BEAM DIAGNOSTICS IN THE RING CYCLOTRON
T. Itahashi, T. Saito, I. Miura and S. lchida*
Research Center for Nuclear Physics, Osaka University,*Accelerator Business Center, Technical Department,
Sumitomo Heavy Industries, Ltd., Niihama, Ehime 792, Japan

Abstract
Beam diagnostic components are newly designed for thering cyclotron. They are distributed over the beam injection
or extraction line and in the acceleration chamber.

BS-ACC-1

SP\1-ACC-3z2

Injection line
The beam from the AVF cyclotron, which is selectedin momentum, emittance and in phase, enters the ring cyclotron. There are two variable width slits (VSL-1,-2), three
three-wire-profile monitors (TPM-1,-2,-3), one emittance monitor system(ESL+EP:M) and one phase probe (PP-INJ) in thebeam injection hall.
The beam shapes in transversal phase space are definedby the VSL-1, and -2 to fit the eigenellipse of the beam of thering cyclotron. The transverse beam shape and position aremeasured with the TPM-1, -2 and -3, while the beam emittance both in horizontal and vertical planes are measured witha single slit (ESL) and a harp-type monitor (EPM).
At the entrance of the valley chamber of the ring cyclotron, TPM-4, TV-monitor (TVM-INJ) and the beam stop(BS-INJ) are located, housed in the one unit of a diagnosticchamber. The beam is investigated in size and position once
more with the TPM-4 and TVM-INJ. When necessary, thebeam is interrupted by BS-IN J. The actual phase of the beamfrom the AVF cyclotron relative to the acceleration r.f., is measured by the non-intercepting capacitive pick-up (PP-INJ).
In the valley chamber, a fast rotary scanner (RPM-INJ)
driven by a supersonic motor is used for the beam to travel tothe bending magnet (BM-2) through a narrow space between
EIC-1 and EIC-2.
Beam diagnostic components distributed along the beam
injection line up to the 1st sector magnet are shown in Fig. 1.

d4~----~------~-,----~----~------,

PP-"JTVM-INJ

3

TPM-4
VSL-INJ

TPM-INJ-1' I \_I \ I \IX

2tlyBS-INJ

\f\j

TPM-3

SL,,.

120"

iSP"·ACC-i~---SL_I_T_P\_,:~_ -~ -~S-l-VS-LtJ

180"

240"

Fig. 2. Beam diagnostic components along the beam injection
orbit. Injection line, 1st-turn and 2nd-turn in a half part of fullorbit are shown to clear the turn separation between them.

They are located at efficient points for the various beam diagnositcs, as they are expected positions from the calculated
optics 1 l.
Injection Orbit
At the entrance of the first magnetic inflection channel(MIC-1), the beam should match the eigenellipses of the accelerator orbit. To define the beam_ size correctly, the horizontal
and vertical beam widths are redefined with a horizontal slitwith variable width (VSL-INJ) and a vertical slit with a fixedwidth (FSL-INJ). These are combined with a profile monitor(TPM-INJ-1,-2). At the entrances and exits of the two magnetic inflection channels, buffer slits are also installed as diagnostic devices in the horizontal plane (SL-.5 ~ 12). To measure
the vertical positions of the beam, single-wire profile monitors(SPJ\I-ACC-1,-2,-3) are available. Fig. 2 shows these diagnostic
components on the injection orbit.
Energy-Phase Probe (PPEN-INJ,EXT)

1____ /

D0I814. - · - - -·-- -·-·-·-

813

Fig. 1. Beam diagnostic components distributed along thebeam injection line up to the 1st sector magnet. They are
shown with calculated beam envelopes. Horizontal and vertical beam envelopes are described in x and y respectively.

The energy-phase probe is prepared to measure the time
structure of the beam at the radius of the injection orbit andto measure the correlation of the beam phase and beam radius(energy) 2 ). The same device is installed in the extraction orbit
to observe the beam phase at final few turns. A thin single
wire target is driven radially. Scattered particles are detectedby a plastic scintillator. The time interval between the particle
signal and r.f. of the accelerator is measured with a time topulse height converter and the signals are processed digitally.
Two dimensional (time- radius) analysis becomes available.
All these monitors are to be used while the beam is stopping at the beam stop (BS-ACC-1).

-234-

, r~

B
SLzcl\!EC-2.

SL.,.,~

i·. MEC-1~"""w

320-TURN<TVM-ACC

if1

EEC-1 EEC-2.i.
SL sL .

SP~!-EXT

BS-EXT

1 1.-L_../'~ SLSL

TP~!-EXT'' ·~l~~==============::::;•~·~~~~~~~~R~P~~~~~-2~===== ~:~~~~:~

0-1soot-360°

-300°

-240°

Fig. 3. Beam diagnostic components along the extraction orbit.
The beam extraction orbit (320-turn) and the last accelerated
orbit (319-turn) and the 318-turn are shown to clear the turnseparation between them.
Acceleration Orbit
In the valley chamber, there are several beam diagnostic
devices for the accelerating beam; main probe (M.P), phaseprobe (PP-ACC) and three additional beam stops (BS-ACC2,-3,-4).
Extraction Orbit
Along the extraction orbit, several types of beam diagnostics devices are located; single-wire energy-phase monitor (PPEN-EXT), TV-monitor (TVM-ACC), beam stop (BSACC-5), single-wire profile monitor (SPM-EXT), a fast rotary
scanner (RPM-EXT), and three-wire profile monitor (TPMEXT). The TPM and the RPM are used to measure the orbit
separation and beam width, while the SPM set in front of theTPM-7

3TPM-6

DII2SLSLSLl/ \The extracted beam is finally monitored with three TPM(TP:\I-6, -7, -8), variable width slits (VSL-EXT), phase probe(PP-EXT) and TV-monitor (TVM-EXT). They are shown inFig. 4.
By scanning the current of the quadrupole magnets andby using two or three TPMs the transverse beam emittance canbe measured. 3 l.
Main Probe (MP)A main probe measures the current and the transverse
shape of the beam in the cyclotron. It consists of a tomography head of three thin wires (W) and an indirectly cooled beamstop. The probe can be adjusted for the head to face the tangential direction of the beam orbit at any radius. The driving
speeds can be chosen between 20 mm/sec and 200 mm/sec.

4X

first extraction channel is used to see whether the separation issufficient for the septum. Buffer slits (SL-13 "-" 20) for all theextraction elements are helpful to protect these elements andto guide the beam correctly. All these components are shownin Fig. 3.

TPM-8

TVM-EXT

Beam Stop (BS)~SL-EXT\II'I

There are two types of beam-stops; differential type ininjection or extraction orbit and integral type in the accelerator chamber. These are set at the radius of r=2000, 2395,2872, 3350 and 4000 mm. At minimum and maximum radii
two beam stops can be moved in radial direction about a few
tens mm. And the other three stops can be moved pneumatically up and down. All the heads are thick enough to stop
the beam at each radius. The total beam current interceptedcan be measured. These stops are used to optimize the accelerator condition without serious activation of other accelerator
components.

I\I10- 1 L-J...J..-.L.-1-.-'---'UI..--.J.....I...L.I...--~-I..J-U....l.L--.1~[EC2BElQMIU

QWDBmPhase Probe

Q~l2Fig. 4. Typical beam optics from the extraction system of thesse to the transfer point (right extreme in this figure) of thefur! her beam transport. By scanning the current of the quadrupole magnets and by using two or three TPMs the transverse
beam emittance can be measured.

The beam phases relative to the accelerator r .f. phaseare measured by eight capacitive phase detectors, mounted ona single carriage, separated by 300 mm from each other. They
are installed along the line at the same azimuthal position aseach accelerating gap between the sectors. They cover the full-235-

We have tested some components of the diagnostic instruments as mentioned above.
i) In order to move the single wire up and down in themagnet vacuum chamber (SPM-ACC-1,-2,-3), ferrofluidic
seals are considered for use. We examined two types ofthe seals in the presence of the strong magnetic field. Oneof them showed the clear defect; the vacuum leak started
at the magnetic field about 100 Gauss. The other wasstably operated at more than 600 Gauss.

SII'"PtlkC PUUtk- •.

ii) The supersonic motor without water cooling was foundusable at the magnetic field of 1.6 kG inside the vacuumchamber.

The total beam diagnostic components are shown inFig. 6.
Fig. 5.
pulses.

Circuits for sampling pulses and horizontal trigger

References
1) A. Ando, RCNP Annual Report (1987).

radius continuously by driving the carriage. One unit of thedetector has two electrodes (upper and lower).
The beam phases are measured by the sampling method.
Sampling pulses and horizontal trigger pulses are generated bythe circuits shown in Fig. 5. The sampled signals are digitallyprocessed with a digital oscilloscope and transmitted the computer control system.

'3) P. Strahl, Proc. of the 9th International Conference onCyclotrons and their Applications, Caen, France, Sep.,
1981, p.545.

\'II.

2) S. Adam and M. Humbel, Proc. of the 11th International
Conference on Cyclotrons and their Applications, Tokyo,Japan, Oct., 1986, p.418.

Iii

Till EITUL EXTTPIIIIS UT00

ISL t TPI I
ISL·t TPI t
YPI 3

£SL I
UL t!

Fig. 6. The layout of the beam diagnostic components.

-236-(PI IEPII 2'