Some notes on what and when the things should be prepared for the RHIC ramp measurement

Osamu Jinnouchi Dec. 2004

(this note is written based on the measurement condition till run-04, after run-05 the things might be changed due to the newly installed RHIC polarimeter application)

Basic concepts

Final goal of the ramp measurement is to get the asymmetry information of RHIC polarimeter as a function of time during the ramp. To achieve we need to get following information during the data taking time assigned for this work.

1. Beam energy information synchronized with RHIC polarimeter data acquisition system (why we need this? Because we want to see the asymmetry behavior in terms of beam energy so that accelerator physicists can tell which energy point the asymmetry drops) we need the resolution of about 1 second for this synchronization.

2. RHIC polarimeter data in event by event mode

Data acquisition time would be 3-6 minutes depending on up to which part of the ramp you are interested in. The data are temporally stored in on-board memory. For the readout to local hard-drive, the time of about 40miniutes was needed in Run-04, this will be expected to be fasten to a few minutes after Run-05 because of the newly introduced fast CAMAC controller.

3. (important but never fully succeeded) During the ramp, the RHIC beam traverse drastically in both X, Y directions. There will be an effort to reduce this beam motion to a certain level, but on the other hand, if this movement is predictable from the previous fills, the carbon target position should be controlled and be kept at the center of the beam all the time to avoid asymmetry drop from the polarization profile.

Preparation what will be used for data taking

The following explanations are corresponding to the items above.

4. For item 1, we use the “BeamGamma.mon” application from Gpm (RHIC à Polarimeter à BeamGamma.mon) . The energy info is stored by selecting, logging à start logging à start logging (Using Existing Log Request) à ….. à stop logging when the data taking is over. The format of this logging can be modified from logging à Submit New Log Request. The log data will be stored in “/app_store” as a “sdds” format, here is the example. /app_store/RunData/rhic_pp_fy04/05331/RHIC/Polarimeter/BeamGamma/2004-05-12.1523.sdds. This BeamGamma.mon might be integrated on the new RHIC polarimeter application for Run-05.

5. For item 2, RHIC CNI daq configuration file needs to be optimized for this measurement. Before each measurement, the configuration file “rhicpol.ini” is replaced (copied) with the already prepared initial files according to the data acquisition mode. In case of “event mode”, the file “rhicpol_at.ini” is used. Important variables need to be set for the ramp measurements are,

o SleepFraction – Since the ramp measurement is a huge data, there will be a memory flow depending on the luminosity (proportional to target density, beam intensity, size and depending on the target position in the beam). To avoid this, data acquisition program will intentionally make a dead-time for the fraction of time within each second, for example SleepFraction=0.70 will cut 70% of the data, and default value is 0.0. This value needs to be empirically optimized from memory size and signal rate.

o ETLookUp – this define the ADC x TDC range to look at for the data acquisition rate. By default, this variable is set as 0, and counts only the range within banana cut. Since we want to monitor the count rate which corresponds to the event data counts, we need to define the range as the rectangular with the same size as the actual data storage. ETLookUp=1 change this area to rectangular defined as same as event data taking.

o RevolutionDelim – this change the RHIC polarimeter internal timing information from 20Hz (when set to 0) to 144Hz (when set to 1) from Run-05, this should be always set to 1.

6. For item 3, what we can do at most is to speculate the beam path from the previous records of BPMs.

Procedures of the measurements

Followings are very simplified summary on the RHIC polarimeter side

1. Take regular runs (usually twice), from Run-05 this regular runs are supposed to be the event mode all the time.

2. prepare the configuration file

3. start logger of BeamGamma.mon

4. set the limit of measurements on RHIC polarimeter application (or pet page) to proper values (number of events and time of measurement)

5. start the special run

6. stop manually when the ramp end

7. stop the BeamGamma.mon logger

8. when the data readout is finished, do the regular runs

Offline Analysis tips

After the data collection, there are several points we need to take into account for the offline analysis

1. The RHIC clock signal is shifting smoothly from injection to flattop beam energy, due to the finite signal speed inside the cable and long cable length from 4 to 12 o’clock for the clock, thus so called “banana locus” in RHIC polarimeter data also shift as the energy goes up, and we need to adjust the timing cut at offline analysis according to this movement

2. The internal timing information in RHIC polarimeter is a relative time from the beginning of data taking. Although the start time (when the command was issued) was logged in the RHIC polarimeter log file, there is a gap between this written time and the real data taking time (carbon target movement time). Ambiguity is about a few second. The real data taking start time needs to be embedded in the data stream from Run-05.