that section in conformity with the shielding in other parts of the tunnel: indeed the shielding is “depressed” in that section from the construction of the tunnel. The civil engineering interventions will be done such as in the future will be possible to increase even more the shielding by 50 cm of earth if necessary.
Laurent asked if the dummy septum would be installed during the LS1 or before. Massimo replied that it will never be ready before that. Only some beam tests could be performed before and in particular tests for the hybrid-MTE option.
Rende asked if a two-month shutdown would not be enough to install the dummy septum. Massimo answered that even if the gamma-jump quadrupoles could be moved, the construction of the dummy septum could not be finished before the LS1. -
16:45
Discussion 10m
-
16:55
Ideas Path to constructionSpeaker: Mr Jan Borburgh (CERN)Impact of MTE on PS septa (J. Borburgh) - Discussion
Massimo asked if an answer on the use of the CT septum and related elements should really be provided by the end of 2011. Jan answered that an answer on the dummy septum option should also be given by the end of the year.
Thomas asked what was the expected lifetime of the dummy septum. Jan answered that the dummy septum would be built to require a minimum amount of maintenance.
Roland asked how much time is required to replace the septum 31 that is in operation. Jan answered that only a couple of days are required. It can easily fit in the Christmas shutdown.
Simone asked if a spare dummy septum would be built. Jan answered that, as the device is simple, two dummy septa could be built. -
17:10
Discussion 10m
-
17:20
Ideas Cost Path to constructionSpeaker: Laurent Ducimetiere (CERN)Kicker options for MTE (L. Ducimetiere) - Discussion
Roland asked what exactly is included in the hybrid solution. Laurent answered that all CT and MTE elements are included and that is would allow operation of both methods.
Simone asked what is included in the consolidation budget. Laurent answered that 260 kCHf were already included. -
17:40
Discussion 10m
-
17:50
Speaker: Etienne Carlier (CERN)
-
18:00
Discussion 10m
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14:00
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14:00
→
18:25
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11:00
→
12:30
Convener: Roland Garoby (CERN)
- 11:00
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11:00
→
12:30
