Minutes of ATF2 weekly meeting, 1 June, 2011

June 1 15:00 - 16:00 (JST time), Webex and ATF LC meeting room, KEK

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Recovery Status of ATF, N.Terunuma

We are now tuning the DR. So, our work is a half month advance from the schedule. On 25 and 26 May, we started the commissioning of RF gun and injector, respectively. On next day, the beam was transported to the BT in last week. In this week, we injected beam to DR. However, there was a large beam loss ! So we could operate at 0.78 Hz. The beam intensity was 0.8 x 10¹⁰ and 0.2 x 10¹⁰/bunch at LINAC and end of BT, respectively. The intensity was very small in DR, so the BPM signal was very small. Actually, on Monday, we could have one turn orbit in the DR. On Tuesday, we adjusted/aligned the magnets for the storage to accumulate the beam for 60usec. We found that the QM5R was 1mm lower et al., and the east arc needed to be re-aligned by looking at the orbits. Today, we aligned the magnets in the east arc. Also, the DR frequency must be adjusted for expanding the circumference, since we started the DR operation at the previous frequency which should be updated. After we succeed to circulate the beam in the DR, we will try to extract the beam. For the moment, our daytime will be devoted to site works. After the works, we will operate the beam for tuning.

C : On 3 June, a good news was announced, i.e. "Today, we confirmed a test beam reached to the beam dump at ATF2 end. The beam intensity stored in the DR was 0.3E+10 e/bunch and extracted without a significant amount of loss. ..... "

Hardware status, G.White and J.Nelson

We worked on the magnet mover system. We completed the hardware initialization. We replaced motors ( re-assembled ?) and 6 LVDT position sensors which have been broken by the earth quake. Now, the magnets are all positioned in the midway with the POT read-back. Also, the BPM system is under normal operation. VME crate and bipolar power supply (in the HA system) etc. will be arrived tomorrow from SLAC. Their installation will be done in this weekend.

Multi-OTR Progress report, Javier Alabau-Gonzalvo

As reported at the ATF2 project meeting, January 2011, the calibration and alignment have been made. The OTR system has been used for the coupling correction. The earthquake prevented us from a systematic measurement campaign in this March. After the earthquake, the hardware was checked to be OK. There was an improvement in the hardware, which is installation of de-magnifier system for easier finding the beam and for larger beam size in x.

The 2D emittance reconstruction is fully implemented in a case of no coupling , while systematic study is needed with experimental results. The 4D reconstruction is under study in any case with coupling. Both methods are based on the reconstruction of 4x4 sigma (beam) matrix by beam sizes measured at the 4 OTRs and the optics between them, where the emittance and Twiss parameters can be calculated from the matrix elements.

There is an issue of imaginary emittance in the reconstruction, which is unphysical solution, since ε_y = SQRT ( σ₃₃ σ₄₄ - σ₃₄² ) in the 2D emittance. This issue is investigated by simulations (1,000 times with 50,000 particles in each time, tracking by Lucretia) as follows.

First, the frequency (percentage) of solutions with imaginary emittance (2D and 4D) is plotted as a function of beam size error measured at the OTRs. It rapidly grows at the error larger than 10% and the 4D frequency is about double of the 2D, where the actual error is about 2%.

Also, the standard deviation of emittances, the effect of each OTR error, the coupling factor and standard deviation of beam matrix elements were plotted as a function of the OTR error.

In summary, during first part of the year no systematic measurements were made. There are some records of tests but they are chaotic and not easy to analize. Got this week the lattices corresponding to these days and will try if there is agreement within the measurements and the simulations and to test the emittance algorithm with these real measurements.

Q : What is the x axis ?
A : It is a relative fraction, i.e. 0.1 means 10% error.
Q : How much is the systematic error ?
A : It is now under study. We also like to know it.
Q : Can you have analysis with constraint, i.e. the emittance must be real ?
A Angeles : We try to find the analytical solution. Major issue is coupling. We are now working in mathematical way which is not so simple. Also, we can estimate numerically with constraints.
C : We need more time for the 4D emittance to be ready.
C : There is a special tool box of optimization in MATLAB. We could estimate/calculate beta, emittance with forced fitting. We can fit it to see systematic error.
Q : What is the dynamic view/range with the de-magnifier system ?
A : The view is widened 10 times than one without it. So, it becomes to 20 sigma's, which is about 2mm.
Q : How much is the measurement error of beam size by the OTR?
A : The statistical error is 2 % .
Q : Does it include the beam jitter ?
A : No since it is measurement in shot by shot, i.e. no fluctuation of beam size.
Q : Can you see the beam jitter ? Is there any correlation to another OTR ?
A : No for the shot by shot measurement.

References are listed below;

M. R. Rees, L. Rivkin SLAC-PUB-3305 (1984).

C. Rimbault et al., 4D EMITTANCE MEASUREMENTS USING MULTIPLE WIRE AND WAIST SCAN METHODS IN THE ATF EXTRACTION LINE, Proceedings of EPAC08, Genoa, Italy.

C. Rimbault et al., COUPLING MEASUREMENTS IN ATF2 EXTRACTION LINE, Proceedings of IPAC10.

Next meeting is 8th June, 2011.