Before revision: Alternatively the heated cathode can be used as one of the reflectors, eliminating the need for a dedicated URL URL or a directly heated cathode is URL Oxygen or oxide based gases such as carbon dioxide can also be used for ions such as carbon.
After revision: Alternatively this heated cathode can be used as one of the reflectors, eliminating the need for a dedicated URL URL or a directly heated cathode is URL Oxygen or oxide based gases such as carbon dioxide can also be used for ions such as carbon.