Z. Phys. C - Particles and Fields 56, $258-$260 (1992) Zeitschrift P a , r t i d e s far Physik C

and © Springer-Verlag 1992

K i c k e d s u r f a c e m u o n b e a m s

J.L. Beveridge

TRIUMF, 4004 Wesbrook Mall, Vancouver, B.C., Canada V6T 2A3

1-August-1991

A b s t r a c t . The possibility of splitting a surface muon beam into three separate components using an electro- static kicker is examined. Such a beam seems technically feasible and could be very effectively used to provide muons to time differential #SR experiments.

the beam is allowed to continue in the straight through direction until another muon is required by the exper- iment. Since a typical TD #SR experiment can accept only one muon every 10-20 #sec (i.e. 105 /~+/sec) such an arrangement can, in principle, provide beam simulta- neously to two such experiments while the majority of the beam remains available for a third experiment. In addition, the TD #SR experiments can operate at up to 4 times the rate possible on a conventional beam line due to the lack of pileup effects.

1 I n t r o d u c t i o n

The concept of a kicked surface muon beam or "magic beam line" was first discussed at TRIUMF by Spencer and Garner in the early 1980's [1]. Their idea was to address the muon pileup problem encountered in time differential (TD) #SR experiments while making more use of the > 106 muons available in modern surface muon beams. The principle is illustrated in Fig. 1. A kicker element is inserted in a beam line which is capable of directing the beam via a septum to either the upper or lower leg of the line. When a muon is detected entering the apparatus on either leg the kicker is turned off and

~ t ~ \ detector

beaml]ne ~.

" ~ / d e t e c t o r kicker septum

+V

-y

7 - U -~ I

tg 2 - 20 sec

t . 0.5 - 3 sec

Fig. 1. Schematic diagram of a "kicked" surface muon beam and

the kicker timing sequence.

2 B e a m Line

A possible realization of the above principle at TRI- UMF is shown in Fig. 2. Here, an electrostatic kicker is placed in the last section of the existing M15 beam line. A septum, bending magnet and quadrupole triplet are used to form a new "kicked" muon leg. First order TRANSPORT cMculations indicate that an acceptable focus can be obtained with this arrangement and that good separation at the septum is attained with the kicker parameters listed below:

• length 50 cm

• gap 20 cm

• plate voltage 15-20 kV

Unfortunately, more realistic calculations using the program REVMOC indicate (Fig. 3) that higher order aberrations in the beam line create tails on the beam spot at the septum and that there is substantial overlap between the kicked and straight through beams. Higher kicker voltages give bet ter separation but lead to beam loss in the elements prior to the septum. This implies that some improvement will have to be made in the beam optics before this kicker scheme will work practically in this beam line.

259

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Beo, mLine HI5 Fig. 2. Proposed insertion of a kicker in the existing TRIUMF M15 beam line.

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~- 4 0 0

300

2O0

IO0

0 - 1 0 - 9 - 8 - 7 - 6 - 5 - 4 - 5 - 2 - 1 0 1 2 3 4 5

X P O S I T I O N ( C M )

Fig. 3. Muon beam spot at the septum location for various kicker voltages.

3 Kicker

The kicker for the above arrangement must produce high voltage pulses (15-20 kV) with the shortest possible rise times (<100 nsec) and with repetition rates of up to 500 kHz. These specifications lead to very high in- stantaneous and average power requirements for the high voltage power supply. One possibility to circumvent such problems is to use a synchronous kicker similar to the 1 MHz Chopper developed for the TRIUMF KAON Fac- tory [2]. This device (Fig. 4) is capable of producing pulses of the required voltages with very short (,,~10 nsec) rise times and has the advantage that power re- quirements are relatively low due to the storage of energy in the delay lines. Modification of this device required to lengthen the pulses and reduce their repetition rate by

increasing the length of the delay lines seems feasible. However, such a chopper does not take full advantage of the "kicked" muon scenario as the muons are not delivered to the experiment on demand and the fixed frequency and pulse width can only be optimized for one muon beam rate. A more attractive option is an asynchronous pulser (Fig. 5) which could more closely reproduce the timing sequence of Fig. 1. This device appears to be within the capabilities of existing tetrodes provided rise times of the order of 100 nsec are accepted and would provide experiment driven pulse width and frequency. However, multiple high power, high voltage power supplies are required which make its realization expensive.

260

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100 OHW STRIPUNE_ ~ - > L - - ~ / , , . , ~ /~;;.¢X'.-"* ~ _ . /L+v /2

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Fig. 4. The KAON prototype 1 MHz chopper.

"t'y~ltup * , ~ 4-15kV

Pulse P J t t e ~

- U u ~v~'2 ~ DEFLECTOR PLATES ~ ( l m Ionl, 25 era epar t )

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,u,, t,,~"T- c'Yll72 ~ pF"

- V " - -15kV

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AVE CURREHT FOR 500kH: - ?~ Amps

POWER DISSIPATION PER TETRODE - 0.5 C V 2 • 5OOkHz - S6k'W

Fig. 5. A possible pulser for an asynchronous kicker.

4 Conclusions

A kicked surface muon beam has many attractive features for efficient use of available muons in certain

experimental situations. It seems to be possible to pro- duce the required kicker with existing high voltage pulse technology. Some care will be required in producing good beam optics to provide adequate beam separation at the septum, however, this should be possible and a kicker option should be seriously considered in the design of future surface muon beams.

5 References

1. D. Spenser and D. Garner, private communication. 2. G.D. Wait, M.J. Barnes, D. Bishop, G. Waters and C.B. Figley, "Prototype Studies of a 1 MHz Chopper for the KAON Factory", 1991 Particle Accelerator Conf., San Francisco (in press).

This article was processed using Springer-Verlag TEX Z.Physik C macro package 1991 and the AMS fonts, developed by the American Mathematical So- ciety.