# Presentation: 163035

**LANL Wire scanner**
**Final Design Review**
**Los Alamos, Mar. 12, 2002**
**by Michael Plum**

*and Lisa Day, Matt Fagan, Dave Ireland, Ross Meyer, Chris Rose, Dave Sattler, Bob Shafer, Matt Stettler*

## Agenda

**Introduction -- M. Plum**
**Overview of the wire scanner system -- M. Plum**
**Mechanical design of the DTL/CCL actuator -- R. Meyer**
**Mechanical design of the SCL actuator -- R. Meyer**
**Wire scanner electronics -- C. Rose**
**Laser wire scanner -- R. Connolly**
**Committee deliberations**
**Committee outbrief**

## Review Committee

**Bob Webber, Chairman, FNAL**
**Jim Crisp, FNAL**
**Glen Decker, ANL**
**Ron Johnson, SLAC**
**Tom Powers, JLab**
**Marc Ross, SLAC (via e-mail)**
**Mark Wiseman, JLab**

## Overall design review process

**Preliminary Design Review**
**Respond to committee observations and suggestions**
**Final design review**
**Respond to committee observations and suggestions**

## Final Design Review Process

**Evaluate design against design criteria and functional requirements**
**Items to for committee to address**
- Assumptions
- Relevant calculations
- Options considered
- Interface requirements
- Manufacturing/ Procurement plan
- Actions taken from PDR to FDR
- Have the design criteria been met?
- Have the right analyses/ tests been done to support fabrication?
- Are there any “holes” from the PDR left unaddressed?
**LANL will consider committee’s feedback**
**LANL will respond to the committee’s written report**

## Charge to the committee

**Review the design**
**Categorize findings**
- Critical (potential “show stoppers”)
- Observations/ recommendations
**Consider key observations from audience participants**
**Give us an outbrief**
**Written report**

## Design review `scope

**Design Review Scope**
- DTL, CCL, and SCL actuators mechanical design and prototype performance.
- Electronics design and performance.
- Interface issues
- Schedule
**Areas covered by other reviews**
- MEBT actuator already reviewed.
- Actuators downstream of the linac covered by later reviews.
- Electronics for ring and RTBT covered by later reviews.

## Outline

**Locations of the wire scanners.**
**Action items from the preliminary design review.**
**Actuator accuracy requirements and measurements.**
**Wire signals.**
**Wire heating.**
**Interfaces.**
**Schedule.**
**Summary.**

## LANL diagnostics deliverables

**Injector**

**2.5 MeV**

**RFQ**

**1000 MeV**

**DTL**

**86.8 MeV**

- To
- Ring
- and TGT

**CCL**

- 402.5 MHz

- 805 MHz

**SRF, ß=0.61, 0.81**

**186 MeV**

- HEBT

- _MEBT_
**5 WS (elec. only)**
- 6 BPM (elec. only)
- 2 Sl&Col (act. only)

-   _DTL_
-  ** ****5 WS **
- 10 BPM
-   6 CM (p/u only)
-   5 ED/FC

-  _CCL_
**  ****8 WS**
- 12 BPM
-   2 CM (p/u only)
-   1 ED/FC

- _SCL_
**32 WS (16 elec.)**
- 32 BPM

-  _HEBT_
-  ** ****3 WS (dumps)**
- 22 BPM (elec. only)

- _RTBT_
- 1 Harp

- _D-plate (7.5 MeV)_
**1 WS**
- 3 BPM
- 1 CM (p/u only)
- 1 ED/FC
- 2 Sl&Coll emit
- 1 Phosphor screen
- 1 8 seg. halo scraper
- 1 Beam stop / F-Cup

**MEBT**

- _Key_
- WS = wire scanner
- BPM = beam position monitor
- Sl&Col = slit and collector emittance station
- CM = current monitor
- ED/FC = energy degrader & Faraday Cup

## DTL wire scanner locations

**1 ea. at the ends of DTL tanks 1 – 5.**
**Share beam box with ED/FC and CM.**

## CCL wire scanner locations

## SCL wire scanner locations

- SCL

## From the Preliminary Design Review...

**Action items from preliminary design review.**
**Recommendation – LANL, JLAB, and ORNL collaborators should determine whether or not any useful tests could be defined and carried out at the JLAB vertical test facility.**
*Response – It would indeed be illuminating to make some tests at the JLab facility. However, JLab has no plans to do so. The JLab stance is “any wire material making its way into the cavity will destroy the cavity performance and must be avoided.”*
**Recommendation – LANL, JLAB, and ORNL collaborators should very soon begin detailed specification of the processing, cleaning, and assembly steps for wire scanners that will need to be performed probably in a JLAB clean room.  It is important to identify if and how these procedures may drive design parameters.**
*Response – We agree. We have received drafts of the cleaning process, and we are working with JLab to determine its impact on the wire scanners.** The SCL actuator is now at Jlab for testing. *

## From the Preliminary Design Review...

**Recommendation – SNS management is encouraged, for the sake of efficiency, to explicitly state the extent to which direct halo measurement capability is or is not to be included in the baseline instrumentation...**
*Response – After many discussions with Linac and Ring physicists, we came to the conclusion that halo measurements are not necessary for the CD4 and the initial phase of intensity ramp up. The MPS people are also in favor of excluding the halo measurement from the present wire scanner system. If we need to measure the halo due to unforeseen physics at startup, then we require a separate system, which could have a substantially different interface to the MPS.*

## From the Preliminary Design Review...

**Committee Observation – The question was asked by an audience member whether the quantity and location of Linac wire scanners had been agreed upon.  Mike Plum answered in the affirmative and cited quantities of 5 in the DTL, 8 in the CCL, and 32 (minus empty cryomodule locations) in the SCL.  Quantitative beam physics justifications were not offered in support of the quantity and location requirements.**
*Response – It is true we do not have a complete set of beam physics justifications. We are working to remedy that. For example, a recent beam physics study recommended adding more wire scanners to the CCL to check the DTL to CCL match (D. Jeon et al.,”Transverse matching of CCL to DTL using the rms beam size from wire scanners.”) The same study also found that 7% accuracy requirement on the width measurement is sufficient to determine if the DTL is correctly matched to the  CCL. *

## Accuracy and placement requirements

**D. Jeon et. al., “****Transverse matching of CCL to DTL using the rms beam size from wire scanners,” SNS/AP Tech Note. **
- Calls for two more wire scanners in first CCL module, after segments 6 and 8, to measure match from DTL to CCL. Other wire scanner locations are sufficient to observe optics problems in the CCL.
- Specifies accuracy requirement for CCL wire scanners – must measure rms width to accuracy of 7% (i.e. rms of error distribution must be less than 7% of true rms beam width).
**DTL wire placement: wire scanner located at every possible location (beam boxes at ends of DTL tanks).**
**SCL wire placement: wire scanner located at every possible location (warm inter-segment regions).**
**Master spreadsheet of requirements for commissioning and tuning maintained by S. Assadi.**

## CCL wire scanner locations

- = new wire scanner locations

## DTL/CCL position accuracy measurement

**Measurements made with 4.3 kg weight suspended from shaft.**
**Worst case repeatability error was 0.051 mm, equal to measurement accuracy. **
**Largest deviation from straight line fit is 0.066 mm. **
**Wobble in ball lead screws (which will be removed in the next version) adds another 0.15 mm to horiz. and vert. signal wires.**
**Total position error is 0.18 mm. **

## SCL position accuracy measurement

**Measurements made at air pressure (worst case, but not much worse than under vacuum).**
**Maximum backlash observed was 0.20 mm.**
**Worst-case repeatability error was 0.038 mm, equal to measurement accuracy.  **
**Largest deviation from straight line fit (i.e. position accuracy) is 0.13 mm. **

## Width error vs. number of positions

**Model of errors in width due to number of wire scanner positions.**

- 40,000 particle PARMILA model of SNS at 7.5 MeV at D-plate wire scanner.  rms width = 0.180 cm.
- Absolute error = 2% of max.
- Relative error = 1%
- Gaussian fit to data.
- 12 positions corresponds to 1 sample per rms beam size

*error = abs[(true width) – (fitted width)] **+ (error in fit width)*

## Width error vs. position error

**Model of errors in width due to errors in accuracy of wire position.**
**Assume absolute error of 2% of signal at center of beam.**
**Assume 1% relative error.**

- 40,000 particle PARMILA model of SNS at 7.5 MeV at D-plate wire scanner.  rms width = 0.180 cm.
- Absolute error = 2% of max.
- Relative error = 1%
- 15 positions.
- Gaussian fit to data.

*error = abs[(true width) – (fitted width)] **+ (error in fit width)*

## Width error vs. position error – 1⁄2 beam size

**Same as previous slide, but beam one half as big. **
**Note that error is not linear in beam size. **

- 40,000 particle PARMILA model of SNS at 7.5 MeV at D-plate wire scanner.  rms width = 0.090 cm.
- Absolute error = 2% of max.
- Relative error = 1%
- 29 positions.
- Gaussian fit to data.

*error = abs[(true width) – (fitted width)] **+ (error in fit width)*

## Width error vs. position error – 1⁄4 beam size

**Beam one quarter as big. **

- 40,000 particle PARMILA model of SNS at 7.5 MeV at D-plate wire scanner.  rms width = 0.045 cm.
- Absolute error = 2% of max.
- Relative error = 1%
- 57 positions.
- Gaussian fit to data.

*error = abs[(true width) – (fitted width)] **+ (error in fit width)*

## Width error vs. absolute and relative amplifier errors

**Error in width vs. absolute and relative error.**
**Gaussian fit. **

- 40,000 particle PARMILA model of SNS at 7.5 MeV at D-plate wire scanner. rms width = 0.180 cm.
- 21 wire positions across +/- 1 cm.
- No error in wire position.
- Gaussian fit to data.
- Abs. error of 150 = 10% of peak.

*error = abs[(true width) – (fitted width)] **+ (error in fit width)*

## Beam position error vs. wire position error

- 40,000 particle PARMILA model of SNS at 7.5 MeV at D-plate wire scanner.  rms width = 0.090 cm.
- Absolute error = 2% of max.
- Relative error = 1%
- 29 positions.
- Gaussian fit to data.

*error = abs[(true pos’n) – (fitted pos’n)] **+ (error in pos’n)*

## Position accuracy measurement summary

**DTL/CCL position accuracy is 0.18 mm with wobble in lead screw, and 0.07 mm without. **
- Next version of wire scanner will have much less wobble and thus approach an accuracy of about 0.08 mm.
- Minimum beam size (at a wire scanner) in DTL/CCL is 0.09 cm.
- To meet 10% width accuracy requirement with this beam size need wire position accuracy of about 0.25 mm. Wire scanner thus meets requirements.
- To meet 7% width accuracy in CCL wire scanners (0.10 cm rms beam size), need wire position accuracy of about 0.010 cm. Next version of wire scanner will meet  this requirement also.
- To meet ±2 mm beam position accuracy requirement need about 4 mm wire position accuracy. Easily meet this requirement.
- Note that simulations do not take beam jitter or beam intensity fluctuations into account. This will result in a increased error. We are working closely with the physics teams to quantify the beam jitter and to develop beam tuning algorithms.
**SCL position accuracy is 0.13 mm. **
- Minimum beam size (at a wire scanner) in SCL is 12 mm.
- To get 10% width accuracy for this beam size need wire position accuracy of about 0.30 mm. Wire scanner thus meets requirements.
- To meet ±2 mm beam position accuracy requirement need about 4 mm wire position accuracy. Easily meet this requirement.
- Note that simulations do not take beam jitter or beam intensity fluctuations into account. This will result in a increased error. We are working closely with the physics teams to quantify the beam jitter and to develop beam tuning algorithms.

## From the Preliminary Design Review...

**Recommendation – Take advantage of the LEDA setup to study wire material and heating issues under real beam conditions.**
*Response – We are in regular contact with LEDA beam diagnostics personnel, and we continue to discuss what they have learned about wire scanners. We plan to take full advantage of the LEDA results. *

## LEDA carbon wire tests

**Broken wire shows evidence for ablation at the broken end, but nowhere else. **
**We have chosen 32 micron C wire for all the linac wire scanners.**

## From the Preliminary Design Review...

**Recommendation – ****Radiation dose tolerance requirements should be specified. SNS Oak Ridge should provide best estimates of the radiation environment as a function of position within the tunnel.  These estimates should include the short-term loss conditions experienced during tune up, the steady state losses expected during beam delivery and an overall dose estimate per year of operation.**
*Response – **The ORNL target group has made calculations based on controlled beam losses ( losses due to magnetic and gas stripping subject to the designed vacuum pressure). There will be a report on these studies.  To summarize, the maximum radiation dose equivalent to the silicon quality factor at the surface of beam pipe is listed here:*
*DTL = 3 rads/hr*
*CCL = 14 rads/hr*
*SCL medium beta = 2.5 rads/hr*
*SCL high beta = 8 rads/hr*
*SCL spare module section = 30 rads/hr*
- For a 30 year facility lifetime, 10 months operation per year, the maximum dose from normal operations is 30 x (10/12) x 365 x 24 x (30 rads/hr) = 7 Mrads. Since the tune up and off-normal loss rates occur for such a short time compared to the normal loss rates, the overall radiation exposure will be only slightly more than that for normal losses. All beam diagnostics components located by the beam line should therefore ideally be rated for 10 Mrads.

## Rad hard components

**Radiation dose over 30 y lifetime of SNS has been calculated to be about 10 MRad.**
- Burndy connectors on wire scanners use polycholroprene insulator, rated to 100 Mrad.
- BNC connectors use rexolite insulator, rated to 1000 Mrad.
- LVDTs: Use “radiation resistant” model. No rad spec from manufacturer. No teflon, no PVC. Should be sufficiently rad hard.
- Stepper motors not rad hard due to expense, but designed to be easily replaced.

## From the Preliminary Design Review...

**Committee Observation – Fly mode and step mode operation of the wire actuators were identified and scan times for individual profiles were presented.  It was not apparent if these individual scan times are consistent with making enough measurements in a timely manner to represent a useful set of beam data.  How many wires can scan at once? ... from the beam physics perspective? ... from the allowable beam loss perspective?**
*Response – **A maximum of about 0.5% of the beam hits the wire and gets converted to protons. This is a negligible effect on the downstream wire scanners, especially considering that the protons are mismatched to the lattice and are quickly lost. For crossed wires on the same fork, the displaced x and y wires will minimize the effect of the upstream wire on the downstream wire *
*The allowable beam loss is about 1 Watt/m during full-current operation (1.4 mA average current). 1 watt/m corresponds to about 100 nA, 10 nA, and 1 nA per meter at 10, 100, and 1000 MeV respectively. The wire scanners will be run at reduced duty factor (50 to 100 ****s, 1 to several Hz) to avoid damaging the signal wires. For 10 Hz, 100 ****s duty factor, the average beam current is 1.4 ****A. About 0.5% of the beam, equivalent to about 7 nA, is converted to protons lost over several FODO periods. This is less than 1 nA per meter, and should not exceed the loss limit. *
*Therefore the number of wires that can be run at a time is not limited by beam physics, but rather by beam loss, and the limit depends on the beam energy and the beam duty factor. For example, at the worst case of 1000 MeV, 5 wires could be run with a 2 Hz beam*

## From the Preliminary Design Review...

**Committee Observation – Tom Shea stated his requirement for remote calibration/health monitors on all beam instrumentation systems, but detailed functionalities appear to be left up to designers, not supplied to them based on operational requirements.  News of the calibration/health monitoring requirement apparently had not reached at least one of the presenters. **
**Recommendation – Timely communication between “customer” and “supplier” should be strengthened in this area.**
*Response – We have formed a jointly agreeable strategy to test from prototype to the final hand off product. Both supplier and customer are working hand in hand to make sure all requirements are understood by all of us. For the first iteration, please refer to the Acceptance Strategy documents.** *

## From the Preliminary Design Review...

**Committee Observation –Integration of the wire scanners with the Machine Protection System (MPS) is an important issue to protect from burning out wires and/or causing excessive beam loss...**
*Response – As of now, the limit switches will reduce the pulse length to the predefined 50 or 100 microseconds and limit the rep rate. The interlocks cannot be bypassed by a physicist or an operator. An MPS expert is required to install a bypass. The risk of damaging  the wires is well known and the decision to increase the pulse length will not be casually treated.*

## From the Preliminary Design Review...

**Recommendation – The beam diagnostics team and SRF electronics team at LANL should consider standardizing on a single set of drive electronics.  The need for the snubber electronics should be understood, as a similar circuit may be required in the linac portion of the machine.**
*JLab – no response*
*LLRF – don’t care.*
*RF – don’t care.*
*Diagnostics – don’t care.*
*Conclusion: This doesn’t seem to be an issue.*

## From the Preliminary Design Review...

**Committee Observation – ****Consider using the standard BPM/BCM data acquisition systems...**
*Response – We have considered using the BPM PCI motherboard solution, and have discarded it. We believe it is more cost effective and a more integrated solution to use off-the-shelf motion control and data acquisition components from National Instruments. We have considered having multiple channels in one computer chassis, and it is in fact part of our baseline plan to have two channels per computer chassis.*

## DTL, CCL, and D-plate actuators

## Wire scanner signal levels

- 32 micron C wire
- 38 mA beam current

- Wire signal

- Electrons stop until about 110 MeV

- Energy deposition in wire, max at about 110 MeV

- Protons pass thru for energies over about 1.5 MeV

## Wire scanner signal levels

**Wire scanner signal levels**

**32 micron dia. carbon wire.**
**Electronics should measure down to 1% of weakest signal from 5 mA avg. beam current, and up to about 200% of strongest signal from 26 mA avg. beam current**
**Total current range is 16 nA to 1.8 mA.**

- *Transition from neg. to pos. signal at about 107 MeV.
- Note: Signal levels are accurate to about a factor of two.

- Signals at center of beam, 26 mA avg. beam current

## Wire temperatures

- 32 micron C wire
- 380 MeV
- 0.12 cm x 0.12 cm rms beam

## Wire temperatures

**32 micron C wire.**
**Temperatures at center of beam.**
**Max temp is 1225 deg. C.**
**Requirements are met for all except MEBT (outside the scope of this review).**

- 0 WS #5
- 1 1 Hz, 50 us, 26 mA beam
- 2 10 Hz,
- 3 106 MeV
- 4 200 MeV
- 5 1 Hz, 100 us, 26 mA
- 6 10 Hz, 100 us, 26 mA

## Interfaces

**The mechanical interface occurs at the beam pickup flange or weld joint. The mechanical teams are responsible for installation and alignment of the pickup.**
**The electrical interface occurs at the rack (except for pickup cables) where the electronics are mounted. I/O from the RTDL / event link, Ethernet, MPS, 120 Vac on/off.**

- Network attached
- instrument

- BPM pickup

- IP

- RTDL

- Event link

- Ethernet
- Channel Access

- Machine protect

- Application programs

- 120 Vac on/off

- Control system

## Interfaces & responsibilities

**Acceptance strategy documents have been developed ***(see advance materials)***.**
**LANL**
- Design and fabricate the actuators.
- Design and fabricate the electronics.
- LabView software (w/ ORNL/Diag help).
- Channel access software.
**ORNL**
- DTL & CCL actuator installation (w/LANL help).
- EPICS screens.
- Interface to machine protect.
- System tests and troubleshooting (w/ LANL help).
- Wim Blockland at ORNL has overall wire scanner responsibility.
**JLab**
- SCL actuator cleaning and installation.

## Schedule

**Delivered 6 ea. electronics systems to LBL in January 2002. **
**Finish cleaning, vacuum, and particulate count tests on SCL actuator at JLab in March.**
**Test SCL actuator to failure.**
**Receive and test next version of DTL/CCL actuator in April.**
**Deliver D-plate actuator late summer.**
**Deliver DTL actuators end of year.**
**Deliver SCL actuators spring 2003.**

## Summary

**Issues raised during the preliminary design review have been addressed.**
**Models have been developed for wire signals, wire temperatures, and beam parameter accuracy vs. wire position errors. **
**Prototype actuators have been fabricated and tested.**
- 10,000 cycles each with no problems.
- Position accuracy is good and meets requirements.
**Physics requirements have been firmed up (work continues).**
**Wire scanner systems meet all requirements.**
**Wire scanner systems are on schedule.**