Minutes of the 60th Machine-Time Committee Meeting
Date and time: November 16, 2012; 13:30–15:05
Place: RIBF Bldg., Room 203aa

Attendees: Sakai (Chair), Abe , Aoiad,†,‡aKase , Kubo , Motobayashi
Imaoa, †, Kajia, †, Morimotoa

Absent: Kamigaito , Miyatakec, †、En’yoa,†a, †a, †a, Fukunishi , Haba a, †, Hirayama b (in lieu of Miyatake),a, †baaba, †, Okunoa, †a, †aa, Morita a, Sakurai , Uesaka , Yamaguchi , Yoshidaaa, Nishimura , Shimoura , Ueno , Uwamino , Wakasugi , Hasebe ,RNC /bc

CNS / KEK /dRIBF-UEC /†Observer /‡TV Attendee(in random order)
Reports
1.

Changes of the beam-time schedule (Ueno)
It was reported that the beam-time (BT) schedule for November–December was revised on October 29 tocomply with the adjustments in the latest schedule of the official RIBF facility inspection. A further
modification to the BigRIPS-tuning schedule of each BT was also made. After the start of the 238U beamseries of the BigRIPS-based experiments, the BT schedule was modified twice on November 13 and 15
due to the delay of the beam delivery. Details of the modifications are summarized below.
Exp.-Prog.-Num.
RILAC:
MS-EXP12-07 (Kuboki)previous
Dec 7, 9:00

– Dec 9, 9:00

changed→Dec 8, 9:00

– Dec 10, 9:00

SRC:
Nov 6, 21:00 –NP0702-RIBF10-04 (Nishimura)
NP0802 -RIBF60&62R-01 (Watanabe) Nov 14, 9:00 –Nov 26, 9:00 –MS-EXP12-04 (Kubo)
Nov 26, 21:00 –NP1112-RIBF85-01 (Simpson)Dec 1, 21:00 –NP0802-RIBF60&62R1-02 (Watanabe)Nov 14, 9:00 →Nov 21, 21:00 →Nov 26, 17:00 →Dec 1, 21:00 →Dec 7, 9:00→(conditional)2.

Nov 6, 21:00 –Nov 16, 21:00 –Nov 26, 21:00 –Nov 27, 21:00 –Dec 2, 21:00 –Nov 16, 9:00
Nov 23, 9:00
Nov 27, 5:00
Dec 2, 21:00
Dec 8, 9:00

(conditional)

RIBF operation status – report on the 238U beam delivery (Fukunishi)
In the currently running 238U86+ beam series, beam delivery started on November 5 at 0:52 with only 4hours delay from the original BT schedule. Taking into account the total suspended BTs due toaccelerator troubles, the beam delivered so far is 185 hours compared to the originally scheduled BT of
264 hours, suggesting that the accelerator reliability defined by the ratio of the former to the latter is70.4%. The reduction in the reliability is mainly due to unexpected full-scale accelerator tunings
conducted twice at the beginning of the series. In this series, beam was delivered at the current of
500–750 enA (5.8–8.7 pnA) on an average, which already exceeded the instantaneous maximum beam
current 3.8 pnA recorded the last year. The current is still increasing. A key to the high current is theimproved performance of the 28-GHz ECR ion source and fRC. The ECR ion source is providing the Uions at 75–80 eμA, and fRC was modified to accept and accelerate U ions at q = 64+. It was also notedthat the stability and sustainability in beam delivery had been improved significantly by the installation ofa He-gas charge-stripping system downstream of RRC at the A02 site, and a rotating Be-foil charge

stripping system between fRC and IRC at M04 site, as the first and second-stage charge strippingsystems.
3.

MS reports

KISS R&D (MS-EXP12-10) (Hirayama)
The facility-side BT

in the machine study (MS) category was conducted using a 1-pnA 56Fe beam

at E/A = 90 MeV from September 29 at 22:00 to October 1 at 12:00. KISS (KEK Isotope SeparatorSystem) is designed to stop beam in an Ar gas cell after the energy was degraded to E/A = 1 MeV
with a degrader plate. Then, only a particular isotope is selectively extracted based on the techniqueof the double resonance laser spectroscopy. Although the measurement of the extraction efficiency as
a function of the Ar-gas pressure was originally planned, the extraction of 56Fe ions was not observed
due to an unexpected large background (BG) produced by the beam irradiation. To identify the originof the BG, offline R&D studies are in progress.
Charge-stripping foil R&D (MS-EXP12-05) (Hasebe)
The MS BT was conducted using a 340-enA 238U35+ beam at E/A = 11 MeV from October 25 at 9:00
to 31 at 10:10. Details are as follows:–Tests of fixed-type charge stripping foils: As a candidate of the first-stage charge stripper at theRRC–fRC (A02) site, performance of three different 300-μg/cm2 carbon nanotube (CNT) foils
were investigated, where charge-state distributions of 238U ions and endurance times of the CNT
foils were measured. It was revealed that the endurance time varies substantially depending on
the difference in the shape and density. One showed much longer endurance time than 3 hours
shown by the other two. For all these three foils, an increasing equilibrium charge state of 238U
was observed as a function of the irradiation time. There was no more increase beyond q = 71+
after irradiation of 2 hours.

–Tests of rotational charge stripper foils: Performance of three foils, C (19 mg/cm2), Ti (40 μmt),and Be (100 μmt) as a second-stage charge stripper at fRC–IIRC (M04) site were investigated.
In a charge-state distribution measurement, an equilibrium charge state was observed as a peakin the charge-state distribution with the Ti and Be foils at q = 82+ and 86+, respectively, while
such equilibrium charge state was not identified with the C foil due to widening of thedistribution. This observation indicates that U ions cannot be collected and transported
efficiently with the C foil. In the next test on durability conducted with the Ti and Be foils, they
were not damaged by the beam irradiation of 600 enA13h and 700 enA17h, respectively. Itwas determined from these results that rotational Be foils will be used in the U beam series ofthe BigRIPS-based experiments scheduled for this autumn.

GARIS-II commissioning (MS-EXP12-9) (Kaji)The MS BT was conducted for a performance investigation of GARIS-II, a QDQQD-type new
RIKEN Gas-filled Recoil Ion Separator, using 1-pnA 40Ar beams at E/A = 2.93 and 4.93 MeV fromNovember 10 at 9:00 to 12 at 12:10. The 169Tm(40Ar, xn) and 208Pb(40Ar, xn) reactions were utilizedto discuss the performance. Details are as follows:–Beam current monitor: The current of a beam incident on a target at GARIS-II was measured
from the yield of the elastic-scattering beam particles from a target. In this monitoring system, afilter was installed to restrict the counting rate so that the system can measure the current
correctly under the beam current higher than 1 pμA.

–

Target system: Recoil particles detected at the focal plane can be recorded together with theirradiated position of a rotating target. The system enables to measure, e.g., excitation functions
efficiently without changing beam energy.

–

Acceptance: An acceptance of GARIS-II was measured to be Ω = 12 msr using 209Bi recoil
particles to 0 degrees, indicating that 67% of the recoil particles were accepted by GARIS-II.

–

The overall performance of GARIS-II was first tested through the 169Tm(40Ar, 4n)205Fr reaction.
The produced 205Fr particles were well separated from the beam particle and other reaction
products due to a high resolution and a low background (BG) provided by GARIS-II.

–The performance was then tested through the 208Pb(40Ar, 3n)245Fm reaction having a small crosssection (σ ~ 20 nb). The cross section was measured with a high S/N ratio in a relatively shorttime due to the high acceptance and the low BG environment provided by GARIS-II.

From these results, the group concluded that GARIS-II functioned well as designed, and that it isexpected to play a significant role in the field of SHE researches.,
4.

Status of the PAC meetings (Ueno)
12th NP-PAC: It was reported that the schedule for the PAC meeting was set for June 28–29, 2013. The
request for submission of proposals will be announced at the end of March.

Topics discussed
1. Approval of the minutes of the previous meeting (Sakai)
2. Modification of the BT for the FY2012 second half (Sakai)
The extension of the currently running 238U beam series of the BigRIPS-based experiments originallyscheduled to end on December 8, and the additional BigRIPS BT allocation in January were discussed.
The Committee, however, had to postpone making a decision until RNC meets the requirements forbudgetary restrictions and the electric power circumstance. The decision was left to the discretion of theMT Committee Chair, since this issue cannot be discussed at the next MT Committee meeting due to theschedule limitation. It was also determined to schedule experiments using RILAC, AVF, and RRC, forFebruary and March. Note that SRC cannot be operated during this period, since the CGS (Co-GenerationSystem) will not be available due to a scheduled regular maintenance work. Kase commented that RRC
will be shut down for two weeks in February–March to perform maintenance work on the RRC main coil.
3. BT for the FY2013 first half (Sakai) relatively
The outline of the BT schedule for the first half of FY2013 was discussed. It was decided that theBT-scheduling process which newly includes a124

Xe beam that could not be scheduled forBigRIPS-based experiments for the second half of FY2012 will start in addition to the announced beamsof 238U and 78Kr. The BT scheduling process will be conducted as follows:
Today: MT Committee Meeting (discussions on the BT outline for FY2013)
Tomorrow–Mid December: Period for submission of beam-time scheduling requests (BTs to bescheduled for February–March (up to RRC) and for the first half of FY2013)
Mid–End of December: Planning of the BT schedule
End of December–Mid January: Period for submission of Accelerator-Use Planning Sheets
End of January: In-house Safety Review Committee Meeting
End of January: MT Committee Meeting (approval of the BT plan)
4. Priority of the kind of heavy ions to be developed (Sakai)
Beams which should be developed after 238U and 48Ca were discussed. The discussions on this issue willbe continued.
5. Next meetings
The next meeting will be held on Friday, December 21, 2012, at 13:30.

The meeting after the next will be held on Friday, January 18, 2013, at 13:30.