Minutes of 66th FFIR/BDSIM meeting on 1/14/2004

The meeting was held in a room of 425 at KEK, 10:00-12:30, 1/14/2004. We discussed on next year plan, final focus system with L*=4.3m, FEATHER and FFIR test facility.

(1) Next year plan

Since this fiscal year is running out, we would like to look again the plan of support tube R&D in this year. Among the plan, there are a heavy load effect to be measured and an optimization of thickness of the central part of the support tube. In next year, we would like to concentrate on a R&D of active mover of final focus magnet inside the support tube in order to demonstrate a namometer control of vibration at the magnet. Also, we requested budget for FEATHER (control electronics ) and NanoBPM (optical anchor ) R&D to the IPNS, KEK.

(2) Final focus system with L*=4.3m (S. Kuroda)

(transparencies, 4 pages, pdf, 130KB)

Kuroda inspected final focus optics with longer L* since LC experiments prefer L*>3.5m in general. First, he showed two final focus optics with L*=4.3m, which are the original Pantaleo's one and the NLC2001's one with total length of 511.6m and 747.8m, respectively. The major parameters are listed below;
Ebeam250GeV500GeV
total length&beta*x&beta*y&sigma*x&sigma*y&sigma*x&sigma*y
mcmμmnmnmnmnm
Pantaleo 511.61.31332802.34713.0
NLC2001 747.81.31122012.03173.3
while the standard optics has L*=3.5m and total length of 500~750m in the GLC project (roadmap report, 2003).

Second, he studied vibrational responses of a final focus magnet(QD0 in his convention) which is the closest to IP for the standard optics (L*=3.5m) with Ebeam=500GeV and Δp/p<±0.3%. Both vertical and horizontal beam sizes (&sigma*x, &sigma*y) remain the same values for the horizontal displacement of QD0 (DX) within ±1μm. Since horizontal displacement of focal point (x*) is given by x*=-2 DX, the DX must be less than ±5nm for x*< (0.1&sigma*x)/2. In the similar way, he studied effects due to the vertical displacement of QD0 (DY), where the vertical components are only relevant. The vertical beam size (&sigma*y) was calculated to be less than 3nm for DY<0.5μm, while displacement of the vertical focal point (y*) requires for DY to be less than ±0.09nm because of y*< (0.1&sigma*y)/2 and y*=-1.52DY. Finally, the longitudinal displacement (DL) should be less than 50μm for &sigma*y<3nm . However, this DL is a systematic movement of the final doublet (i.e. QD0 and QF0). So, longitudinal one for each QD0 and QF0 must be considered. Also, there were following questions; how much is the momentum acceptance, what are vibrational tolerances for other magnets, and is there any difference between L*=3.5m and 4.3m, etc. .

(3) FEATHER (N.Delerue)

(transparencies, progress report,3 pages, pdf, 156KB, and report at ISG11, 9 pages, pdf, 523KB)

Nicolas reported present FEATHER status, especially on the beam test. Movable electrode kicker and BPM have been installed and commissioned at the ATF extraction line. Also, a high power RF amplifier (45dbm, 500MHz~1GHz) has been bought for the kicker drive pulse. Some problems have occurred when the amplifier was operated at 500MHz, where too small kick intensity was observed. The problems were caused by large negative overshoot in BPM signals. In next beam test, the negative overshoot will be cut by high power PIN diodes which have been purchased.

Then, he introduced his talk at the ISG11. After he briefly explained the system and setup at the ATF, he showed a time budget breakdown of the system at the beam test as follows;
Time Budgetnsec
500MHz~1GHz kicker amplifier (measured)5.6
beam flight (1m)5
cable delay7
various electronics delay<5
total without delay loop22.6
delay loop11
total33.6
20 bunches at 2.8ns56
As seen in above table, the total time budget is 33.6nsec including a delay loop. Since a beam-train has 56nsec with 2.8nsec bunch-separation, the delay model can be also tested. In advance of the beam test, impedance of the kicker has been measured as a function of gap between two electrodes at the center and the end of 40cm long electrode. The central impedance gradually increases from 20&Omega to 130&Omega at the gap of 0.4mm and 4.5mm, respectively, while the end one is saturated to be 80&Omega at the gap of 1mm.

At the beam test, kicker intensity was measured as a function of gap for two cases of pulsing from the upstream and downstream of the electrode, where one of the electrodes were grounded to the earth, by using 50KHz and 100KHz high power amplifiers. As naively expected, the input downstream has higher intensity than that of the upstream, while the calculated one with magnetic effect is between the two. The 50KHz amplifier has higher intensity than the 100KHz. He speculated that difference between 50kHz and 100kHz may come from the@integration method. Sensitivity to the pulse shape was observed to be important for the input downstream but not for the input upstream. Apparent difference in the input method is the magnetic effect. At next beam run (after 19 January 2004), smaller gap operation will be tested with a method which M.Ross suggested at the ISG11. Gap of less than 1mm is expected to be possible since the ODR group can steer the beam close to the metal edge within 1μm. The magnetic effect will be measured with the 500MHz-1GHz amplifier. Phase effect will be also studied by kicking in phase and 180o phase shift etc. . Calibrating a new button BPM and cavity BPM, feedback and feedforward will be tested. So, exciting tests are coming.

(4) FFIR test facility (T.Tauchi)

(transparencies, 28 pages, pdf, 4.9MB)

Tauchi reported a general outline of FFIR test facility which has been presented at the 25th Linear Collider Project Committee on 9 January 2004. The facility should be organized by an international collaboration.

The FFIR test facility has two goals and an option of PLC (Photon Linear Collider) test facility.
Primary goal is a final focus test beam at the ATF, KEK. Experimental issues are listed as;

Present final focus system is based on the "local chromaticity correction" scheme (optics) which has been invented by Pantaleo Raimondi (SLAC), 2000, so it is called as "Pantaleo's optics". This FF system has great advantage of compactness; i.e. shorter total length with less energy dependence than the conventional system with "non-local chromaticity correction". However, there is no experimental verification, while the conventional one has been verified at the SLAC-FFTB, 1994. The FFIR test facility could achieve smaller vertical beam size for the smallest (invariant) emittance at the ATF. Permanent magnet is also an important R&D issue for the final focus quadrupole magnet especially in case of large crossing angle.

The second goal is nanometer stabilization of final doublet. The R&D issues are listed as;

Recent development of cavity-BPM and laser technology could measure a beam position at the focal point (IP) with nanometer resolution. Together with acitve mover system, nanometer stabilization can be demonstrated at the final doublet. Also, we could verify a fast feedback system (FEATHER, FONT) at nanometer level, which is also on-going R&D at the ATF/KEK and NLCTA/SLAC but at μm level.

For the both goals, the ATF beam has an essential role, i.e. nanometer reference scale, for small emittance.

An an option, a test facility for photon linear collider (PLC) can be added. The option comprises of laser facility and IP optics for collision with the focussed ATF beam. Requirements of the laser should be as same as those at PLC; the laser intensity is 1.3J/pulse with a spot size of 3μm and the laser is operated at 192 pulses with 1.4ns time-separation at 150Hz ( reference: KEK Report 97-17, March 1998). Also, experiments should be encouraged for "strong" QED investigations.

The next meeting will be on 28 January, 2004,10:00 -noon at 3 gokan, 325 .