Beam Loss Monitoring using Scintillation Counters

Introduction

We use collimations to remove some of unwanted particles such as beam halo and particles in abort gaps in the accelerator. We want to study scattering rate at the crystal for it gives us some idea of how particles are passing through the crystal. The crystal is located at E0 in Tevatron, and there are two scintillation counters working and taking scattering data at E0. There are four more scintillation counters placed in E1, downstream of the crystal, but these counters have not been used. My project is to set up a working system using these counters to monitor scattering rate near the collimator. Tasks to be done are the followings:

Plan and create logic unit of the counter system.
Acquire necessary modules for the system.
Set thresholds of discriminators and calibrate the counters 1, 2, and 3.
Set up the logic unit

signal * bunch signal
signal * abort gap siganl
signal * anti-bunch * anti-abort signal

Analyze the data via ACNET

How the counters work

When particles in a beam scatter off the tungsten target or crystal, they hit the collimator, accelerator pipes and surrounding instruments and create radiation. The scintillation counters detect the radiation. Thus, the observed signal out of the scintillation counter is related to scattering rate near the target and crystal. The goal of the project is to set up a working system to monitor the rate of scattering at the collimator.

A scintillation counter consists of a scintillation crystal attached to a photo-multiplier tube (PMT), which converts light to an electric signal. The electric signal is sent to a logic unit that passes the signal only when it coincides with a timing signal. By turning off the high voltage for PMT, we find the amplitude of the noise and set the discriminator threshold to be higher than the noise. Then, we vary the high voltage to measure the efficiency and calibrate the counters.

Logic Unit

In order to increase signal to noise ratio, we gate the signal with timing signals that we construct. When the detector measures scattering, the signal goes through discriminator. The discriminator is set to a threshold of 30mV to eliminate noise and outputs signals with uniform width. Then the discriminator signal is sent to logic unit where the signals are gated according to various timing signal. The gated signal is sent to a module that is connected to ACNET devices and rates are calculated. The logic used in the system is shown in the figure.

Timing Signals

Figure on the left shows the timing signals used in this experiment. B0 indicates the revolution signal of the first bunch. BC indicates each bunch, and ABORT indicates the abort gaps. We require signals to coincides with one of these timing signal that we select. This allows us to observe scattering rate at specific time: BC when a particle bunch is at the location of counteres, ABORT when there *should* be no beams.

Calibration of the counters

We calibrate these counters by measuring the efficiency of a counter as a function of high voltage. We see a plateau of the curve and a optimal operation voltage is the lowest voltage that gives the highest efficiency. The efficiency of counter 3 is defined as the (rate of 1*2*3)/(rate of 1*2), and similarly for the counter 1 and counter 2. From the plot on the right, we decide that the optimal operation voltage for the counter 3 is around 1.4 kV.

ACNET variables

We defined 7 variables in ACNET and a revolution timing signal. The following are the definitions:
Ch0: Revolution Signal -- 47.7kHz
Ch1: T:E1LTOT -- 1*2*3
Ch2: T:E1LBNC -- 1*2*3*BC
Ch3: T:E1LABT -- 1*2*3*ABORT
Ch4: T:E1C34 -- 3*4
Ch5: T:E1Ch5 -- 1
Ch6: T:E1Ch6 -- 2
Ch7: T:E1Ch7 -- 3

Overview of the Counter system

Scintillation counters used in the project at E1.

Analysis of E03 Collimator Position

E03 Collimator Position Study

Analysis of Counter signals

Click on any image to link to an .eps file

Figures	Description
	Store 5993 E1 counter signal (Green: ungated, Cyan: gated with abort gaps) and particle intensities (Yellow: proton, Red: antiproton).
	Setup before the store 5993. We observe small proton intensities around at the tune-up, but we do not see counter signals. While we do not see the counter signals at protong injection, we see abort gap counter signal at pbar injection, indicating that something is scattering at pbar injection.
	After the pbar injection, we see a sudden increase in ungated counter signal (green). This time corresponds to scraping of protons and antiprotons before the collision (red).
	Various instrumentation signals and particle intensities at the initial set-up sequence.
	Counter signals along with various other signal. The green step function is the low beta sequence to change the optics to colliding optics. After the store, the magnets must be returned to original state, so the low beta sequence is reversed after the store (narrower step function at theright hand corner). ls
	Same, but without counter signals

Figures	Description
	Store 5990 This store had really rough beginning and a sudden drop in scattering rate around 13:00.
	Store 5990 Same as above, but enlarged to see the sudden change around 13:00. The p and pbar intensities, B0 integrated luminosity, and DC current are smooth at this time.
	Trying to figure out what caused the sudden drop in total scattering rate and increase in abort gap scattering rate. I suspect something was done and particles were kicked to abort gaps, but I could not find any collimators that were moved at this time.
	B0 proton and antiproton beam halo were also affected similarly to our ungated counter at E1.
	Rate of proton loss decrease at this time... I'm not sure what caused this sudden drops. This may be caused by a study???
	Rough period at the beginning of the store. Instantaneous luminosity dropped suddenly and our ungated counter also records sudden dip in scattering rate and abort gap counter records sudden peak. This was caused by a sudden sparkling of A17 Horizontal separator.