CDC preamp LV checkup

Following a tip-off from Lubomir that the LV reaching the preamp card might not be correct, I checked it at the board and found it to be 2.6V rather than 3V. This is due partly to voltage drop along the cable and partly to the preamp taking more current than the supply can put out. The original LV supply unit was a HPsomething. I switched it first for a Lambda LH121FM which could put out enough current (0.5A) at 3V but found this to have a wavering pedestal - +/-30 adc bins over the course of 24h, and then for a Global Specialties 1305 which is looking good after 3d. Both have more pedestal noise (pedestal s.d. ~15 bins) than the HP (~10 bins).

Things to check:

1. pedestal height - this was previously set to ch 100 - adjust offsets to bring this back to 100

With GS1305: ADC contents, one event (noise), first 3 are logic signals, rest are CDC prototype

2. pedestal noise and stability (did this before setting height)

Pedestal mean of samples 0-99, ch7, over 2.5days

Pedestal std. dev. of samples 0-99, ch7, over 2.5days

Pedestal std dev has increased from ~11 to ~16 bins 4sigma for new setup is 64 ~ 6sigma old setup 3. tails from large pulses 4. gain (pedestal height was a little low, 35-50 instead of usual 100)

Max amplitude at 2100V, 45 degrees, old and new, hit thresholds matched at 6sigma and 4sigma respectively

Gain has increased also, Landau fit MPV from 260 to 400. This is a little scary.

5. resolution at 2100V (pedestal height was a little low, 35-50 instead of usual 100)

Resolution, ch 20

6. Try a lower HV and look at efficiency also. Something unfortunate happened at 1.30am - LV dropped due to bad contact with -ve cable.

Pedestal mean of samples 0-99, ch7, over the following day

Another try

Pedestal mean of samples 0-99, ch20, over 2days

Pedestal std. dev. of samples 0-99, ch20, over 2days

Max amplitude of 2000V and 2100V runs

Max amplitude at 2000V and 2100V, 45 degrees, hit threshold 4sigma

Resolution at 2050V

Resolution, ch 20

New LV supply

2050V, 50/50 gas, prototype horizontal

Pedestal mean of samples 0-99, ch20, over 1.8 days

Pedestal std. dev. of samples 0-99, ch20, over 1.8 days

Max amplitude ch20, hit threshold 4sigma

--- CO2 ran out, replaced tank, found corrosion inside one LV cable connector, cleaned out & resoldered... ---

2050V, 50/50 gas, prototype horizontal

Pedestal mean of samples 0-99, ch20, over 1 day

Pedestal std. dev. of samples 0-99, ch20, over 1 day

Max amplitude ch20, hit threshold 4sigma

2075V, 50/50 gas, prototype horizontal

Pedestal mean of samples 0-99, ch20, over 1 day

Pedestal std. dev. of samples 0-99, ch20, over 1 day

Max amplitude ch20, hit threshold 4sigma, excluding last 7k events

2100V, 50/50 gas, prototype horizontal

Pedestal mean of samples 0-99, ch20, over 1 day

Pedestal std. dev. of samples 0-99, ch20, over 1 day

Max amplitude ch20, hit threshold 4sigma, excluding first 2k events

2090V, 50/50 gas, prototype horizontal

Pedestal mean of samples 0-99, ch20, over 1 day

Pedestal std. dev. of samples 0-99, ch20, over 1 day

Max amplitude ch20, hit threshold 4sigma

1. efficiency

MPV of max amplitude histogram with HV

Track/triggers with HV