MKI Erratics: Hardware and Electronics Related Aspects

M.J. Barnes

Acknowledgements:A. Antoine, R.A. Barlow, P. Burkel, E. Carlier, N. Magnin,

V. Mertens & R. Rosol

One MKI System: 4 PFN’s & 4 Magnets

LMC: August 9, 2011 M.J. Barnes 2

DS TankMS

Tank

TDRRG220U cables to magnet

RCPSControls

PFN(~5m)

Inside a PFN: 2-way electrical delay 9µs

Magnet in the vacuum tank with ceramic beam pipe

UA23 / UA87

1 of 4 Magnets at Point 2Kicker in vacuum tank

Schematic of an MKI System

M.J. Barnes 3

-0.500.511.522.533.544.555.5

-505

10152025303540455055

0 0.5 1 1.5 2

Prim

ary

Curr

ent (

kA)

Seco

ndar

y (kV

)

Time (ms)

V(Secondary)V(PFN)I(Cstorage)

00.030.060.090.120.150.180.210.240.270.30.330.36

-0.50.00.51.01.52.02.53.03.54.04.55.05.5

0 2 4 6 8 10 12 14 16

∫B.d

l (T

·m)

Term

inat

or C

urre

nt (k

A)

Time (µs)

Current

∫B.dl

Protons Injection from

SPS

Thyratron can be triggered

After resonant charging

During resonant charging

LMC: August 9, 2011

MKI2 MS3 Erratic on 28/7/2011 @ 16:30hrs At 16:30:43hrs, on 28/7/2011, an erratic turn-on of MKI2 MS3 (Melton) at full PFN voltage; Interlocks detected an MS erratic and correctly triggered MS’s and DS’s of system (within 2µs), emptying PFN via both ends. Hence all 4 kicker magnets pulsed for up to 4.5µs, emptying PFNs of energy. Circulating beam was not in IP2 and therefore not disturbed. Batch was extracted from SPS but saw no kick at MKI2 and went straight into the TDI.Note: this MS, Melton, was put in place during the last TS (July 2011) and has since made 5 erratics (only last 2 effected beam).

4.5µs2µs

MS3 erraticMS3 erratic, after resonant charging

Charging current & PFN voltage Current in kicker magnet

M.J. Barnes 4LMC: August 9, 2011

MKI2 MS3 Erratic on 28/7/2011 @ 18:03hrs At 18:03:09hrs , on 28/7/2011 , an erratic turn-on of MKI2 MS3 (Melton) occurred during resonant charging – sending current to 1 of the 4 kickers (Note: it is unusual to have an erratic at such low voltage); Interlocks did NOT detect erratic of MS3 (at 33kV): hence no immediate action was taken to turn-on other thyratrons. Therefore the full 9µs of PFN pulse length sent, via MS3, to kicker C. Other 3 PFNs correctly discharged via the DS after 4ms (no further kicker magnet current); The erratic occurred ~500µs into the charging process, and the extraction from the SPS was inhibited; Circulating beam was swept over the aperture and protection elements (~17% of normal kick) for ~9µs.

0

5000

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Appr

ox P

FN V

olta

ge

Sample Number

MKI2. 28 July 2011, 6:03:09 PM

7/28/2011 6:03:09 PM PFN1

7/28/2011 6:03:09 PM PFN2

7/28/2011 6:03:09 PM PFN3

7/28/2011 6:03:09 PM PFN4

Erratic (untriggered) turn-on of MKI2 MS3

PFNs 1 & 2 at normal voltage (~50kV)

PFNs 4 at low voltage (~33kV) because of MS3 erratic

~9µs circu

lating

beam not dumped

J. WenningerM.J. Barnes 5LMC: August 9, 2011

MKI Erratic SummaryMS Melton (MKI2) erratics (total: ~12): April 2010: SoftStart - 1 @ 1.7kV above nominal August 2010: SoftStart - 3? (1 recorded) @ 1.7kV+ above nominal

Normal Op – 3? (1 recorded) 2/9/2010: Melton replaced by Moulin July 2011: Melton installed during TS of July 2011 (replacing Moulin)

SoftStart – 3 (1 @ ~40kV; 2 @ 2kV above nominal) Normal Op – 2 (1 recorded) Melton replaced by Moulin on 29/7/2011

Other MKI2 Switch erratics since April 2010 (total: 6): MS1 Millbrook: SoftStart - 3 MS3 Moulin: SoftStart – 2 & Normal Op – 1 (4/7/2011). Replaced by Melton during July 2011 TS.

Moulin reinstalled 29/7/2011. DS3 Doncaster: SoftStart – 1

MKI8 Switch erratics since April 2010 (total: 2): MS2 Manchester: SoftStart – 1 DS2 Dagenham: SoftStart – 1

M.J. Barnes 6LMC: August 9, 2011

MKI Summary of Investigations & Actions After replacing MS Melton, and following two MS3 erratics and a further intervention (30/7/2011), the erratics have stopped (since 10 days) and the immediate danger of more erratics seems to be gone. MS Melton brought back to lab. Current regulator on bias-board found to be damaged – supplying current corresponding to maximum of thyratron specification: this could increase rate of erratics.

Remote trending of current presently being implemented to allow possibility of remote diagnosis of this current regulator fault.

Long-term: fibre optic read-back to monitor thyratron G1 and bias-board. Thyratron in MS Melton may be damaged – to be returned to E2V for diagnosis. Spare MS from MKI8 now in lab for re-conditioning; can be used at Pt 2 or Pt 8. Occasional missing G1 triggers to MS3 (5% to 10% missing) & MS4 thyratrons. This accounts for jitter noted (IQC) on MS3 & MS4.

Missing G1 accelerates wear of thyratron, hence may have contributed to quantity of erratics.

New trigger cards designed and built but not yet installed in MKI – but further investigations of cause are also required.

Long-term: detection of missing outputs of G1 power trigger unit. Tests in UA23 have demonstrated that:

Erratic occurring after resonant charging is correctly detected; Erratic occurring at 500µs into resonant charging was not detected.

Non-detection of MS erratics (thus no retriggering of other thyratrons) – High Priority

Inhibit/masking due to one or more modules or a noise-filter, in the erratic detection chain, may be responsible. Awaiting access, in the shadow of another intervention, to investigate further.

Low voltage fast interlock inhibition mechanism will be removed (implemented for the SoftStart) during next short TS.

May require further investigations …..

Bias-board

M.J. Barnes 7LMC: August 9, 2011

Thyratron