A NOVEL THIN FILM DIAMOND STRIPPER FOIL FOR TANDEM ION ACCELERATORS

ONCE DEVELOPED, THIN FILM DIAMOND STRIPPER FOILS SHOULD SIGNIFICANTLY ENHANCE PERFORMANCE AND MAINTAINABILITY OF DOE'S HIGH ENERGY TANDEM ION ACCELERATORS. SUCH REACTORS ARE USED FOR BASIC RESEARCH IN THE STUDY OF NUCLEAR STRUCTURE AND HEAVY-ION REACTIONS. HIGH ENERGY TANDEM ION ACCELERATORS CREATE MEV POSITIVE ION BEAMS IN TWO STAGES. NEGATIVE IONS ARE CREATED IN THE FIRST STAGE AND ARE THEN ACCELERATED AND FIRED THROUGH A STRPPER FOIL. THE FOIL STRIPS AWAY TWO ELECTRONS, PRODUCING HEAVY POSITIVE IONS WHICH ARE THEN ACCELERATED IN THE SECOND STAGE TOWARD A TARGET IN THE ACCELERATOR'S END STATION. STRIPPER FOILS ARECURRENTLY MADE OF GRAPHITE AND AMORPHOUS CARBON. THEIR LIFETIMES ARE VERY SHORT (6 TO 10 MINUTES) WHEN BOMBARDED WITH HEAVY IONS. THE ACCELERATOR MUST BE SHUT DOWN TO REPLENISH THE STRIPPER FOILS. DIAMIND IS WELL SUITED AS A STRIPPER FOIL MATERIAL OWING TO ITS EXCEPTIONALLY HIGH THERMAL CONDUCTIVITY, EXTREME HARDNESS, AND HIGH MODULUS. FURTHERMORE, ELECTRICALLY CONDUCTING BORON-DOPED DIAMOND WOULD PROVIDE LOW RESISTIVITY AND THUS MINIMIZE THE POSSIBILITIES OF CHARGE BUILDUP IN THE FOIL. THE OBJECTIVE OF THIS PROJECT IS TO ESTABLISH A CONTROLLABLEPROCESS FOR PRODUCING THIN FILM DIAMOND STRIPPER FOILS FOR HIGH ENERGY TANDEM ACCELERATORS. THE DEVELOPMENT EFFORT WILL BE ACHIEVED THROUGH A TWO-PHASE PROGRAM. PHASE I EFFORTS WILL DEVELOP A PROCESS FOR PRODUCING FREE-STANDING FILMS OF POLYCRYSTALLINE DIAMOND, 200 TO 1000 ANGSTROMS IN THICKNESS, TENSIONED OVER A CIRCULAR SUPPORT STRUCTURE. ACHIEVING HIGH NUCLEATION DENSITY OF VAPOR DEPOSITED DIAMONDFILM IS ESSENTIAL TO PROVIDING THE REQUISITE DIAMOND FILM UNIFORMITY. FILMS DEVELOPED IN PHASE I WILL BE DOPED WITH BORON TO CHANGE THEM FROM INSULATING TO ELECTRICALLY CONDUCTING. IN THE PHASE II EFFORT, PROTOTYPE DIAMOND STRIPPER FOILS WILL BE SUBMITTED TO SELECTED DOE NATIONAL LABORATORIES FOR TEST AND EVALUATION IN TANDEM VAN DER GRAAFF ACCELERATORS. BASED ON EXPERIMENTAL RESULTS, EFFORTSWILL BE MADE TO ENHANCE THERMAL CONDUCTIVITY AND STRENGTH OF THE FILMS TO PROVIDE IMPROVED LIFETIME AND PERFORMANCE.