Online Plots
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PREX Main
See Also: Alarm Documentation
We assume that our main detectors are simultaneously measuring the helicity correlated motion and fluctuations of the electron beam from CEBAF, as well as physically interesting Parity Violating Asymmetry (Apv) of highly longitudinally-polarized electrons on an isotopically pure Lead 208 (Calcium 48) target of appreciable, but intentionally small scattering length.
The way that we can disentangle the beam position, angle, current and energy fluctuations due to helicity correlated beam (i.e. generated in the polarized source non-uniformly between helicity states and then damped or amplified farther along the beamline) are myriad.
Live and Online Analysis Result Plots
Critical Systems
List of Critical Systems and Descriptions
Beam Current Monitor
BCMs measure the current entering the hall. They should be reading less than 90 uA at all times. This is important to not destroy our target or generate excess ion chamber trips.
Hall A Arc, Energy Degree of Freedom-Sensitive BPM 12
This BPM is located in the BSY and measures beam position. It's also most sensitive to beam energy fluctuations. If the wires in the BPM saturate then its indicative of unacceptably high energy fluctuations. Therefore the readout must be kept below 50,000 at all times.
Missed Triggers in the DAQ
Main Detectors
What are our main detectors, and what happened to the rest of the HRS?
List of kinds of plots we care to make from main detectors
Raw Signal Voltage into the DAQ
Yield (signal in Volts/Microamps of Beam Current)
This measures our detector response as a function of beam current, with higher current generating stronger signal. Signals should be roughly the same for both left and right HRS's.
Asymmetry
Small Angle Monitors (SAMs)
What are SAMs?
The SAMs consist of eight small pieces of scintillating quartz placed in the beamline roughly seven meters downstream of the target. Placed into the beamline, circularly at 45 degree intervals, these act as luminosity monitors, measuring both flux and scattering cross-section of the beam after hitting the lead target. PREX requires high luminosity to achieve the statistic necessary to observe the ppm-level asymmetries required.
Lists of kinds of plots
Detectors Yields (not-normalized to beam current)
SAM signal vs event number. Will read higher values at higher beam current. If signal is zero, check first whether or not SAM HV is off.
SAM Asymmetries
SAM asymmetries are plotted first by themselves, and then correlated with BCM asymmetry.
SAM beam profile/halo sensitivities around the circle/combining 8 Degrees of Freedom
SAM signals and asymmetries are plotted in a circle with the center plot indicating which SAM number corresponds to which SAM position as seen looking downstream along the beam line. Positional differences in the SAM readout may correspond to excess beam halo or give information about the beam profile. They may also act as a diagnostic for the detector expert crew if SAMs are behaving incorrectly.
Regressed SAMs as a noise floor limit indication (Advanced Plots)
Beam Position Monitors (BPMs)
What is a BPM and how does it work?
As the name suggests: a Beam Position Monitor monitors the beam position. A BPM consists of four wires arranged along the beam line
Continuation of Measuring, Controlling and Removing Helicity Correlated Noise in our Main Detector Measurements
Using beam position monitors, to keep track of the momentum/energy fluctuations in the magnetically energy selecting Hall A arc, as well as the 4 degrees of X and Y position and angle onto the target information, allows us to measure helicity correlated beam fluctuations to fairly high precision and then calculate correlation slopes over various time scales and modes of beam motion (normal beam motion and intentionally large modulation induced beam motion) which are then subtracted, per event, from our main detectors to arrive at the remaining physics asymmetry.
Calculated position yield
Beam Position on the target
Abstractly: Beam Angle on the Target
More Abstractly: Beam position as a measure of energy fluctuations in incident electrons
The same, but their multiplet/helicity state averaged differences
The same, but w.r.t. other detectors (SAMs, Mains, AT)
Beam Current Monitors (BCMs)
What is an Unser BCM and how does it work?
What is an analog/normal BCM and how does it work?
What is a digital BCM and how does it work?
What is a cavity BCM/BPM and how does it work?
List of BCM plots we care about
The Beam Current, Micro Amps
Beam charge Asymmetry
Beam charge Asymmetry, correlations with SAMs
Beam charge Asymmetry, correlations with already BCM normalized Main Detectors
Beam Modulation (BMW) Cycle/Response Plots
What is BMW and how does it work?
List of BMW plots
BMW Cycle Heartbeat
Beam Monitors vs. BMW Cycle Number/Phase
DAQ Timing and Synchronization Plots
Our Data Acquisition system (DAQ) is comprised of 5 VME crates and several NIM crates. There is one VME crate in the injector, counting house, and in each HRS hut. These crates are synchronized to all integrate the same time windows and read out the integrated signals at the same time and report them to the Trigger Supervisor (TS) VME crate and the CODA system for online analysis and storage of raw data to disk. We have several redundant systems in place to ensure that the various DAQ components are all measuring exactly the same data and to alert us when anything changes and by how much.
