1) Discussion of the plan what we should do to come to a decision on the power supplies, cable plant, electronics, and service tunnel configuration in BDS. -- All
2) Work on ILC2006b optics of BDS -- Mark Woodley
3) Sacrificial collimators in BDS -- Lew Keller


The group started discussion of the issue of power supplies, electronics, cable plant, service tunnel in BDS.

Discussed configurations included:
a) full length service tunnel in BDS
b) short service tunnels in BDS entry and IR
c) short service tunnels in BDS entry and IR and alcoves every 50-200m
d) no service tunnels, all PS in main tunnel
e) no service tunnel, multiple small penetration from surface where PS are installed

Relevant issues that was mentioned were
1) cable size and cost
2) power dissipation in the tunnel and needed temperature stability
3) radiation environment in BDS
4) maximum length of cables for BPMs

The rough constrain on the cable length for the cavity BPMs is less than 100m (Steve Smith). If there are no service tunnel, this drives a requirement of the alcoves every 200m or less.  The alternative is radiation hard electronics with corresponding R&D.

Power dissipation in the tunnel and stability: the discussed target number in less than 10W/m into the air. According to Marc Ross, the achieved number at Swiss Light Source (where special care was taken to minimize this heat) is about 100W/m and the tunnel temperature changes by 0.5 degree C, which may be not sufficiently stable for BDS.   In the earlier NLC configuration, the power supplies were located on surface and cable run down via penetrations located every 500m so that total cable length was <250m. The cables were oversized by 2AWG numbers, to achieve <10W/m. 

Evaluation of these configurations will be done in the following steps. According to Tom Markiewicz there is a 1999 spreadsheet which can automatically "design" magnets based on aperture and field, determine power and cable layout and power dissipation along the tunnel. This can be reprogrammed for various locations of power supplies. This tool will be updated and used for BDS.

In meantime, real design of magnets in BDS will proceed, and for this to be done, a set of assumptions need to be fixed. For example, the pressure and temperature of cooling water, allowable temperature increase of the water, etc. 

There were other issues discussed which are not captured in these sparse notes.


Mark presented the updated BDS optics ILC2006b. The tune-up extraction line was redesigned for 10% bandpass. Sacrificial energy collimator is included into the chicane. The first betatron sacrificial collimator is removed to provide more than 20m from the end of the linac. Parameters of kickers and septa were optimized. Beam sweeping system is included into the tune-up beamline.


Lew presented evaluation of sacrificial collimators. FLUKA model shows that 200 full energy bunches would melt and vaporized the material over a length of about a meter. Carbon collimators are somewhat better, but the damage from the full power beam is still substantial. The spoiler-absorber configuration was not checked but expected to be difficult to implement. Therefore, the sacrificial collimators are indeed sacrificial and would need to be inspected and replaced after every incident.

Andrei Seryi, 04/14/06