INJECTION IN THE STORAGE RING VEPP-2000
B.I.Grishanov, F.V. Podgorny, BINP, Novosibirsk, Russia
Abstract
In the spring of 1999 the decision was taken on themodernization of the VEPP-2M complex to increase theluminosity and the maximum achievable energy of up to2 GeV. This will to essentially improve the experimentson the collider. The new project was named VEPP-2000.
Engineering aspects of injection at VEPP-2000 areconsidered in this report. The energy of injection is900 MeV. The scheme of injection with a prekick of astored beam is used. As the collider has got one ring, boththe electron and the positron beams co-exist andsimultaneously move in counter directions. The kickers
operate in a traveling wave mode and affect the countermoving particles only. Every kicker has one asymmetrical
50-Ohm strip lines with a unipolar feed. The geometricalaperture of the vacuum chamber is 34 x 70 sq. mm. The
plates of the kickers are located inside the bending
magnets and are 136 cm long. Such tiny sizes of thechamber cause additional difficulties with ensuring boththe placement and the electric strength of the plates in thechamber. The present report describes the feed circuit ofthe kickers. The generators form pulses in the travelingwave mode with an amplitude of up to 60 kV, 80 ns pulse
duration (Full width half maximum (FWHM)) and 60 ns
raise/fall time at a repetition rate of up to 1 Hz. The
circuit is constructed on the basis of a step artificial linewith a pulse hydrogen thyratron as the switchboard.

1 INJECTION SYSTEM
The injection of beams in a new ring is planned to
be done in the horizontal plane into the drift space

opposite to the RF cavity. The proposed scheme usesthe principle of a one-turn injection with prekicking
the accumulated bunch. Two kickers are used. Thekickers are designed as asymmetrical strip lines andwork in a counter traveling wave mode. Every kicker
plate is placed near the inner side of a vacuum
chamber in a bending magnet at the end of theinjection space. The advantage of such a scheme is
the independence of the injected beam trajectory of
the solenoid's field. This gives us an opportunity totest different optics variants – usual round beams,"Mobius", and flat beams with a zero rotation of thebetatron oscillation plane.

2 CONSTRUCTION
2.1 Feed scheme
Each kicker has one plate with an impedance of
50 Ohm and a length of 136 cm matched at the end,
and is powered from an individual generator in orderto tune the kick amplitude and time delay
independently. The pulse of the amplitude of up to
50 kV is fed to the entrance of the kicker. In thepositron accumulation mode both kickers are fed withnegative polarity pulses, and in the electron
accumulation mode – with positive pulses. When themode is changed both the pulse polarity and thedirection of the wave propagation in the kickers
should reverse, because the kickers operate in acounter traveling wave mode. The feed scheme forthe kickers is shown in Fig. 1.

Figure 1: The kicker feed scheme.

Two kicker schemes were examined: two plateswith a symmetrical feeding and a single plate with aunipolar feeding. The choice of the single plate
variant has the following reasons. The outside plate is
exposed by an intense SR-heating, this makes
additional difficulties for it's cooling. One of theways to reduce the heating problem is to make alongitudinal slot of about 10 mm in the outer plate for
SR outlet. But this essentially decreases theefficiency of using the second plate.
For the selected single plate variant there wasperformed a simulation of the field distribution in theworking aperture and the field gradients on the platesurface in the most strained points.

2.2 Field distribution
All field distribution computations were made bymeans of "MERMAID" program. This program isdesigned in the BINP as a universal tool for designing ofmagnets in two dimensions. In addition, 2D-electrostatics
is supported. An axisymmetric problem is also a possible
option. For example, applications of the program tononlinear magnetostatics include: dipole and quadrupole
magnets, solenoids with iron core, etc.
The beam comes into the kicker with the coordinate of–5.9 mm. The kicker should compensate the angle of
6.3 mrad. The estimated field along the beam trajectory isabout 21 kV/cm. In Fig. 2 the field distribution in thevacuum chamber is shown.

Figure 2: The field distribution in the vacuum chamber. Dimensions are shown in millimetres.
Fig. 3 shows the region with a field nonuniformity of± 15% relative to the field magnitude in a median plane at
the bold point. The arcs on the all figures show theaperture borders with radii of 6 and 10 mmcorrespondingly with respect to the equilibrium orbit.

Figure 4: The kicker field graph in the median plane.
Figure 3: The field region with a nonuniformity of ± 15%.

2.3 Technical design

Fig. 4 presents the kicker field graph in the medianplane. The zero corresponds to the equilibrium orbit.

The complex profile of the plate cross-section isjustified by the small size of the vacuum chamber;therefore the calculations in "MERMAID" were dedicatednot only the field distribution and the wave resistance, but
to the electric strength at the most "dangerous" points also.
The maximum electric intensity on the plate surface
reaches 160 kV/cm at the travelling wave voltage of
50 kV. Taking into account the short pulse duration thearising intensities can be considered as admissible for areliable operation. Fig. 5 shows the field map andgradients in the most strained points of the plate surface.

Figure 5: The field map with gradientsin the most strained points, kV/cmThe plate is fixed at every end by the feed-throughinsulators. There is an additional supporting insulator in
the plate longitudinal middle point.

3 PULSERSThe kickers feeding generators are designed as linear
modulators based on double forming lines (DFL).
Hydrogen thyratrons are used as switches. In Table 1 themain parameters of the generators are listed.
Table 1: The main parametersof the kicker feeding generator
Charging voltage
up to 40 kVPolarity of charging voltage
positive
Amplitude of the output pulse
up to 30 kV
Pulse duration (FWHM)
80 ns
Pulse rise/fall time
60 ns
Output pulse polarity
negativeOutput impedance
12,5 Ohm
Each PFL of DFL impedance
6,25 Ohm
Thyratron current amplitude
up to 4,8 kA
Repetition frequency
1 Hz
The generator with such parameters is designed in theBINP for damping ring kickers feeding of the injection
complex VEPP-5. We consider this generator as a basefor this system. Simultaneously we study a possibility touse other type generator with rise/fall time of about 5 nsec
and pulse duration of about 15 nsec. It's assumed thatsuch kind of generators could base on solid-state switches.
In particular, a very fast kicker with high repetition rate
for accelerator applications was designed and delivered inDESY [2].
BINP has a big experience in designing, manufacturing
and using of kicker systems with rise/fall time of somenanoseconds at pulse duration of order several tens
nanoseconds. We use spark-gap-switch generators for thispurposes till now. The injection system described above
is designed to be proper for working at such timeparameters.
Pulse transformers are used at the generator outputs toincrease the pulse amplitude in the travelling wave from
25 kV to 50 kV. Both the wave direction and the pulses
polarity switches are integrated into circuits with pulse
amplitude of 50 kV.
Taking into account that this scheme is loaded with apulse transformer excitation current the value of theoutput generator impedance (and PFL of DFL) should besomewhat decreased. The final values of these parameters
will be known after selecting a transformer type.
Mechanical commutators are used for these purposes.
Such kind of the commutator was designed in the BINPand operates many years on the accelerator's kickersystems.

4 REFERENCES[1] Project of a New Electron-Positron Collider VEPP2000 YU.M. Shatunov, A.V. Otboev, I.A. Koop.
EPAC 2000, 26-30 June 2000, Austria Center Vienna.
[2] B.I. Grishanov,
F.V. Podgorny,
J. Ruemmler,
V.D. Shiltsev. "Very fast kicker with high repetition
rate for accelerator applications", NIM A 396 (1997)
28-34.