# Presentation: 518525

## NSLS II Accelerator Systems

- S. Ozaki
- NSLS-II Accelerator Systems Advisory Committee
- April 23-24, 2007

- Activities Since the Last ASAC Meeting on October 2006
- Response to the Committee’s Recommendations

## Activities Since the Last ASAC Meeting

- DOE Lehman Review for CD-1 approval in December 2006:
- Overall accelerator configuration, design, and cost estimates supported as reasonable.
- Notable recommendations are
- Decide the placement of booster, hopefully in a separate tunnel.
- Consider use of room temperature RF cavities instead of superconducting cavities.
- As a whole, the review was successful and DOE is moving toward the CD-1 approval in May or June, 2007.
- With a hope of keeping the construction budget in the FY 2009 budget cycle,  the program office has advanced the schedule for the Lehman Review for CD-2 from spring 2008 to November 2007.
- The accelerator physics effort was shifted to work needed to define the footprint of the facility.
- Enhanced the effort to understand the beam stability issues.
- Began design of the “compact” booster and its placement in separate tunnel.

## NSLS-II Concept

_**NSLS-II Machine Concept**_
- New Electron Storage Ring
- Medium Energy (3 GeV)
- Large Current (500 mA)
- Superconducting RF
- Top-Off Operation
- DBA30 Lattice
- Ultra-Low Emittance (<1 nm)
- Damping Wigglers (21 – 56 m)
- Large Dipole Bend Radius (25 m)
- Provision for IR Source
- Three-pole wiggler x-ray sources

_**Selected Technical Challenges**_
- Lattice Design: dynamic aperture, energy acceptance
- Source Stability: vibrations, thermal issues, feedback
- Impedance Budget: Small gap (5 mm) ID tapers, etc
- Insertion Device: CPMUs, EPUs, SCUs(?)

## Injection System

- We received endorsement of the ASAC in its last meeting that the the proposed design of the injector with a low emittance (~10 nmrad), low power consumption (air cooled) booster ring injected by a 200 MeV linac in which a possible klystron failure can be tolerated. Such a solution has shown to be very reliable and economical to operate in a number of existing facilities.
- The DOE Lehman Review Committee, however, gave a strong recommendation to change the in-tunnel booster to a compact booster in a separate tunnel.
- The current booster design, essentially is an extension of the ALS booster built by DANFISK, circumference enlarged to 144 m to accommodate 3.6 GeV injection capability.
- Reference design of this booster is in progress at NSLS II
- In spite of a small ring, the injection linac is kept at 200 MeV to retain the possible klystron failure tolerance.

## CD-2 Lattice Candidate: Half-Superperiod

## CD-2 Storage Ring Lattice Development

- Further studies of the storage ring lattice continued with the goal of fixing the ring footprint by the end of April or early May.
- Careful optimization of the ID straights identified a need of 1.6 m for the transitions, gate valves, other vacuum components, and user BPM.
- Quartet of quadrupoles as well as Sextupoles on either side of ID straights was reduced to triplets.
- This has freed up space but reduced the flexibility of lattice tuning,
- The length saved by reduction was distributed to improve the performance of the ring as follows:
- Some of the flexibilities lost was restored by a small quadrupole in the center of the dispersion region,
- Space for 3-Pole Wigglers (active length ≤0.4m) was added just upstream of the dipole. With magnetic fields 2.5x the ring dipoles, this will serve as a source of dipole like radiation with higher critical energy > 6KeV,
- The ID straight lengths (Magnet to Magnet distance) were increased from 8 and 5m to 8.6 and 6.6m (Net ID length = 7 m and 5 m)

## 3-Pole Wigglers (3PW)

- Since they give no net deflection to the beam they can be added or removed at any time without resurveying the ring
- Insertion of 3PW’s will increase the emittance of the beam.  However, the growth of emittance (≤ 10%) is small enough compared to the advantage of having more hard X-ray beam line.
- These beamlines are suitable for transfer of existing dipole beam lines from the NSLS X-ray Ring to NSLS-II and operated with similar flux but >200x brightness up to the 12-15KeV energy region.
- In order to provide the best brightness the 3PW’s are place where the dispersion is smallest (i.e. close to dipole)
- This required placing a symmetric drift after the upstream dipole adding 0.8m to the cell even if only 0.4m is useable.
- Placing the TPW in the center of the dispersion region (like SOLEIL or ALBA) would have saved this doubling of the drift length but at the cost of more than 2x less brightness for the user beams.

## Storage Ring Magnets

- Development of reference design for lattice magnet began, particularly with an objective of establishing potential higher order multipole errors.  This is critically needed as the source of systematic error in tracking.
- A collaboration with IHEP Beijing is anticipated in this area of work
- A study of interferences between closely placed multiples and dipole and 3-Pole Wiggler is in progress.  It appears that the standard 15 cm separation will be acceptable.
- We have received a loan of spare quadrupole and sextupole magnets from SLS and SSRL
- These magnets are vital elements to characterize the magnet performances, and support our development of the vibrating wire alignment technology with the help of the Cornell Group.
- The new corrector scheme, a six coil system with four poles, was developed in a prototype is being built to test it performance and frequency response.

## Storage Ring Vacuum System

- Realistic space requirement for vacuum equipment (i.e. gate valves bellows, and pump) and heat absorbers was studied for a superperiod of the storage ring.
- A space of ~80 cm is needed on the both side of an insertion device for a transition taper, gate valve, and BPM.  This will reduce the effective length of the ID straight by 1.6 m
- Heat absorber for the 7 m long Damping Wiggler is with 2.5 mrad fun can be handled with relative ease.  Further study is needed in the case the Damping Wiggler is canted.
- Team of NSLS II have toured facilities available at APS/ANL and established a plan to use their facility of the major part of vacuum chamber preparation and cleaning, saving DOE a significnat amount of money

## Storage Ring RF System

- Taking all aspect of the pros and cons of the superconducting vs. room temperature system, we favor strongly the use of the superconducting technology for fundamental as well as harmonic cavities.
- Superconducting cavity is more suitable for a ring that requires a high level of stability
- Capital investment can be higher with superconducting technology, depending somewhat on which vender will be chosen, but the operating cost, even including the cryogenic plan, will be lower.

## Beam Stability Task Force

- _Beam Stability Workshop:_
- Stability requirement
- Settling and (natural and self-inflicting) vibration issues on the accelerator tunnel and beamlines and experimental floor
- Temperature stability
- Mechanical engineering consideration
- Magnet power supply and RF noise issue
- Closed orbit correction with slow and fast feedback
- External Participants brought
- Extensive experience and lessons learned:

- M. Boege (SLS/PSI)				J. Byrd (ALS/LBL)
- J. Chen (Taiwan)				Y. Dabin (ESRF)
- R. Hettel (SSRL/SLAC)  Chair		J. Jacob (ESRF)
- J. Maser (APS/ANL)				R. Mueller (BESSY)
- D. Shu (APS/ANL)				J. Sidarous (APS/ANL)
- O. Singh (APS/ANL)				C. Steier (ALS/LBL)

## Accelerator Systems Division Staffing

|  | Current (FTE) | MOU/Cont. Staff | Requisitioned | Prospect |
| --- | --- | --- | --- | --- |
| Scientific Staff | 10 | 1 | 1 | good |
| Mechanical Engineer | 4 | 4 | 3 |  |
| Mechanical Designer | 4 |  | 1 |  |
| Vacuum Scientist | 1 |  |  |  |
| Electrical Engineer | 1 | 1 | 2 |  |
| Electrical Designer |  |  | 2 |  |
| Pulsed Power Engineer |  | 0.5 |  |  |
| RF Scientist/Engineer | 1 |  | 2 |  |
| Controls Scientist/Engineer |  | 0.5 | 2 | good |
| Instrumentation Scientist/Eng | 1 |  | 2 | 1 good |
| Total | 22 | 7 | 14 |  |

- With formal recognition of the NSLS II Project, we began to have staff members dedicated to the Project since the beginning of FY 2007

- Notable Additions: F. Willeke from DESY: to arrive this summer as Director of ASD,
- George Ganetis (SMD), Dick Hseuh (CA-D), Erik Johnson (NSLS)

## Accelerator System Cost Estimate in k$as Presented for DOE Review

| WBS Description |  
Direct $ |  |  | Total Burdened & Escalated | Bottoms up Contingency |  | Total with Contingency |
| --- | --- | --- | --- | --- | --- | --- | --- |
|  | FTEs | Labor  | Material  |  | % | $ Value |  |
| Injection System | 103.2 | 11,721 | 16,231 | 34,133 | 28.8% | 9,837 | 43,970 |
| Storage Ring | 273.5 | 31,366 | 86,006 | 137,965 | 35.0% | 48,308 | 186,273 |
| Total | 376.7 | 43,087 | 102,237 | 172,098 | 33.8% | 58,145 | 230,243 |

- We plan to revisit the cost estimates as soon as the centralized schedule is established in May in preparation for the DOE CD-2 review in November

## Overall construction Schedule

## Response to Recommendations/Suggestions 1

- Discuss with the users the possibility of having smaller horizontal beta in some Insertion Device (ID) straights. It appears that a factor 10 reduction in horizontal beta should be possible and could have a dramatic impact on the micro-focusing beamlines, resulting in an image size a factor of 3 smaller.
*In principle, it should be possible to let individual straights have different optics even for a medium energy light source.  However, it would come with some sacrifice in the performance of the storage ring such as the momentum acceptance and Touscheck life time.  We also found that it would have been easier in the CDR lattice with the four quadrupoles since it had less impact on the tunes and emittance.  The CD2 lattice with three quadrupoles, which is tuned with smaller βx in the short ID (2.08 vs. 2.72 m), can still be made smaller but with some changes in tune, emittance and/or beta functions in long ID straights.  Further studies will be continued.*

## Response to Recommendations/Suggestions 2

- Increase the length of the space available for Insertion Devices. There are several roads that could be explored. One is to add short ID straight in some achromats with mini vertical beta, which will be ideally suited for high energy in-vacuum undulators with the ultimate smallest magnetic gap. Another one is to consider changing the quadruplet upstream and downstream of the ID to a doublet. In this respect there exist 3 GeV light sources which accommodate the variable extra focusing from IDs by retuning only a doublet.
*Two actions were taken in this direction.  *
*As recommended by ASAC, studies were made to change the quartet of quadrupoles on both sides of the ID straights with triplets.  For the CD-2 lattice, triplet scheme will be used but with an additional quadrupole at the center of the dispersion straight to improve the tunability. *
*A space was created in the dispersion straights (+40 cm in length) just up-stream of the second dipole of each sector (and the same space at the other end to maintain the symmetry), for insertion of 3-pole wigglers for hard X-ray beamlines.*
*The length gained by this change was distributed to increase the length of the ID straight, 3-pole wiggler space and the addition of space for the tuning quadrupoles.*

## Response to Recommendations/Suggestions 3

- Explore a more advanced and innovative design for the bending magnets with variable field along the length. We take note that, as has been presented in the presentations, to minimize horizontal emittance and energy spread while keeping RF power under control a low field has been selected for the bending magnets. Such low field dipoles with zero input dispersion could be redesigned with sections with higher and lower field with the objective of further reducing the emittance or saving circumference for a given emittance. This concept has been visited by several people in the past but never really implemented because the magnet design is generally too close to saturation. It is the opinion of the committee that the proposed lattice design of NSLS-II meets the best conditions to succeed in this direction.
*We considered the variable bend radius dipoles in the past and found that it could give at most a factor of ~2 decreases of the bare emittance of the ring. Unfortunately the optimal configuration indicates that the high field part is on the ID straight side of dipoles. This increases the energy of the dipole fan that overlaps the ID beam, making the separation of the ID beam harder.  Also increasing our dipole field would increase the radiation power, making the emittance reduction less effective. *

## Response to Recommendations/Suggestions 4

- The committee recommends looking at a larger energy acceptance beyond the proposed 3%.
*We indeed agree and will continue to address this consciously from the lattice point of view.  **However, for now we consider a 3% momentum aperture a conservative realistic goal; for a ~1.0 nmrad light source** *
*The superconducting RF cavity will not present a problem for larger momentum acceptance, having voltage headroom to handle momentum spread larger than 5%.*

## Response to Recommendations/Suggestions 5

- In view of the small emittance, the issue of beam stability has been recognized by the team as critical. A number of concepts for beam position feedback were proposed. The committee would advise the team to concentrate on SVD-based global feedback with a variable number of eigenvector corrections in order to minimize the missteering from malfunctioning beam position monitors. The committee discourages the use of multiple local feedback systems which may drive unstable orbit oscillations due to non-perfect closure of the bump as a function of frequency. The issue of integrating Xray beam position monitors in the loop should be carefully addressed in view of the large variety of IDs and the dependence of the position on ID gap which can be a complicated issue with EPU type IDs.  It is also suggested to have, in the baseline machine, regular Beam Position Monitors (BPM) at both ends of every ID straight section, rather than to wait for the progressive ID installation.
*Acknowledging the importance of the beam stability, the Beam Stability Task Force was organized at the beginning of this year.  The report of the Task Force was presented and discussed at the Beam Stability Workshop that took place on April 18 – 20, last week...  Sam Krinsky, who led the Task Force, will present the report of the Task Force, which addresses items on feedback discussed above.*

## Response to Recommendations/Suggestions 6

- An optimization of the non linear lattice as well as the study of a number of lattice error have already been performed. Such studies may have to be restarted if the linear lattice is changed (as suggested above). Simulations of lattice errors will need to be further developed including multipole magnet errors and coupling errors. It is recommended that injection efficiency studies continue with all field errors from the lattice as well as IDs with their reduced gap, nominal focusing and their associated multipole field errors, in order to verify the chosen beam stay clear apertures. A complete set of field quality specifications for the ring magnets and insertion devices should be developed early in the project, to be coupled with a magnetic measurement plan for quality assurance.
*We agree that these are very important issues, which are being worked on by our accelerator physics group. *
*Since the beam emittance of a compact booster will be larger than that expected from the in-SR tunnel booster: ~35 nmrad vs. ~10 nmrad, simulation for the injection efficiency including some of errors is in progress.  Results, so far, indicate that the emittance of ~35 nmrad that can be achieved by a booster with ~150m circumference, is acceptable.  *
*A detailed 3-D magnetic field calculation and estimation of higher harmonics and field errors is in progress.  Johan Bengtsson will cover this subject in detail at this meeting.*

## Response to Recommendations/Suggestions 7

- Considering the rather weak effect of extra damping wiggler above an initial number of 5 or 8, the committee is not convinced of the need of adjustable damping wigglers to compensate for ID gap configuration. In addition, an adjustable damping wiggler used in this way would be of limited use as a source for an x-ray beamline.
*Following this advice, it was decided to make all damping wigglers to be a fixed gap.*

## Response to Recommendations/Suggestions 8

- The committee takes note that the limited budget and resources may not allow the commissioning to take place with the full complement of damping wigglers and RF stations. The assumed number of damping wigglers and the associated lattice damping times were not consistent among the various presentations. The committee encourages the project team to clarify this point in a consistent fashion, with the goal of developing a baseline design with a horizontal emittance close to 1nm.
*The baseline configuration of the storage ring is as follows:*
*	**DBA30 with 783 m circumference*
*	**Emittance with no ID’s (Bare lattice): ~2.0 nmrad*
*	**Emittance with fifteen 3-Pole Wigglers:**	**~2.2 nmrad*
*	**Emittance with three 7-m long Damping Wigglers:**	**~1 nmrad*
*	**Two superconducting RF cavities each @ 270 kW,*

## Response to Recommendations/Suggestions 9

- No major concern on the proposed building infrastructure has been identified except some worry concerning the occupation of components in the tunnel and specifically the placement of the booster hanging from the ceiling above the storage ring.  The main worry is the installation and servicing of the beamline front-ends when the full hardware for the booster (magnet, pipes and pumps) as well as the cables and water hoses for the accelerator magnets are in place.  The committee takes note that some specific slab and roof arrangements has to be provided for the RF cavities of the Storage ring and Booster
*Following a strong recommendation of the DOE review committee, the booster has been removed from the storage ring tunnel and ratchet doors for personnel and light equipment access to the front ends are in the plan, we believe that we have mitigated the concerns expressed above.*

## Response to Recommendations/Suggestions 10 A

- Many members of the committee have a preference for a crane and removable roof with a booster supported on the inner wall of the storage ring tunnel (as made at SLS and planned for ALBA). Such a solution will give a tremendous benefit during the installation of the ring, booster and beamline front-end as well as beamline. The committee takes note that several recent facilities with tight budget have followed this approach successfully and is therefore not fully convinced by the cost argument raised during the presentations. The committee asks the project team to revisit this issue through more detailed engineering and consider the implications of the two choices in detail (to be reported at the next meeting of ASAC).
*A synchrotron light source facility can be successfully built and operated with a wide-area crane (as in ESRF) or without such a crane (as in APS).*
*Pros and cons of removable tunnel roof and building crane to service the storage ring components as well as experimental beam lines were studied.  *
*Some pros are:*
*Vertical access to the ring components and insertion devices for installation and removal after the roof beams are removed.  *
*Easier transportation and installation of hatches and some beam line components.  *
*Some cons are:*
*A wide-area crane would make a large vertical space of the facility unavailable for any other use.  For instance, power supply and instrumentation racks cannot be placed at their optimum locations on top of the storage ring roof.*
*A removable tunnel roof will make the tunnel structure non-monolithic, resulting in a less rigid tunnel structure which will reduce the overall vibration filtering effect of the structure.*

## Response to Recommendations/Suggestions 10 B

*However, the most significant of the cons is the overall cost increase as estimated by our conventional facility’s team as follows:*
*The overall cost impact is $36 million. The cost estimate assumes the following:*
*A minimum 20 ton bridge crane will be required due to the weight of the tunnel roof sections*
*A 20% increase in structural steel column cost to support the bridge crane*
*Added cost for the bldg foundation*
*Added cost for the ~50,000 SF of electrical equipment space displaced by the need to have an accessible tunnel roof *
*Added cost for pre-cast tunnel roof sections*
*Added cost for HVAC ductwork and piping that will now have to be routed out of the way of the bridge crane travel*
*Associated engineering, escalation and contingency*
*Also note that the need to maintain free bridge crane travel will complicate and increase costs for routing of experimental floor services to the hutches and **there will be a non negligible cost increase for longer cabling from power supplies in service building to the ring*

## Response to Recommendations/Suggestions 10 C

|   | Description | Quantity | Multiplier | Cost | Unit Cost | Total |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 20 ton Building crane  |   |   |   |   |   |
|   | crane | 1 |   | $100,000  |   | $100,000  |
|   | railing | 1 |   | $270,000  |   | $270,000  |
| 2 | Building frame |   |   |   |   |   |
|   | Steel columns |   | 20% | $910,799  |   | $182,160  |
|   | Foundation  |   |   |   |   |   |
|   | forms |   | 5% | $141,980  |   | $7,099  |
|   | placing concrete |   | 5% | $20,000  |   | $1,000  |
|   | footing concrete |   | 5% | $1,154,143  |   | $57,707  |
| 3 | Tunnel roof | 4,580  | 15% |   | $400  | $274,800  |
| 4 | Extra square feet for Electrical  | 50,000  |   |   | $350  | $17,500,000  |
| 5 | HVAC ductwork complexity |   | 20% | $5,055,283  |   | $1,011,057  |
| 6 | Piping complexity |   | 20% | 3,655,887  |   | $731,177  |
|   |   |   |   |   | Sub-total: | $20,135,000  |
|   |  |  |  |  |  |   |
|   | Added Engineering & Design and Inspection @ 15% |  |  |   |   | $3,020,250  |
|   | Escalation FY 10 @ 5% per year |   |   |   |   | $3,473,287  |
|   |   |   |   |   | Sub-total: | $26,628,537  |
|   | Contingency @ 35% |   |   |   |   | $9,319,988  |
|   |   |   |   |   | Total: | $35,948,526  |
|   |   |   |   |   | say | $36,000,000  |

## Response to Recommendations/Suggestions 10 D

*We also note that:*
*The beamline equipment is usually small in size and does not require such a crane. The main justification for a wide-area crane is that it would allow rapid installation or replacement of the storage ring girders and undulators.*
*Transportation of the girders and undulators within the ring takes a small fraction of the installation schedule that also covers survey and alignment, vacuum connections and bake-out. Moreover, the experience at the APS has been that the transportation time within the ring is in the range of 1-2 hours. *
*We note that the beamline equipment is usually small in size and does not require such a crane. The main justification for a wide-area crane is that it would allow rapid installation or replacement of the storage ring girders and undulator.  We also note that transportation of the girders and undulators within the ring takes a small fraction of the installation schedule that also covers survey and alignment, vacuum connections and bake-out.  Moreover, the experience at the APS has been that the transportation time within the ring is in the range of 1-2 hours.*
*Considering all of these issues, we have decided to stay with our original plan of not having the removable roof on the storage ring tunnel.*

## Response to Recommendations/Suggestions 11-12

- As civil engineering is most frequently on the critical path of a project, the committee recommends implementing a staged beneficial occupancy of the building infrastructure in order to squeeze the installation time.
*The CF construction will be divided into five pentants, and the construction plan calls for completing pentant by pentant with the interval of about 3 months, which is close to the time we estimate the installation of one pentant of the storage ring will take.  This allows us to proceed with the installation of the ring pentant by pentant, keeping pace with the completion of the conventional facility.*
- Only 10 to 11 people in the NSLS II project team are working on conventional facilities. This seems to be a rather low figure, as they will have to ensure tight coordination between building design and machine design requirements as both are developed.
*Since much of the construction service will be provided by the construction management firm under a contract, we believe this is a reasonable level of staffing for CF activities.  *

## Response to Recommendations/Suggestions 13 - 15

- The committee is pleased to learn that other buildings inside BNL will be made available to the project for all sort of preparation work.
*There will be a tour of these building this afternoon.** *
- Safety regulations are becoming increasingly restrictive with time. As a consequence the shielding type and thickness should be carefully studied and compared with other facilities in the world. The injection area is of particular concern and should be the object of specific reinforcement. The thickness of the ring tunnel roof must also be sufficient to allow access to equipment while the machine is operating. The committee requests a presentation on this topic at the next Meeting of ASAC.
*Presentation on this subject is scheduled during the morning of the second day.*
- The committee recommends the same regulated temperature in the tunnel and experimental hall to avoid long term drift.
*We believe that the long term drift is not an issue once equilibrium is reached.  Whether we will lower the tunnel temperature or not is a matter of economics and energy saving and further investigation will be made.*

## Response to Recommendations/Suggestions 16

**Injector   System **
- The committee is pleased with the proposed design of the injector with a low emittance, low power consumption booster ring injected by a 200 MeV linac in which a possible klystron failure can be tolerated. Such a solution has shown to be very reliable and economical to operate in a number of existing facilities.  The linac design looks solid and demonstrates sufficient redundancy.  The booster lattice looks robust.
*Although the original design of the injector system with low power and low emittance met with ASAC’s **favorable** evaluation, we have changed the injection system to have the booster in its own tunnel external to the storage ring.  This change followed the recommendation of the DOE review that expressed concern on potential interference in the installation and operation of the facility.  Even for a “compact” booster, we maintained the 200-MeV linac to tolerate possible Klystron failure.*

## Response to Recommendations/Suggestions 17 - 18

- The committee agrees with the proposed procurement strategy of purchasing of a turn-key system for the linac. Concerning the purchase of the booster, the committee believes that a stronger involvement of the technical staff will be beneficial and would encourage the project team to specify and purchase the booster by subsystems.
*Agreed:  The present procurement plan is as follows:*
*The 200-MeV 3 GHz linac: “turn-key” procurement*
*The complete booster system other than RF: “turnkey’ procurement*
*PETRA 500 MHz cavities: “loan” from DESY *
*RF power system: “turn key” procurement*
*Beam transfer lines: in house design, procurement, installation and commissioning*
- The committee requests to be presented more details about the supporting and alignment of the booster magnets.
*Since we have moved the booster out of the storage ring tunnel, the support and alignment of booster magnets will be by conventional way.*

## Response to Recommendations/Suggestions 19

**Bending Magnet and infra-red beamlines **
- The committee takes note of the proposition made to satisfy the infra-red user community by collecting infra-red radiation from inside a bending magnet. The committee suggests deepening this issue and consider both the core bending magnet and edge radiation in relation to the figure of merit of the beamline (spectral flux or spectral brightness, wavelength, polarization,...).
*The IR group states that both options are being considered depending on the wave length.  *
*A total of 10 infrared beamlines are planned, 5 in the far-infrared region and 5 in the mid-infrared region.*
*Far-infrared beamlines will require 93-mm aperture dipoles. To maintain symmetry both dipoles in a cell with a far-infrared beamline will be of 93-mm aperture, resulting in 10 large aperture dipoles.*

## Response to Recommendations/Suggestions 20

- The committee does not see the opening of the bending magnet gap from 35 to 60 mm on some or all bending magnet is a critical issue. Both strategies of a limited number of bending magnet with increased gap powered by one or a few additional power supplies or all magnets with increased gap are possible and no preference for one or the other emerged in the discussions.
*The magnet gap of 93 mm is required for far-IR beamlines, with corresponding increase in the height of the vacuum chambers.  Our concern is in the increase of ring impedance with several wide gap vacuum chambers.  Impedance calculation is being carried out but the progress has been slow due to the shortage of computer power.*

## Response to Recommendations/Suggestions 21

**Collective Effects**
- The committee is pleased to see that collective effects are already being investigated. The committee fully agrees that the longitudinal impedance be carefully controlled to prevent energy spread increase below the single bunch current of 0.5 mA. An increase of energy spread would result in a reduced and potentially fluctuating emission on the high harmonics of the undulator radiation.
- 	The committee encourages to further develop the study of the current threshold for the coupled bunch instability versus lattice chromaticity and determine the need or not as well as the specification of a bunch by bunch feedback.
- 	The committee believes that the broadband impedance from the Landau cavities should already be accounted.
*These are the issues that have been discussed in the stability Task Force and Workshop.*

## Response to Recommendations/Suggestions 22 - 23

**Mechanical Engineering and Vacuum System  **
- The vacuum system looks safe and benefits from extensive experience at the APS. One mm clearance between magnet and chamber looks small. The committee recommends that the magnet pole tip design be reviewed to allow this to be increased, alleviating unnecessary concerns about vacuum-induced stress.
*We have increased the clearance to 2 mm.*
**Magnet Power Supply**
- A sound approach is proposed.  It is important to consider the integration of the corrector magnet power supplies, beam position monitors, and data networking into a high-speed global orbit feedback system at an early phase of the project.
*Will be done*

## Response to Recommendations/Suggestions 24

**Insertion Devices**
- The presentation made was an excellent overview of up-to-date technology. The program appears suitably ambitious. It capitalizes on the competence already existing at NSLS.  The committee suggests to study in detail the dynamic aperture modifications computed from the precise 3D magnet design of the IDs and damping wigglers with particular attention to the pole width.
*The work is in progress in this area and the result will be presented in the next ASAC meeting in the early fall.  As an initial **installment**, a study on the effects of a 3-Pole Wiggler was done.  **While the obvious choice was to pursue the kick-map approach developed at the ESRF and supported by Radia, realistic modeling of the 3-pole wigglers turned out to be somewhat of a challenge; since kick-maps can only be computed for a full period.  So, eventhough the impact of the 3-pole wigglers is expected to be small, we decided to extend our model (Tracy-3) to support arbitrary 3D field maps for evaluation of the impact on dynamic aperture, emittance, etc.  And, for simplicity (and cross checks), we are also implementing a generalized Halbach basis with fitted coefficients.  Johan will cover this further.*

## Response to Recommendations/Suggestions 25

- Superconducting solutions have shown to work and meet the requirements of beam stability but are expensive. The committee suggests to watch the recent developments in term of room temperature HOM damped cavities.  The committee sees limited redundancy in the proposed klystron approach. While the committee recognizes that this approach constitutes a working solution, it recommends investigating an IOT based solution which would provide more redundancy and flexibility, and for which there exist more suppliers.  The committee recalled the requirement to optimize the waveguide to cavity matching under different ring current, cavity number and power conditions.
*We have surveyed both superconducting and room temperature options, including my visit to IHEP Beijing to see KEK-B cavities and discussions with Ernst Weihreter, the developer of the room temperature HOM damped cavity.  This survey and the discussions at the Beam Stability Workshop led us to the conclusion that a superconducting system will serve us better.  Detailed analysis will be given by Jim Rose.*
*As to the power source, we will continue to look at IOT amplifiers.  We note that we do not have to decide for another year or so.** *

## Response to Recommendations/Suggestions 26 - 27

**R & D**
- The committee supports the proposed R & D approach. It is the opinion of the committee that future upgrade of the facility will largely be based on IDs and it is therefore crucial that extensive competence is developed through R&D.
- The committee suggests, as a possible R & D effort to look into the development of solid state high power RF amplifiers.
*SOLEIL is using solid-state amplifiers, but at 352MHz. SLS has developed the same technology at 500 MHz. We will continue to look at these developments, but recognize that efficiency of solid-state amplifiers is ~50% efficient, ~60-65% for klystrons and 65-70% for IOT's. *
**Future Upgrade**
- If the electron energy is planned to be raised, shielding and heat load should be specified accordingly from the very beginning.
*Radiation shielding and higher heat load issue will be addressed for energy upgrade to 3.6 GeV and beam current upgrade to 600 or 700 mA.*

## Response to Recommendations/Suggestions28

**Budget, Manpower and Planning**
- The 108 M$  estimated capital cost for the linac, transfer lines, booster and  storage ring  looks 10 to 20 % too low in comparison with recently built facilities.
- The staffing also looks somewhat light. The committee takes note that the staffing and organization which were presented are the ones necessary only for the construction of the facility and not for the operation.
- A total 4 years construction time is short. The committee would recommend identifying long delivery items (building, linac, magnets,.. ) and convince DOE to proceed with their procurement ahead of time.
- The committee suggests the construction of a centralized master schedule that will be revisited from time to time as needed and will serve as a reference document for all groups participating in the project.
*We note the comments made above with appreciation.  A comprehensive and centralized construction schedule is being developed.  Also addressed is the streamlining of the WBS structure for the accelerator systems.  As soon as the centralized schedule is completed, we plan to revisit the cost estimates in preparation for the DOE CD-2 review in November.*