IAC 1-7-08
Accelerator Tuning
Accelerator: 100 ns, 60 Hz, 15 MeV
Configuration: Collimated rear scint + 2" Aluminum brick
Rates:
- Coinc both PMTs =484/4min = 121/min
- PMT Coinc Both PMTs & Metallica DC =25/4min = 6/min
Configuration: Collimated rear scint
Rates:
- PMT Coinc both PMTs = 308/2min = 154/min
- PMT Coinc Both PMTs & Metallica DC =17/2min = 8/min
The ratio of double/triple =36/1054 = 3.1%
Configuration: Collimated rear scint+ 2" Aluminum brick + 2" lead brick
Rates:
- PMT Coinc both PMTs=105/10min = 10/min
- PMT Coinc Both PMTs & Metallica DC =4/10min = 0.5/min
We see a lot of events in the Scintillator and very few in the Chamber. There is no clear electron signal so let's debug the beamline.
Our tests on Friday showed that inserting an Aluminum brick in front of our first collimator decreased the first scintillator's count rate by approximately 60 %. A 15 MeV electron should stop in 2cm of Aluminum. We believe our 2" (5 cm) thick Aluminum brick will stop electrons but not photons. We do not observed the same change in rate when we insert the Aluminum brick in front of the rear scintillator. We believe our collimation system is blocking most of the electrons.
We insert an Aluminum brick in front of the first scintillator.
Aluminum block in front of first scintillator between experimental side wall and large scintillator is in place we did not remove the Aluminum block in front of the 2nd (last) scintilaltor.
Rates:
- First PMT singles =6128/2 min = 3064/min
- PMT Coinc both PMTs=132/2 min = 66/min
- PMT Coinc Both PMTs & Metallica DC =3/2min = 1.5/min
Now take the brick out.
Rates:
- First PMT singles = 6949/2min = 3474/min
- PMT Coinc both PMTs= 183/2min = 91/min
- PMT Coinc Both PMTs & Metallica DC =3/2min = 1.5/min
Electrons are a small fraction of our signal.
We remove the 1/16" collimator in front of the first scintillator paddle. Rates:
- First PMT singles = 3795/min
- PMT Coinc both PMTs= 145/min
- PMT Coinc Both PMTs & Metallica DC =46/min
We move the drift chamber 9 mm beam left (toward counting house wall) and removed Aluminum brick in front of the last scintillator. (This is 9 mm from the edge of the trumpet). Now there is only a 1/4" diameter collimator on the Accelerator side of the wall and a 1/8" diameter collimator in front of the last scintillator.
Rates:
- First PMT singles = 3771/min
- PMT Coinc both PMTs= 220/min
- PMT Coinc Both PMTs & Metallica DC =67/min
Now we return:
Give Kevin the front PMT, he changes the dipole to maximize output, then he lowered the current to minimize pile up. This dipole setting corresponds to 20 MeV electron energy.
Aluminum block out:
Rates:
- First PMT singles = 7582/2 min =3791/min
- PMT Coinc both PMTs= 25/min
- PMT Coinc Both PMTs & Metallica DC =1/min
Aluminum block in:
- First PMT singles = 426/min
- PMT Coinc both PMTs= 0/min
- PMT Coinc Both PMTs & Metallica DC =0/min
Take block out and repeat to see if Accelerator returns to prior performance.
- First PMT singles = 3777/min
- PMT Coinc both PMTs= 11/min
- PMT Coinc Both PMTs & Metallica DC =0/min
So the technique is reproducible. Ask the operator to change the dipole so the front scintilaltor output is maximum then lower the beam current until pile up is gone.
We will now try to improve the beam tuning procedure.
We place an aluminum block in front of the last scintillator. We send the accelerator operator the difference between the front scintilator PMT output and the back scintillator output. We ask him to maximize that signal while minimizing the last scintillators PMT output.
Front PMT/Back PMT =11743/798 = 15/1 = "electrons + gammas"/"gammas" ?
Now put an Aluminum block in front of the first scintillator to see if we get the same ratio.
Our attempt to construct a beam tuning signal did not appear to work well.
DAQ
I looked at signals in the ADC with the RF and GUN off but the Gun pulser running to generate triggers.
Pedestal no fan in/out
Drift Chamber HV is off and Fan in/out is not used for ADC7(Metalica sense wire #4) and ADC8 (Plastica sense wire #4).
Run 291
Pedestal WITH fan in/out
Drift Chamber HV is off and Fan in/out is not used for ADC7(Metalica sense wire #4) and ADC8 (Plastica sense wire #4).
Run 292 (I left CODA running so ignore events after event 10,000)
No there is no mistake. It seems the Fan In/Out attenuates the pedestal and perhaps improves the ground connection. Notice ADC9 (Metalica wire #5) is more gaussian than the other pictures. ADC9 is not going through the Fan In/Out.
Pedestal WITH fan in/out HV on
Run 293
