Development of a single and multichannel biplanar vacuum photodiode for x-ray detection is reported, which has been used to study the x-ray emission from laser produced plasma expanding across an externally applied magnetic field. Two to three times enhancement in x-ray emission has been observed which was found correlated with decrease in size of the x-ray emitting plasma plume (expansion velocity of plasma). Experimental observations were found in close agreement with the analytical model based on an increase in plasma density as a result of plasma confinement in magnetic field. Temporal evolution of x-ray emission indicates that recombination radiation seems to be playing an important role in x-ray enhancement.