Both TARPOS and cryoTARPOS are provided with three gas systems that enable in situ target filling with various combinations of cryogenic and condensable gases. Each positioner contains five gas lines that run from the target interface through the positioner boom to the wall-mounted target gas manifolds (TGMs) in the target bay. One line is a high-pressure line, normally used to ll cryogenic capsules. Two additional lines are typically used to ll hohlraums with low-pressure cryogenic gases. The final two lines are normally used to fill warm targets with low-pressure condensable gases. Lines are typically 0.030” internal diameter stainless steel, ending in VCR fittings near the target interface.
Three nearly identical TGMs are provided for each positioner (Figure 5-7). These provide the remotely operated valving, sensors, and vacuum resources necessary to pump/purge the targets and associated gas lines and ll them with the proscribed gas ll at the requested pressure.
With the exception of 4He, gases are filled from individual shot bottles that are filled on site with the requested gas mixtures. Shot bottles may be used for one to several shots, depending on the gas type, requested shot pressure, and bottle size. The target operations group manages the gas bottle preparation and operations. Custom gas mixtures are characterized on-site by mass spectrometry. Certifications for all gases used are available through the Location, Component, and State (LoCoS) system.
A number of different gases and gas mixtures and various pressures have been shot to date. Tools to assist in calculating cryogenic gas properties are available; a target gas density calculator can be requested from the NIF User Office, or see the Target Operations group for assistance.
Commonly used gas fills (the combinations of gas mix, fill pressure, and temperature) are listed in Appendix D. (A current version may be obtained from the Target Operations group). These are considered standard, and may be routinely specified by experimenters. Other combinations are possible, but may require significant advance planning and effort (or may not be possible due to physical or equipment limitations). Contact the Target Operations group very early in the planning process to help ensure that your request can be accommodated.