MUID Status: General Detector Health

• In addition to two disabled HV chains there are four other chains (out of a total of 600) that are largely or totally disabled.– Three LV/Signal issues.– One gas issue.

• There are also ~25 tubes (out of 6340) with broken wires.  

• Recent LV module (North Vertical) problem believed to be fixed.. [occurred and fixed Tue]

• Breaking news: problem with 1 (out of 20) LL1 signals in North Vertical [found and fixed Thu]

Monitor ~OK; some recent tweaking (limits and linguistics)..

• Plots are ratios relative to expected hit distributions (so values near 1 are good).

• Larger values on the right-hand side of the plots indicates higher hit rates due to beam backgrounds in deep gaps.

• Also used for clock trigger studies..

HV Info [Vince]

• One channel is disabled on South.

• One on North, although you can’t see it because it is on one of the channels that’s doubled up on supply side.

• One series of channels (all in one supply slot) occasionally trips all at once.– Will replace when we get

spares. – Please reset trips

immediately.• High currents from

backgrounds (more on effects later).

South Monitor

[No problems with gas or LV.. So focus on HV here]

Efficiency vs HV – 2006 scans https://www.phenix.bnl.gov/phenix/WWW/publish/silvermy/muon/muid_eff/chun_hvscan_Apr2006/Use cosmic runs for efficiency checks..

Example: South Horizontal

Approx. similarturn-on curves for the chains in all 6 panels.[X-axis is HV, and Y-axis is efficiency]

Efficiency loss vs HV drop – a parameterization from the scans

The average loss of efficiency as a function of HV drop from 4400 V can be well described by a quadratic function. We can then describe the eff. as a function of voltage sag like

Eff ~= 96 (1 – 2.4e-6 VS2)

HV Drop (V)

Eff. loss

–5 uA causes a few % efficiency drop. 10 uA causes 10-15% efficiency loss (if an average current flow is assumed).

Scintillator vs Time [John / Donny]

• This is after collision-part estimate (MJL) is subtracted off.

• Recommendation is to turn HV on when collision-subtracted rates are below 40 kHz, which so far seems to correspond to reasonable HV currents.

Effectively I guess it has meant first run in a store without MUID.

• Expect update of instructions later in the run as more studies are made (lessons learned from Vernier scans etc) and conditions change..

Since Dec 1

Recent store

HV vs Time

• Working on getting HV values into DB (John H – thanks!, Donny will follow up) for easier correlation checks with scintillator scaler info

1 out of 600 chains

Request for Shift Crews

• Please be sure to take daily cosmic data run daily..

• This is how we can monitor for additional sagging in HV supplies (see backup slides for more info on that).

• Also continue to look at HV currents and scintillator background levels

• EXTRA INFO

Other monitoring

• Not by shift crew: trends in hit rate, LL1 eff., LL1 rejection etc.

MUID HV Algebra

2.5n)(1

1GR n

kV)(in V 2.5n)(1A)(in In

tube tube

1GΩ 400MΩ

N Tubes in a chain

Vt

Overall Resistance with n broken wires (2.5 factor is from 1 / 0.4 ) :

=> Current draw with n broken wires [normal : n=0; 4.4 kV & 4.4 A]:

Extra current over the basic current draw gives HV sag a la:

n) - (N

A)(in I)kVin (V extra

s

[5A extra current => ~100 V

sag and potentially noticeable eff. loss]

HV Supplies info [Vince]• LeCroy HV supplies determine the applied voltage by measuring the current

across a high impedance resistor in parallel with the load.

• Some of our supplies were built with faulty resistors whose resistance is too high (seems to change with age, temperature, voltage).

• As a result the panels say they are putting out more voltage than they are. • We found 13 bad 8-channel supplies during commissioning.

– Sal Polizzo has repaired 5.– 5 more are being repaired now.– These are a pain to fix – the resistors are buried in HV potting compound.

Thanks Sal!– The remaining bad ones are programmed to put out V > 4400, so that they

actually put out 4400V, but we cannot be sure they aren’t sagging more.– Some channels doubled up (two chains) on one supply.

HV

GND

LoadFeedback

High Currents [Vince]• Bleeder resistor drains the charge stored in the Iarocci tubes (large capacitors store a

lot of energy).– Chains draw 4.4uA nominal current at operating voltage (4.4 kV).

• They will draw an additional 10 uA for each tube with a broken wire (but the chains can still operate thanks to the current limiting resistor).

– Monitor shows current over and above this nominal current.• This additional current flows through the tubes and causes a voltage drop across the

current limiting resistors.– 5 uA causes a few % efficiency drop. 10 uA causes 10-15% efficiency loss (if an average

current flow is assumed).• The tubes are never accessible, so the value of the current limiting resistor was

chosen, based on expected rate of broken wires, to limit the fraction of chains that would be disabled after 10 years to 10%.

Bleeder Resistor (1 GOhm)

Current limiting resistor (400 MOhm)

Iarocci tube (0 if wire broken, infinity otherwise)

HV

GND

HV Effective