AbstractThe Beam loss Ion Chamber System (BLICS) wasdeveloped to protect Jefferson Labs transport lines, targetsand beam dumps from a catastrophic "burn through." Rangechanges and testing was accomplished manually requiringthe experiment to be shut down. The new upgraded systemis based around an "off the shelf" Programmable LogicController located in a single control box supporting up toten individual detectors. All functions that formerly requiredan entry into the experimental hall and manual adjustmentcan be accomplished from the Machine Control Center(MCC). A further innovation was the addition of a HighVoltage "Brick" at the detector location. A single cablesupplies the required voltage for the Brick and a return linefor the ion chamber signal. The read back screens displayrange, trip point, and accumulated dose for each location.The new system is very cost effective and significantlyreduces the amount of lost experimental time.

BEAM LOSS ION CHAMBER SYSTEM UPGRADE FOR EXPERIMENTAL HALLS*

D. Dotson, D. Seidman, Jefferson Lab, Newport News, VA. 23606, USA

Thomas Jefferson National Accelerator FacilityNewport News, Virginia, USA

Work performed under DOE Contract #DE-AC05-84ER40150

Figure 1A: Schematic Layout of Probe

HIGH VOLTAGEThe need to string high voltagecables has been eliminated byusing a High voltage ‘Brick”. DCPower 0 to 5 V to the brickproduces 0 to 1000 volts to bias theion chamber. Typically the biasvoltage is set to 500 vdc.

INTRODUCTIONThe original beam loss protection system components haveproven to be reliable with over ten years of use. Thesecomponents are incorporated into the new upgraded systemwith added functions to enhance performance andinformation retrieval. Each system can be functionallytested from the Machine Control Center (MCC) withoutentering the hall. A local touch screen control panel locatedin the base cabinet allows for local testing andtroubleshooting. Each card channel has monitoring ledsindicating circuit status. The coaxial Argon filled ionchambers, a Jefferson Lab design, have proven to bereliable and very resistive to radiation damage. The originalsystem was tested at Georgia Tech from 100 rads to onemillion rads/hr.

Figure 1B: 1 Foot Detector in ABS Housing

Figure 1C: 10 Foot Ion Chamber in ABS Housing

READ BACK AND DATA LOGGINGThe readout and data logging screensdisplay dose rate in rads/hour, total doseand elapsed dose since last reset. Thisfeature allows Users to monitor theabsorbed dose of their radiation sensitiveelectronics and to map the radiation fieldsfor a given target energy and current.

Figure 3: Read Out and Archiving

Figure 4: Typical Ion Chamber Placement

Figure 2: Electronics Base and PLC Controller

THE PLCThe PLC interface allows for configuration changes without requiring an access to theexperimental halls. The gain/range can be configured from the control room through an EPICSinterface or locally at the PLC through a touch screen. The high voltage thresholds remainedconfigurable through hardware limits to prevent damaging the ion chambers. The PLC isdesigned to handle 8 ion chambers but can be upgraded to 16. A fast shutdown circuit is providedfor each channel.PLC Functional Features► Signal Response range 0 – 999,999 rad/hr ► Reaction time <200us from fault detection to

Removal pf FSD permissive ► Fault protection of probe is disconnected► Complete EPICS control► Local control through a touch screen► Off the shelf PLC parts► Heartbeat (read only)► Dose Rate (read only) ► ADC read back of the dose rate (read only)► Current gain setting (read/write)► Channel fault indicator (read only)► Input limit threshold settings (read/write)► Channel Status (single/multiple► Confidence test controlled to produce an FSD

THE DETECTORA simple rugged coaxial designconsisting of two Copper pipes, twoend caps, a high voltage feed throughand a Schrader valve for back fillingwith Argon gas. Lengths from 1 to 20feet have been constructed andtested. This is illustrated by Figure1A, 1B, and 1C.

Figure 5: Calibration Testing of System

Radiation levels produced by each target, energyand current can be graphed and archived to assistin selecting trip points levels for a given experimentand hall conditions.

Future Upgrades and ImprovementsA new detector using 2” Helax cable with internal checksource is being evaluated this fall. The detector, withslight modifications to the electronics will be radiationposition sensitive and is flexible enough to be bent into an8 foot radius. This will allow radiation position detection ina 350 degree arc or linearly.

CONCLUSIONThe new upgrade will decrease the lost beam time whichis about $10,000 per hour. Using the remote featuresthree times will pay for the upgrade. The upgrade allowsfor future expansion of system to 16 channels per base.