BEAM MONITORS IN TARN
N. Tokuda, T. Hattori, T. Katayama, H. Tsujikawa
S. Watanabe and M. Yoshizawa
Institute for Nuclear Study, University of Tokyo
Abstract
Several kinds of beam monitors are installed in TARN. A
nondustructive beam monitor is necessary for an accumulation
ring: A ferrite core monitor and electrostatic monitors areDestructive monitors, i.e. multiwire, single rod
prepared 1 ).
and a scintillation monitors, are also used, as they provides aprecise beam profile and position 2 ) .
Ferrite Core Monitor
The phase of a beam bunch is detected by the monitor, and fed
to the phase locking system for the RF stacking. Three ferrite
cores (382 mm O.D., 260 mm I.D., 20 mm thick) are piled, and two
one-turn coils are wound round them in opposite directions for a
The monitor is mounted surrounding
common mode noise reduction.
a vaccum duct with a ceramic ring as shown in Fig. 1. Figure 2
shows the signal of an injected beam.
Electorstatic Monitor
This monitor 1s designed to observe the phase and the positIt consists of a pair of electrodes and shiels
ion of the beam.
as illustrated in Fig. 3. The electrode and the inner shieldform a capacitor of 180 pF, and the induced Joltage between themis measured with a 100 k~ FET probe followed bY an amplifier.
Figure 4 shows beam bunches detected by this monitor.

The ferrite
Fig. 2
core monitor detects a
7 MeV/u Ht beam injected by the multiturn
method.
Mounting
Fig. 1of the ferrite
core monitor.
The shield isadditively covered with a copper
plate and wrappedwith aluminum
foil.

Structure ofFig. 3
the electrostaticmonitor.

Bunches of aFig. 4
Ht beam 60 ~s afterthe injection. The
monitor is the electrostatic one.
About 5 x 10 7 ionsare contained in abunch.

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Noise Reduction
As it is difficult to reject the RF noise, synchronizing
with the beam signal, the S/N ratio is improved by extracting aharmonic of a higher order in the beam signal.
In contrast to
the RF noise, the beam signal contains higher order harmonics
as shown in Figs. 5 (a) and (b). A resonator for the third
harmonics is used against the RF noise. Figure 6 shows a beam
bunched by the RF field.
The monitor is the electrostatic one.
Multiwire Monitor
The chamber consists of 16 beryllium copper ribbons, 60 x 2x 0.5 mm , fixed on a ceramic frame with a 1 mm spacing.
It isdisplaced by a driving apparatus with a pulse motor. The electric charges in each ribbon are transfered and stored in a concenser in a read-out circuit, and the voltage is measured. Figure 7 shows the horizontal profile of an injected bea~.
Single Rod Monitor
The senser of the monitor is a beryllium copper rod of 3 mmin diameter. Disturbing the beam less than a multiwire monitor,
this is suitable ofr observing the profiles of a beam injected bymultiturn and a stacked beam. The senser is attached to a driving apparatus with a pulse motor or an air cylinder.
Scintillation Monitor
A 5 mm~ rod of plastic scintillator, of which the surface isprocessed with vacuum evaporation of aluminum, is attaced to adriving apparatus with an air cylinder. This monitor is efficient to detect a beam of reduced intensity long after the injection.
References
1. N. Tokuda, T. Katayama, H. Tsujikawa and M. Yoshizawa, "Multiwire and Single Rod Beam Profile Minotors in·the TARN", INSNUMA-19, 1980.
2. N. Tokuda and s. Watanabe, "Electrostatic and Ferrite Core
Monitors in the TARN", INS-NUMA-21, 1980.
Figs. 5 (a), (b)The
spectra of the RF noiseia, left), and of thebeam signal (b, right).
Spectrum lines appear
at every 8 MHz.

Fig.7

Fig. 6-160-