Ans Pardons(with input from Jean-Marc Cravero)

CERN

CNGS Horn Experience (issues since NBI2010)

Ans Pardons, CERN 1NBI2012

Outline

• Introduction – CNGS Horns– Memorable Moments– Electrical Properties– Power Convertor Circuit

• CNGS horns operation issues 2010-2012– Exit Inductances– Thyristor– Capacitor Banks

• Summary

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Introduction: CNGS horns

• 150/180kA, 0.3Hz avg.(20Hz inst.)

• Water-cooled• Design lifetime:

20 106 double pulses

CERN

Gran Sasso

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Introduction: CNGS horns

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Underground:

150/180kA

7.7kV, 9.4kA (horn)6.3kV, 5.6kA(refl)

Water cooling &Demineralisation (20m)

High Voltage cables (1km, 12 per horn)

On the surface

HORN/REFLECTOR

POWER CONVERTORS

TRANSFORMERSX16(H) x32 (R)

Jan-06 Jul-06 Dec-06 Jun-07 Dec-07 Jun-08 Dec-08 Jun-09 Dec-09 Jun-10 Dec-10 Jun-11 Dec-11 Jun-120.0E+00

2.0E+06

4.0E+06

6.0E+06

8.0E+06

1.0E+07

1.2E+07

Introduction: Memorable Moments

Reflector outlet water leak

Broken stripline cable

Water conductivity issues

Electronics radiation damage

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Inductances&

thyristors broke

Capacitors

measured

Double pulses

Introduction: Memorable Moments

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• 2006: water outlet leak– Badly designed brazed &

machined ceramic assembly– All brazed ceramics in horns

replaced

• 2007: broken stripline cable– Insufficiently restrained &

brazing-weakened cables– Replaced with restrained &

(more) rigid solution of Ag-plated copper plates

Introduction: Electrical Properties

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Converter Circuit Diagram

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1st

2nd

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• History– Recuperated from WANF, no

documentation at the time– Found later from manu-

facturer’s documentation:Under-dimensioned for CNGS

– Replaced with new, correctly dimensioned inductances all OK

• Failure detailsMechanical fatigueInsulating foil degradation Short circuit at the exit of the

power converters

Exit Inductance Failure: mid 2011

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Thyristor Issues: Mid 2011

Thyristor firing board

InductanceFor pulse 1- Pulse 2

Thyristor stack for pulse 1 – pulse 2• At each inductance failure– The output of the converter

is in short-circuit, leading to the destruction of the thyristor stacks

• Additional observation– Sometimes pulse 1&2 fired

at the same time due to the EM susceptibility of the thyristor firing board

– Problem solved with filter added on the board and additional EM shielding

Capacitor Banks Issue: Early 2012

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• History– New capacitors installed in 2006,

24 capacitor cans per horn– Designed for 20 million pulses at

10kV • Performance

– During machine stop early 2012, measured capacitance value found to be at ˜50% (horn) and 90% (reflector) of nominal

– At this moment, only 10 million pulses and max. 7kV

life time issue

Capacitor Banks Issue: Early 2012

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• Solution– For 1st half of 2012: 7 spare cans

(original design) were installed horn up to 84% ok until new

– In June 2012: 24 new cans installed in the horn converter (new design from manufacturer)

– No degradation observed since• Reason for premature wear-???

– Unknown (awaiting tests results from manufacturer)

Summary• 2006-2010: Many mechanical issues, lots of repair &

re-design work done, many lessons learnt(and in parallel: enhancement of other systems) This seems to have paid off:

no mechanical or cooling issues in 2010-2012• 2010-2012: Electrical issues found and solved• Lessons learnt:

– Double check when recuperating existing equipment Do look the gift horse in the mouth!

– Capacitor banks have to be measured on a regular basis to detect life time issues (early).

– EM compatibility is always a tricky issue when dealing with kA current pulses

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