All Staff Memos
|Date:||March 30, 2000|
|From:||Larry Cardman and Andrew Hutton for the Nuclear Physics
Experiment Scheduling Committee
|Subject:||Accelerator Schedule: April 2000 - June 2001|
Attached is the accelerator operations schedule for the period through June 2001. The overall operations continues to be constrained to a level of 31 weeks/year as a result of the laboratory’s operating budget level for FY2000.
The Jefferson Lab Nuclear Physics Experiment Scheduling Committee developed the schedule. Committee members are: Larry Cardman and Andrew Hutton (Co-Chairmen), Hari Areti, Roger Carlini, Bernhard Mecking, Kees de Jager, Mike Seeley, Charlie Sinclair, and Will Oren. Nathan Isgur provided advice. As has been the norm, a number of meetings of this committee were necessary to resolve conflicting requirements and to ensure that sufficient resources would be available at the laboratory to properly stage and carry out each of the experiments. The schedule was derived by looking at the requests for major installation work in the experimental halls, evaluating the number and kinds of people needed, and then scheduling to minimize overlap. The schedule request forms again proved quite useful in identifying the detailed requirements of each experiment. Information on other laboratory engineering priorities was included to ensure that the required preparatory work could be completed in time. This provided a rough overview of when each hall would be down.
Each hall leader took the requests for running time submitted by the experiment spokespersons and prioritized them based on the PAC recommendations and other considerations as outlined in the scheduling committee charter. Scheduled time for Hall C was again calculated using an estimated overall efficiency of simultaneous hall and accelerator operation of 50%; this value is consistent with last year's experience for the hall. The same 50% was used for Hall B scheduling, even though the actual availability was higher; since most running in Hall B involves fractions of very long run groups, cutting the scheduling as tight as possible has no long term benefit, and we take advantage of higher running efficiency (when achieved) to complete a larger fraction of a run group’s program. Scheduled time for Hall A was calculated using an estimated overall efficiency of 60%, consistent with recent experience. In a number of cases the scheduled beamtime has been adjusted to reflect significant changes in facility capabilities since the time of PAC approval of the experiment; the most obvious of these is the availability high polarization beams with significantly higher current than was the case a few years ago. The final schedule was then reached by a series of compromises in running order within each experiment and between halls to work around incompatibilities.
In the attached schedule you will note that the winter shutdown for 2000-2001 has been shifted from the traditional late December-January period to March 2001. This shift was made so that two major installation experiments (E93-038 in Hall C and eg1 in Hall B) could complete data-taking before the down so that the time necessary to reconfigure the halls after those experiments would overlap with the accelerator down.
This is the sixth schedule with substantial polarized beam operations. There are only two beam energies (2.115 and 4.230 GeV) at which purely longitudinal spin can be delivered simultaneously to all three halls when the halls have the same energy. There are, however, many combinations of passes and linac energies at which it is possible to deliver beams with precisely longitudinal polarization to two halls simultaneously, and many combinations at which it is possible to deliver nearly longitudinal polarization to three halls. (See the note at the end of this memo for further information.) Experimenters scheduled for periods involving multiple-hall polarized beam delivery should consider the possible impact of a transverse polarization component on their measurements, and provide the laboratory with a maximum allowable transverse component if appropriate. It is clear that we will continue to have a great deal less flexibility for changing energies in the different halls during polarized beam running. This is because there are many instances where the nominal linac energy and number of recirculations for the running halls provide reasonable polarization, but where changing the number of recirculations for one of the running halls results in nearly transverse polarization.
In an effort to optimize polarized beam running, we have scheduled many weeks of operation at "unusual" energies that are consistent with good polarization in multiple halls. The details vary from run period to run period and hall by hall. In the worst case, the effective polarization delivered to a hall will be reduced to about 89% of the nominal maximum available from the cathode. This reduction is due to the angle at which the polarization vector will be set relative to the beam direction in the hall in a compromise that will optimize delivery to all halls. For two-hall operation we can optimize the figure of merit for both running experiments by simply setting the Wien filter to a value that results in identical longitudinal polarization components for the two halls. For three-hall operation we have previously used an algorithm that set the Wien filter to a value that maximized the overall figure of merit (the sum of the squares of the polarization provided to all halls scheduled to receive polarized beam). It has been noted that this sometimes results in situations where the delivered polarization is significantly different for the three halls. To "equalize the pain" for three-hall operation, we are adopting a refinement to this algorithm. The Wien angle for three-hall operation will now be set to minimize the differences between the hall polarizations (by minimizing the dispersion) so long as this scheme does not result in a reduction of the "sum of squares" figure of merit by more than 2% compared to the optimum figure of merit. In all cases involving polarized beam delivery the setting of the Wien Filter shall be fixed throughout the running period unless all parties scheduled to receive polarized beam agree to a different setting.
The standard section at the end of this memo on "the meaning of priority on the accelerator schedule" is included for reference; there were no changes in the policy this cycle. All users with running experiments should read it carefully.
The schedule attached represents our best effort to optimize the physics output of the laboratory consistent with our resource constraints and the technical evolution of the accelerator and the experimental equipment. In the material that follows, we outline the technical considerations that influenced the scheduling, and outline the planned program.
During the January 2000 shutdown, a new cryomodule was installed in the last slot of the south linac, and cryomodules were interchanged between the north and south linacs to equalize the energy gain available from each linac. These improvements are anticipated to significantly reduce the RF trip rate during operation at higher energy, and should allow operation at, or very close to, 6 GeV. Tests of 6 GeV operation are scheduled during May and June of this year, and the first 6 GeV beam delivery for physics is scheduled for April 2001.
The polarized injector now has two fully operational, horizontally mounted polarized guns. All beam operation, polarized or unpolarized, is now conducted with high polarization cathodes. When polarized beam is not required, shorter wavelength lasers are used to take advantage of the higher quantum efficiency at these wavelengths. This has been very successfully demonstrated during the current running period, where "unpolarized" beam up to 130 mA has been delivered to Hall A, while high polarization beam was delivered to Hall B at 5 A. Typical values for the "feedthrough" from Hall A to Hall B are about 50 pA. The photocathode lifetime in the new horizontal guns is excellent. The current value is over 35,000 mA-hours. Though this long lifetime makes absolute statements difficult, our current experience is that the cathode deterioration can be completely removed by a simple heat treatment and reactivation. This cathode recovery can be accomplished during a normal maintenance period. This implies that a single cathode could be used essentially without limit. During the past year, over 280,000 mA-hours were delivered from the polarized guns.
During January, a test run was conducted with a new Ti:sapphire laser, which delivered ~400 mA of high polarization beam. The final version of this laser will allow this current to be more than doubled. We plan to install this laser during the August shutdown. Once this laser is operational, we will be able to deliver high polarization beam at full current to one hall. A second laser of this type will be prepared, to allow high polarization operation to both Halls A and C. Based on the very successful operation of the new guns, and the coming installation of this new laser, we have removed some of the components that allowed beam to be delivered from the thermionic gun. While we could restore these components and operate the thermionic gun again, there is no plan for any further running with unpolarized (or low polarization) beam.
The new three-week maintenance cycle was started this year, and appears to be working very well. This cycle offers improved opportunity for accelerator and injector related tests, as well as somewhat higher availability for physics. The details are provided below in the section on Maintenance/ Development for reference.
Since the last schedule was released, Hall A completed a very successful run of three photodisintegration experiments: E89-019 (Gilman/Holt/Meziani), which measured proton polarization in the reaction; E99-008 (Gilman/Holt/Meziani), which measured deuteron photodisintegration at large angles; and E94-012 (Gilman/Holt), which measured photo-proton polarization in the reaction. We were able to complete E89-028 (Finn/Ulmer/Jones), a study of polarization transfer in the reaction, and a short (~10% of the anticipated final data set) run of E94-004 (Ulmer/Jones), which began an effort to measure high momentum structure in d(e,e'p)n. In November and early December we installed the Hall A high power helium cryotarget, and began a run of E89-044 (Saha/Epstein/Kuss/Voutier), an experiment to study 3He through electro-disintegration at high momentum transfer. The target was initially limited to operation at about half the design luminosity, but improvements to the heat exchanger subsystem made over the January down permitted it to reach design performance early in 2000. The experiment is running well and will be completed shortly.
The remainder of the firm schedule in Hall A starts with E93-049 (Ent/Ulmer), an experiment to study polarization transfer in the reaction in the quasi-elastic scattering region. Following the running of E93-049, the cryotarget will be restored to hydrogen operation, and we will start E91-011 (Frullani/Kelly/ Sarty), a high precision separation of the polarized structure functions in electroproduction of the Roper and delta resonances. This experiment will be followed by: E97-111 (Templon/Mitchell), a systematic probe of short-range correlations via the reaction , and E99-007 (Perdrisat, et al.), the extension of the measurement to higher momentum transfer. The long shutdown between E91-011 and E97-111 is necessary to swap the detector packages between the two Hall A spectrometers so that the ‘new’ hadron spectrometer no longer has the maximum momentum operating limit now necessitated by the coil short in the present hadron spectrometer.
The tentative portion of the Hall A schedule begins with interleaved running of E94-104 (Gao/Holt), a measurement of the fundamental gn®p-p process in 2H and 4He, and E98-108, a study of the electroproduction of kaons up to Q2=3(GeV/c)2 (Markowitz, et al.). These experiments will be followed by the installation of the polarized 3He target, which will be used in E99-117, a study of the neutron asymmetry, , at large x (Meziani/Souder/Chen) and E97-103, a search for higher twist effects in the neutron spin structure function (Averett/Korsch). This sequence replaces the original plan of installing the new septa in Hall A early in 2001. That installation was originally planned to take place in the first half of 2001, but delays in the construction of the septa have necessitated a schedule slip.
With this release of this schedule we announce our (revised) intent to install the new septa in Hall A early in the second half of 2001 and then run the first two experiments using them. To retain this tentative installation start, the collaboration behind these experiments and the septa must pass its second readiness review before the September 2000 meeting of the scheduling committee (which would place the installation and execution of this experiment on the tentative schedule). This review can be arranged through the hall leader, Kees de Jager, at the convenience of the collaboration, but it must take place no later than August 2000 if the collaboration wants to keep its place on the long-range schedule.
Hall B continues to interleave runs of the various "groups" that have been created for experiments with common running conditions. Since the last schedule release we completed the second g1 run (real photons on a hydrogen target, 6 experiments concentrating on strange particle and eta production), followed by the first g3 run (real photons on 3He, three experiments to study few-body problems, such as the modification of nucleon resonances in the nuclear medium, three-body forces, etc.). Presently in progress is the 3rd e1 run (polarized electrons on hydrogen and deuterium targets, fifteen experiments, mainly N* excitation). Additional running planned for the firm portion of the schedule includes the measurement of the neutron magnetic form factor (e5 run) and E94-016 (Rubin), the study of rare radiative decays of the f-meson, followed by the second eg1 run (polarized electrons on a polarized solid-statehydrogen or deuterium target).
The tentative portion of the Hall B schedule begins with the completion of the second eg1 run, which is followed by the g8 run (the first use of linearly polarized photons with CLAS) and then the beginning of the first 6 GeV running of CLAS – the first portion of the e1-6 run group (the higher energy extension of the e1 run group).
Since the last schedule was released, Hall C running has included the completion of the final portion of E91-016 (Zeidman/Reinhold), a study of the electroproduction of kaons and light hypernuclei, and the installation and commissioning of the hypernuclear spectrometer system (HNSS) needed for experiment E89-009 (Tang/Hungerford). E89-009 is the third major installation experiment in Hall C, and is expected to be completed by mid-May. The firm portion of the Hall C schedule then proceeds with the tear-down of the HNSS and the reconfiguration of the hall for E93-038 (Madey, Kowalski), a measurement of the neutron electric form factor and the fourth major installation experiment in Hall C. E93-038 will not be completed until March 2001. If the transition between E89-009 and E93-038 proceeds smoothly, we will insert E99-118 (Keppel/Bruell/Dunne), a measurement of the nuclear dependence of longitudinal to transverse cross section ratio at low Q2.
The tentative portion of the schedule follows the completion of E93-038 with the reconfiguration of the hall for the execution of the remaining portion of E93-026 (Day/Mitchell), the polarized target measurement of the neutron electric form factor. The transition between the two neutron form factor measurements takes advantage of the fact that the two experiment collaborations have identified a set of kinematic running conditions that will permit the same neutron detector blockhouse to be used for both experiments, and by running E93-026 immediately after E93-038 we will save the time that would otherwise be used for tear-down and reconstruction of the neutron detector blockhouse. The blockhouse cannot be left on the floor during most other planned Hall C experiments because it interferes with the rotation of the SOS spectrometer. We regret the fact that this precludes the execution (at this time) of a few smaller scale experiments that do not require major installation equipment. The G0 experiment (E00-006) has requested scheduling in the second half of 2001. We will consider that request at our September meeting, folding information from the annual (DOE/NSF) progress review of the project and a preliminary (JLab Hall C) readiness review that must be scheduled before the committee meets.
Information about the Schedule
The accompanying revised schedule is fixed for the nine-month period March 2000 – January 2001, and tentative for the following six months. Because of the complex couplings between the hall operations during polarized beam running, all halls must continue to run in "calendar-driven" mode. The firm schedule for the first half of 2001 (and the tentative schedule for the second half of 2001) will be released late September or early October, following the meetings of the next cycle of the scheduling committee.
Footnotes to the Schedule
We summarize here the detailed footnotes to the schedule. They appear in the rightmost column of the schedule listing, and are listed at the earliest date in the schedule when they are applicable; many extend for a considerable time after they first appear. The first five footnotes apply to the entire schedule. All of the footnotes are repeated here for clarity and information.
- When two or three halls are scheduled, the relative priority listed in the schedule (in the order listed from left to right) is the relative priority of the halls. For example, A/B/C means that Hall A is the highest priority, Hall B has second priority, and Hall C has the lowest priority. If one of the halls has an asterisk, it means that its priority is conditional, and the conditions are given in appropriate footnotes at the beginning of the running of the affected experiment. If the conditions are not met, then the remaining two halls will have priority in the order listed.
- Energies listed in the schedule for the halls receiving polarized beam are the actual, delivered energies; they include the energy of the injector.
- In the "Accelerator" column, a "low" under Pol(arization) indicates planned use of either a bulk or a thin (but unstrained) GaAs cathode, implying that medium (~40%) polarization can be expected. A "high" under Pol(arization) indicates planned use of a strained GaAs cathode, implying high (~75%) polarization can be anticipated.
- When polarized beam is delivered to all three halls, it is not, in general, possible to provide pure longitudinal polarization to all users. We have optimized the beam energies to provide the highest longitudinal polarization (generally over 90%) to all halls during extended periods of scheduled two- and three-hall operation with polarization. For two-hall operation we have occasionally used less than ideal linac energy settings when one or more of the halls has a scheduled pass change in order to optimize polarization delivery over the entire run. This avoids the loss of beamtime associated with a linac energy change and it avoids energy shifts in the hall that has no interest in changing energy at the time of the transition in the other hall. See the note in the "polarization" subsection of the text on the meaning of priority in the schedule; the note is attached below.
- In all cases, the orientation of the polarization at the injector will be optimized by setting the Wien angle to a value that minimizes the differences between the hall polarizations (by minimizing the dispersion) so long as this scheme does not result in a reduction of the "sum of squares" figure of merit by more than 2% compared to the optimum figure of merit as determined by summing the squares of the polarization provided to all halls scheduled to receive polarized beam. If minimizing the dispersion results in a loss of more than 2% relative to the optimum figure of merit, we will revert to our earlier algorithm of setting the Wien filter to maximize the overall figure of merit. In all cases involving polarized beam delivery the setting of the Wien Filter shall be fixed throughout the running period unless all parties scheduled to receive polarized beam agree to a different setting.
- When polarized beam is provided at a new energy, as much time as necessary during the first shift of polarized beam operation will be used to verify polarization in the halls. This can be done by direct polarimetry in the hall(s) and/or by taking data on a reaction that is adequately sensitive to the beam polarization. By the end of the first shift of production running with polarized beam, the run coordinator(s) for any experiment(s) receiving polarized beam must report to the Program Deputy that they have measured the beam polarization and determined it to be acceptable. Otherwise, a measurement of the beam polarization will be scheduled immediately.
- The value of 0.61 listed for the linac energy is to be taken as a three-digit accuracy number for this run period - the minimum acceptable energy for Hall A during this period is 1.245 GeV.
- The maximum beam current available to the remaining experiment that is scheduled using a high power helium cryotarget experiments in Hall A may be limited by available refrigeration power; it will have to be determined empirically at the startup of the experiment.
- On 5/15 and 6/5 we will carry out tests of the capability of the various accelerator system components to support a final energy of 6.0 GeV in preparation for future running at that energy. A major effort to refine high energy running will be the focus of the summer 2000 shutdown.
- While E94-016 (the RadPhi experiment) is running, the CLAS control system will be upgraded from TACL to EPICS. The experiment will be shut down for about one shift per week (details will be coordinated with hall staff, and all efforts will be made to minimize the loss of running time) to facilitate the installation and testing effort associated with the transition. I will probably also be necessary to shut down the experiment for about a day during the warm-up cycle for CLAS because of the need to deal with gas pressure buildup – the CLAS has never been warmed up since its initial cooldown, and the amount of "ice" is unknown.
- The beginning of the installation effort for the Madey/Kowalski GEn experiment (E93-038) will be overlapped to the maximum extent possible with the removal of the HNSS. The E93-038 collaboration should develop an overall plan in consultation with Hall C management and engineering that minimizes the total down time between the end of data-taking for the HNSS experiment and the beginning of commissioning for E93-038.
- On July 10 and 11 we tentatively plan a "spin dance" in an effort to improve our knowledge of the absolute beam energy in all the halls, and to compare the polarimeters in the halls. This plan will be reviewed at a meeting of the Scheduling Committee during the week of June 26, when the time is allocated for all facility development work during the July 8-11 period.
- E99-118 has been scheduled on a “best effort” basis. It will be run during the period July 13-31 inclusive if (and only if) the transition between E89-009 and E93-038 is going according to plan and running the experiment will not delay the start of E93-038. Details have been documented in a memo to the collaboration.
- For the first week of the summer 2000 down we will be carrying out tests to determine the maximum reliable operational energy for the accelerator. For Saturday and Sunday, August 5 and 6, Hall A will be closed to provide a beam dump for high beam power tests at high energy.
- For E93-038 running, which begins with commissioning efforts on September 8, we will promise to deliver the 30 mA and try to deliver as much as 50 mA from the strained cathode. This will, of course, depend on both the capability of the polarized source and the ability of the experiment to run with the higher luminosity. If this is possible, we will "split the difference" with the collaboration on the P2Q associated with any delivered P2Q above that associated with 35 mA @ 75% polarization (the beam current approved by the PAC and the polarization we can deliver with confidence). They will receive half the advantage in the form of higher net charge than originally scheduled, but the other half will be used to reduce the total days of beamtime for the experiment, permitting us to begin the changeover to the next experiment sooner and/or to run portions of a single-arm experiment or carry out beam development activities, thereby increasing throughput in Hall C.
- On October 5, 2000 the APS/DNP meeting will be held in Williamsburg. As part of that meeting there will be a general tour of the experimental facilities at Jefferson Lab. We anticipate that roughly a shift of beam operations will be lost on this day to permit the tour to take place in an orderly and safe manner.
- For the run starting November 3, we will attempt to set up the linac for an energy gain of 1.134 GeV/pass, implying energies of 5.734 GeV for Halls A and B and an energy of 2.331 GeV for Hall C. This higher energy provides significantly better polarization to all three halls (worst case loss of polarization is 11%, rather than the 15% at the 1.113 GeV setting listed on the schedule). However, running at this higher energy will depend on the success of our energy upgrade efforts during the summer. If things are going very well, we will push further (to a linac energy gain of 1.155 GeV/pass, where the polarization loss is reduced to 7% in the worst case, and 5.840 GeV beams are provided to Halls A and B with 2.375 GeV to Hall C.
- The run starting April 6 is our first run at 6 GeV. If necessary, the beam energy will be reduced to keep the beamtime losses due to rf trips under 10%.
Additional General Information on Operations and Scheduling Constraints
The accompanying schedule is fixed for the nine-month period April 2000 thru December 2000 and tentative for the following six months. Priorities have been assigned as "firm" for the period of the schedule that is fixed; the tentative priorities set for the January-June 2001 period will be reviewed in September, when the schedule for that period becomes fixed. As noted earlier in this memo, the operation of polarized beams in more than one hall puts severe constraints on our ability to change beam energies.
The Meaning of Priority on the Accelerator Schedule
Generally, the assignment of priority to a hall means that the identified hall will have the primary voice in decisions on beam quality and/or changes in operating conditions. We will do our best to deliver the beam conditions identified in the schedule for the priority hall. It will not, however, mean that the priority hall can demand changes in beam energy that would effect planned running in the other halls without the consent of the other halls. Of course, final authority for decisions about the unplanned changes in machine operation will rest with the laboratory management.
The operation of more than one hall at Jefferson Lab substantively complicates the interaction between the experimenters and the accelerator operations group. It is in the interests of the entire physics community that the laboratory be as productive as possible. Therefore, we require that the run coordinators for all operating halls do their best to respond flexibly to the needs of experiments running in other halls. The run coordinators for all experiments either receiving beam or scheduled to receive beam that day should meet with the Program Deputy at 7:45 AM in the MCC on weekdays, 8:30 AM on weekends.
To provide some guidance and order to the process of resolving the differing requirements of the running halls, we have assigned a "priority hall" for each day beam delivery has been scheduled. We outline here the meaning of priority and its effect on accelerator operations.
The priority hall has the right to:
- require a re-tune of the accelerator to take place immediately when beam quality is not acceptable
- insist that energy changes occur as scheduled
- obtain hall access as desired
- request beam delivery interruptions for experiment-related operations such as Mott measurements of the beam polarization or pulsed operation for current monitor calibrations, temporarily blocking normal beam delivery to all halls. These interruptions shall be limited by a sum rule - the total time lost to the non-priority hall(s) due to such requests shall not exceed 2.5 hours in any 24-hour period. It is, of course, highly preferred that these measurements be scheduled at the morning meeting of the run coordinators whenever possible, and coordinated between halls whenever possible.
When the priority hall has requested a re-tune, if the re-tune degrades a previously acceptable beam for one of the other, lower priority running halls, then the re-tune shall continue until the beam is acceptable to both the priority hall and the other running halls that had acceptable beam at the time the re-tune began.
Non-priority halls can:
- require that a retune of the accelerator take place within 2.5 hours of the desired time (it will nominally occur at the earliest convenient break in the priority hall's schedule)
- require access to the hall within 1 hour of the desired time (again, it will nominally occur at the earliest convenient break in the priority hall's schedule)
- request Mott measurements in the injector within 2.5 hours of the desired time (it is preferred that this be scheduled at the morning meeting of the run coordinators and coordinated between the running halls whenever possible).
The ability of non-priority halls to request retunes and accesses shall be limited by a sum rule - the total time lost to the priority hall due to such requests shall not exceed 2.5 hours in any 24-hour period. (To facilitate more extended tuning associated with complex beam delivery, with the agreement of the run coordinators for all operating halls, the sum rule may be applied over a period as long as three days, so long as the average impact is less than 2.5 hours/day.) In the event that two non-priority halls are running, the 2.5 hours shall be split evenly between them in the absence of mutual agreement on a different split.
During operations in which the thermionic gun is being used as the electron source, when a non-priority hall needs changes to the accelerator state (re-tuning, access, etc.), then all halls currently receiving beam need to agree on the timing of the change, and the shift leader for the priority hall should contact the crew chief to make the formal request. (The upgrades to the PSS and MPS system, together with the three-laser drive, eliminate the need for this constraint during normal operations using the polarized electron source. However, it may be necessary to reinstate it on a temporary basis in situation such as a laser failure in which we are forced to operate the polarized source in a non-standard manner.)
- can negotiate with other halls, and with the Accelerator and Physics Division for changes in scheduled energy changes (either direction)
Initial Tune-up of New Beams:
- Normally one shift is set aside for tune-up whenever a new beam setup is being tuned (for unusual beam setups more time may be scheduled explicitly for tuning at the discretion of the scheduling committee). It is understood that beam tune-ups shall always be done in the order in which the accelerator operations group believes will minimize the total time needed to tune all scheduled beams (i.e., the "priority hall" beam is not necessarily tuned first). In the event that obtaining the new beam setup requires more than the scheduled time, the Accelerator Program Deputy is authorized to spend up to one additional shift of tuning in an effort to deliver all scheduled beams instead of just the "priority hall" beam.
- Note that the setting of the Wien filter, which determines the polarization orientation in all halls, is NOT affected by the hall priority assignment. For two-hall operation we will always optimize the figure of merit for the two running experiments by setting the Wien filter to a value that results in identical longitudinal polarization components for the two halls. For three-hall operation we set the Wien angle to a value that minimizes the differences between the hall polarizations (by minimizing the dispersion) so long as this scheme does not result in a reduction of the "sum of squares" figure-of-merit by more than 2% compared to the optimum figure of merit as determined by summing the squares of the polarization provided to all halls scheduled to receive polarized beam. If minimizing the dispersion results in a loss of more than 2% relative to the optimum figure of merit, we will revert to our earlier algorithm of setting the Wien filter to maximize the overall figure of merit. In all cases involving polarized beam delivery the setting of the Wien Filter shall be fixed throughout the running period unless all parties scheduled to receive polarized beam agree to a different setting.
Finally, any change in the accelerator schedule that has implications for running beyond one week and/or is not agreed to by the run coordinators for all affected experiments and the accelerator program deputy must be discussed and confirmed at meetings to be held (as required) each Tuesday and Friday afternoon at 4:00 in the office of the AD for Physics.
Facility Development Time
Experiments that do not get beam when scheduled, or which are unable to obtain the data required in the scheduled period due to problems with accelerator and/or experimental equipment availability will not be able to request a schedule slippage. However, the experiment may re-apply for additional beam time to complete the experiment at a later date. To facilitate the timely completion of experiments via this process, a period of about one week every few months has been put into the schedule for Facility Development. This time will be awarded by competition between experiments needing to complete data-taking, preparatory tests for future experiments, and testing new capabilities of the experimental equipment. This allows the schedule to be more rigidly adhered to (this has been a clear request from all users) but provides a degree of flexibility for unforeseen circumstances (this is, after all, an experimental program and things do not always go according to schedule). The schedule for the Facility Development periods will be determined at a meeting of the Scheduling Committee to be held one week before the start of the period. Requests for use of this time should be addressed to the Committee.
The schedule includes maintenance/development periods of 11 shifts every three weeks. They begin at 8:00 am on the day scheduled (nominally Monday). The initial half shift will be used for machine development work, focusing on studies of the beam transport lines to the halls. This implies that it may be necessary to keep one or more halls closed for this half shift, but all the halls may be opened after 12:00 noon.
It will be expected that the Physics ARMs will assist in opening the halls at this time. The rest of the day shift will be spent on diagnosing machine problems with the beam, to improve our ability to fix them the next day on the first try. This will be followed by a two shifts of Injector studies, with some RF work done in parallel. Two shifts on Tuesday will be devoted to maintenance, followed by six shifts of machine development and beam restoration. It is expected that the halls will be locked up by 8:00 am on Thursday so that the beam can be properly tuned in each hall line. Beam will then be re-established to the experiment(s) by 12:01 A.M. on Friday morning. The details of the schedule are outlined in the table at the end of this section.
The machine development time will be used to prepare new experimental set-ups (such as polarization, non-standard energies,
three-beam operation etc.) needed for the immediate future as well as preparatory work for higher energy operation. On a few
occasions the maintenance period has been slipped a day in order to provide uninterrupted completion of a scheduled sequence of
measurements within an experiment. We cannot, however, eliminate or drastically reschedule these maintenance and development
Machine Maintenance/Development Schedule
Week 1 of three-week cycle
06:00 Rad Service
|Hot Checkout by Ops (no beam)
|Restore Accelerator (Halls locked)||Start Physics|
Software priority 12:00 - 20:00
12:00 Restore Injector
MD on Hall lines
|Swing||Injector||Lock-up when work complete||Accelerator
23:00 Lock Halls
|Legend: Physics Running; Halls Locked for Accel. Use|
Weeks 2 & 3 of three-week cycle
- A major block of time for Maintenance and Machine Development will be scheduled for 11 shifts every three weeks, rather than 9 shifts every two weeks, our present schedule.
- The first four hours will be spent doing MD that may require beam to the halls.
- The halls will be open for experimental equipment maintenance from 12:00 on Monday through 23:00 on Wednesday.
- A designated period of time is provided for pre-maintenance diagnosis with beam (AES Group, Beam Physics & Instrumentation, and others) so that the maintenance time can be utilized effectively.
- Monday Swing and Tuesday Owl will be assigned to the Injector for the foreseeable future.
- There are two shifts for maintenance on Tuesday. It is anticipated that mechanical installations will start early and be finished around 6 PM. To avoid interference, the Software Group will have priority from 12:00 – 20:00, and the AES Group will have priority before 12:00 and after 20:00.
- The Wednesday Owl, "Hot Checkout by Ops," means that:
- System Owners need to write Hot Checkout procedures to be used by Ops.
- System Owners will be required to be physically present during Hot Checkout until procedures are provided to Ops.
- These procedures will be the basis for troubleshooting and repair documentation.
- Systems found to be defective will usually be fixed on the Wednesday Day Shift although major problems may have to be addressed immediately.
- Wednesday morning is available for completing installations and for final repair of systems found to be defective during Hot Checkout.
- The accelerator will be restored starting 12:00 on Wednesday, continuing through Thursday Owl. Some additional Machine Development may occur during these shifts.
- Restoration of beam to the halls will be done on Thursday Day and Swing shifts. This will include Machine Development on the hall beamlines, which would benefit from more dedicated time.
- On the weeks when no major maintenance is scheduled, 4 hours will be assigned on Tuesday morning. This will be used for recovering RF cavities to maintain a high active cavity inventory, and for tests of Beam Applications that would profit from frequent, short tests.
For holidays shown on the schedule (such as Thanksgiving) the beam will be shut down at ~noon on the last day shown as beam delivery (e.g. Wednesday noon before the Thursday Thanksgiving holiday). Beam operations for physics will be resumed at 8 AM on the first day after the holiday shown as beam operations, with the first shift devoted to beam restoration (i.e. it will be treated as initial tune-up of a new beam from the point of view of operations).
Energy Constraints on Multiple Hall Operations
The standard constraints for the different energies in the three halls during multiple hall operation are reiterated here for your information. The RF separators are able to extract one beam after each pass or, alternatively, to deliver beam to all three halls after five passes.
Therefore, it is always the case that:
- All three beams can have the same energy only on the fifth pass.
- No two halls can have the same energy, except on the fifth pass.
- Unusual beam energies in one hall will sometimes preclude multiple beam operation and impose shutdowns on the other halls, unless one or more of the other halls can also use a commensurate, unusual energy.
Polarization Constraints on Multiple-Hall Operations
A technical note covering all combinations of 2-hall polarized beam running is available (TN 97-021). Tables of ideal energies for two-hall operation and optimal energies for three-hall operation are available at the url:
You can also determine the dependence of the polarization in all three halls on the Wien filter angle for the actual settings of the accelerator.