All Staff Memos
|Date:||April 27, 1999|
|From:||Larry Cardman and Andrew Hutton for the Nuclear Physics
Experiment Scheduling Committee
|Subject:||Accelerator Schedule: April 1999 – June 2000|
Attached is the accelerator operations schedule for the period through June 2000. As noted before, the overall level of operations has been constrained to a total of 30.5 weeks/year as a result of the laboratory's operating budget level for 1999.
The Jefferson Lab Nuclear Physics Experiment Scheduling Committee generated the schedule. Committee members are: Larry Cardman and Andrew Hutton (Co-Chairmen), Hari Areti, Roger Carlini, Bernhard Mecking, Kees de Jager, Claus Rode, 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 kind 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 also fed in 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 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 all the halls except Hall A, and the difference in Hall A was not enough to consider a separate scheduling constant for that hall alone. The final schedule was then reached by a series of compromises in running order within each experiment and between halls to work around incompatibilities.
This is the fourth schedule with substantial polarized beam operations. As is well known by now, 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 and all 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.
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 is reduced to about 89% of the nominal maximum available from the cathode (due to the angle at which the polarization vector is set relative to the beam direction in the hall in a compromise that optimized delivery to all halls). In all cases we intend to set the Wien filter to a value that maximizes the sum of the squares of the polarization provided to all halls scheduled to receive polarized beam. The standard section of this memo on "the meaning of priority on the accelerator schedule" has been revised to clarify this policy.
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.
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 drove some of the scheduling, and outline the broad program as planned.
This past year the accelerator has delivered high power beams to physics experiments (up to 750 kW was delivered for a period of weeks, split between Hall A and Hall C). The 5 GeV beam originally scheduled for August was successfully delivered in March to all three Halls. This was followed in April by successfully setting up the accelerator at 5.5 GeV, again delivering beams to all three Halls for experiments. At this time, the accelerator availability appears to be as good at 5.5 GeV as it has been at lower energies, but the trip rate is currently higher than it has been in the past. This can be expected to improve with time but the asymptotic limit is difficult to estimate at the moment.
There continue to be occasional problems with tails on the Hall B beam from the beams delivered to Halls A and/or C. The laser amplifiers used to illuminate the cathode were changed from CW to pulsed operation, which improved the situation, but the problem is still not definitively solved. Scrapers have been installed in the injector and are being commissioned and halo monitors under test. This continues to be a prime focus of attention.
The big success story this past year continues to be the polarized source. As previously announced, The bulk gallium arsenide cathode produced in excess of 35% polarization and up to 110 µA current. For the HAPPEX run, the helicity correlations were measured by the experimental group to be smaller than at any previous facility (position-helicity correlations averaged to < 2 nm, energy correlations < 10-8). The strained gallium arsenide cathode now produces polarization up to 75% and currents up to 50 µA delivered for months at a time to up to three Halls simultaneously. The present cathode lifetime is still too long to be estimated reliably; it is of order 10,000 μA-hours. We have now demonstrated that we can now deliver currents on this scale from high polarization photocathodes for long periods of time. Recent studies by the HAPPEX collaboration indicates that it will be possible to run their next experiment with the strained gallium arsenide cathode with the consequent improvement in statistics.
Separate lasers for each Hall are combined optically to provide independent control of the three beam intensities, and obtaining the desired spin orientation has been reasonably easy due to the availability of the fast Mott measurements in the injector. However, the detailed layout of the laser combining optics has been modified several times to minimize the cross-talk between Halls. The constraints of obtaining the correct polarization orientation in two, or three Halls influence the scheduling process. At present, and for the foreseeable future, this issue may reduce the polarization available on experimental targets to as low as 0.8 times the polarization of the beam at the cathode; for the present schedule we have managed to limit the polarization loss to no more than 11%.
We are continuing the 72 hour scheduled maintenance and machine development periods every two weeks. As noted when this cycle was instituted, it provides enough time to change out the cathodes and rebake the gun during the scheduled maintenance period when (and if) this is necessary. It is also part of a major push by the laboratory to increase the availability of the accelerator by providing enough time to perform desperately required preventive maintenance, a highly disruptive activity. Although this change corresponds to a reduction of one day per month in the scheduled beam to experiments, the improved availability that has already resulted from this effort has already provided more delivered beam time for physics.
Since the last schedule was released, Hall A completed a very successful run on the polarized 3He experiment (E94-010) of Meziani et al. on the Q2 evolution of the GDH sum rule. This was followed by an equally successful run for E95-001 (Gao et al.), an investigation of 3He structure and a measurement of GMn at modest q2. Following that experiment the polarized 3He target was removed from the pivot, and the standard Hall A cryotarget was installed to permit the second (and final) run of HAPPEX. This experiment is just underway.
The firm portion of the Hall A schedule begins with the completion of HAPPEX, which will be followed by the running of two photodisintegration experiments: E89-019 (Gilman/Holt/Meziani, denoted G/H/M on the schedule), which will measure proton polarization in the d(g,p)n reaction; and E94-012 (Gilman/Holt), which will measure photo-proton polarization in the H(g,p)p reaction. These two experiments are run "interleaved" because they require frequent energy changes and therefore provide real constraints on parallel running in other halls. Since there is substantial overlap between the collaborations carrying out these experiments, they are requested to coordinate their run plans and present a united front to the other halls. Just after the first portion of the photodisintegration experiments, we have conditionally scheduled a four-day run of E89-028 (Finn/Ulmer), which aims to measure polarization transfer in the reaction, which will provide a check on the assumptions of the Hall C experiment of Madey and Kowalski, which is aimed at a determination of GEn. E89-028 will be run so long as E89-019 and E94-012 have met their scientific goals for the running scheduled for the period 8/7/99 thru 8/22/99.
Following the completion of E89-019 and E94-012, Hall A will shut down for four weeks to install the high power helium cryotarget that will be used to run E89-044 (Saha/Epstein/Mougey, denoted S/E/M on the schedule), an experiment to study 3He through electrodisintegration at high momentum transfer, and then E93-049 (van den Brand/Ent /Ulmer, denoted B/E/U on the schedule), an experiment to study polarization transfer in the 4He(e,e'p)3H reaction in the quasi-elastic scattering region. These two experiments are being mounted at this time to take advantage of the helium refrigerator capacity that is freed up by the installation (and subsequent running) of the HNSS experiment (E89-009, Tang) in Hall C. (We cannot run high-power helium targets in one hall simultaneously with high-power hydrogen targets in another due to refrigerator limitations.) The first of these two experiments (E89-044) begins just before the end of the firm portion of the schedule.
The tentative portion of the Hall A schedule begins with completion of E89-044, followed by the running of E93-049. These are followed by the running of E91-011 (denoted F/K/S on the schedule), a high precision separation of the polarized structure functions in electroproduction of the Roper and delta resonances. The remainder of E91-011 will begin the first portion of the next schedule to be released.
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 first portion of the eg1 run (Kuhn), which used the new CLAS polarized target. This was followed in early 1999 running by the second portion of the e1 run group (Dytman). It will be followed shortly by the first run of the e2 group (Weinstein), which is the first CLAS data-taking on multi-nucleon emission from nuclear targets. The firmly scheduled portion of Hall B 1999 running begins with the g6 run group. The "Rad Phi" experiment (E94-016, Dzierba), which aims to measure rare radiative decays of the phi meson, will run parasitically during the entire g6 run, and has been given four days in a dedicated mode on the schedule to optimize the detector performance at higher beam fluxes than have been used heretofore in the hall. The firm portion of the schedule continues with runs of the g2, g1, and e5 run groups. The tentative portion of the schedule in Hall B (which begins in January 2000) includes runs of the g3 and e1 groups. These will be followed by the RadPhi data run, subject to their demonstrating to a readiness review that (based on data taken during their summer 1999 run) the experiment can meet its physics goals. The RadPhi experiment will complete its data-taking early in the next schedule to be released. We also here give the eg1 group, which requires a major installation effort, notice that we intend to re-install the CLAS polarized target and carry out more running for eg1 in the period immediately following the RadPhi experiment (probably in August 2000).
Since the last schedule was released, Hall C has been restored to conventional operations using the HMS and SOS spectrometers and the standard cryotarget. 1999 began with three days of running for E91-007 (Milner), a measurement of the nuclear dependence and momentum transfer dependence of quasi-elastic (e,e'p) scattering at large momentum transfer. This was followed by the extension of the Holt photodisintegration experiment to higher energy (E96-003), which is now underway. The remaining portion of the firm schedule for Hall C running includes further running on E91-007 (Milner), a down period for conversion of the Hall C cryotarget from the long (beer can) targets to the short (tuna can) targets in preparation for the next run cycle, and then the completion of E91-007. E91-007 was split into two parts to fit its beam energy needs into slots that were compatible with running in other halls. These experiments will be followed by a measurement of the longitudinal and transverse contributions to the nucleon resonance region (Keppel, E94-110), running for E97-006 (Sick), which is an investigation of the correlated spectral function and (e,e'p) reaction mechanism, conversion of the Hall C cryotarget from hydrogen to helium operation, and then running of the final portion of E91-016 (Zeidman), a study of the electroproduction of kaons and light hypernuclei.
The firm portion of the Hall C schedule ends with the beginning of the installation of the hypernuclear spectrometer system (HNSS) in preparation for the execution of experiment E89-009 (Tang). E89-009 will be run as the first Hall C experiment in the tentative portion of the schedule. However, to retain its place in the schedule for the start of the experiment installation, the collaboration must pass a final readiness review before the September 1999 meeting of the scheduling committee (which would place the execution of the experiment on the firm schedule). This review can be arranged through the hall leader, Roger Carlini, at the convenience of the collaboration, but it must take place no later than August 1999 if they want to keep their place on the schedule. E89-009 will be the third major installation experiment in Hall C.
With this release of the schedule we reaffirm our intention to run the second measurement of the neutron electric form factor (E93-038, Madey), in the second half of the 2000. This late run start will permit the use of beams with both high polarization and high current, resulting in a significantly improved measurement of GEn. This experiment is now tentatively scheduled to begin installation immediately following the removal of the HNSS (a process which begins in May 2000). To retain its scheduled installation start, E93-038 must pass a formal readiness review before the September 1999 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, Roger Carlini, at the convenience of the collaboration, but it must take place no later than August 1999 if the collaboration wants to keep its place on the long-range schedule.
As a further note on long-range planning, we indicate here our intention to reinstall the UVa/Basel polarized target in Hall C immediately following the running of E93-038. The E93-026 and E93-038 collaborations have identified a set of kinematic running conditions which 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 teardown 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 rotation of the SOS spectrometer. Current estimates of the schedule for the running of E93-038 would place the beginning of the polarized target re-installation in January 2001.
With this schedule release we encourage the E93-026 and E93-038 collaborations to investigate the feasibility of using the same neutron detector for both experiments, potentially saving additional installation and setup/checkout time. Between now and the September 1999 release of the tentative schedule for the first half of 2001, we will meet with the Hall C polarized target group to fully develop plans for additional running of E93-026 (GEn) and one additional experiment utilizing the target.
Information about the Schedule
The accompanying revised schedule is fixed for the nine-month period April 1999 - December 1999 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 2000 (and the tentative schedule for the second half of 2000) will be released late September or early November, 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 effected 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 (~70%) 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 periods of scheduled two- and three-hall operation with polarization. In all cases, the orientation of the polarization at the injector will be optimized to maximize the sum of the squares of the polarization delivered to all halls using polarized beam.
- When polarized beam is provided at a new energy, the first shift of polarized beam operation should be used to verify polarization in the halls. Unfortunately, many users have tended to skip this step in the interests of more running time, thereby risking significant periods of data-taking with incorrect polarization.
- Based on experience to date we anticipate no difficulties with the delivery of 5.5 GeV beam as scheduled. However, if the additional stress of high current simultaneously with high beam energy operation reduces availability to an unacceptable level then the maximum accelerator current will be dropped back to a value that provides reliable operations, and the running currents provided for Finn/Souder, Milner, Keppel, and g6 will have to be modified. If total current reductions are necessary, Hall B current will be maintained at nominal values, and both Hall A and Hall C currents will be reduced keeping the ratio of the currents (after correction for P2 effects for Hall A if appropriate) as listed on the schedule.
- Where "high" appears under polarization (4/15/99 – 5/28/99) we will make every effort to deliver highly-polarized electrons from a strained photocathode, but may be forced to install a lower polarization bulk photocathode if the combination of parity quality beam delivery and high current unpolarized delivery simultaneously with moderate current polarized beam delivery proves to be beyond the current state of the art of our injector.
- Beam time has been allocated to Hall C during the May 8-10 facility development period in order to permit Milner’s experiment to get the total amount of 5.5 GeV running required. This implies that machine development will not take place during that period, and that running in Halls A and or B during that period must use energies that are compatible with the linac setting used for Milner’s 5.5 GeV running
- The accelerator energy has been modified during this period to provide good polarization simultaneously to Halls A and B. During the sequence of runs scheduled for the period August 8 – 26 the Wien filter settings will be determined by applying the "standard rules" outlined in the section on polarization at the end of this memo.
- G/H/M is used to indicate Gilman, Holt and Meziani, the co-spokespersons for E89-019
- Finn/Ulmer (E89-028) will run as scheduled if E89-019 and E94-012 (Gilman/Holt and G/H/M) have met their scientific goals for the running period 8/7/99 thru 8/22/99. Otherwise, this period will be used by those two experiments as needed.
- On May 25, June 8, and June 22 we have scheduled accelerator tests (for 3 shifts) aimed at preparing the accelerator for running at 6 GeV.
- For the October and November polarized beam running, we will provide high polarization beam if experience with high polarization crystals indicates that we can reliably deliver the currents requested for these runs. If not, we will continue running with a thin GaAs photocathode.
- S/E/M is used to indicate Saha/Epstein/Mougy, the co-spokesmen for E89-044. The maximum beam current available to this experiment may be limited by available refrigeration power; it will have to be determined empirically at the startup of the experiment.
- The value of 0.6 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.
- B/E/U is used to indicate van den Brand, Ent, and P. Ulmer, co-spokespersons for E93-049. The maximum beam current available to this experiment may be limited by available refrigeration power; it will have to be determined empirically at the startup of the experiment.
- The scheduling of the RadPhi experiment for this period is conditional on the experiment passing a readiness review, as outlined in the Hall B comments of this memo.
- 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 5/25, 6/8, and 6/22 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.
- The scheduling of the GEn (E93-038) installation to begin during this period is conditional on the experiment passing a readiness review, as outlined in the Hall C comments of this memo.
Additional General Information on Operations and Scheduling Constraints
The accompanying schedule is fixed for the nine-month period October 1998 - June 1999 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 June-December 1999 period will be reviewed in March, 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
- to insist that energy change occur as scheduled
- to obtain hall access as desired.
- to request Mott measurements of the beam polarization, temporarily blocking normal beam delivery to all halls (it is 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 effected by the hall priority assignment. The Wien filter will be set to a value that maximizes the sum of the squares of the polarization delivered to all halls scheduled to receive polarized beam, and this setting 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 two months or so 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 three days every two weeks. They begin at 12:01 AM on the day scheduled (nominally Tuesday) - i.e. at midnight on Monday. The initial shift will be used for machine development work, implying that it may be necessary to keep one or more halls closed for that shift. This will be followed (nominally) by a shift of maintenance (generally the day shift on Tuesday), and then by seven shifts that will include, as necessary, additional maintenance, machine development work, and beam restoration. Beam will then be re-established to the experiment(s) by 12:01 A.M. on the day shown as the first run day after the maintenance/development period (nominally just after Thursday midnight). 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 periods.
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). A tech note on 3-hall polarized running is under development, as is a web-interfaced computer program for identifying optimum energies for different beam setups. 3-hall polarized running is considerably more complex due to the many constraints that must be fulfilled.