SCIENCE GOAL AND SCIENCE QUESTIONS: WE PROPOSE TO LEVERAGE THE UNIQUE DATASET OF VAN ALLEN PROBE ELECTRIC DRIFT MEASUREMENTS TO REASSESS PLASMA TRANSPORT IN THE EARTH'S INNER MAGNETOSPHERE. IN PARTICULAR WE PROPOSE TO FOCUS ON ONE OF THE OLDEST AND MOST CHALLENGING RESEARCH TOPICS IN RADIATION BELT DYNAMICS: THE RADIAL DIFFUSION PROCESS. WE PROPOSE TO ANSWER THE FOLLOWING SCIENCE QUESTIONS: 1. HOW CAN WE BEST TRANSLATE EXPERIMENTAL INFORMATION RELATIVE TO PARTICLE RADIAL TRANSPORT INTO RADIAL DIFFUSION COEFFICIENTS? 2. WHAT IS THE INTENSITY OF THE RADIAL DIFFUSION PROCESS INSIDE AND OUTSIDE OF THE PLASMASPHERE? 3. WHAT IS THE LOCAL INTENSITY OF THE RADIAL DIFFUSION PROCESS? RELEVANCE TO ONE OR MORE OF THE FOUR DECADAL SURVEY GOALS: INSIDE AN EQUATORIAL ALTITUDE OF APPROXIMATELY 3 EARTH RADII THE ELECTRIC FIELD ORIGINATES MAINLY FROM THE COUPLING WITH THE IONOSPHERE. OUTSIDE 3 EARTH RADII THE ELECTRIC FIELD IS MAINLY DUE TO THE INTERACTION OF THE EARTH'S MAGNETIC FIELD WITH THE SOLAR WIND. THE RADIAL DIFFUSION PROCESS IS A RESULT OF THESE VARIATIONS IN THE ELECTROMAGNETIC FIELDS. THEREFORE THIS STUDY ADDRESSES THE 2ND DECADAL SURVEY GOAL: "DETERMINE THE DYNAMICS AND COUPLING OF EARTH'S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR AND TERRESTRIAL INPUTS". RADIAL DIFFUSION HAS ALSO BEEN OBSERVED AND STUDIED AT OTHER PLANETS SUCH AS JUPITER AND SATURN SO THE PROPOSED STUDY IS ALSO RELEVANT TO THE 4TH DECADAL SURVEY GOAL: "DISCOVER AND CHARACTERIZE FUNDAMENTAL PROCESSES THAT OCCUR BOTH WITHIN THE HELIOSPHERE AND THROUGHOUT THE UNIVERSE". BRIEF STATEMENT OF THE METHODOLOGY: THE PROPOSED STUDY RELIES PRIMARILY ON A MORE THAN TWO YEARS OF SPIN-PERIOD-AVERAGED MEASUREMENTS OF THE ELECTRIC AND MAGNETIC FIELDS FROM BOTH VAN ALLEN PROBES TOGETHER WITH MEASUREMENTS OF THE SPACECRAFT POTENTIAL. THE ANALYSIS OF MAGNETIC FIELD TOPOLOGIES WILL BE CARRIED OUT USING THE INTERNATIONAL RADIATION BELT ENVIRONMENT MODELING LIBRARY (IRBEM-LIB). EACH SCIENCE QUESTION WILL BE ANSWERED VIA THE COMPLETION OF TWO SUCCESSIVE TASKS. TO ANSWER THE SCIENCE QUESTION 1 WE WILL EVALUATE THE DIFFERENCE BETWEEN RADIAL DISPLACEMENT IN SPACE AND DISPLACEMENT IN THE L* INVARIANT COORDINATE. THEN WE WILL EVALUATE THE AUTOCORRELATION FUNCTION OF THE ELECTROMAGNETIC FIELDS. TO ANSWER THE SCIENCE QUESTION 2 WE WILL DETERMINE THE INTENSITY OF THE RADIAL DIFFUSION PROCESS EVERYWHERE BELOW L=3. THEN WE WILL DETERMINE WHICH PARAMETER BETWEEN THE RADIAL DISTANCE TO THE EARTH THE L* INVARIANT COORDINATE OR THE DISTANCE TO THE PLASMAPAUSE IS THE BEST PARAMETER TO SORT RADIAL DIFFUSION COEFFICIENTS. TO ANSWER THE SCIENCE QUESTION 3 WE WILL DETERMINE THE MAGNETIC LOCAL TIME DEPENDENCE OF "RADIAL DIFFUSION" (THE INVERTED COMMAS ARE HERE TO INDICATE THAT STRICTLY SPEAKING RADIAL DIFFUSION IS THE RESULT OF STOCHASTIC VARIATIONS OF THE ELECTROMAGNETIC FIELDS AVERAGED OVER MAGNETIC LOCAL TIME). THEN FOR THE COURSE OF THE PRIME PHASE OF THE MISSION WE WILL DETERMINE THE ENTIRE SET OF EVENT-SPECIFIC RADIAL DIFFUSION COEFFICIENTS. RESULTS AND PERCEIVED SIGNIFICANCE: THE RESULTS OF THE PROPOSED PROJECT WILL INCLUDE: (1) THE FIRST EVER CALCULATION OF RADIAL DIFFUSION COEFFICIENTS EVERYWHERE BELOW L=3 BASED ON IN-SITU MEASUREMENTS (2) THE FIRST EVER CALCULATION OF RADIAL DIFFUSION COEFFICIENTS IN THE RADIATION BELTS AS A FUNCTION OF THE PLASMAPAUSE LOCATION (3) THE FIRST EVER CALCULATION OF LOCAL RADIAL "DIFFUSION" COEFFICIENTS AS A FUNCTION OF MAGNETIC LOCAL TIME AND (4) THE FIRST EVER CONTINUOUS CALCULATION OF EVENT-SPECIFIC RADIAL "DIFFUSION" COEFFICIENTS. OUR RESULTS WILL CONTRIBUTE TO ENHANCE BOTH OUR UNDERSTANDING OF RADIATION BELT DYNAMICS AND OUR NUMERICAL MODELING CAPACITY.