Minutes of 13th FFIR meeting on 7/19/2000

The meeting was held in a room of 3-425 at KEK, 13:30-15:30, 7/19/2000. We discussed on (1) QC properties of l*=4.5m for the new FF optics, (2) reports from BDIR2000, (3) plan of support tube prototype, (4) dump line update and others.

(1)QC properties of l*=4.5m for the new FF optics : !(transparencies, 5 pages of pdf, 60kB) ) First, N.Yamamoto showed properties of final doublet at the new(Pantaleo's) FF optics with l*=4.5m. Field gradients of QC1 and QC2 are 100.9 and 73.3 T/m with lengths of 3.04m and 3.05m, respectively. The gradient of QC1 is about half of the present JLC design. At a distance from IP=l*=4.5m, two beams separate by 3.6cm horizontally because of 8mrad crossing angle.

(2) Reports from BDIR2000 :(transparencies parts of which are written in Japanese, 38 pages of pdf, 1.75MB) ) Linear collider beam delivery and interaction region workshop (BDIR2000) was held at Daresbury laboratory, 7/3-6,2000. Total number of participants is 37, of which are 7 from SLAC/US, 9 from DESY, 1 from KEK and others are from UK and the other European countries. There were 4 working groups of WG1:luminosity stabilization/diagnostics, WG2:collimation systems, WG3:background and interaction region related issues and WG4:novel concepts for linear colliders. Since there was only one talk in WG4, that is "NLC new final focus" so called Pantaleo's FF, the three groups (WG1-3) had parallel sessions. Detailed informations including copies of transparencies are available on a web page of http://accelerator.dl.ac.uk/ap/bdir2000/ .
The workshop was started by welcome address (Daresbury director), followed by overviews of beam delivery system at 4 linear colliders; CLIC, JLC, NLC and TESLA. Since I mainly participated in two working groups (WG2 and WG3), I briefly reported some topics discussed in them.

Collimation: We listed up failure modes for machine protection system such as energy variation ( due to injection error and klystron failures ) , focusing mismatch, transverse feedback, magnet failure, vacuum burst, near wall Wakefield, magnet mover and earth quake etc. . Most of them are protected by passive collimators and some of them need more simulations and new ideas. As one of highlights at this workshop, P.T.(SLAC) reported results of his experiment of wakefield measurements on collimators at SLAC. The result was about 1/10 of calculated one. However, after the measurement a good agreement was obtained by MAFIA-simulations, where only geometrical effect was taken account of with no resistive wall effect. Apparently, more studies are needed.
Non-linear optics got somehow spot lights at BDS. An example was given by R.Brinkmann as "Effective Acceptance Expander". Placing a doublet of octupoles at 50m upstream of final doublet, beam tail can be spatially made smaller by about 40%. If it works, collimation depths can be shallower. It is also good news at JLC.

Backgrounds and Interaction region: There were no new informations on mask systems at TESLA and NLC. which have been discussed at LCWS99 and LC99. TESLA group has tried to make larger aperture of the conical mask. There may expected to be large X-ray backgrounds into TPC. In order to estimate properly them, threshold energy must be decreased to 10keV at least. So, we agreed to set the 10keV threshold for photons in our GEANT simulations. For NLC design, Beryllium-ring mask got an attention, which is set very near the vertex detector, because of producing X-rays there. The small detector does not care of them since the central tracker is Silicon strips. However, the large detector may have background problem because of TPC.

TUC ( Towards Ultimate Codes ) discussion led by Nick Walker: There are many softwares for beam dynamics; in Europe, PLACET(linac), MERLINE(BDS) Guinea-PIG(IR), in USA, LIAR(LINAC), DIMAD(BDS), Guinea-PIG(IR) and in Asia, Kubo-original(LINAC), SAD(BDS), CAIN(IR), etc. . There is a general hope to have ultimate codes for linear colliders with an international collaboration, for an example GEANT4 in high energy physics, although it may not be best way. In Europe, authors have already started to talk on an unification of three programs at least by standardization of input/output formats. They would like to expand this effort globally, specially standardization of lattice descriptions. I was asked to inform it to KEK-experts, Oide and Kubo. At this FFIR meeting, we also discussed. Since SAD formalism is so different from others, the standardization may be difficult. Since a direct translation of lattice descriptions is not enough, we have to tune up optics in details due to different descriptions of fringe fields etc. .

International collaborations: TESLA group has concentrated on completion of CDR in next spring and the first draft in this September. They look for international collaborations towards the end.
(a) FFTB-2 : At SLAC there is a desire to test Pantaleo's new FF optics at FFTB-2. TESLA people are interested in beam size monitors (laser wire, Shintake interferometer) and collimators. We are also interested in achievement of 40nm beams (understanding of vibration problem) and the new FF optics. In order to realize the FFTB-2, a strong international collaboration should be formed. We agreed to discuss on this collaboration(FFTB-2) at KEK, DESY, CERN and SLAC. Then, we will meet again at LCWS2000, 10/22-28, Fermi lab., bringing our individual lab.'s wills. Philip Burrows volunteered to be an organizer of the meeting.
(b) Ground Motion : At SLAC A.Seryi et al. measured SLC tunnel drifts during December 1999 through January 2000. They observed large movements due to tidal and atmospheric pressures. They also found that a systematic motion, which is linear in time, dominates for time-scale of days and weeks (t > 10^4 sec). Therefore, their previous estimated A (coefficient of ATL-law) is over-estimated. At LEP-site, a similar systematic motion was observed. They refined their model of ground motion. A.Seryi proposed a workshop on ground motion in future accelerators which will be held at SLAC, 11/6-9,2000, as the 22nd advanced ICFA beam dynamics workshop ( http://www-project.slac.stanford.edu/lc/wkshp/GM2000/ ).
)c) Instrumentation : Manfred Wendt (DESY) proposed to have a workshop on instrumentation. The subjects will cover instrumentations of BPM, beam size monitor and luminosity stabilization with fast (intra-beam) and slow feedback systems. JLC group is highly expected to contribute at the workshop because of a lot of experiences at ATF in this field. The workshop will be help in next summer, somewhere in Europe. Grahame Blair (university of London) is going to start a laser-wire R&D borrowing one set of laser wire system from SLAC. He is also very interested in the Laser-wire experiment(led by Kyoto university) at ATF. He will communicate with the Kyoto univ. group while he participates in ICHEP2000.
(c) others : There may be other mini-workshops such as collimation/beam halo, sources including polarized positrons, bunch compression with pre-linac collimation and operational aspects. We are expected to participate actively in such workshops which are invaluable for realization of linear colliders.

(3)plan of support tube prototype:(transparencies in Japanese, 6 pages of pdf ,172kB) H.Yamaoka explained a plan of support tube prototype in this year. The purpose is to evaluate a validity of ANSYS calculations by measuring oscillation properties of the prototype support tube. The prototype system consists of two long stroke shakers, two seismic monitors and two kinds of tubes (square bar of 100mmx20mm and rod of 50mm diameter). Each tube consists of two tubes which are connected by thin plates or thin pipe. Input signals are provided at both ends of the tube by two manual sine controllers so that the two ends can be shaked by different phases. The total length is 1.8m. Study items are listed as follows; (a)measurement of natural frequencies and amplitudes of the oscillations, (b)measurement of amplitudes with different phases at both ends, (c)comparison between both-ends and cantilever support cases, (d)effects of supporting methods, that is, number of bolts and its sizes etc. , (e)measurement of dumping coefficients, and so on . In this system, the frequency can be varied from 1Hz to 500Hz and the strength of the shaker is 10kgf. The amplitudes will be measured by the seismic monitors and laser interferometer independently. The measurement will be done in this October-November.

(4) Dump line update: (transparencies, 7 pages of pdf,54.5kB) ) Kubo found bugs in his program and corrected the previous results. For the calculations, he set following aperture of major optical elements on the line;

QC1 entrance   -0.01 < x < 0.1    -0.01 < y < 0.01
QC1 exit       -0.02 < x < 0.1    -0.01 < y < 0.01
QC2 entrance   -0.02 < x < 0.1    -0.01 < y < 0.01
QC2 exit ~     -0.08 < x < 0.1    -0.05 < y < 0.05
BV1,BV2        -0.02 < x < 0.02   -0.05 < y < 0.05
,where unit is meter(m) and x,y are measured from the extracted beam axis. Vertical bending magnet (BV1) is located at about 65m from IP. Incoming beam passes through at minus side horizontally(x). Total energy loss is 0.93% at E/E0 <0.68 . As seen from trajectories of lost electrons (figure), the nearest neutron source seems to be totally avoided by increasing horizontal aperture of QF, QM1 magnets. Neutrons between 40 and 60m can be shadowed by proper shield. The largest neutron sources are vertical bends (BV1 and BV2) which are caused by the second doublet (QF, QD). For effect reduction of the neutrons, pole-tips of BV1 and BV2 must be optimized. At next step, the shield and magnetic configurations shall be designed.

The next meeting will be on 24 August (Thursday), 2000 13:30 - 15:30 at 3 gokan, 425.