Power Supply Upgrade for ATLAS Liquid Argon Front End Crate

1. Power Supply Upgrade for ATLAS Liquid Argon Front End Crate • Motivation for Upgrade • Potential Companies • Work to date and future work

2. Motivation for Upgrade • Reliability – Power supply made by Modular Devices Inc has been made more reliable but is still not at a comfortable point yet. • The upgrade environment is harsher in terms of radiation requirements (MDI supply is not qualified) • Different voltage/current/distribution requirements (no information yet)

3. Environmental Qualifications in Fingers Anticipated Radiation Environment for Upgrade (including safety factors) • TID 4500 Gray • NIEL 7.7 x 1013 neutrons/cm2 for 1MeV neutrons • SEU 2 x 1013 cm-2 of 20 MeV or greater protons/neutrons • These numbers will change when actual data is available. Magnetic Field Environment • 70 Gauss when shielded with top plate. This number is changing (increasing) at this point but should not pose any problems

4. Approach • RELIABILITY Whatever power supply approach is selected the # 1 priority must be reliability. • Other configurations than our present system should be considered. For instance 1) Centralized or Distributed (i.e. board level) system or perhaps a combination. 2) AC or DC input. If DC what is the lowest voltage we can supply from outside? Constraints. There are some things which can not easily be changed from the present configuration and need to be incorporated in any upgrade.

5. Constraints in Approach • The only practical way to deliver power from the outside is in higher voltage/lower current to keep the size and mass of the cables reasonable • Very difficult to change existing cooling system • Existing cabling should be used, specifically the input cable (280 Volt) leading down to the tile fingers • Monitoring and control configuration should be maintained • Limited volume requires a high power density inthe converters

6. Three Potential Paths at this point • Vicor – commercial products with no radiation hardening • Wiener – produces power supplies for existing applications at Cern. Units have been tested in radiation environments but are not specifically designed for a radiation environment. • AEi Systems – engineering firm experienced in dc-dc converter design and components used in radiation environments. Also industry leaders in WCCA (Worst Case Circuit Analysis)

7. Vicor Advantages and Disadvantages • Advantages • Very high power density equal to the best products available, • good noise characteristics • Very flexible architecture which should make it possible to easily design for custom applications. Parts are readily available for testing. Power density allows • Disadvantages • Products not intended for radiation environments requiring parts changes and multiple iterations of testing of changes. This could be very expensive • Company is only mildly interested in making the product line radiation hard. Most of the work is on our side. However, we do have a non-disclosure agreement in place with them and we are getting information • “Factorized” architecture uses a low voltage (48-70 volts) which would require new cabling or a front stage converting the 280 volt to 48 volt. .

8. 100% effective duty cycle at any Vout PRM VTM Isolation & Transformation Regulation NP NS L Wide range DC bus e.g. 36–75 Vdc K = NS / NP Factorized bus PRM (Pre Regulator Module) + VTM (Voltage Transformation Module) Combination Provides Regulation and Isolation/Transformation(slide courtesy of Vicor) Regulated load voltage

9. Vicor module configuration as might be used in our present requirements • 7 voltages with redundancy using 24 pairs of PRM + VTM combination. • 70 volt input • Would require replacing the existing cable from USA 15 with a larger diameter cable for current requirements or using a front stage converting 280 volts to 70 volts.

10. Vicor VTM module(figure courtesy of Vicor) • Voltage divider (or current multiplier) with isolation but no regulation • VTM at 50 – 60 krad due to failure of the control chip (PWM) failure mode was determined by Vicor • VTM MOSFETs were tested separately and failed at 3.5-4.5 Mrad (good news)

11. Other Vicor modules tested • PRM (non-isolating buck converter) was not tested independently but along with VTM to 50 – 60 krad. No failures observed • BCM (Bus Converter Module) – works as a functional combination of PRM and VTM. Voltage input shorts after 35 - 40 krad. Reason is not known.

12. Vicor ( future work) • The MOSFET in the VTM module will be tested for Single Event and displacement damage effects. • The control chip (PWM) in the VTM fails at a dose of 50 -60 krad. Determine what is required (time and resources) to produce a radiation hard control chip • Test the PRM module independently of other modules to determine radiation damage effects. • Use multiple VTMs in parallel to investigate issues of current sharing and noise. • Determine magnetic field effects for VTMs and PRMs

13. Wiener Advantages and Disadvantages • Advantages • Company has a history of cooperating in producing products for radiation and magnetic field environments particularly for high energy physics. • Disadvantages • Products are not specifically designed for radiation environments • For the existing power requirements power density is an issue and the existing products would have to be redesigned and/or repackaged • Small company – has limited staff and resources

14. Wiener ( future work) • The MOSFET that is used in their existing products will be tested for Single Event and displacement damage effects. • Testing of the present product line to the qualifying Total Ionizing Dose • As part of a backup solution to the MDI power supply a repackaging of the current Wiener modules might be done to achieve and demonstrate the required power density. • Parallel multiple modules to investigate issues of current sharing and noise.

15. AEi Systems Advantages and Disadvantages • Advantage • Experienced in power supply design and circuit analysis. This approach has the greatest probability of being trouble free. • Company is very interactive, cooperative and open with information • Disadvantages • Expensive Uses radiation hard components in design. Estimate of cost would be > $4 million for upgraded power supply system. • Company is and engineering firm, not manufacturing firming. A manufacturing partner would have to be found (Algen?) which complicates this approach and increases the risk.

16. AEi Systems ( future work) • We have initiated a discussion with AEi on strategies to develop a supply for the upgrade. • They are open to finding ways to produce a lower cost solution using commercial component part substitution for radiation hard components. An initial suggestion from them includes the substitution of an IGBT for the MOSFET. Another possibility would be the use of a p-channel MOSFET rather than an n-channel MOSFET. • As part of a backup solution to the MDI power supply the MOSFET and other components selected by them will be tested for ionizing radiation, Single Event and displacement damage effects.

17. Conclusions • Power supply has been much harder than originally anticipated. • Lessons learned on the present power supply should be taken to heart and the power updating should be started now. Any solution should include a Worst Case Circuit Analysis as performed by AEi Systems. This gives some confidence that the power supply system would have an adequate life. • Testing of Wiener, Vicor, AEi and perhaps other vendors should continue.

18. Conclusions (FY08 Budget) • Manpower • EE: 0.25 FTE - 40k • Tech: 0.25 FTE - 30k • Material costs • Lab Instrum. - 12k • Material/Samples/Modules - 10k • Radiation Testing • Beam/Travel - 16k • Total: 108k