[Neutron] Response from ESS-Hungary and ESS-Scandinavia

[Christian Vettier]

                                                             Debrecen/ 
Budapest & Lund, 17th October 2008
Comments of ESS-Hungary and ESS-Scandinavia

In a press release of 26th September 2008 the ESS Bilbao team launched  
a Call to prepare “a modernized baseline for the coming European  
Spallation Source”. We are convinced that this call was launched with  
good intentions, however, we must point out that it is neither timely,  
nor does it represent a proper use of resources at this stage. Our  
carefully considered position is that there is no need for the  
additional site independent study on ESS proposed by this Call.  
Actually the approved schedule of the ongoing EU FP7 ESS Preparatory  
Phase project contains all necessary site independent work and has  
been carefully elaborated in consensus between the coordinator PSI/ 
ENSA, the teams of the 3 ESS site candidates, including Bilbao, and 7  
leading European research institutions interested in ESS.

Indeed, recent developments in accelerator design at various  
laboratories around the world strongly confirm the enduring validity  
of the basic design choices made by the ESS project team up to 2003.   
The outstanding work of this team paved the way for SNS at Oak Ridge  
to decide to switch to superconducting technology after their project  
started, and it is vindicated by the convincing success of the SNS  
linac. In particular the ESS reference design consists of “mostly  
superconducting cavities”, currently for 70 % of the acceleration of  
the protons. The option for 86 % has been considered in the original  
ESS study and the option for more than 90 % at Los Alamos in the  
framework of the preparation of the LANSCE refurbishing proposal in  
2005. These in-depth evaluations have shown that the decisive  
advantages of superconducting linacs primarily include the reduction  
of the induced radioactivity in the accelerating structures. They  
offer no essential savings in construction and purely operational  
costs. By going to nearly fully superconducting acceleration, instead  
of 70%, the additional saving in energy consumption would also be  
marginal (e.g. 1 MW extra power would be needed for refrigeration),  
while the total length of the accelerator would indeed be reduced by  
about an extra 100 m. In itself, however, this is a real advantage  
only if available space is constrained (which is not the case for  
Debrecen and Lund). Thus the site independent work suggested in the  
ESS Bilbao Call has already been basically accomplished.

By contrast, what remains to be done is a detailed, site specific  
technical update and optimization of the ESS reference design in view  
of the latest developments and experience gained world wide (such as  
superconducting cavity systems with higher acceleration capability per  
meter length) and benefit potentials of co-ordination with current  
accelerator projects.  This update will:
a) amount to an effort of about 30 M€ and is a process envisaged by  
all sites to be completed before construction starts
b) be performed by the best Pan-European team of experts and will  
result in the same optimal use of latest state-of-the-art technology  
whichever site will be selected
c) provide the additional technical input required to refine the  
precision of the project costing.
Such an effort would require a siting decision for ESS: site specific  
boundary conditions (such as sloping or flat terrain, ground water  
conditions,…) and funding time lines should be known in order to  
achieve optimum efficiency.

László Rosta, on behalf of the ESS Hungary Team	, and Colin Carlile,  
on behalf of the ESS Scandinavia Team
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