Due to federal restrictions contained in the current National Defense Authorization Act, citizens of the People's Republic of China-including the special administrative regions of Hong Kong and Macau-as well as citizens of the Islamic Republic of Iran, the Democratic People's Republic of Korea (North Korea), and the Russian Federation, who are not Lawful Permanent Residents ("green card" holders) are prohibited from accessing facilities that support the mission, functions, and operations of national security laboratories and nuclear weapons production facilities, which includes Los Alamos National Laboratory. The LLRF team works on ultra stable frequency sources, solid-state and vacuum tube based amplifiers, temperature controlled coaxial lines spanning the length of the accelerator, electronics detecting the beam amplitude at the injector, resonance control systems compensating for cavity changes due to RF heating and fast electronics meant to prevent a cavity arc from damaging amplifiers producing megawatts of power.