HBD Operation HBD Operation in Run 9in Run 9

Thomas K HemmickThomas K Hemmick

for the HBD Crewfor the HBD Crew

Avg. Trans. of HBD East

0.00

0.20

0.40

0.60

0.80

1.00

1.20

110 130 150 170 190

Wavelength [nm]

Tra

nsm

itta

nce

[%

]

data

FitFitH2O: 59ppmO2: 7ppm

PanametricsH2O: ~8ppmO2: ~3ppm

~29pe

Flow=4slpmMore O2 than Before?

HBD ImprovementsHBD Improvements

• Reconstruction of HBD should improve voltage holding (does).

• Other considerations should improve light yield:– Improved gas transparency.– Precision Reverse Bias.

• All of these seem at first look to be achieved.

(2.5hrs. of flow thru cells)

HBD-Ar @ 2.25lpm (straight-through mode, no scrubbing)

HBD-CF4 @ 4.5lpm (Recirculation mode, incl. scrubbing)

Transmission ScansTransmission Scans

““Traditional” Traditional” GEM operationGEM operation

charged

particle

or photon

primaryionization

HV

Mesh drifts ionization trail towards GEM stack

Usually operated in Ar/CO2

~300-400V across GEMs

Mesh drifts ionization trail away from GEM stack, but allows Cherenkov photons

Operate in CF4 - radiator and avalanche gas

~450-550V across GEMs

Hadron BlindHadron Blind GEM operationGEM operation

~350nm CsI

primary ionizationHV

photoelectron

Reminder of HBD PrincipalReminder of HBD Principal

E-Field Line Directions

Forward BiasReverse Bias

Lines go to meshLines go to padLines go to GEM bottom

In this simulation…

• electrons were created at the surface of the GEM. • electron path follows E-Field lines• recorded PE’s final destination.

Reverse Bias (-30V): • most (~91%) e’s from the GEM surface end up on pads.• ~3% are swept up to mesh.• ~6% lost to GEM bottom.

note: field line destinations and actual charge destinations are differentdue to diffusion and avalanche.

Line density does NOT represent field strength!

E-Field Line DirectionsReverse Bias

For an intuition of what different negative drift fields look like… • notice that “reverse bias” doesn’t turn on immediately

Lines go to meshLines go to padLines go to GEM bot

Line density does NOT represent field strength!

Experimental resultsExperimental results

• Hadrons (actually 55Fe) drop suddenly in efficiency as bias goes reverse.

• Photon-electrons fall off slowly with increasing reverse bias.

• HBD will operate best when placed “just barely” into the reverse bias mode.

• Since voltages are roughly 4000 V, need 0.1% precision to get bias correct to 4V!!!

Photo-Electrons vs Mesh Bias

0

1

2

3

4

5

6

-150 -100 -50 0 50 100 150

dV (Mesh)

Npe

Nearest Fe

Average Fe

Median Fe

55Fe

Scintillation

Spectra in BeamSpectra in Beam

• Spectra show two components:– Single Scintillation Electrons (expo)– MIP (Landau)

Scintillation

MIPs

FORWARD

REVERSE

Goal List for HBDGoal List for HBD• Gain Calibration (Standalone):

– Observe scintillation signal in every channel.– Fit scintillation slope to get gain.– Adjust voltages to get nearly uniform gain.– DONE (better than 10%...WOW)

• Forward/Reverse threshold (standalone):– Change bias step-by-step.– Search for loss of MIP peak.– DONE (and we thought this would be hard)

• High Statistics Reverse Bias (tracking)– Determine Hadron Response.– Determine isolated electron response.– Determine “double” electron response.– NEXT UP…

DV Scan Color scheme

RUN LINE COLOR BIAS274058 Red +30V 059 Black 0V 060 Green -5V 061 Blue -10V 062 Yellow -15V 063 Magenta -20V

EN1 -15V EN2 -10V

EN3 -15V EN4 -10V

EN5 -10V ES1 =-10Vred,black (0V)green(-5V),blue(-10V),rest(-15V)

ES2 -10V ES3 -15V

ES4 -10V ES5 -10V

WN1 -10V WN2 -10V

WN3 -10V WN4 -10V

WN5 -15V WS1 -15V

WS2 -10V WS3 -10V

WS4 -10V WS5 -10V

Live AreaLive Area• There are several troubles.• Minor:

– Individual bad strips take away 0.8% of the live area.

– Require access for resistor swap on 2 strips.

• Major:– ES1 (edge of acceptance) has the grid

touching a shorted strip.– Unless “burning” works, this sector will not

function.– 5% of overall area.

SummarySummary• HBD seems to work well.• Data that are forthcoming should

show exact single & double electron performance.

• The upcoming dataset will provide the basis for estimating Run-10 performance to the PAC.