Progress of the BEPCII Injection System

Kang Wen

1. Introduction

The requirements of kicker system

Number of Kicker 4Length of magnet 1.9Beam aperture 90mm×38mm Integral field 200Gs*m Good field region ±20mm Field uniformity ±1% Waveform half-sinePulse Width 600nsThe Max. Pulse Repetition 50Hz Stability of current 1%Time jitter <5nsBeam impedance of the magnet <0.025Ω

BEPCII injection system consists of four kicker magnets and two Lambertson magnets. The Lambertson magnets of BEPC are reused by BEPCII. And the four kicker magnets and their power supplies are reproduced and now are finished.

Firstly, a ferrite kicker magnet with ceramic chamber coated metal film was studied, but due to the large beam aperture and fast rise time of the pulse, both the field waveform and the field uniformity of the kicker magnet could not meet the requirements of its design.

Further, due to the short injection straight section, synchrotron radiation hitting on the inner wall of ceramic chamber could not be completely blocked, the cooling of the chamber is a difficult problem to be solved.

Therefore the ferrite kicker magnet was finally refused.

Secondly, the slotted pipe kicker magnet, which was developed at Delta, was also studied for BEPCII injection. However, it can be seen that the two metallic bands shield the pulsed field completely at the center of the magnets and spoil the field uniformity seriously. So it could not be adopted by BEPCII injection yet.

In order to solve the design problem of the kicker magnet, a new idea using the ceramic plates with coating films instead of the metal bands as the image current path of the slotted pipe kicker magnet is proposed. The simulated results show that both the field uniformity and beam impedance satisfy the design requirements. The wave form of magnetic field had also no obvious deformity.

In addition, since there are water cooling tubes on the current buses, the blocking of synchrotron radiation is not necessary.

2.   Manufacture of the Kicker Magnet

The kicker magnets consist of current buses, ceramic plates coated with metal films, end transition parts, high voltage feedthrough and vacuum tank.

3.   Assembly of the Kicker Magnet

The kicker magnet and its vacuum tank

The kicker magnet is putting in the vacuum tank

After alignment in the tank

After assembly

4. Manufacture of the pulsed power supplies

(1) The slotted pipe kicker magnet need a symmetric pulser as its power supply. So a baloon transformer, which is made by nano-crystal magnetic material, is used for this purpose.

(2) To controls the stray inductance of the elements, the main discharge circuit of the pulser adopts the coaxial structure.

(3) To alleviate the arc-back of the thyratron, a 4.5Ω serial resister and a saturable inductor are added in the circuit.

5. Assembly of the Kicker Power Supplies

CMD5005 ferrite used for saturable inductor

HVR high power SiC disc used as the serial resistor

The pulser is being assembledThe pulser is being connected to the charging power supply

5. Connection of the Power Supply and the Kicker Magnet

6. Measurements

Field and current wave forms, no obvious deformity as simulated

Measured stability of the current, better than 1%

Measured time jitter of the current, less than 5ns

Measured field uniformity, better than ± 1% in the central plane, ± 2% in y=5mm plane, ± 5% in y=10mm plane

Required MeasuredNumber of Kicker 4 4Length of magnet 1.9m 1.7mAperture of magnet 90mm×38mm 90mm×44mm Integral field 200Gs*m 218Gs*m Good field region ±20mm ±20mm Field uniformity ±1% ±0.82% Waveform half-sine half-sinePulse Width 600ns 570nsThe Max Pulse Repetition 50Hz 50Hz Stability of current 1% 0.69% Time jitter <5ns 4.16nsBeam impedance of magnet <0.025Ω < 0.02Ω

All the measured specifications are better than that of the requirements!

7. Comparison of the measurements and the requirements

8. Some difficult problems about the kicker magnets encountered in the experiment

(1) The production of the large ceramic plates with metal films was troublesome work , after many times of failures, the ceramic plates with high quality films for all kicker magnets were finally finished. Since the production of the film was made at 650 degree, the material of the resistive paste combined tightly with the ceramic plates, the adhesion of the films have no problem. In addition, when we reopened the vacuum tank of the kicker magnet after continuous operation of several days at full current, we had also not found obvious changes on the surface of the films.

(2) Due to leak of some welding joints and production problems of some flanges, the vacuum of one kicker magnet did not reach the required value until last week. Now the vacuum pressure of all kicker magnets are better than 2.0×10-10Torr.

9. Some difficult problems about the pulsed power supplies encountered in the experiment

(1) The voltage stability of the first charging power supply was much worse than that of the requirement, but we had found another company to reproduce the charging power supply and solved the problem;

(2) At the first stage of experiment, EMI of the pulsed power supply is a serious problem, the local controlling system could not work sometimes. So the whole controlling system of the power supplies had to be redesigned and reproduced, and the EMI problem has been solved.

(3) Although the serial resister and the saturable inductor are added in the circuit, the arc-back(inverse conduction) of the thyratron still incidentally appears. Now we are trying some other toroids made by nano-crystal magnetic material, and the phenomenon of arc-back is greatly alleviated.

10. Installation

All of the kicker magnets and their pulsed power supplies have been finished conditioning, and are ready for installation.

Thank you for your attention!