IAC 1-7-08

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 1/6" 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 3.6 cm beam left (toward counting house wall) and removed Aluminum brick in front of the last scintillator. 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 reproducable.

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.

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