Room Temperature ECR
We imported an ECR ion source - CAPRICE from Grenoble in 1987 and used it as preliminary heavy ion beams injector to HIRFL. This ion source can produce multi-charged ion beams, but the ion beam species, charge state and the extracted beams` intensity are all very limited. It could not satisfy the experimental requirements of IMP. By our years` research and modification on it, many improvements were made on it, and the quantity and quality of the extracted beams were greatly improved.
With our accumulated experience on ECR ion source, we then set about to manufacture an ECR ion source depending all upon ourselves. In 1995, LECR1 was successfully set up in Lanzhou. This was the first multiply charged ECR ion source developed in China. And it was a great progress and breakthrough on accelerator physics and technology in China.
LECR1 has the virtues like long running periods, excellent repetition, low energy dispersion and emission. It can provide multiply charged ion beams of all gaseous elements, as well as some solid ones. The key technique parameters of it have reached or even exceeded the international levels of alike ECR ion sources.
While designing, we based ourselves upon our present experience, and moreover we paid more attention to the latest techniques adopted abroad. The typical adopted special techniques are the designing of magnetic field configuration, the insulted structures, and the cold cathode electron gun. Especially, a new ECR working mode and a new magnetic field configuration were successfully tested. Thereby, it gave a new method to the research on the establishment of the plasma in multi-charged ECR ion sources.
This ion source has been in running for many years, and served many rounds of atomic experiments with highly charged ion beams. The results prove that LECR1 can provide intensive ion beams and its capability is stable and reliable. Now it has been removed from the ion injector beam line of HIRFL and placed at the hall of our lab.
This ion source is the first 14.5GHz ECR ion source that can produce highly charged ion beams in China. The typical performance of it greatly exceeds that of LECR1's. Besides, many of its results have reached or even exceeded the international levels of the alike facilities. It can now produce 22 species of ions, amongst which 9 kinds of metallic ions included. The typical ion beams are Ar11+185 euA, Xe26+50 euA, Kr20+25 euA, Ca11+140 euA, Mg7+60 euA, Fe10+65 euA, Pb27+20 euA. It has been running for HIRFL for more than 20000 hrs, and was proved stable and reliable. It has very important effects on the improvement of HIRFL's capability and running efficiency. With it, we provided HIRFL with metallic ions for the first time.
While designing, we based ourselves on our own experience and techniques, as well as the adoption of latest international techniques. Furthermore, we took lead in trying very high axial magnetic field and hexapole permanent magnetic field, adopting a double-wall water-cooling chamber with large volume, testing a kind of simple and reliable cold cathode electron gun successfully. This indicates that the techniques on multiply charged ECR ion source in China have reached the advanced international level.
After the acceptance test by the Expert Checking Team in May 1998, 14.5 GHz ECR ion source was soon used for the ion beam injection to HIRFL. It was proved to be a reliable, stable ECR ion source and it can sustain long period operation. And the metallic ions greatly fulfilled the aspiration of our physical scientists'experiments. Till now, it has been providing ion beams stably for more than six year.
In the Summer 2000, we carried out a set of prophase experiments on this ion source. Many methods to produce metallic ions and the afterglow mode were tested. Now this ion source can be widely popularized to other kind of accelerators to enhance their performance, and extend their application field.
In the past several years, LECR2 has provided HIRFL with various charge state ion beams of 18O, 16O, 20Ne, 22Ne, 36Ar, 40Ar, 40Ca and etc. The 40Ca11+, 40Ca12+, Mg7+ and some other metallic ion beams were injected to HIRFL for the first time. With the development of ECRIS techniques and skills, LECR2 needs to be updated to enhance its performance. This source was successfully updated to LECR2M at the end of August 2005.
We always keep up with the latest development of international ECR Ion Source, especially the new methods and new techniques. Recently with the development of ECRIS, superconducting and double-frequency heating ECRIS has become the highlight in ECRIS development. As we were devoting to designing our SECRAL source, we had made some improvement on the 14.5 GHz LECR2 source. So the newly built double-frequency heating LECR3 source was designed.
The magnetic part of the ion source is based on the 14.5GHz LECR2 source, but we have made many improvements on the other parts of it. The fed RF frequency is 10+14.5GHz. The RF feeding method is altered from the original coaxial mode to off-axis direct injection method. According to the results we got, by direct axial injection, the RF power feeding efficiency and the stability of the plasma can be greatly enhanced. The diameter of the plasma chamber was enlarged to 76mm. The material was changed into aluminum in order to utilize the active action of Al2O3 to the plasma.
The comparison of IMP LECR3 with LECR2
The typical gaseous and metallic ion beam performance of LECR3 is given below. It is obvious that the performance of LECR3 is better than LECR2's. When running with 18GHz, 1.1emA Ar8+ was obtained for the first time in Lanzhou. By careful tuning of the source, 500enAAr17+ ion beam was obtained and has been successfully used for atomic physics experiment. The high performance of LECR3 owes a lot to its adoption of many new methods and new techniques such as: higher axial magnetic field provides better plasma confinement; large plasma volume increases the high charge state ions' production efficiency; rectangular waveguide off-axis rf power feeding system is more efficient and stable than the coaxial feeding system especially when feeding large rf power (e.g. more than 1000W); the plasma chamber is made of aluminum with better cooling; an aluminum biased disk is installed inside of the plasma chamber at the injection side to produce supplementary secondary cold electrons.
LECR3 was constructed in 2001 and since then, it has delivered series of different charge state ion beams of different elements for atomic and material physics research. It turns out to be a stable and reliable high charge state ECR ion source. High charge state uranium ion beam was produced from this source for the first time in IMP.
LECR2 (Lanzhou Electron Cyclotron Resonance ion source No.2), which was built in 1997, has been running for more than 30,000hrs and provided more than one hundred kinds of ion beams for HIRFL. This ion source was considered to be one of the best ECRISs in the world when it was under commissioning because of its excellent operation results. But, by now, with the development of ECR ion source techniques and the higher requirements of HIRFL accelerators, some deficiencies of the LECR2 ion source were found.According to the performances of LECR3, which are much better than LECR2's, it is necessary to upgrade the LECR2 with new design to satisfy the requirement of the HIRFL-CSR which requires the ion source to provide ion beams with not only higher intensity but also higher charge states.
Comparison of the typical parameters of LECR2M and LECR2
LECR2 should be renamed to LECR2M after modification. The design of LECR2M is based on LECR3 and some components were improved to enhance the performance of the ion source. The most important part modified is the hexapole, which was built with N48M NdFeB material. According to the calculation of axial magnetic field distribution, the shell of hexapole was divided into 3 rings. The middle one was made of aluminum and the other two were made of soft iron. The inner diameter was enlarged from 76mm to 84mm, but the magnetic field on the inner pole face is 1.35T, which is stronger than that of the former one which is made of N42M NdFeB. This new hexapole has already been successfully fabricated in IMP. The magnetic field at inner wall of the plasma chamber (where the diameter is 76mm) was measured to be 1.12T. Another important modification is that an all-aluminum 430mm long plasma chamber has been adopted. The chamber wall, which is 4mm thick, was made into double-layer structure with cooling water flowing between the two layers to protect the hexapole from being demagnetized by heat caused by microwave. The microwave will be fed into the chamber directly through a rectangular waveguide instead of a co-axial system. To study how the ion source works when it is fed with RF power of the same frequency at the same time, two WR62-flange waveguides were fixed at the injection system. To prevent the microwave power leaking at the injection side, a phosphor bronze Contact Usor ring will surround the inner iron block which is cooled by water and used to enhance the injection axial magnetic field. The extraction region design is similar to that of LECR3. Anyway, the design of LECR2M is to enhance the performance of the ion source and make the maintenance of the ion source more convenient.