Jefferson Lab > Physics
Privacy and Security Notice

All Staff Memos

Date: October 31, 2000
To: Distribution
From: Larry Cardman and Andrew Hutton for the Nuclear Physics
Experiment Scheduling Committee
Subject: Accelerator Schedule: October 2000 - December 2001

Schedule

Attached is the accelerator operations schedule for the period through December 2001. The overall operations continue to be constrained to a level of approximately 30 weeks/year as a result of the laboratory’s operating budget level for FY2001.

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, Dennis Skopik 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 of 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.

There are three unusual aspects to this schedule. First, the previously released "tentative" schedule for January-June of 2001 and some details of the previously-released "firm" schedule for now through the end of 2000 have been modified to provide additional time for the just started Madey/Kowalski GnE experiment in Hall C. There was a rupture in the target cell used for this experiment just as final preparations were underway for commissioning. Repairs and a thorough review of the target failure resulted in a loss of one month of planned running. Since this experiment is a major installation effort and a one-time installation, it was decided to take the unusual step of adjusting the run schedule to restore the lost beamtime. Remounting the experiment at a later date would have simply been too inefficient. We regret any inconvenience these changes may have caused researchers who made plans based on the previous schedule. Second, 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 April 2001. This shift was made to ensure that E93-038 received its allocated beamtime and so two major installation experiments (E93-038 in Hall C and eg1 in Hall B) could complete data-taking before the down. The latter will allow us to overlap the reconfiguration of the halls with the accelerator down. Third, we have not included facility development periods during this run period because of the unusually long experiments that are scheduled to run. However, there will be time available during the running period that will be available for testing detectors, etc. Contact the appropriate hall leader for more information if you wish to request development time. There has been one, two-day period (8/30-31) set aside for an energy calibration study with all three halls slated to receive the same, 5-pass beam energy to continue our efforts to inter-calibrate the energy measurement systems in the halls and understand their systematic errors.

This is the seventh schedule with substantial polarized beam operations. 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. Details on the constraints associated with polarized beam operation are discussed in a note at the end of this memo.

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.

Accelerator

Tests of 6 GeV operation were carried out in August 2000. While the accelerator briefly reached 6 GeV, 107 μA, the RF trip rate was extremely high and would not have been acceptable for physics running. In addition, there were many klystron failures (one per day of the test) due to running them at a higher voltage to obtain more power. A series of action items have been established, and another 6 GeV test has been scheduled in April 2001. Until then, the accelerator will be operated for physics at up to 5.7 GeV, a compromise between reaching new physics and achieving acceptable availability.

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: "unpolarized" beam up to 130 μA has been delivered to Hall A while high polarization beam was delivered to Hall B at 5 nA. Typical values for the "feed-through" 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 μA-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 μA-hours were delivered from the polarized guns. Unfortunately, the production of high polarization (strained) photocathodes is not yet reliable, and we have been experiencing difficulties with procuring cathodes with both high polarization and high quantum efficiency. Alternate vendors are being investigated.

During January, a test run was conducted with a new Ti:sapphire laser, which delivered ~400 μA of high polarization beam. The final version of this laser will allow this current to be more than doubled. This laser was installed during the August shutdown giving us the ability 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 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 three-week maintenance cycle that was started last year has proven to be a considerable improvement. In the present running cycle we will try extending the time between full (12 shift) maintenance periods even further – to roughly once per month. We will be switching back and forth between the 3-week cycle and an even longer, 4-week cycle that we hope will result in even higher availability. During the 4-week cycle periods the (now monthly) maintenance/ development cycle remains the same, but the weekly, non-invasive maintenance periods will be extended from 4 to12 hours every Tuesday (7am - 7pm). This cycle offers improved opportunity for accelerator and injector related maintenance, and should result in even higher availability for physics. The details are provided below in the section on Maintenance/ Development for reference.

Hall A

Since the last schedule was released, Hall A completed successfully three experiments: E89-044, E93-049, and E91-011. E89-044 (Epstein/Kuss/Saha/Voutier) performed selected studies of 3He through electro-desintegration at high momentum transfer. E93-049 (Ent/Ulmer/Van den Brand) studied the reaction 4He(e,e'p) 3He in the quasi-elastic region via polarization transfer. After completing these two experiments, the cryotarget system was switched from Helium to Hydrogen operation. Experiment E91-011 (Frullani/Kelly/Sarty) then took data to investigate the N-∆ transition via polarization observables.

Hall A was shutdown during August and September 2000 to swap the detector packages between the two Hall A spectrometers. The "new" hadron spectrometer is now able to reach 4 GeV/c in preparation for experiment E99-007 late in 2000. The new data taking cycle started late September with experiment E97-111 (Templon/Mitchell), a systematic probe of short-range correlations via 4He(e,e'p)3He. The experiment is running well and will be completed shortly.

The firm Hall A schedule continues with E99-007 (Brash/Jones/Perdrisat/Punjabi), the extension to Q2 = 5.6 (GeV/c)2 of the GpE/GpM ratio measurement via polarization transfer. Experiments E94-104 (Gao/Holt) and E98-108 (Baker/Chang/Frullani/Iodice/Markowitz) will follow in early 2001. E94-104 will study the fundamental process γn ® pp in 2H and 4He. E98-108 will perform Kaon electro-production measurements including an L/T separation up to Q2 = 3 (GeV/c)2.

After completion of E98-108, Hall A will use the April shut down to remove the cryogenic target system and install the polarized 3He target system required by experiments E99-117 (Chen/Meziani/Souder) and E97-103 (Averett/Korsch). E99-117 will carry out precise measurements of the neutron asymmetry An1 at large Bjørken x while experiment E97-103 will search for higher twist effects in the neutron spin structure function gn2 (x,Q2).

With respect to the tentative experimental schedule for the later half of 2001, the E94-107 (Frullani/Garibaldi/LeRose/Markowitz/Saito) collaboration successfully completed their second readiness review in late August 2000. Following this review, it is our intention to begin the installation of the septum magnet required by this experiment in early September 2001. E94-107 will perform a high resolution 1p-shell hypernuclear spectroscopy. That installation will begin September 4, 2001, presuming that the collaboration and the laboratory can meet the intermediate milestones outlined in the report of the second readiness review committee. It is then our tentative plan to follow this experiment with E97-110, the low-Q2 (forward angle) extension of E94-010, measuring the Q2 evolution of the GDH sum rule. This will permit us to spread the "overhead" of the septum installation over two experiments.

Hall B

Since the last schedule release Hall B completed the 3rd e1 run (polarized electrons on hydrogen and deuterium targets, 15 experiments mainly from N* excitations). The e5 run (electrons on deuterium and hydrogen target using a double target cell) is a precision measurement of the magnetic form factor of the neutron and was completed successfully. This was followed by experiment E94-016 (Rubin), a non-CLAS experiment to measure rare phi decays using a high energy photon beam. The experiment was completed before the summer shutdown.

Currently, the second part of the eg1 run group (polarized electrons on polarized hydrogen or deuterium) is taking production data for 3 experiments. The run is scheduled to be completed in March 2001. Energies from 1.6 to 5.7 GeV have been scheduled for this run. After the accelerator shut down in March/April the g8 run group (linearly polarized photons on hydrogen target) will take data for 2 experiments to study vector meson production in and above the resonance region. This will be followed by a short period of final g6 running (photon beam on hydrogen).

The tentative part of the schedule in the second half of 2001 has data taking for the four experiments in the new e1-6 run group (polarized electrons on hydrogen targets at ~6 GeV) to study high-Q2 N* excitations and deep virtual vector meson production.

Hall C

Since the last schedule was released, Hall C has completed the first run of the hypernuclear spectrometer system (HNSS) E89-009 (Tang/Hungerford). E89-009 was the third major installation experiment in Hall C. The reconfiguration for the fourth major installation experiment E93-038 (Madey, Kowalski), a measurement of the neutron electric form factor, has been completed and running has commenced. E93-038 will not be completed until April 2001. As mentioned above, the duration of this run was extended to recover from problems associated with the recent failure of the Hall C cryotarget, permitting the full dataset to be accumulated without the need to remount the experiment. After the completion of E93-038 the hall will again be reconfigured 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 collaborations have identified a set of kinematic running conditions that will permit the same neutron detector blockhouse location to be used in 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) is tentatively scheduled to begin dedicated installation in the new year after E93-026 has been removed. We will reevaluate that date during the March 2001 scheduling meeting, folding in information from the annual (DOE/NSF) progress review of the project, JLab Hall C readiness reviews, and the meeting of technical milestones agreed upon by the laboratory and the G0 collaboration. The initial run of G0 (for commissioning and initial data taking) will take place as early in 2002 as possible consistent with the installation schedule. We are planning to use the September 2001 break in accelerator operations to pre-install as much of the G0 apparatus as possible. Following the Spring 2002 run of G0, Hall C will most probably run a significant string of shorter experiments prior to the next major G0 data acquisition run. Our goal is that a transition to or from G0 running should take less than a month, minimizing the impact of this experiment on other running in the hall.

Information about the Schedule

The accompanying revised schedule is fixed for the nine-month period October 2000–June 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 last half of 2001 (and the tentative schedule for the first half of 2002) will be released in April, 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.

  1. 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.
  2. Energies listed in the schedule for the halls receiving polarized beam are the actual, delivered energies; they include the energy of the injector.
  3. 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.
  4. 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.
  5. 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.
  6. 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. When the polarized beam energy is being changed in only one hall (e.g. a "pass change") then that hall should measure beam polarization by the end of the first shift of production running. Further, if the change in settings of the Wien filter are substantial, all three halls should measure and report beam polarization by the end of the first shift of production running with the new setup.
  7. For E93-038 running we promise to deliver 30 μA and try to deliver as much as 50 μA 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 μA @ 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.
  8. 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 2.332 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 past summer, and it may be necessary to back of in the maximum energy.
  9. In April 2001 we will carry out our second major set of 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.
  10. The "switchover" between teardown of E93-038 and the installation of E93-026 is nominally listed as April 30. Of course, the two activities will be coordinated throughout the transition period between the running of the two experiments.
  11. The septum installation scheduled to begin on September 4 will take place presuming that the collaboration and the laboratory can meet the intermediate milestones outlined in the report of the second readiness review committee.

Additional General Information on Operations and Scheduling Constraints

The accompanying schedule is fixed for the nine-month period October 2000 thru June 2001 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 affect planned running in the other halls without the consent of the other halls. Of course, final authority for decisions about 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:

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:

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 a single, 1500 MHz laser is being used to drive the electron source for all 3 halls, 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.)

All Halls:

Initial Tune-up of New Beams:

Polarization:

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.

Maintenance/Development

The three-week maintenance cycle that was started last year has proven to be a considerable improvement. In the present running cycle we will try extending the time between full (12 shift) maintenance periods even further – to roughly once per month. During the upcoming year we will be switching back and forth between this cycle and an even longer, 4-week cycle that we hope will result in even higher availability. During the 4-week cycle periods the (now monthly) maintenance/development cycle remains the same, but the weekly, non-invasive maintenance periods will be extended from 4 to 12 hours every Tuesday (7am - 7pm). This cycle offers improved opportunity for accelerator and injector related maintenance, and should result in even higher availability for physics. The details are provided here for reference.

3-week Maintenance/Development Cycle

For the standard, 3-week schedule, we have 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. At least one hall will be available for such activities, if needed, and more halls will be made available by prior agreement as necessitated by the program of activities planned. For maintenance periods that follow a Monday holiday (and we have tried to schedule as many as possible following a holiday to minimize the number of times we recover the machine), the machine will stop operations for experiments at 12 noon on the Thursday to allow the machine development work to be completed before shutting down for the holiday.

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 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 (i.e. Thursday midnight). 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 periods.


Machine Maintenance/Development Schedule – 3 Week Cycle

Week 1 of three-week cycle
Monday
Tuesday
Wednesday
Thursday
Friday
Owl Physics Injector Hot Checkout by Ops (no beam) Restore Accelerator

(Halls locked) 		Start Physics
06:00 Rad Survey

Maintenance

Software priority 12:00 - 20:00

Injector check-out 18:00-20:00

Lock-up when work complete 		06:00 Open

Maintenance/Final Repairs
Day MD
(Halls Locked)

 		Restore Halls
(Halls locked)

MD on Hall lines 		Physics
12:00 Diagnosis 12:00 Restore Injector

Accelerator

23:00 Lock Halls
Swing Injector Restore Halls
(Halls locked) 		Physics
Legend: Physics Running; Halls Locked for Accel. Use

Weeks 2 & 3 of three-week cycle
Monday
Tuesday
Wednesday
Thursday
Friday
Owl Physics

 Physics

 Physics

 Physics

 Physics
Day Physics RF Recovery/MD

12:00 Start Physics		 Physics Physics Physics
Swing Physics Physics Physics Physics Physics

Notes:

  1. A major block of time for Maintenance and Machine Development will be scheduled for 11 shifts every three weeks.
  2. The first four hours will be spent doing MD that may require beam to the halls. At least one hall will be available for such activities, and more halls will be made available by prior agreement as necessitated by the program of activities planned.
  3. The halls will be open for experimental equipment maintenance from y12:00 on Monday through 23:00 on Wednesday.
  4. 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.
  5. Monday Swing and Tuesday Owl will be assigned to the Injector for the foreseeable future.
  6. 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.
  7. The Wednesday Owl, "Hot Checkout by Ops," means that:
    1. System Owners need to write Hot Checkout procedures to be used by Ops.
    2. System Owners will be required to be physically present during Hot Checkout until procedures are provided to Ops.
    3. These procedures will be the basis for troubleshooting and repair documentation.
    4. Systems found to be defective will usually be fixed on the Wednesday Day Shift although major problems may have to be addressed immediately.
  8. Wednesday morning is available for completing installations and for final repair of systems found to be defective during Hot Checkout.
  9. The accelerator will be restored starting 12:00 on Wednesday, continuing through Thursday Owl. Some additional Machine Development may occur during these shifts.
  10. 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.
  11. 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.

4-week Maintenance/Development Cycle

The new, 4-week cycle of the schedule includes maintenance/development periods of 11 shifts every four weeks. As can be seen below, the 11-shift cycles have the same structure as the maintenance/development periods of the standard 3-week cycle. However, the weekly, non-invasive maintenance periods will be extended from 4 to 12 hours every Tuesday (7am - 7pm). This cycle offers improved opportunity for accelerator and injector related maintenance, and should result in even higher availability for physics. The details are provided here for reference


Machine Maintenance/Development Schedule – 4 Week Cycle

Weeks with long maintenance periods
Monday
Tuesday
Wednesday
Thursday
Friday
Owl Physics Injector Hot Checkout by Ops (no beam) Restore Accelerator

(Halls locked) 		Start Physics
06:00 Rad Survey

Maintenance

Software priority 12:00 - 20:00

Injector check-out 18:00-20:00

Lock-up when work complete 		06:00 Open

Maintenance/Final Repairs
Day MD
(Halls Locked)

 		Restore Halls
(Halls locked)

MD on Hall lines 		Physics
12:00 Diagnosis 12:00 Restore Injector

Accelerator

23:00 Lock Halls
Swing Injector Restore Halls
(Halls locked) 		Physics
Legend: Physics Running; Halls Locked for Accel. Use

Weeks with no long maintenance period
Monday
Tuesday
Wednesday
Thursday
Friday
Owl Physics

 Physics

 Physics

 Physics

 Physics
Day Physics RF Recovery, Injector work, software tests, MD

12:00 Start Physics		 Physics Physics Physics
Swing 20:00 Physics Physics Physics Physics Physics

Notes:

  1. A major block of time for Maintenance and Machine Development will be scheduled for 11 shifts roughly every 4 weeks.
  2. The first four hours will be spent doing MD that may require beam to the halls. At least one hall will be available for such activities, and more halls will be made available by prior agreement as necessitated by the program of activities planned.
  3. The halls will be open for experimental equipment maintenance from 12:00 on Monday through 23:00 on Wednesday.
  4. 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.
  5. Monday Swing and Tuesday Owl will be assigned to the Injector for the foreseeable future.
  6. 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. Injector checkout should occur from 18:00 – 20:00.
  7. The Wednesday Owl, "Hot Checkout by Ops," means that:
    1. System Owners need to write Hot Checkout procedures to be used by Ops.
    2. System Owners will be required to be physically present during Hot Checkout until procedures are provided to Ops.
    3. These procedures will be the basis for troubleshooting and repair documentation.
    4. Systems found to be defective will usually be fixed on the Wednesday Day Shift although major problems may have to be addressed immediately.
  8. Wednesday morning is available for completing installations and for final repair of systems found to be defective during Hot Checkout.
  9. The accelerator will be restored starting 12:00 on Wednesday, continuing through Thursday Owl. Some additional Machine Development may occur during these shifts.
  10. 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.
  11. On the weeks when no major maintenance is scheduled, 12 hours will be assigned beginning 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.

Holidays

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:

  1. All three beams can have the same energy only on the fifth pass.
  2. No two halls can have the same energy, except on the fifth pass.
  3. 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

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. 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: http://claspc10.jlab.org/spin_rotation/

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. 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. Because of the limitations on beam energies associated with the different combinations of linac settings and numbers of passes delivered to the different halls, we 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 schedule 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 typically reduced to no less than ~90% 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.