Beam Lock System for TARN
S. Watanabe, N. Tokuda, T. Katayama, M. Takanaka, M. Yoshizawa
Institute for Nuclear Study, University of Tokyo
Abstract
The preliminary experiment on RF system was reported.!)Which is mainly

described about hardware system and its operation experience with some resultsof experiment on capture, sweep and deposit of the beam.
Recently, reconstruction of hardware system have been carried out
including the beam feed back system.

The new system prepares the high slew

rate ferrite of RF cavity and the composit beam lock mechanism so as to avoida miss capturing of injected beam. The new ferrite is available for not only
storage mode but also synchrotron acceleration mode.
A beam capture frequency of the RF system is set to bunching frequency of
circulating beam in the TARN.
In the case of 7 Mev proton beam the bunching frequency is about 8 Mhz
and longitudinal phase length is few nano-second at injection period.

It isevident that RF bucket area must cover the area of injected beam, however,beam capture process is variable so that the many different type of beam is
injected from SF cyclotron.
A new type of beam lock system have been developed to ensure the beamcapture process which depend on not only longitudinal phase length but also
the energy-spread of injected beam.
The new system have Two phase lock loop independently.

The one refers

the injection beam frequency which depend on the operation frequency of SF
cyclotron (PLl), and the other refers the circulating beam phase in the TARN
(PL2).

Before the beam injection procedure the phase lock loop (PLl) is

established which is locked to frequency of SF cyclotron, and RF voltage is
not appeared on the RF cavity. After the beam injection the phase lock systemis switched to the beam lock loop (PL2) at once.

The switching operation is

performed with electronic switch in the beam lock system.

The schematic draw-ing is as shown in Fig. 1.
The PLl is provided the lock range of 300 Khz which is 10 times of lockrange of PL2.

As the PLl have a wide capture range frequency setting of RFsystem is carried out without a complex procedure.

After the frequency setting

a control voltage of frequency generator which determines the RF frequency isremained with level hold circuit because of prefer the lock-in action to thePL2.

If beam bunch does not comes loose and applied RF bucket is suitable for-251-phase area of beam, the beam capture process grows up and then the beam bunchis narrowed smoothly with PL2.

It is important that an accelerating energy
per turn is supplied to circulating beam without frequency modulation due toelectronic noise in the low level RF system.

To avoide the electronic noise

which is mainly including the phase detection components at the phase detector,
new phase detection circuit is applied in the PL2.
The frequency weep voltage is added to the control input of frequency
generator through the mixing circuit as well as control of phase lock procedure.

The phase advance due to this control voltage is controlled to set thesynchrotron phase angle of 60 degrees.

1)

3rd symposium on acc.elerator science and Technology at RCNP

FIG.l

SF

BEAM

CYCLOTRON
TIMINGPHASEMONITORSWEEPVOLTAGE

1~PHASE
DETECTORl-LEVELHOLD
CIRCUITPHASE
DETECTOR2VOLTAGECONTROLOSCILATORHIGH POWER RF SYSTEM-252-~