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.