ATTENDEES: S. Benson, G. Biallas, C. Bohn, D. Douglas, E. Feldl, K. Jordan, G. Krafft, C. Murray, G. Neil, C. Rode, M. Wiseman

Decisions/Comments:

D. Douglas reports that the error budget is defined and is being documented. No show stoppers. Diagnostics and correction systems defined and are being studied.

Report from the vacuum meeting:

Dillon-Townes/Parkinson/Murray - Defined the vacuum levelregions (currently proposed) for the machine and defined bake out regions. Strawperson vacuum specification being generated.

Dillon-Townes/Murray - Continuing to define all the transport discontinuities for B. Yunn's impedance/ion trapping analysis.

Dillon-Townes/Parkinson - Proposed plan to develop and fabricate vacuum chambers to meet schedule:

1. Injector dump chamber.

2. Recirculating dump chamber.

3. Up & Down beam chicane chambers.

4. E. & W. Arc Chambers, plus all return bends.

Biallas - Discussed the support, mounting, and alignment of vacuum chambers in the magnet. Proposed incorporating the mounting and alignment accomodations in the design of the magnet.

Action Items:

L. Dillon-Townes/C. Murray/B. Yunn - Maintain latest layout/ define the vacuum tube at all discontinuities, refine impedance analyses and write the Tech. Note. Definition of discontinuities in process.

C. Bohn - Establish a clean statement of the energy range of the machine. Status: Need help from Biallas/Harwood to plot cost vs. maximum energy for the magnetic optics. Division Leadership Group wants to see this data. Presentation to M7 set for tomorrow, June 21. New power supply stability and resolution assessment by W. Merz lead to simplification of the coil design and magnetic measurement process. for upgraded dipoles

D. Douglas - Check if the existing QJs can be used in the new injection line. C. Bohn will request getting the official Injector DIMAD published.

G. Biallas - Get the BT contracts signed. Contracts needed to be changed to new DIMAD configuration. No action.

T. Siggins/K. Jordan - Review proposed Shielded Viewers for vacuum construction properties. T. Siggins reviewing the drawings.

G. Biallas - Start definition of a girder for the wiggler, diagnostics and quad telescopes that maintains position of the elements within 50 µm (0.002 in.) during change-out of the wiggler. Meeting held. Minutes are attached.

L. Harwood - Determine if placing additional dipole(s) or temporarily substituting a stronger dipole at the first dipole of the dump chicane after the cryomodule is the best method of bending pulsed 42 MeV beam into the dump during cryomodule phasing. No action.

G. Biallas/L. Harwood - Provide a good value for field enhancement factor for the style of magnets we are anticipating. Verify the K value of 0.45 that D. Douglas uses in his optics calculations. Prototype dipole is being made.

C. Bohn - Have B. Yunn establish the vacuum specification for the remainder of the vacuum system using the criteria of ion trapping. No news

G. Biallas - Examine the categories on the Web and propose alterations. No action.

C. Bohn - Have B. Yunn examine the impedance effects of a 4 inch wide pipe in the optical chicane area. C. Murray to provide cross sections.

W. Merz - Determine from the actual response of power supplies with respect to jitter, short term drift and long term drift. Analysis written. Attached to the minutes.

G. Biallas - Construct a Prototype Reverse Bend. Drawings being sent out for bid.

E. Feldl - Construct and test a Prototype Sparse Lamination Quad. Quad assembled with NP prototype coils . Actual coils in process. Damaged board in CAMAK module in the Magnet Measurement Stand is being repaired (2 weeks ) or may have to be replaced by a new one from the vendor (6 weeks)

New Action Items :

M. Wiseman - Thermal analysis of the 45 MeV Dump for 30 kW & beam scraper analysis for 45, 79 and 200 MeV. P. Kloeppel assigned.

G. Neil - Find out if the mirror mounts can fit and function within proximity of the optical chicane dipoles

New Action Items for the Vacuum Meeting:

L. Dillon-Townes - Assess the pumping and power supplies required near the dumps in order to maintain the vacuum at the beam line at the 10-8 level.

L. Dillon-Townes - Propose how we do differential pumping.

New Action Items from the Diagnostics/Commissioning Meeting:

none

Completed Action Items:

G. Biallas - Define the trim quad for start of engineering design. No progress. Dropped. Not on present critical path.

C. Murray - Layout the Optical Chicane Bends in a the proposed 4 inch beam pipe configuration with fully upgradable coils. Complete.

Attachments:

This is a brief summary of the meeting held to discuss how the beamline elements around the IR Demo wiggler should be supported and aligned. Some discussion also arose about how to measure the optical resonator mirror spacing to an absolute accuracy of better than 100 µm.

Requirements: The elements to be supported around the wiggler are as follows:

1 Wiggler

2 OTR viewers on the beamline

3 OTR viewers in the wiggler vacuum chamber

2 BPMs

4 type QA quadrupoles

The OTR viewers in the wiggler vacuum chamber must be supported independently of the wiggler so that the wiggler may be remove and reinstalled without losing the alignment of the viewers. The quadrupoles, the OTR viewers and the wiggler must be aligned as accurately as reasonably possible along a straight line. All the elements must hold their position to an accuracy of 100 µm transversely over several months of operation.

Discussion: It was suggested that the wiggler be referenced off of the support for the wiggler OTR viewers so that it could be removed and reinstalled without losing the alignment.

Although individual girders are easy to align and we have a great deal of experience in using them it was generally agreed that the potential differential drift in several stands of differing designs would lead to changes in the relative positions of the beamline elements over time. It was also noted however that the elements would probably have to be aligned in place in addition to being aligned on the girder in an alignment area. The stands which mount the individual elements on a long girder must be matched as carefully as possible so that they do not lead to relative drift with temperature. The girder would be mounted on heavy duty cartridges. The total weight of the loaded girder should be on the order of 2 tons.

Two options were discussed for a long girder design. One way to go is to use a 12 foot long optical bench. The cost of such an option should be around $6k. The other option is to build a girder out of steel ourselves. W. Oren had some ideas of designs which may be cheaper that were used at SLAC. He also mentioned that they sometimes use a grout with a low coefficient of thermal expansion in girders, but that it would be quite difficult to use in this case since the girder must have holes for the OTR viewers.

The issue of how elements would be attached to the girder was discussed. The possibility of using shims was discussed. If the surface of the girder was reasonably flat one could just mount the elements on the girder with shims and then only adjust the horizontal position using pushers. It was noted that this would make realignment quite difficult, especially if the vacuum chamber were already installed. If adjustable elements were used one should try to use cartridges since they are well characterized. G. Biallas suggested using them upside down and just mounting the cartridge heads on the girder.

The BPMs do not need to be positioned accurately since they will be calibrated against the quadrupoles. W. Oren suggested defining their position with respect to the quads so that they are stable with respect to the quad center.

One of the critical design issues is the effect of temperature on the mounts and elements. This should be looked at very carefully since it will be the dominant cause of drift in beamline position. The effect of the LCW water temperature and the production of temperature gradients in the tunnel must also be considered.

Optical resonator mirror spacing: A long discussion was held on the topic of determining the separation between the mirrors of the optical resonator. Two possible options are available. We would use an HP interferometer or a Micon measuring device. Both use lasers to gauge distance. The critical design issue in either case is how the prisms are referenced from the mirror surface. An ideal way is to use the mirror socket itself to hold the prism. The prism must then have a double sided mount with both sides very accurately measured with respect to the prism center. The issue then arose of where to put the Micon instrument. This detail still has to be resolved. Using the HP interferometer would require the construction of a rail to transport the prism from mirror to mirror. W. Oren had some ideas of how to do this but it is not clear how much effort is involved.

The Box Power Supply specifications have in general called for a total Envelope Of Uncertainty of 10 parts per million (PPM) of rated full scale output capacity. This envelope is the sum of all contributions to output error (line, load, thermal, drift, etc.). Each individual contribution is not specified explicitly in PPM, but instead is defined as a contributor to the output error while other influence parameters are held constant and the defined variable is adjusted over a specified range. This relieves the manufacturer from performing a multiple variable test but requires him to design with sufficient care such that the arithmetic sum of errors does not exceed the total specification under a reasonable estimate of potential operating conditions. It also allows him to allocate the actual level of contribution of each error source in a way in which he is comfortable. Therefore, the error due to, say, the thermal variations likely to be well below the 10 PPM range over the specified operating range. The same is true of the other influence parameters. In actual practice, the variation of all influence parameters over their entire specified ranges simultaneously (or at least during an 8 hour period) is highly unlikely, but still should

For our 66 kW, 220 Amp, 300 Volt power supply the 10 PPM specification results in a total envelope of current uncertainty of 2.2 milliamps. I have reviewed both test data from the manufacturer and data taken by CEBAF on several of the delivered 66 kW supplies. The data shows that these supplies have a variation of 3-6 PPM over an 8 hour period and less than 2 PPM over 1 hour. The caveat is that the test conditions and procedures are not well documented nor are the test instruments described. The measurements appeared to have been made at 90-100% of rated output in all cases. Also the tests seem to have been made with all influence factors in a quasi-stable or un-monitored state (i.e. temperature relatively constant, line voltage at the mercy of the power company and un-monitored, etc.).

In actual operation, it is unlikely for the supply to experience the full range of influence variation ever, let alone over an 8 hour period in the FEL building. With this in mind, what kind of performance can we expect from the supplies? It seems reasonable to expect less than a 1 milliamp variation (4-5 PPM) in output current during an 8 hour period. A short term transient disturbance ( caused by the a line voltage change, for example) may cause the error to be larger for a brief time but should be corrected by the power supply control loop current regulator and would not cause a problem as discussed in yesterday's meeting. Repetitive disturbances will be unlikely to occur and will have to be addressed as they arise. Problems of power supply ripple should be negligible. The output voltage ripple into a resistive load is less than 100 PPM. Load inductance, skin depth and eddy current effects will reduce this value to less than 1 PPM of current ripple. I believe that we can expect the 1 milliamp of long term variation (8 hrs.) to occur over the entire operating range of the output with the possible exception of outputs below 5-10% of full scale (due to potential non linearities). Since the variations during steady state operation are due to both random and systematic drifts of the electronics (gain and offset), they will generally be independent of excitation current once the power supply warm up period is over.

For periods of longer than 8 hours the variations are harder to quantify without actually performing a test. I would guess that these variations should remain on the order of a few milliamps over something like a week's time, with stable operating conditions, independent of output current level. Beyond that time period it gets even more difficult to predict the supply performance. Absolute current variation for a given set point probably cannot be guaranteed without frequent calibration checks. Even then one may be suspicious of the calibration instruments.

The bottom line is that I believe that the 220 amp rated power supply will likely have variations of 1 milliamp over any 8 hour period and 2 milliamps over a period of a week, independent of the output current. It would not surprise me to find 10 milliamps or more for a year. The beam opticians will have to answer as to whether this is an acceptable situation. If you wish to see the test data or have me present it at the meeting to justify these conclusions, let me know.