What is vascular cambium?
I know nothing about plant physiology but I googled your question and here is what I found
Vascular cambium
From wiki

The vascular cambium (plural cambia) is a plant tissue located between the xylem and the phloem in the stem and root of a vascular plant, and is the source of both the secondary xylem growth (inwards, towards the pith material at the center of plant, often dead and/or deteriorated, that is composed of parenchyma tissue) and the secondary phloem growth (outwards [to the bark, rough or smooth, of the plant]). It is a cylinder of unspecialized meristem cells that divide to give new cells which then specialize to form secondary vascular tissues.

Intra fascicular cambium
From Biology.easlife

The cambial strip which is present between the primary xylem and primary phloem is known as the intra fascicular cambium. The intra fascicular cambium is also known as the vascular cambium. During the secondary growth the cambial ring is formed by the inter connection of the intra fascicular and inter fascicular cambium. - See more at: http://www.biology.lifeeasy.org/5040/what-is-intrafascicular-cambium#sthash.aY3SPblI.dpuf

What is the difference between fascicular cambium and inter fascicular cambium?
From biology.lifeeasy

The cambium present within the vascular bundle is called intra fascicular cambium or vascular cambium. It is present between the primary xylem and primary phloem. The intra fascicular cambium is primary in origin.
The new strip of cambium which is formed from the permanent cells of inter fascicular parenchyma is called the inter fascicular cambium.  The inter fascicular cambium is secondary in origin since it is derived from the permanent cells of medullary rays.

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