From syphers@fnal.gov Fri Mar 23 18:10:55 2001 Date: Thu, 17 Feb 2000 16:05:13 -0600 From: Mike Syphers To: Jim Hylen , Greg Bock , Sam Childress , Dixon Bogert Cc: Steve Holmes , John Marriner , Phil Martin , augustine@fnal.gov, cossairt@fnal.gov, Paul Czarapata , rod@aps.anl.gov, Alan Hahn , Dave Johnson , Walley Kissel , hamburg@fnal.gov, Jim Morgan , Howie Pfeffer , Al Russel , tartaglia@fnal.gov, vaziri@fnal.gov, Mike Syphers Subject: NuMI Review Final Report Fermilab Review of NuMI Beam Extraction and Beam Transport Systems Final Report February 17, 2000 The Fermilab Beams Division held an internal review of the NuMI Beam Extraction and Beam Transport systems at Fermilab on January 25-26, 2000. A list of the committee members can be found in Appendix I, and the schedule of presentations in Appendix II. What follows is a report from the Committee on this meeting. First of all, the Committee would like to commend the members of the NuMI Project for their efforts to present the design and relevant project issues. The presentations were well organized and thorough given the one-day format of the review. NuMI constitutes a major physics and construction program at Fermilab, and a large amount of effort was evident. NuMI is expected to deliver in one year an equivalent number of protons on target as has been delivered by the entire Fermilab Fixed Target Program to date. The need to accomplish this with a loss rate of about 0.01% shows that a high-level of support is required by the Beams Division and Laboratory management. The level of rigor required to maintain NuMI in its operational state is very high. The Committee cannot emphasize enough the need to provide NuMI with enough support from the Beams Division to realize its very stringent goals. This would imply not just more people on the job, but the "right" people to ensure success. The findings of the Committee will be discussed now in approximately the order of presentation. BEAM EXTRACTION MODE The Committee concurs with the choice of single-turn extraction over resonant extraction. The latter would introduce losses on the electrostatic septa which are inherently a few percent and would be unacceptably high. It was noted that Lambertson magnets are often loss points in accelerators, but that much of the time this is at injection when the beam size is larger. The aperture at the Q608 quadrupole magnet is tight. However, the extraction system to be used for NuMI is similar to the systems used at other Main Injector locations for extraction (Tevatron transfers and abort system). The Committee recommends that beam loss at Tevatron beam transfers and/or during antiproton production be examined in detail. The latter should be indicative of the NuMI extraction process. BEAM EXTRACTION KICKER The beam extraction process to NuMI is operationally tied to beam extraction for antiproton production. The operating scenario proposed is to have 6 batches of beam from the Booster injected and accelerated to 120 GeV in the Main Injector. The bunches are then put through a process in the Main Injector known as bunch rotation, in which the bunch length is minimized and momentum spread increased. One of the six batches is extracted to the Pbar Source. The NuMI beam is saved for last so that the NuMI kicker fall time can be relaxed. A system to bring the kicker magnet's field down in the short gap between batches would be much more expensive than that designed. However bunch rotation maximizes the momentum spread of the entire beam and thus could lead to losses in the NUMI transfer line unless precautions are taken to either extract the NUMI beam after another 90 degrees rotation (or odd multiple thereof), or to recapture the beam in a low voltage bucket. Either method would minimize the momentum spread. Members of the Committee noted that the bunch rotation process can generate small longitudinal emittance growth which can be non-reproducible from cycle to cycle. With an eye to controlling losses at the 0.01% level, it may be better for the NuMI beam to be extracted prior to doing bunch rotation. This would require kicker system improvements. Again, beam studies are recommended to study the beam loss expected during bunch rotation at very high intensities. The extraction process introduces a large horizontal orbit excursion in the extraction region. This practice is used in the other extraction regions, and the orbit excursion is generated by moving MI quadrupole magnets. For NuMI, MI corrector magnets are to be used, the required strength of which is roughly 50% of the maximum strength available. The Committee recommends looking at moving quadrupole magnets to achieve the required extraction trajectory of the circulating beam at flattop, reserving the corrector magnets for their intended use. PRIMARY BEAM TRANSPORT The primary beam transport system is made up of two major vertical bends near the beginning and end of the line and a major horizontal bend at the beginning of the line. The horizontal bend establishes the horizontal direction toward Sudan, MN. The first vertical bend gets the Target Hall into the bedrock. The second vertical bend sets the final grade toward the Sudan detector. One aspect of the design that may need more attention is the momentum dispersion generated by the vertical bends. The vertical drop of approximately 60 feet (20 m) generates approximately 20 m of vertical dispersion. Thus, a particle whose momentum is off by 0.1% will arrive at the Target Hall with a trajectory displaced from the ideal trajectory by 20 mm. The momentum spread of the beam coming from the MI was projected to be on the order of 0.02%. Using this number, the spot size due to momentum spread is comparable to the spot size due to betatron emittance, making the spot size 40% larger. Recent measurements of the momentum spread in the MI appear to be 2-5 times larger than this number during antiproton stacking studies. Additionally, variations of the average extracted momentum from the MI have been recorded recently as +/- 0.1%. Efforts have begun to redesign the optics to reduce the momentum dispersion, though its slope is still quite large at the target making it sensitive to quadrupole mistuning. Further tweaking of the optical design to reduce its sensitivity to momentum spread and tuning errors is strongly encouraged. The range of momentum spread expected to be extracted from the Main Injector should also be verified. Additionally, the initial conditions for the optical design have been the design lattice function values of the Main Injector; these assumptions should also be verified now that the Main Injector is operational. A sensitivity analysis of the beam transport system design was not presented. Studies were not presented of the effects of magnet mispowering (of both bending and focusing magnets) and misalignments to see if the correction systems and power supply arrangements can correct errors to the required tolerances. Specifications and tolerances on power supplies -- regulation, granularity of control, etc. -- need to be developed and checked against foreseen beam based correction algorithms. While beam instrumentation is included in the design, it was not clear that instruments -- loss monitors, beam position monitors and, in particular, profile monitors -- had been placed in optimal locations for useful and meaningful measurements during operation. An additional beam toroid in the middle of the beamline may also prove useful. It will become important to make measurements such as * correlation of beam loss to energy spread * beam emittance arriving from the Main Injector * amplitude function measurements and beam matching * targeting angle and positions with desired accuracy during routine operation and the number and layout of devices should be determined in conjunction with the optical design of the line. RADIATION SAFETY One of the most challenging -- if not the most challenging -- issues for the NuMI project is the monitoring of beam loss. Groundwater protection is one of the primary drivers of the beam transport design. Many calculations have been carried out to study the effects of beam loss in the various geological regions of the project. The following issues were brought up by the Committee: * Mitigation of Carrier Pipe Loss Control The Carrier Pipe region of the beamline passes through the glacial till/bedrock interface. It was pointed out that the loss of only a few beam pulses per year (at full intensity) can be tolerated in this region. It is difficult to see how to tune up and maintain an operational system with this restriction. If 10 seconds elapse before full intensity beam losses are detected to be in this region, then the experiment is shut off for a year. While beam intensities will be computer monitored very closely, it is still an uncomfortable margin for the Committee. If a method for increasing the tolerated losses by, say, a factor of at least 10 in this region could be developed, the Committee believes it would be well worth the money and effort. Examples would be extra shielding in this region, or a better drainage system for moving activated water to the bedrock region. The loss tolerance in this area could cause significant operational problems. A passive method, such as shielding or better drainage, for increasing the tolerated losses by a factor of at least 10 (preferably 100) should be investigated and implemented. The time, effort, and expenditures up front to eliminate this tight tolerance on losses will prove worthwhile in the long run. Accidents and potential ground water contamination in this area could prove to be a major problem for not only the experiment but for the lab as well. * Loss Monitor Calibration Calibration of loss monitors was seen to be an issue, in particular the use of heliax monitors which require periodic maintenance (changing of gas bottles, for instance). There are only three such monitors -- is this enough spatial resolution? While much of the beam loss monitoring will depend upon the use of sealed units (BLM's), their calibration needs to be addressed for use in monitoring total beam losses at the 0.01% level. * Fault Analysis A detailed Fault Analysis and Radiation Source Analysis should be conducted. These analyses should investigate the various failure modes which could be hypothesized during operation of the beamline, including power supply failures, magnet failures, kicker magnet misfires, orbit motion in the Main Injector, energy errors from the Main Injector, and so forth. This could influence the optical design and/or placement of instrumentation, correction magnets, shielding, etc. * Testing of Measurement Procedures The Committee recommends that NuMI beam loss instrumentation and procedures (such as AutoTune, loss monitoring and integration, etc.) be testing using existing accelerator beamlines. For example, NuMI style beam loss monitors could be placed in the Main Injector at the Tevatron/Pbar extraction point and carefully monitored and studied during antiproton stacking cycles. A measurement of the performance criteria needs to be made. (Can 0.01% beam loss be detected and measured accurately?) POWER SUPPLIES AND CONTROLS The Power Supply system and the Controls system both appear to be in good shape. The power supply requirements have been defined and many supplies from earlier Fermilab operations are being reused for this project. A thorough spreadsheet of has been compiled which contains magnet requirements and corresponding power supplies which have been identified. In several cases, Transrex power supplies are being reused for this project -- a Committee member noted that the internal insulation of these supplies is a problem when they are used in modes other than 100 V operation. This should be reviewed. The power supply interface to operations is straightforward and should be easy to use. This is strongly endorsed by the Committee. It was questioned whether operating NuMI simultaneously with mini-BooNE will be an issue for power and cooling considerations. This needs to be looked at closely over the upcoming months. It was felt that the Controls System is using well understood, standard Fermilab equipment and procedures and is not seen to have any outstanding issues. INSTRUMENTATION, ALIGNMENT, WATER, ETC. The following list of issues for instrumentation, alignment, and water systems was generated as a result of the Review: * Temperature and humidity control in the tunnel, especially in the pre-target area, is seen to be a difficult problem and needs careful consideration. * The plan to put small orifice devices in the LCW system to regulate flow could eventually lead to problems with plugging from copper oxide. Similar problems have occurred in the Antiproton Source and elsewhere, and people familiar with these problems should be consulted. * Long-term maintenance and redundancy of components needs more attention. For instance, access to water pumps located in the tunnel-level enclosure, which could require heavy radiation shielding, needs to be carefully planned. * More details (cranes, etc.) concerning the installation of the B2 magnets are required. * As mentioned earlier in the report, the beam instrumentation requirements need to be consistent with the optical properties of the beam line. Are 1 mm and 0.5 mm wire spacing enough for the multiwire profile monitors? Are there enough Beam Position Monitors in the line? As is common in a review of this nature, it is easy to point out deficiencies and forget to comment on the work that was well done. The above comments are to be regarded as constructive criticism. The amount of hard work and dedicated time put into the NuMI Project thus far is very evident. The NuMI Project is seeking to deliver beam at an unprecedented rate and with extremely high efficiency. As stated earlier, the Beams Division and Laboratory management must provide the necessary resources and motivational backing to continue the project along its path to success. Appendix I -- Review Committee Members Mike Syphers, Chair syphers@fnal.gov Dave Augustine augustine@fnal.gov Don Cossairt cossairt@fnal.gov Paul Czarapata pcceed@fnal.gov Rod Gerig rod@aps.anl.gov Alan Hahn ahahn@fnal.gov Dave Johnson dej@fnal.gov Wally Kissel kissel@fnal.gov Tony Leveling hamburg@fnal.gov Jim Morgan jpmorgan@fnal.gov Howie Pfeffer pfeffer@fnal.gov Al Russell russell@fnal.gov Mike Tartaglia tartaglia@fnal.gov Kamran Vaziri vaziri@fnal.gov Appendix II -- Presentation Agenda NuMI Extraction / Primary Beam Review 01/25/00 i) Overview S. Childress 15 min. 09:15-09:30 ii) Beam Extraction Mode P. Lucas 20 min. 09:30-09:50 iii) Extraction Kicker C. Jensen 15 min. 09:50-10:05 iv) Extraction / MI Beam A. Drozhdin 20 min. 10:05-10:25 Break 15 min. 10:30-10:45 v) Primary Transport P. Lucas 30 min. 10:45-11:15 vi) Radiation Safety N. Grossman 30 min. 11:15-11:45 vii) Power Supplies S. Hays/N. Grossman 20 min. 11:45-12:05 Lunch 60 min. 12:10-1:10 viii) Instrumentation G. Tassotto 20 min. 1:10-1:30 ix) Alignment W. Smart 15 min. 1:30-1:45 x) Water, Vacuum, Gas D. Pushka 15 min. 1:45-2:00 xi) Installation T. Anderson 20 min. 2:00-2:20 xii) Inst. Schedule Constraints S. Childress 10 min. 2:20-2:30 xiii) Controls R. Ducar 25 min. 2:30-2:55 Break 15 min. 3:00-3:15 xiv) Commissioning S. Childress 20 min. 3:15-3:35 xv) Beam Operation S. Childress 20 min. 3:35-3:55 xvi) Plans / Goals P. Lucas 20 min. 3:55-4:15 xvii) Summary S. Childress 15 min. 4:15-4:30 \/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/ Mike Syphers Fermilab M.S. 220, P.O. Box 500, Batavia, IL 60510 (630) 840-8863 fax: -6039 email: syphers@fnal.gov /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\