Minutes of 47th FFIR/BDSIM meeting on 2/6/2003
The meeting was held in a room of 425 at KEK, 13:00-15:00, 2/6/2003. We discussed on beam dump and FEATHER.
(1) Beam dump(S. Ban, KEK)
(transparencies, 6 pages, pdf ,555KB )
First, S. Ban reviewed specifications of beam dumps at various accelerators; CEBUF, SLC, TESLA and NLC, in terms of beam energy, beam power, artificial beam blowup, absorber, windows (number, material, size), diameter and length of beam dump, material of apparatus, water circulation system and hydrogen abundance, etc. .
Beam power of future colliders (JLC,NLC, TESLA) is about 11 MW , which is several times higher than those of previous ones. Material of absorber must be water in the case of high beam power, while a combination of water in front and Al or Cu or Fe back has been used. Diameter of window size ranges from 10cm to 15cm. Diameter of dump ranges from 120cm to 150cm. Absorption length of dump widely ranges from 18 to 50 r.l. , where metallic dump has longer radiation length. Temperature rise is controlled within 40 degree C by flow rate of water. Hydrogen abundance is estimated to be 3.3 liters/sec at JLC,NLC and TESLA, while it was 0.7 liters/s at SLC (2.2MW operation at 360Hz).
He listed the zero-th order specifications of JLC beam dump as follows, which correspond to the case of 1TeV center-of-mass energy;
He also estimated products in the dump as follows;
|Average beam current||23||micro-A|
|No. of electrons/train||1.44 x 1012||/train|
|Size||dia. 1.6 x L 9.75 (27 r.l.)||m|
|Capacity of water||19.6||m3|
|Inlet water temperature||max. 50||degree C.|
|Temperature rise||max. 30||degree C.|
|Outlet water temperature||max. 80||degree C.|
|Water pressure||0.7||M Pa|
|Boiling point||160||degree C.|
Preliminary Parameters of JLC Beam Dump
- Hydrogen gas (H2) generated at a rate of 3.5 liters/s, which shall be recombined with oxygen gas (O2) . The recombination with 0.1 liters/s is accompanied by heat generation of 1kW. There must be an interlock system in order to warn and inform the abnormal at the H2 concentration of 1% and 2%, respectively.
- H2O2 ; unknown abundance, which shall be decomposed by radiolysis and chemical treatment.
- O2 ; unknown abundance, which shall be recombined with the H2.
- N2 ; unknown abundance, which shall be released in air.
- 7Be will be produced at 53.8 T Bq/year.
- 3H will be produced at 4.4 T Bq/year, which must exist in form of water and vapour.
The radiation issue can be briefly summarized as;
"When the beam dump is constructed in the tunnel 30 m deep, neutron and
gamma-ray doses above the beam dump is below 0.01 micro-Sv/year, which
is far below the natural environmental dose. But many radioactive nuclei
will be produced in the dump, especially 3H and 7Be. The
cooling water system must be kept in the restricted area because
gamma-ray dose from these nuclei is high even after the beam operation."
We discussed on possibility of single dump for beam and beamstrahlung photons from a view-point of neutron background. In this case, there are two windows. Configuration must be determined by the background simulations as well as the mechanical structure. Tokyo group is going to study these issues in cooperation with accelerator physicists who design the optics of extraction line.
(2) Fast feedback system "FEATHER"(N.Delerue, KEK)
(transparencies, 1 page, pdf ,142KB )
Nicolas showed results of beam test. He found a wrong cable and he also found that the amplifier to kicker did not have enough power. He is waiting for a powerful one which may be available soon.
The next meeting will be on 5 March (Wed.), 2003,10:00 - 12:00 am at 3 gokan, 425 .