STATUS OF OPERATION OF THE VARIABLE FREQUENCY HEAVY-ION LINAC, RILAC
M. Odera and RILAC group
Riken: Inst. Phys. & Chern, Research. Wako-shi, Saitama, 351
Abstract
RILAC is a sole tunable linac in the world. High frequencies are used
for light ions and low frequencies for heavy projectiles. It is being usedby the various disciplines in IPCR. Its status of operation is described.
Introduction
The variable frequency scheme of the RILAC has been introduced tofacilitate focusing of the low velocity heavy-ions having a small charge tomass ratio. The scheme also relaxes the requirement of the high accelerating
gradient, hence the large power consumption for acceleration of the very
heavy elements. By further keeping accelerating rate lower than that of theaverage linacs, RILAC has been made capable of CW operation.
This frequency variable and CW operation scheme is also a consequence ofthe design study of the Riken multi-stage heavy ion research facility project,
proposed in 1972. (Ref. 1) In that plan, a large separated sector cyclotron
has been chosen as a post-stripper accelerator. The pre-stripper part shouldbe able to function in a CW regime and its acceleration frequency be tunable
to the same or submultiple of the cyclotron RF, so that longitudinal phasematching of the beam between the two accelerators can be made easily.
§ 1.

Operation
Figure 1 shows statistics of operation for the latest 8 months. Shaded
area is the time used for research and others for machine development. Timefor preparation of the experiments, for ion source tuning and for maintenanceand repair is not included. Figure 2 gives frequencies and ions realized in
the specification map. As seen in those figures, Argon ions are used mostin the variable energy mode. Table 1 gives research themes in FY 1981 and1982. At present, atomic physics is the largest customer to use machine time.
§2.

Time required to guide beams onto the targets varies considerably,according to whether a good parameter set has been already accumulated or notin the previous operations. When the good set is not available in thecomputer memory, the calculated values are used as the starting sets andoptimization of beam is made manually.
Transmission efficiency of beam through cavities is improving in time,by getting better parameter sets. At present, it is around 40 to 60 % for
the first cavity and 10 to 20 % to go through all the cavities and the beamtransport pipings 15 to 20 meters long.
Various unwanted ions having equal or nearly same charge to mass ratio
to that of ions wanted are frequently found mixed in the output beam. The
simplest way to discriminate those contaminant ions is measurement by a solidstate detector inserted in the beam path. However, the detector will bedestroyed at once unless the intensity of beam is attenu·ated by a factor
larger than 10 7 . Two mesh filters are inserted in the distant position along
the injection beam line by the pneumatic cylinders from the operator console.
By tuning the two dipole and one quadrupole triplet magnets in the interval
between the two attenuators, the necessary reduction of the beam intensity
can be made.
Effect of the secondary electron emission must be taken care of in thebeam diagnostics. Accurate measurement of the beam by suppression of thesecondary electron in a narrow space presents a problem. Other paper givesa case in which this phenomenon is used advantagiously. (Ref. 2)-53-Energy of ions can be changed by a large factor combining the threemethods; change of accelerating frequency, turning off of the later cavities
and tuning of the phase of the last cavity. The last method is ··the easiest
and allow5more than 30 % reduction of energy \vithin a fe•.,r minutes. Readjustment of the focusing elements allows more than 80 % of the beam intensity beobtained even for the largest phase excursion from the standard value. (Ref.3).
TABLE-1Themes of experiments

Disciplines

ThemesAtomic physics

Auger-electron spectroscopy,
Inner shell ionization and X-ray polarization,
Beam foil spectroscopy,
Recoiled-ion spectroscopy,

Nuclear physics

Coulomb excitation,
Polarization of nuclei by use of slow HI,

Solid state physics

Internal field of ferro-magnetic materials,
Secondary electron emission from metal,
Radiation damage of materials,
Hodification of metal surface by ion implantation,
Heavy ion channeling,
Relaxation of dense excitation in crystal,

Chemistry & biology

Effect of chemical bond on satellite X-rays,
Depth distribution of Hydrogen in amorphoussilicon,"Study of chemir.al bond by Hossbauer effect,
PIXE by heavy ion,
Effect of heavy ion irradiation on bacteria,

References
1)

2)
3)

N. Odera and T. Tonuma: Proc. 6th Intern. Cyclotron Conf., Vancouver
1972, p283, AlP Conf. Proceedings No. 9 (1972)
M. Kase: Bunch Signal Sensitization by Use of Secondary ElectronEmission, This Proceedings
H. Kase et al.,: Linac Energy Tuning by Phase Control of Last Cavity,
This proceedingso>23 -< 5" Energy./nI' I ' I I, I(!ieV/nl

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