"initial prototype" is correct and can be used in written English.
You can use it when discussing the first iteration of a design or product, such as the "initial prototype of the photovoltaic cell".
However, Google calculated the cost of a building an initial prototype at close to $200m£144m4m).
On Monday, the Vanish researchers responded that they had now modified their initial prototype to use multiple file sharing networks, complicating the task of an attacker.
Morrill built a lot of the initial prototype herself.
They built the initial prototype in four months.
The initial prototype implementation interfaced to the Objectivity/DB.
Experimental results obtained from an initial prototype are also presented.
This result is also supported by initial prototype results.
We stumbled through an initial prototype that barely booted, but we finished it in a month.
An initial prototype looked like a 'tween in footie pajamas and a full-face hood.
An initial prototype was made by a compact computerized numerical control machine.
The initial prototype also includes implementations of clustering algorithms and feature selection tools.
