Minutes of 56th FFIR/BDSIM meeting on 7/16/2003

The meeting was held in a room of 425 at KEK, 10:00-, 7/16/2003. We discussed on FEATHER status, SLEPT- LINAC simulation with ground motion and movers for active feeback.

(1) FEATHER status:Beam test layout (N.Delerue)

(transparencies, 6 pages, pdf,379KB ) Nicolas begun a talk from constraints on the relative position of the BPM and the kicker. The longer distance must be preferable for fast amplifier of the kicker with less power. However, a shorter feedback time, therefore shorter distance is also important since the total length of the bunch is 56ns. So, the present distance was chosen to be about 1m at the ATF beam test. Configuration of setup is a nano-BPM, kicker, button BPM and monitoring BPM from upstream (please see transparencies for details). The feedback loop is consisted of the kicker and the button BPM, both of which will be fabricated in this summer, while the feed-forward loop can be constructed by the nano-BPM and the kicker. So the nano-BPM is right in front of the kicker. The nano-BPM and the monitoring BPM are available.

Electronics devices such as amplifier and programmable attenuator will be chosen soon. Typical power of the amplifier is 40dBm, which corresponds to 22V amplitude applied to 3mm gap between 40cm long electrodes with 50 Ohm impedance, in order to kick a beam with 5 um at the BPM. The most suitable one is LZY-2 (45 dBm) of Minicircuits, whose internal delay is expected to be less than 10ns from a measurement of lower power model. The programmable attenuator must have step sizes as small as possible, but the range must cover at least 8dB. The candidates are Weinschel 3200-2 (0.25dB step, 63.75dB range) or 3209 (0.1dB step, 64.5dB range), which can be controlled by CAMAC or serial mode from PC. The kicker and the button BPM have been ordered to a company.

(2) Vibration attenuation by levitation (N.Delerue)

(transparencies,5 pages, pdf,245KB) Nicolas shortly reviewed a vibrational attenuation by magnetic levitation. First example is "microgravity vibration isolation system"(g-LIMIT), which has been developed by NASA to stabilize experiment on the International Space Station (ISS). The system has large vibrational attenuation of -40dB/decade as a function of frequency (f=0.001~1000 Hz) based on measurements in space without gravity. So, the system can achieve micro-G environment, which is close to our goal, in space. However, no results are available on the ground.

In Japan, a significant number of studies on magnetic suspension and levitation has been conducted by companies and universities; Mitsubushi Heavy Industries (National Aerospace Laboratory of Japan), Musashi Institute of Technology and Japan Railways. So, Japan is a leading country in this field. He would like to contact them with help of Matsuda san.

He proposed a possible test experiment based on a paper by M.T. Thompson, "Electrodynamic Magnetic Suspension", IEEE Trans. on Education, 43, No.3 August 2000. First target is to reproduce Thompson's experiment of levitating coils. A table can be hold (levitated) by 4 coils. Vibrations shall be measured on the table as well as on the ground. This experiment must be cheap.

During discussions, it was pointed out that before initiating the experiment, more paper work must be necessary, especially on possibility of "g-LIMIT" on the ground, levitation of heavy materials (final Q magnet etc. ), interference by detector magnetic field, and effect on nanometer beam etc. for nano-meter stabilization.

(3) Requirements for movers at LINAC(K.Kubo, KEK) and discussion with R.Sugahara

(transparencies, 1 page, pdf ,4KB) First, Kubo explained requirements for movers at LINAC and the SLEPT correction scheme.

There are two kinds of mover for quarupole magnets (Q) and accelerating structures. For the Q-mover correction, every Q must have independent mover with BPM. Meaning of "independent" includes capability of independent current control. Magnetic centers of Q must be "known" by BPM with accuracy of 2um. The spatial resolution of BPM was assumed to be 0.2um for 10% correction of Q-strength. Also present simulation assumes that BPMs are set at center of Qs. However, BPM can not be set there because the BPM is cavity-type. So, the simulation must take account of off-centered BPM. The Q-positions shall be corrected within 0.2 sec with a 50nm step in every 10 sec. So typical magnitude of movements is a few um. Setting error must be less than 10nm. While the magnitudes of correction may differ at Qs, the completion time must be same.

For acceleration structures, each structure or one unit of structures has a mover. The structure positions must be corrected in the same way as the Q-positons except for step-size of 1um instead of 50nm.

Summarizing discussions, these requirements can be satisfied with appropriate R&D. Sugahara et.al has started a R&D on stabilization of magnets. They setup a vibration isolation system based on air-suspension at Oho experimental hall (B4). They will also construct one quadrupole magnet for this goal.

The next meeting will be on 30th July, 2003,10:00 - noon at 3 gokan, 425 .