JPH01116482A - Microcurrent monitor - Google Patents

Abstract

PURPOSE:To measure a current value of a 10<-9>A-range microcurrent and a beam position simultaneously by arranging a superconductive quantum interferometer in a magnetic shield. CONSTITUTION:A microcurrent monitor consists of a vacuum duct 4 forming a vacuum tank, a ceramic duct 5 partially made of ceramic and a magnetic shield 6 which is placed outside the duct 5 and circulates a refrigerant while shielding all but a magnetic field made by a beam. A superconductive quantum interferometer 1 is disposed in the shield 6 so that it can measure unbalance of the magnetic field made by a beam. The interferometer 1 combines a Meissner effect and a Josephson effect of a superconductor to determine the amount of a magnetic flux passing therethrough. This enables the measuring of a current value of a 10<-9>A-range microcurrent and a beam position simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a particle accelerator, and particularly to a monitor system suitable for measuring current in a microcurrent generator such as a heavy ion accelerator.

[Conventional technology]

The current obtained with an ion accelerator is generally smaller than that with an electron accelerator. In particular, the final extraction current in a heavy ion accelerator is 1 to several tens of nA. Conventionally, a current transformer type monitor has been used to measure this current, and this is described in IE Transactions on Nuclear Science NS 32.45 1
985, pp. 1959-1961 (IEEE Trau
s, NuclearScience N532 Vo
125 1959 (1985)).

[Problem to be Solved by the Invention 3] In a heavy ion accelerator, the current obtained at the final energy due to restrictions of the ion source, etc., is very small compared to an 11-son accelerator, and is about 1 to several nA. Conventionally, in order to measure the current value of an accelerator, a non-destructive measurement using a Faraday cup, a fluorescent screen, etc., and a current transformer monitor, an electrostatic monitor, etc. have been used. However, in all cases, noise countermeasures are difficult due to the minute current.

The above conventional example is designed with noise countermeasures in mind, but
(1) Make the toroidal core smaller to increase detection sensitivity and SN ratio. Therefore, (2) the monitor body and some processing circuits are installed in a vacuum. It has the following problems. Heavy ion accelerators must maintain an ultra-high vacuum to extend beam life, so inserting equipment into the vacuum must be avoided as much as possible. In addition, in devices such as heavy ions where the beam size does not attenuate due to orbital radiation, the beam duct should be made sufficiently large to avoid beam loss due to large betatron oscillations. Therefore, the monitor core cannot be made smaller.

An object of the present invention is to provide a monitor that is installed outside a vacuum and measures minute beam current values and beam positions.

[Means for solving problems]

The above objective is achieved as follows.

First, a part of the monitor duct is made of ceramic so that the electromagnetic field in the beam duct leaks out of the vacuum. there,
Superconducting quantum interferometers (hereinafter referred to as 5QUID) will be installed at four locations on the top, bottom, left and right, perpendicular to the magnetic field created by the beam.

[Effect]

The electromagnetic field induced by the beam can leak out of the vacuum at the ceramic duct section. This allows measurement outside a vacuum.

5QUID applies the Meissner effect and Josephson effect of superconductors to determine the amount of magnetic flux passing through the element. Therefore, the circulating beam current value can be determined from the amount of passing magnetic flux. In addition, the lower measurement limit of 5QUID is
~1FIST (Tesla), so as an example, radius 2
Assuming a 5I1m cylindrical duct, the lower limit beam current value for measurement is ~130pA.

Furthermore, by installing monitors on the top, bottom, left and right sides, it becomes possible to measure the imbalance of magnetic flux in the top, bottom, left and right directions that occurs when the beam deviates from the center. This unbalance is used to measure the beam position.

Horizontal position = left - right / left + right Vertical position = top - bottom / top + bottom 〔Example〕 An embodiment of the present invention will be described below with reference to FIG.

A beam duct 4 forming a vacuum chamber, heavy ion beams 3 circulating inside the duct 5, and a ceramic duct 5 leaking the electromagnetic field induced by the 3 to the outside of the vacuum;
It consists of a 5QUIDI that measures the magnetic field induced by 3 and a magnetic shield 6 that shields 1 from external magnetic fields and is used for cooling the 5QUID. 5QUIDs placed on the top, bottom, left and right of the monitors 11, 12 and 13, 14 respectively.
shall be.

Heavy ions have large betatron vibrations, so if 4 is considered as a cylinder with a radius of 50+nm, the magnetic field created by 3 is given as follows.

Or, deviation from the center indicates the angle from X of the measurement point. First, if we consider when the beam passes through the center, x=o
Therefore, B=μoI/2πr.

If I=1nA, the magnetic field created by 'r=50mm is 4
X 10-”T, the lower measurement limit of 1 h/2e~2
It is sufficiently larger than X 10''T.Here, h is a blank constant.At this time, the extra external field is sufficiently shielded by 6, and the 5QUID is cooled.

With this, current values starting from 1 nA can be measured.

When X≠0, it can be expressed as r > x. Therefore, by adding up the monitors placed at four locations, it is possible to eliminate the effect of X≠0.

Next, using equation (2), ■ is the output voltage of each 5QUID When you perform the calculation, Rl　”　　　　X　　　　　Rl　”　　　 A relationship like this arises.

This allows measurement of beam position (horizontal and vertical). According to this embodiment, nA class current values and positions can be measured simultaneously, making it possible to reduce the number of monitors.

Conversely, the current value at each position can be measured.

〔Effect of the invention〕

According to the present invention, it is possible to measure the current value which conventionally measures nA class, which is very repetitive, and it is also possible to measure the position.
A highly sensitive feedback sensor such as an F cavity or a deflection magnet can be provided.

Furthermore, the vacuum duct for heavy ions can be made sufficiently large.

[Brief explanation of the drawing]

FIG. 1 shows an explanatory diagram of an embodiment of the present invention. 1... 5QUID for current measurement, 2... Magnetic field created by beam, 3... Heavy ion beam, 4... Ordinary beam duct, 5... Ceramic duct, 6... 5QUI
Magnetic horse 1 diagram for D

Claims (1)

[Claims] 1. A vacuum duct that forms a vacuum chamber, a ceramic duct that is partially made of ceramic, and a magnetic shield placed outside the ceramic duct to block magnetic fields other than those created by the beam and to circulate the refrigerant. By placing a superconducting quantum interferometer inside so that it can measure the imbalance of the magnetic field created by the beam, 10^-
A microcurrent monitor characterized by simultaneously measuring the current value and beam position of an 8A class microcurrent.