Target EPICS Information

Target EPICS Variables in the Run-End Statements and in the Data Stream

A subset of the EPICS variables which read Hall A cryotarget information are displayed in the run-end halog entries, and are part of the epics events which are appended to the data stream about every 8 seconds. Below you will find a list of the hardware names and the connected sensor. The figure will give you the location of the temperature sensors in the loop and the pressure transducers in the gaspanel.

haBDSPOS	lifter position
haL1_Fan_frequency_R	loop 1 fan / Hz
haL3_Fan_frequency_R	loop 3 fan / Hz
haSC200_6_Sensor_1_R	PT255 / psi
haSC200_6_Sensor_2_R	PT267 / psi
haSC200_6_Sensor_3_R	PT265 / psi
haSC200_6_Sensor_4_R	PT259 / psi
haHe_Omega_DPG_Sensor_R	DPT269 / psi	not calibrated
haITC502_1_Sensor_1_R	CT97 / K
haITC502_1_Sensor_2_R	CT96 / K
haITC502_1_Sensor_3_R	CT93 / K
haITC502_4_Sensor_1_R	CT94 / K
haITC502_4_Sensor_2_R	CT105 / K
haITC502_4_Sensor_3_R	CT116 / K
haITC502_5_Sensor_1_R	CT171 / K
haITC502_5_Sensor_2_R	CT170 / K
haITC502_5_Sensor_3_R	lead target / K
haITC502_6_Sensor_1_R	CT168 / K
haITC502_6_Sensor_2_R	CT169 / K
haITC502_6_Sensor_3_R	not connected

The snapshot was taken when the target was warm.

pressure transducers

In December, the pressure transducers were not shielded. After a few days of high beam, they started to drift, and their readings are essentially not usable. Before the experiment started, the target was filled up to 112.1 psi. The first logged reading (in e89044_1293.dat.0) was 109.5 psi. I don't know if this was a miscalibration or already radiation damage. It should be ok to assume that the target pressure was 112 psi trough December.

During the January shutdown, the transducers were shielded and calibrated, and additionally PT267 was moved behind the green wall. Focussing on PT267 only, it seems the transducer was reading fine, except for an slowly increasing offset versus the mechanical reading, which is believed to be accurate. The offset was +2.3 psi on February 25, +4.0 psi March 16, and +6.5 psi during E93049 (about end of April). This offset has to be added to the PT267 readings for February and March.

temperature sensors

After commissioning, the temperature profile of the target was as follows:

The three sensors CT97, CT96, and CT170 before the beam were showing the nominal target temperature of 6.30 K.
Two sensors CT168 and CT93 after the beam were showing identical temperatures, which were higher than 6.3 K depending on the beam current. This indicates that the gas heated by the beam and the surrounding cold gas is already squirled at the position of CT168, about 3" above the beam.

CT169

The sensor directly before the beam, CT171, was somewhere between both temperatures, also indicating that the funnel in the gas flow creates turbulences so that the deposited heat has also some effect upstream of the flow.

It was expected that the sensors located in the Helium cell block would show radiation damage first. Indeed, after a few days CT171 and CT168, and later CT170 and CT169, indicated radiation damage, i.e. showing higher temperatures than the other sensors, thus there was an offset in their readings. This offset increased slowly, but in this stage the readings were still useful. An offset of the day can be calibrated if the beam is off and the target is stable. Much later sensors broke completely, i.e. they were showing wildly jumping readings and were not useful at all.

Sensors CT97 and CT96 before the beam and CT93 after the beam were working all through E89044 and should be used to monitor the target temperature. It should be emphasized that CT93 gives only the indication that the gas temperature in beam is higher than the nominal one, but does not read this temperature.

Michael Kuss, July 24, 2000