HRRL Electron OSA

Operational Safety Assessment First Beam Tests in the High Repetion Rate Linac (HRRL) at the Particle Beam Laboratory 05/26/2006

1. Accelerator Description and Test Purpose

IAC and the Physics Department have installed an S band linac (HRRL) with a high duty cycle modulator and microwave power system in the linac cell in the Particle Beam Laboratory (PBL). This cell is located in the basement section under the new addition to the Physical Science Building. The cell was designed to house an e-linac, the new system replaces a 4 MeV and a 18 MeV accelerators previously operated for a period of 3 years in this cell. The new HRRL features a short beam pulse (50 ns.) with a repetion rate of up to 2000 Hz. The beam energy is expected to be ~15 MeV. Due to the short beam pulse, high radiation output is not expected. An estimate of output dose can be made based on scaling the new pulse length and rep. rate with the former 18 MeV system’s characteristics (50ns at 2000 Hz vs. 3 microsecond at 120 Hz). This calculation indicates the new system will produce ~1/3 the dose of the former accelerator, thus, the limiting conditions of operation will be determined by the duty cycle of the electron gun. The test objectives covered by this OSA are to inject beam into the accelerator while keeping the rep. rate below 100 Hz. This test will allow various accelerator-tuning issues to be understood as well as give a scalable indication of total radiation dose as a function of gun pulse duty cycle and providing the information that we need to define the safety envelope and associated operational parameters. For this series of tests the beam will only be directed through the 0° port of the accelerator and the two beam holes into the test area will be blocked with shielding material. The intent of this Operational Safety Assessment is to address the radiation safety related aspects for these experiments.

2. Safety

The initial beam injection test will be monitored by the ISU Technical Safety Office (TSO) to establish safe operations (SO). Upon the establishment of SO the TSO will provide monitoring as determined necessary based on initial operations. To address the operational safety needs shielding, interlocks, warning lights, audible signals, manual scram buttons, radiation survey instruments, and in the shielding properties of the building will be utilized. A diagram is attached.

1. Interlocks. The HRRL power supply is interlocked to the current building interlock system such that the access to the operational cell area will break the interlock chain disabling the accelerator. After the interlocks are set and before the accelerator will operate an audible and visual warning will be activated. Interlock characteristics are as per the standard IAC interlock system including, lights, keys, scrams, inspection buttons, etc., as follows: a. Lights. Rotating beacons, yellow for interlocks set, red for beam on. b. Audible Alarms. After interlocks are set a 30-second audible alarm is sounded. Only after the cessation of the audible alarm will the accelerator operate. c. Keys. A key is required to set interlocks and a separate key must be set to allow the enable button upon the accelerator computer touch screen to actuate. d. Scrams. Scram buttons are collocated with inspection buttons. Depressing a scram will deactivate the interlocks shutting off the accelerator and require the interlock arming procedure to be repeated before resuming operation. e. Inspection Buttons. These buttons must be depressed within two (2) minutes of final interlock setting. f. Area Monitors. When operating limits are established area monitors will be interlocked to the accelerator such that at preset limit the accelerator will be caused to trip off. g. Area Monitor #2. This is an independent monitor that will indicate dose rate at the cell door.

2. Survey instruments. No entrance into the cell radiation area will be allowed after tests without the presence of the operator or operator designee with out the Power Supply Key, and a TSO-approved survey meter.

3. Operators. Only IAC professional staff will operate the HRRL during the tests.

4. Radiation surveys. Surveys of the 1st floor areas and other potential hot spots will be conducted by TSO personnel and/or TSO designees.

5. Radiation Measurements to be made. TSO or designee will make radiation field measurements. a. Left East Wall Beowulf room b. Corridor and Control Area c. Upstairs in W end of Physics Offices d. Outside on W end of addition e. In the vicinity of the klystron