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    User name B. Craver

    Log entry time 17:36:17 on July 21, 2006

    Entry number 174738

    keyword=Instructions for taking beam on cryotarget

    This document is also posted near the target computer in the counting house.

    Instructions for taking beam on cryotarget: July 21, 2006

    The following steps are necessary to bring the cryotarget from standby mode (with the target out of the beamline for a significant period of time) to active mode (in preparation for placing the target in the beamline.)

    Communicate with Hall C - Coolant is provided to the halls by the End Station Refrigerator (ESR). There is a limit of 25 g/s on the net flow which may be provided. Therefore, we need to estimate the amount of coolant we require (explained later) and discuss with Hall C before increasing our coolant flow in preparation for the beam.

    Adjust Fan Speed - The appropriate fan speed is 60 Hz ($25 \%$) on the hydrogen loop and 48 Hz (20 %) on the deuterium loop while the cryotarget is positioned in the beamline. Increasing the fan speed results in a significant increase of power on the cell. Therefore, it is necessary to first increase the coolant flow (as explained later) to compensate this increase. Also, one should not alter the fan speed by more than 5 % (less may be better until you are familiar with the response of the system) before allowing the system to stabilize. It may be changed from the "HALL A CRYOTARGET CONTROLS" screen by either clicking "Fan Controls" and selecting the appropriate loop or by clicking the appropriate loop and selecting "Fan Controls." Enter the desired speed in units of percentage of full power (full power = 240 Hz), i.e. 25 will set the fan speed to 60 Hz. During standby mode the fan speed is reduced to 20 %, or 48 Hz.

    Adjust Flow Rate by Opening JT Valve - The beam will deposit energy into the cell and increase its temperature. It is, therefore, necessary to first increase the coolant flow while the beam is not on the target. The high power heater (HPH) will respond by increasing its output to compensate an increased flow rate. This allows a buffer when the beam comes on. The beam deposits 50-60 W of power per 10 A. The target operator must be aware of the intended beam current and estimate the necessary excess heat that will be needed from the HPH to compensate for it. The operator may then step the JT valve open in single steps of stepsize not greater than 1.0. After adjusting the flow rate, allow time for the system to stabilize before further adjustments. The JT valve for each loop is controlled from the "CRYOTARGET CONTROLS" screen similarly to the fan speed. One should insure that the HPH responds as expected and that the stable-state temperatures and pressures do not vary. Continue the process until the HPH is providing the estimated amount of power plus an additional amount which will allow for fluctuations in beam current; typically ~30 W.

    Conclusion - It may not be possible to precisely predict the flow rate required for a given beam current. Therefore, the target operator should monitor closely the flow rate on the ESR charts, especially when adjusting the JT valves, to verify that the flow to Hall A does not cause the net flow to exceed 25 g/s.