Minutes of 67th FFIR/BDSIM meeting on 1/28/2004

The meeting was held in a room of 425 at KEK, 10:00-11:00, 1/28/2004. We discussed on final focus system with L*=3.5 and 4.3m, FEATHER and other.

(1) Final focus system with L*=3.5 and 4.3m (S. Kuroda)

(transparencies, 2 pages, pdf, 145KB)

For estimation of the momentum acceptance, IP beam sizes (σ*x, σ*y) have been calculated as a function of Δp/p at the standard FF-system with L*=3.5m. The functions were well type, and the momentum acceptance can be expressed by Δp/p < ±0.8% at least. Also the both beam sizes were calculated as a function of longitudinal displacement of the final quadrupole magnet (QD0) for tolerance of the longitudinal alignment. Resultant tolerance was estimated to be less than ±100μm.

The collimator section of the standard beam delivery system(L*=3.5m) has been successfully connected to the FF optics with L*=4.3m. Major parameters are listed for the two system below;
L* (m)3.54.3
total length (m)1443.81357.1
β*x/β*y8mm/110μm13.3mm/112μm
crossing angle (mrad)±3±3 to ±7
Eb=250GeV:&sigma*x/&sigma*y212nm/2.67nm310nm/3.63nm
Eb=500GeV:&sigma*x/&sigma*y158nm/4.31nm222nm/3.08nm
, where invariant emittance and momentum spread are assumed to be γεx=3 x 10-6m and δ=0.3%, respectively, and effects of synchrotron radiations have been taken account into the SAD calculations. Kuroda noted that the vertical beam size increased at the beam energy (Eb) of 500GeV from that of Eb= 250GeV at L*=3.5m, while it decreased at L*=4.3m as naively expected. It may be caused by synchrotron radiations. However, further investigation must be necessary, e.g. to calculate the beam size without synchrotron radiations.

Vibrational tolerances should be estimated for all the magnets upstream of the final doublet, too, in both cases with or without correction. In correction scheme, BPM resolution and IP beam size measurement error shall be assumed to be 100nm and 5-10%/pulse, respectively.

(2) LINAC simulation (T. Yamamura, M2 at Univ. of Tokyo)

Yamamura has completed his master thesis, and the PDF is under preparation. He would like to investigate dark current at LINAC. First, electromagnetic property inside accelerating tube must be known, which can be calculated by using MAFIA. So, he will contact experts for such calculations.

(3) FEATHER (N.Delerue)

(transparencies, progress report,5 pages, pdf, 276KB)

Before a beam test in last week, Nicolas tested the high power PIN diode, which has been purchased, in order to trim negative component in BPM signal. However, he observed no effect even for both signal directions. From the specification, the cause was thought to be capacitance of 0.8pF in reverse bias which is constant for frequency region of greater than 20MHz.

First in the beam test, he tried to see the effect of a high power pulse on the beam. Since bunch to bunch timing fluctuations were higher than the pulse width, any effect could not be observed. The ATF experts said that the fluctuations must be controlled by threshold at a trigger module which should be synchronized with the beam. So, the threshold will be adjusted in next beam test. Because of the timing fluctuations, he tried to use BPM signals to kick the beam in multi-bunch operation. However, more than 4 bunches were never seen in the BPM signals. The beam time was ended while he investigated "this problem". Again, the ATF experts explained that the cause was a lack of energy compensation for the multi-bunch operation.

In next beam test, he will try to reach lower gap by tuning the vertical steering magnets. Also, he will try again to kick the beam with the BPM signal in order to realize the simple model.

The next meeting will be on 12 February, 2004,10:00 -noon at 3 gokan, 525 .