Design and performance of the Z magnetically-insulated transmission lines
The authors have designed and tested a 10 nH, 1.5 m radius vacuum section for the Z accelerator. The vacuum section consists of four vacuum flares, four conical 1.3 m radius magnetically-insulated transmission lines (MITLs), a 7.6 cm radius 12-post double-post-hole convolute which connects the four outer MITLs in parallel, and a 5 cm long inner MITL which connects the output of the convolute to a z-pinch load. The authors have demonstrated they can deliver a 100 ns rise-time 20 MA current pulse to the baseline z-pinch load. They can reproduce the peak MITL current to within /spl plusmn/1.6%. Power-flow measurements indicate the vacuum section performs as expected until peak current. Afterward, measurements and simulation results diverge.
Computer simulations of the magnetically insulated transmission lines and post-hole convolute of ZR
An important consideration for the success of the ZR project, refurbishing the Z accelerator at Sandia National Laboratories, is limiting current loss in the vacuum section, ideally to no worse than the 5 – 10% seen on Z. The primary source for this loss is electrons flowing into the post-hole convolute from the four magnetically insulated transmission lines (MITLs). The MITLs on ZR have larger gaps to reduce the electron flow to values comparable to Z when operating at ∼40% higher voltage and ∼30% higher current. Electron flow in the vacuum section is analyzed with electromagnetic, particle-in-cell simulations, using two complementary simulation setups. First, the exact MITL profiles are modeled with high-resolution 2-D simulations out to large radius (typically r = 60 cm), providing accurate values for the electron flow into the convolute. Second, the convolute is modeled in 3-D, but with MITLs extending out only to r ∼ 30 cm. The 3-D MITL geometry is modified to provide the same electron flow into the convolute as the 2-D simulations. The 3-D simulations have detailed diagnostics for current loss and surface deposition heating in the convolute.
Reduction of Surface Flashover of the Beam Screen of the LHC Injection Kickers
The LHC injection kicker magnets include beam screens to shield the ferrite yokes against wake fields resulting from the high intensity beam. The screening is provided by conductors lodged in the inner wall of a ceramic support tube. Operation with increasingly higher bunch intensity, and narrow bunches, now requires improved ferrite screening. This will be implemented by additional conductors; however the good high-voltage behaviour of the kicker magnets must not be compromised by the supplementary screening. Extensive studies and optimisations have been carried out, to better satisfy the often conflicting requirements for low beam coupling impedance, fast magnetic field rise-time, high vacuum and good high voltage behaviour. A new configuration is proposed which reduces significantly the electric field associated with the screen conductors and the secondary electron yield of the surface of the ceramic tube. Results of high voltage test results are also presented.