105th ATF2 weekly meeting

International phone/webex meeting

For considerations on limit of vertical dispersion and coupling corrections in ATF EXT , Kiyoshi Kubo (KEK)

Kubo showed that the large vertical dispersion could be well corrected by QS1X and QS2X with addition of vertical orbit bump less than ±6mm by ZV5,6,7X, where generated couplings are corrected by QK1-4X. In his SAD calculations, &eta_y and &eta'_y are varied in ranges of ±10cm and ±5mrad, respectively, which could be generated by the septum rotation as Okugi said.

EXT Vertical Dispersion Correction, Mark Woodley (SLAC)

ATF2 optics adopted the vertical dispersion correction by "sum knob" with QS1X and QS2X in-phase of Δ&psi_y=180^o, where only &eta'_y are generated. It is good for correcting &eta_y generated in EXT, bad for correcting &eta_y coming from DR and extraction channel. Alternatively, QS1X and QS2X can be used independently to correct arbitrary &eta_y/&eta'_y, but large coupling is generated.

Mark explained 6 possible solutions to correct the vertical dispersion with Pros and Cons as follows. Apparently, the last one i.e. 6 has Cons of new magnets and power supplies, and the 4 / 5 have Cons of perturbation in DR.

1. "sum knob" and correction of residual &eta_y/&eta'_y at IP
   Cons : residual &eta'_y propagates to wire scanners and IP, which is not good for large dispersion
2. "independent knob" and coupling correction with QK1-4X
   Cons : limited correction range as Kubo's analysis, generates large coupling which drives QK1X to maximum current and residual vertical emittance growth
3. "sum knob" and correction of residual &eta'_y with ZVs as Kubo's suggestion
   Pros : reasonable correction range
   Cons : Possible effects of orbit bump such as Shintake monitor backgrounds and emittance growth and/or coupling from sampling kicker (KEX2) field vertically off-axis.
4. "sum knob" and correction of residual &eta'_y using a closed &eta_y bump across DR North straight section
   Cons : limited correction range (only DR skews tried so far) and effects of dispersion bump on DR vertical emittance and DR laserwire operation.
5. correction of &eta_y/&eta'_y at extraction point in DR as part of DR vertical dispersion correction
6. one or more additional EXT SQs

Q : What is the most probable source of the vertical dispersion ?

C : Experience shows that the &eta_y/&eta'_y correction is difficult at IP.

Q : It seems to be clear that the beam is vertically kicked at beginning of extraction line. Shall we check alignment of septa and correct them if we observe misalignment ?

The fast kicker study results and plans for next runs, Takashi Naito (KEK)

Naito reported recent results of fast kicker studies and plan in October run.

First, he explained that in order to extract beam from the DR to the extraction line only replacement of present kicker (KEX1, 4.6mr/3.5mr) with two 60cm long stripline kickers (3mr/2.6mr) is not enough but additional local bump and an auxiliary septum are needed.

When this fast kicker system was tested in this June run, the beam could not be extracted because of smaller kick angle than the designed one. In order to check performance of local bump and auxiliary septum, the fast kickers were replaced with the kicker (KEX1). In this case, the beam was extracted with reduced kicker angle of 2.6mr, i.e. at the kicker-current of 24kA from the nominal 39kA. Next, the stripline kicker performances were studied at the extraction line installing them about 1m upstream of QM16. Measured kick angles are summarized in a following table below.

To understand the above variations in measured kick angles, impedances of each electrodes were measured by the TDR(Time Domain Reflectometry)method with a network analyzer. They are designed to be 50 Ohm. Results are summarized in a following table including the second 60cm long stripline kicker which was not tested by beam at the extraction line.

We have a following plan of improvement.

• Re-fabricate the strip-line electrode
• Using 4ns pulser x 4 (20%)
• Strip-line gap 12mm ->11mm(10%)
• Strip-line length 60cm ->66cm(10%)
• Length of the BS0X 57cm ->37cm
  The orbit difference of the upstream of the BS0X increases ~1mm

Q : Can the beam test be moved to January 2009 ? Many international colleagues are coming in this October, and very few will come in January.

A : It is just one week, it can be back to the normal scheme in the week end. Also it can be done at the same time of DR study, i.e. upgrading DR-BPM system.

Q : How much is the tolerance of straightness etc. ? Is there any estimation ? We need quantitative explanation ? There may be another possible explanations.

Q : Should it be tested at check-out run and extraction line ?

A : I have a plan of test for 1 or 2 days at EXT as check-out run within the same week.

Q : Are you sure the improvement to solve the smaller kick angle issues ?

A : From the TDR results, we could estimate and explain it.

Q : The observed vertical kick is large. Is it understood ?

C : Since there are many uncertainties, we should test the stripline kicker with taking more time. In this sense, January run seems to be better choice.

C : I agree with above suggestion. So, this October run should be focus on ATF2 studies.

Q : Is it possible to operate the beam one week before the present schedule for the fast kicker study?

A : At present, it is difficult since the DR-BPM upgrade is planned from 13th October. However, day or evening check run will be OK.

Q : Why oversea colleagues cannot come in January? If the fast kicker R&D is not done in October, the R&D will stop for three month. It is not good.

C : ATF2 will/may loose all October run if the fast kicker is the first study. For well preparation, it is better to be tested in January.

Q : Is there justification or good plan for the fast kicker study in first week of October run ?

A : Just one day is enough for checkout the stripline kicker performance, i.e. kick angles. If it is good, we can install it , but if not we will continue usual schedule.

C : It is difficult to justify such argument because of uncertainties.

C : We would like to ask oversea colleagues for travel plans since they are important information to plan beam shift schedule.

KEK site meeting

• Cherenkov Detector
  - Simulation of signal resolution was performed.
  - According to the simulation, there is a optimum thickness of convertor, however, it will be better to prepare adjustable thickness convertor.
  - Not only the resolution (RMS/Mean) but also the absolute amount of Cherekov light should be cared.
• CsI(Tl) Detector
  - The reason why it took long time the output of PMTs become stable have not yet been solved.
  - Temperatore is the most probable.
  - How about using a constant temperature reservoir to see the temperature dependence of detector output?
• Make a list of study items for the autumun beam time
  - assign priority to each items