All Staff Memo
|Date:||April 23, 1998|
|From:||Larry Cardman and Andrew Hutton for the Nuclear Physics
Experiment Scheduling Committee
|Subject:||Accelerator Schedule: April 1998 - June 1999|
Attached is a draft of the proposed accelerator operations schedule for the period through June 1999. The schedule will be available for user comment through the public discussion to be held Tuesday May 5, at 11 AM in room A110 of CEBAF Center. Written comments may be sent to the Committee care of Karen Hokansson (email@example.com). The final schedule will be released within one week of the May 5 meeting.
The schedule was generated by the Jefferson Lab Nuclear Physics Experiment Scheduling Committee. Committee members are: Larry Cardman and Andrew Hutton (Co-Chairmen), Roger Carlini, Bernhard Mecking, Kees de Jager, Claus Rode, Mike Seeley, Charlie Sinclair, and Will Oren. Nathan Isgur also 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. 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 second 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 (within ~20 degrees) polarization to three halls. (See the previous memo of the Scheduling Committee and 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 83% 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).
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 numbers 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.
Now that it has been demonstrated that the accelerator can deliver its nominal design current (200 μA at 4 GeV), the focus has turned to improving multiple-hall operation. In December 1997, the previously established availability criteria were met so that three-hall operation could be re-initiated, and the subsequent run was successful for all three halls. Considerable effort was spent in trying to coordinate current calibrations for Halls A and C, which also resulted in improved availability for everyone. In January, the PSS was modified to simplify access into one hall while delivering beam into the other hall(s) and this has also proved successful in practice. Accordingly, three-hall operation is now being scheduled regularly (except for the current limitations from the polarized gun mentioned below).
We have also made real progress with the beam energy, culminating in the delivery of 750 kW of 4.4 GeV beam for physics in December of last year. The behavior of the machine during that run, a detailed analysis of the results of the first round of in-situ helium processing, and ongoing studies of the performance limits of the superconducting cavities provide us with confidence that we can deliver 5 GeV beam, as scheduled, for the last week of August. Background stressing of the RF cavities is underway to get better performance limits and additional helium processing, to increase cavity performance, is scheduled for the July 4th weekend and January 1999. Delivery of 5.5 GeV beams is scheduled for April 1999. The maximum current will be limited by the acceptable RF trip rate and the target cooling. The values of beam current shown on the schedule are indicative of what should be achievable assuming that the helium processing scheduled for this summer and January 1999 is as successful as anticipated.
Polarized beams were delivered to Hall A and Hall C for experiments last year with currents as high as 75 μA, but with reduced availability as we learned how to use this new capability. A number of improvements were made to the source this winter, including: improved pumping in the anode-cathode gap; improved optics in the polarized gun; replacement of the "Z" spin manipulator with a (shorter) Wien filter plus solenoid; and the installation of a three-laser drive system. These modifications should improve source lifetime and operational flexibility. At this time we still do not have a lot of operating experience with this new set-up, so the availability is likely to be ~10% below our recent running for the first few months until we learn how to optimize operation.
Starting in July 1998 and continuing through December, we are committed to run with a high-polarization photocathode. Due to the low beam current demands of the experiments running in Halls B and C during this period, we would expect a very long cathode lifetime if we were only running these two halls. We will add Hall A operations during this period only on a best-effort basis. The maximum current delivered to Hall A will be restricted to a value such that the photocathode's operational lifetime is no less than 48 hours. If this cannot be done with reasonable current delivery to Hall A, then the Hall A running will be cancelled. This is indicated on the schedule by adding an asterisk to Hall A's priority during the period in question. Hall A will have priority in the normal sense if and only if photocathode lifetime stays above 48 hours; if this is not the case then Hall A operations will be cancelled until such time as the photocathode lifetime issues have been satisfactorily resolved, and the remaining running halls will have priority for normal operations in the order listed.
In view of the constraint outlined above on Hall A running during the last half of 1998 (roughly 4 months of running, after installation time has been subtracted), the new schedule gives Hall A priority on source use February-April of 1999. Hall C operations will be added during this period with the same constraint as above - that the maximum current delivered to Hall C will be restricted to a value such that the photocathode's operational lifetime is no less than 48 hours. If this cannot be done with reasonable current delivery to Hall C, then the Hall C running will be cancelled. This is indicated on the schedule by adding an asterisk to Hall C's priority during the period in question. Note that planned operations in early 1999 are an even tougher goal than those in late 1998, because we are asking the source to deliver a total of 40 μA from a strained cathode: 10 μA for Hall A, nA currents for Hall B, and 30 μA for Hall C.
A further caveat on the early 1999 schedule. If the Meziani/Cates spin structure function measurement scheduled for HallA from September 25, 1998 through the end of the year is not able to run (or to run to completion) at that time due to the operations constraint discussed above, then the schedule for the first half of 1999 will be revised to complete the experiment (or run it in its entirety) if strained cathode operations have improved enough to permit this to happen. This will impact both the tentatively planned 2nd polarized 3He target experiment of Gao (which will be postponed) and the running schedule in Hall C during this period. The details will depend on the demonstrated source capability and will be reviewed at the September meeting of the Scheduling Committee.
Starting in July 1998, we have increased the scheduled maintenance and machine development periods from 48 hours every two weeks to 72 hours every two weeks. This will provide 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 upgrade the weak components and to perform proper performance checks of the newly installed equipment (e.g. the CAMAC crates and modules have been in continuous service for over 7 years and desperately require preventive maintenance, a highly disruptive activity). Although this change corresponds to a reduction of one day per month in the scheduled beam to experiments, we anticipate the improved availability that will result from this effort will provide more delivered beam time for physics.
Since the last schedule was released, Hall A had a very successful measurement of the deuteron elastic form factor (Petratos, E-91-026). The "dress rehearsal" for the Souder/Finn parity violation experiment (E-91-010), which is aimed at studying the strange quark content of the sea, was also a success, and, based on the recommendations of the February 6 readiness review, the experiment has been placed on the "firm" schedule for 1999. The virtual Compton scattering experiment of Bertin (E-93-050) has just been completed and polarized electron running for E-91-010 has begun. The first run cycle of the Souder/Finn parity experiment has just begun. It will be followed by the proton electric form factor (GEp) measurement of Perdrisat (E-93-027) and the polarized 3He experiment (E-94-010) of Meziani on the q2 evolution of the GDH sum rule. Both the last portion of E-93-027 and all of E-94-010 will be run in the July/December period contingent on polarized source performance as discussed above. Note also that Hall A is "down" in July for the removal, mapping, and reinstallation of the arc dipole magnets that is necessary to prepare for the use of the arc to determine the absolute energy of the beam to high precision.
In 1999 Hall A running will begin with the study of 3He by Gao et al. (E-95-001), followed by the second half of the Souder/Finn parity violation experiment. Running of the second half of Souder/Finn will be contingent on a review of the results of the first run cycle just underway.
Hall B has completed basic commissioning of both the tagging system and the CLAS detector. The first physics run of CLAS (the e1 group - Dytman) began in December and ran through March 1998. It was followed by photon tagger commissioning and the g5 run group (Berman). The next run group, the g1 group (Miskimen), is scheduled for April and May. This will be followed by the g6 group (Marchand), which will run until the end of June 1998.
Following the April 9 readiness review for the eg1 group, the start of that run group was delayed for a month from the earlier (preliminary) version of this schedule in order to provide adequate time for the target to be ready for installation. The installation of the CLAS polarized target is now scheduled to begin at the end of July (coincident with the start of chamber repair efforts) and continue through August 18. The gap in the schedule created by the delay of the start of eg1 will be filled by a two week run of the g1 group and a drift chamber repair cycle (which will be completed by the end of the polarized target installation). The actual transition date between g1 and eg1 may be delayed further if the target is not fully ready for installation by the end of July. The remainder of 1998 will be used for eg1 (Kuhn) running. Tentatively scheduled for 1999 in Hall B are runs of the e1, e2, and g2 groups.
The pion form factor measurement (E-93-021, Mack) was completed at the end of 1998, with help from the successful re-inauguration of 3-hall running. It was followed by a major rework of the Hall C cryotarget to adapt it to the needs of the pion electroproduction experiment of Jackson (E-91-003), which was scheduled to begin running in February, 1998. Because of difficulties with the helium target and poor accelerator availability, the experiment was only partially completed. The job of mounting the polarized deuterium target for the neutron form factor measurement (E-93-026) began in April. E-93-026 is the second major installation experiment to be run, and it will use beam for the remainder of calendar 1998. At that time the polarized deuterium target must be removed from the pivot to honor a commitment to return it to SLAC.
The first half of 1999 is tentatively scheduled to begin with the extension of the Holt photodisintegration experiment to higher energy (E-96-003). This experiment was originally scheduled for 1997, but was postponed as part of the cutback of operations to only two halls. The measurement of the longitudinal and transverse contributions to the nucleon resonance region (Keppel, E-94-110) has been split into two parts to optimize the overall physics program in view of the constraints associated with polarized beam operation. The first of these will come in the middle of the Holt photodisintegration experiment and the second will follow E-91-007 (Milner), a measurement of the nuclear and momentum-transfer dependence of quasi-elastic scattering at high-momentum transfers.
In Hall C we have promised to give the "major installation" experiments advance notice (of at least one year) of their anticipated start date. As indicated in the previous release of the schedule, it is our intention to mount the HNSS in the second half of 1999, and execute experiment E-89-009 (Hungerford); this will be the third major installation experiment. Before the March, 1999 meeting of the scheduling committee (which would place the experiment on the firm schedule) the collaboration must pass a formal readiness review. 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 February 1999 if they want to keep their place on the schedule.
As noted in the last release of the schedule, we tentatively plan to run the last of the Hall C "big four" major installation experiments, a second measurement of the neutron electric form factor (E-93-038, Madey), in the second half of the year 2000. This late run start should permit the use of beams with both high polarization and high current, resulting in a significantly improved measurement of GEn. A final decision on this plan will be made as part of the March, 1999 scheduling cycle.
Information about the Schedule
The accompanying revised schedule is fixed for the seven-month period April - December 1998 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. This will be the rule for this and all future schedules. The firm schedule for the first half of 1999 (and the tentative schedule for the second half of the year) will be released late September or early October, following the meetings of the scheduling committee in that month.
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 hall; e.g., 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 "yes" 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 periods of scheduled three-hall operation with polarization.
- When polarized beam is provided at a new energy, the first shift of polarized beam operation will be used to verify polarization in the halls.
- The electricity will be off for repairs in the Test Lab, EEL, and CEBAF Center May 23-25, 1998. Arrangements will be made to keep the Computer Center on line.
- The Hall A run schedule shows two days of 1.833 GeV beam during the period from 8/14 to 8/24. This energy cannot be allowed to "slip" without the mutual agreement of all run coordinators as delay will bring it into conflict with the planned startup of the eg1 run at the same energy.
- During the period late August - December, 1998 we are committed to run with a high-polarization photocathode. Due to the low beam current demands of the experiments running in Halls B and C during this period we would expect a very long cathode lifetime if we were only running these two halls. We will add Hall A operations during this period on a best-effort basis. The maximum current delivered to Hall A will be restricted to a value such that the photocathode's operational lifetime is no less than 48 hours. This is indicated on the schedule by adding an asterisk to Hall A's priority during the period in question. If Hall A running has been cancelled, the ability of the source to deliver the necessary beam will be reviewed periodically as experience warrants, and running started in the hall as soon as we have confidence that we can do so within the constraint of >48hour operational lifetime.
- Based on experience to date we anticipate no difficulties with the delivery of 5 GeV beam as scheduled to begin in the last week of August. However, a final decision will be made early in August 1998 after we have had the opportunity to evaluate the impact of high polarization and multiple-hall operations on accelerator availability. If availability without the additional stress of high-beam energy operation has not been adequate, then the maximum accelerator energy will be dropped back to a value that provides reliable operation.
- If the Meziani/Cates spin structure function measurement scheduled for Hall A from September 25, 1998 through the end of the year is not able to run (or to run to completion) at that time due to the operations constraint discussed above, then the schedule for the first half of 1999 will be revised to complete the experiment (or run it in its entirety) if strained cathode operations have improved enough to permit this to happen. This will impact both the tentatively planned 2nd polarized 3He target experiment of Gao (which will be postponed) and the running schedule in Hall C during this period. The details will depend on the demonstrated source capability, and will be reviewed at the September meeting of the Scheduling Committee.
- In view of the constraint outlined in note 8 above on Hall A running during the last half of 1998 (roughly 4 months of running, after installation time has been subtracted), the new schedule gives Hall A priority on source use February-April of 1999. Hall C operations will be added during this period with the same constraint as above that the maximum current delivered to Hall C will be restricted to a value such that the photocathode's operational lifetime is no less than 48 hours. If this cannot be done with reasonable current delivery to Hall C, then the Hall C running will be cancelled. This is indicated on the schedule by adding an asterisk to Hall C's priority during the period in question. If Hall C running has been cancelled, the ability of the source to deliver the necessary beam will be reviewed periodically as experience warrants, and running started in the hall as soon as we have confidence that we can do so within the constraint of >48hour operational lifetime.
- The second major run of the Souder/Finn parity experiment, tentatively scheduled for April-June 1999 in Hall A is contingent on the success of the initial run now in progress. The results of the first run will be reviewed on or before September 1, 1998, and a final decision on the Hall A program for April-June 1999 will be made at that time.
- Based on experience to date we anticipate no difficulties with the delivery of 5.5 GeV beam as scheduled to begin in April, 1999. However, a final decision will be made early in March 1999 after we have had the opportunity to evaluate the impact of the final helium processing and operational experience at higher energies. If availability without the additional stress of high beam energy operation has not been adequate, then the maximum accelerator energy will be dropped back to a value that provides reliable operations, and the highest energy running planned for Holt's experiment will have to be postponed
Additional General Information on Operations and Scheduling Constraints
The accompanying schedule is fixed for the nine-month period April 1998 - December 1998 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 last six-month 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 7:30 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 wheneverr 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 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)
- can 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)
- can request Mott measurements in the injector with 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.
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. (Note that we anticipate that upgrades to the PSS and MPS system, together with the installation of the three-laser drive for the polarized source, will reduce and eventually eliminate the need for this constraint.)
- can negotiate with other halls, and the Accelerator and Physics Division for changes in scheduled energy changes (either direction)
Initial Tuneup of New Beams:
- Normally one shift is set aside for tuneup 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 tuneups 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.
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 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.
As noted above the maintenance/development periods on the schedule have been increased from two to three days every two weeks. We have also changed the timing of these periods. They will now 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. 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.
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.
- Non-standard energies in one Hall will normally preclude multiple beam operation and impose shutdowns on the other Halls, unless one or more of the other Halls can also use commensurate, non-standard beam energy.
We have demonstrated an ability to run low-current beams to Hall B without a higher energy "witness" beam, so the constraint listed in previous scheduling committee memos for Hall B operation has been lifted.
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; the problem is considerably more complex due to the many constraints that must be fulfilled.
As noted earlier, starting in July 1998 the schedule includes one additional day during maintenance/development periods. One of the major motivations for this change was to provide the roughly 3-day period necessary for a complete cathode changeout (involving opening the gun, swapping the cathode, baking the gun to restore the vacuum quality, and activation of the cathode) should such replacements be necessary to achieve good source availability during running periods. Note also that when polarized beam is provided at a new energy, the first shift of polarized beam operation will be used to verify polarization in the halls.