general relativity - How much Energy to create a 'warp field' according to White?

An Alcubierre Drive is a hypothetical device that can move a place someplace else faster than the speed of light without violating known laws of physics. This paper provides some equations as to the energy density in such a field, as well as proposals about testing the theory experimentally and finding modes of applications.

One application is described as follows:

the spacecraft departs earth and establishes an initial sub-luminal velocity $v_i$, then initiates the field. When active, the field’s boost acts on the initial velocity as a scalar multiplier resulting in a much higher apparent speed, $v_{\text{eff}}= γ v_i$ as measured by either an Earth bound observer or an observer in the bubble. Within the shell thickness of the warp bubble region, the spacecraft never locally breaks the speed of light and the net effect as seen by Earth/ship observers is analogous to watching a film in fast forward. Consider the following to help illustrate the point – assume the spacecraft heads out towards $\alpha$ Centauri and has a conventional propulsion system capable of reaching $0.1c$. The spacecraft initiates a boost field with a value of 100 which acts on the initial velocity resulting in an apparent speed of $10c$. The spacecraft will make it to $\alpha$ Centauri in 0.43 years as measured by an Earth observer and an observer in the flat space-time volume encapsulated by the warp bubble.

A formula to arrive at $\gamma$ is given in the paper. Now ...

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  I assume that the lower limit to create such a "warp bubble" is independent of the method or device or whatever used, there's a hard lower physical limit - is this even correct?

  
  



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  Now, as an example, how much energy would be needed to create a boost factor $\gamma$ of 100 for a golf ball (or any other arbitrary sized volume)?

  
  


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  Where does this energy go?

  
  

While White mentions an experimental setup to test the theory with only a ring of capacitors, others mention exotic matter to be neccessary. I don't want to go into details of implemementation in this question. Since my question is about the physical limits, it's here on Physics SE and not over at Space exploration.